...

25 files changed, 1331 insertions, 233 deletions

diff --git a/Timeline.Tests/IntegratedTests/UserAvatarTests.cs b/Timeline.Tests/IntegratedTests/UserAvatarTest.cs
index ad0e4221..ba6d98e1 100644
--- a/Timeline.Tests/IntegratedTests/UserAvatarTests.cs
+++ b/Timeline.Tests/IntegratedTests/UserAvatarTest.cs
@@ -18,6 +18,8 @@ using Timeline.Services;
 using Timeline.Tests.Helpers;

 using Timeline.Tests.Helpers.Authentication;

 using Xunit;

+using static Timeline.ErrorCodes.Http.Common;

+using static Timeline.ErrorCodes.Http.UserAvatar;

 

 namespace Timeline.Tests.IntegratedTests

 {

@@ -52,7 +54,7 @@ namespace Timeline.Tests.IntegratedTests
                     var res = await client.GetAsync("users/usernotexist/avatar");

                     res.Should().HaveStatusCode(404)

                         .And.Should().HaveCommonBody()

-                        .Which.Code.Should().Be(UserAvatarController.ErrorCodes.Get_UserNotExist);

+                        .Which.Code.Should().Be(Get.UserNotExist);

                 }

 

                 var env = _factory.Server.Host.Services.GetRequiredService<IWebHostEnvironment>();

@@ -153,7 +155,7 @@ namespace Timeline.Tests.IntegratedTests
                     content.Headers.ContentType = new MediaTypeHeaderValue("image/png");

                     var res = await client.PutAsync("users/user/avatar", content);

                     res.Should().HaveStatusCode(HttpStatusCode.BadRequest)

-                        .And.Should().HaveCommonBody().Which.Code.Should().Be(UserAvatarController.ErrorCodes.Put_Content_TooBig);

+                        .And.Should().HaveCommonBody().Which.Code.Should().Be(Content.TooBig);

                 }

 

                 {

@@ -162,7 +164,7 @@ namespace Timeline.Tests.IntegratedTests
                     content.Headers.ContentType = new MediaTypeHeaderValue("image/png");

                     var res = await client.PutAsync("users/user/avatar", content);

                     res.Should().HaveStatusCode(HttpStatusCode.BadRequest)

-                        .And.Should().HaveCommonBody().Which.Code.Should().Be(UserAvatarController.ErrorCodes.Put_Content_UnmatchedLength_Less);

+                        .And.Should().HaveCommonBody().Which.Code.Should().Be(Content.UnmatchedLength_Smaller);

                 }

 

                 {

@@ -171,25 +173,25 @@ namespace Timeline.Tests.IntegratedTests
                     content.Headers.ContentType = new MediaTypeHeaderValue("image/png");

                     var res = await client.PutAsync("users/user/avatar", content);

                     res.Should().HaveStatusCode(HttpStatusCode.BadRequest)

-                        .And.Should().HaveCommonBody().Which.Code.Should().Be(UserAvatarController.ErrorCodes.Put_Content_UnmatchedLength_Bigger);

+                        .And.Should().HaveCommonBody().Which.Code.Should().Be(Content.UnmatchedLength_Bigger);

                 }

 

                 {

                     var res = await client.PutByteArrayAsync("users/user/avatar", new[] { (byte)0x00 }, "image/png");

                     res.Should().HaveStatusCode(HttpStatusCode.BadRequest)

-                        .And.Should().HaveCommonBody().Which.Code.Should().Be(UserAvatarController.ErrorCodes.Put_BadFormat_CantDecode);

+                        .And.Should().HaveCommonBody().Which.Code.Should().Be(Put.BadFormat_CantDecode);

                 }

 

                 {

                     var res = await client.PutByteArrayAsync("users/user/avatar", mockAvatar.Data, "image/jpeg");

                     res.Should().HaveStatusCode(HttpStatusCode.BadRequest)

-                        .And.Should().HaveCommonBody().Which.Code.Should().Be(UserAvatarController.ErrorCodes.Put_BadFormat_UnmatchedFormat);

+                        .And.Should().HaveCommonBody().Which.Code.Should().Be(Put.BadFormat_UnmatchedFormat);

                 }

 

                 {

                     var res = await client.PutByteArrayAsync("users/user/avatar", ImageHelper.CreatePngWithSize(100, 200), "image/png");

                     res.Should().HaveStatusCode(HttpStatusCode.BadRequest)

-                        .And.Should().HaveCommonBody().Which.Code.Should().Be(UserAvatarController.ErrorCodes.Put_BadFormat_BadSize);

+                        .And.Should().HaveCommonBody().Which.Code.Should().Be(Put.BadFormat_BadSize);

                 }

 

                 {

@@ -219,13 +221,13 @@ namespace Timeline.Tests.IntegratedTests
                 {

                     var res = await client.PutByteArrayAsync("users/admin/avatar", new[] { (byte)0x00 }, "image/png");

                     res.Should().HaveStatusCode(HttpStatusCode.Forbidden)

-                        .And.Should().HaveCommonBody().Which.Code.Should().Be(UserAvatarController.ErrorCodes.Put_Forbid);

+                        .And.Should().HaveCommonBody().Which.Code.Should().Be(Put.Forbid);

                 }

 

                 {

                     var res = await client.DeleteAsync("users/admin/avatar");

                     res.Should().HaveStatusCode(HttpStatusCode.Forbidden)

-                        .And.Should().HaveCommonBody().Which.Code.Should().Be(UserAvatarController.ErrorCodes.Delete_Forbid);

+                        .And.Should().HaveCommonBody().Which.Code.Should().Be(Delete.Forbid);

                 }

 

                 for (int i = 0; i < 2; i++) // double delete should work.

@@ -253,13 +255,13 @@ namespace Timeline.Tests.IntegratedTests
                     var res = await client.PutByteArrayAsync("users/usernotexist/avatar", new[] { (byte)0x00 }, "image/png");

                     res.Should().HaveStatusCode(400)

                         .And.Should().HaveCommonBody()

-                        .Which.Code.Should().Be(UserAvatarController.ErrorCodes.Put_UserNotExist);

+                        .Which.Code.Should().Be(Put.UserNotExist);

                 }

 

                 {

                     var res = await client.DeleteAsync("users/usernotexist/avatar");

                     res.Should().HaveStatusCode(400)

-                        .And.Should().HaveCommonBody().Which.Code.Should().Be(UserAvatarController.ErrorCodes.Delete_UserNotExist);

+                        .And.Should().HaveCommonBody().Which.Code.Should().Be(Delete.UserNotExist);

                 }

             }

         }

diff --git a/Timeline.Tests/UserAvatarServiceTest.cs b/Timeline.Tests/UserAvatarServiceTest.cs
index d22ad113..7489517b 100644
--- a/Timeline.Tests/UserAvatarServiceTest.cs
+++ b/Timeline.Tests/UserAvatarServiceTest.cs
@@ -63,8 +63,8 @@ namespace Timeline.Tests
                 Type = "image/png"

             };

             _validator.Awaiting(v => v.Validate(avatar))

-                    .Should().Throw<AvatarDataException>()

-                    .Where(e => e.Avatar == avatar && e.Error == AvatarDataException.ErrorReason.CantDecode);

+                    .Should().Throw<AvatarFormatException>()

+                    .Where(e => e.Avatar == avatar && e.Error == AvatarFormatException.ErrorReason.CantDecode);

         }

 

         [Fact]

@@ -76,8 +76,8 @@ namespace Timeline.Tests
                 Type = "image/jpeg"

             };

             _validator.Awaiting(v => v.Validate(avatar))

-                    .Should().Throw<AvatarDataException>()

-                    .Where(e => e.Avatar == avatar && e.Error == AvatarDataException.ErrorReason.UnmatchedFormat);

+                    .Should().Throw<AvatarFormatException>()

+                    .Where(e => e.Avatar == avatar && e.Error == AvatarFormatException.ErrorReason.UnmatchedFormat);

         }

 

         [Fact]

@@ -89,8 +89,8 @@ namespace Timeline.Tests
                 Type = PngFormat.Instance.DefaultMimeType

             };

             _validator.Awaiting(v => v.Validate(avatar))

-                    .Should().Throw<AvatarDataException>()

-                    .Where(e => e.Avatar == avatar && e.Error == AvatarDataException.ErrorReason.BadSize);

+                    .Should().Throw<AvatarFormatException>()

+                    .Where(e => e.Avatar == avatar && e.Error == AvatarFormatException.ErrorReason.BadSize);

         }

 

         [Fact]

diff --git a/Timeline/Controllers/UserAvatarController.cs b/Timeline/Controllers/UserAvatarController.cs
index 5cba1d93..838a3928 100644
--- a/Timeline/Controllers/UserAvatarController.cs
+++ b/Timeline/Controllers/UserAvatarController.cs
@@ -1,6 +1,7 @@
 using Microsoft.AspNetCore.Authorization;

 using Microsoft.AspNetCore.Http;

 using Microsoft.AspNetCore.Mvc;

+using Microsoft.Extensions.Localization;

 using Microsoft.Extensions.Logging;

 using Microsoft.Net.Http.Headers;

 using System;

@@ -8,61 +9,67 @@ using System.Linq;
 using System.Threading.Tasks;

 using Timeline.Authentication;

 using Timeline.Filters;

+using Timeline.Helpers;

 using Timeline.Models.Http;

+using Timeline.Models.Validation;

 using Timeline.Services;

 

-namespace Timeline.Controllers

+namespace Timeline

 {

-    [ApiController]

-    public class UserAvatarController : Controller

+    public static partial class ErrorCodes

     {

-        public static class ErrorCodes

+        public static partial class Http

         {

-            public const int Get_UserNotExist = -1001;

-

-            public const int Put_UserNotExist = -2001;

-            public const int Put_Forbid = -2002;

-            public const int Put_BadFormat_CantDecode = -2011;

-            public const int Put_BadFormat_UnmatchedFormat = -2012;

-            public const int Put_BadFormat_BadSize = -2013;

-            public const int Put_Content_TooBig = -2021;

-            public const int Put_Content_UnmatchedLength_Less = -2022;

-            public const int Put_Content_UnmatchedLength_Bigger = -2023;

+            public static class UserAvatar // bbb = 003

+            {

+                public static class Get // cc = 01

+                {

+                    public const int UserNotExist = 10030101;

+                }

 

-            public const int Delete_UserNotExist = -3001;

-            public const int Delete_Forbid = -3002;

+                public static class Put // cc = 02

+                {

+                    public const int UserNotExist = 10030201;

+                    public const int Forbid = 10030202;

+                    public const int BadFormat_CantDecode = 10030203;

+                    public const int BadFormat_UnmatchedFormat = 10030204;

+                    public const int BadFormat_BadSize = 10030205;

 

+                }

 

-            public static int From(AvatarDataException.ErrorReason error)

-            {

-                switch (error)

+                public static class Delete // cc = 03

                 {

-                    case AvatarDataException.ErrorReason.CantDecode:

-                        return Put_BadFormat_CantDecode;

-                    case AvatarDataException.ErrorReason.UnmatchedFormat:

-                        return Put_BadFormat_UnmatchedFormat;

-                    case AvatarDataException.ErrorReason.BadSize:

-                        return Put_BadFormat_BadSize;

-                    default:

-                        throw new Exception("Unknown AvatarDataException.ErrorReason value.");

+                    public const int UserNotExist = 10030301;

+                    public const int Forbid = 10030302;

                 }

             }

         }

+    }

+}

 

+namespace Timeline.Controllers

+{

+    [ApiController]

+    public class UserAvatarController : Controller

+    {

         private readonly ILogger<UserAvatarController> _logger;

 

         private readonly IUserAvatarService _service;

 

-        public UserAvatarController(ILogger<UserAvatarController> logger, IUserAvatarService service)

+        private readonly IStringLocalizerFactory _localizerFactory;

+        private readonly IStringLocalizer<UserAvatarController> _localizer;

+

+        public UserAvatarController(ILogger<UserAvatarController> logger, IUserAvatarService service, IStringLocalizerFactory localizerFactory)

         {

             _logger = logger;

             _service = service;

+            _localizerFactory = localizerFactory;

+            _localizer = new StringLocalizer<UserAvatarController>(localizerFactory);

         }

 

         [HttpGet("users/{username}/avatar")]

-        [Authorize]

         [ResponseCache(NoStore = false, Location = ResponseCacheLocation.None, Duration = 0)]

-        public async Task<IActionResult> Get([FromRoute] string username)

+        public async Task<IActionResult> Get([FromRoute][Username] string username)

         {

             const string IfNonMatchHeaderKey = "If-None-Match";

 

@@ -74,11 +81,16 @@ namespace Timeline.Controllers
                 if (Request.Headers.TryGetValue(IfNonMatchHeaderKey, out var value))

                 {

                     if (!EntityTagHeaderValue.TryParseStrictList(value, out var eTagList))

-                        return BadRequest(CommonResponse.BadIfNonMatch());

+                    {

+                        _logger.LogInformation(Log.Format(Resources.Controllers.UserAvatarController.LogGetBadIfNoneMatch,

+                            ("Username", username), ("If-None-Match", value)));

+                        return BadRequest(HeaderErrorResponse.BadIfNonMatch(_localizerFactory));

+                    }

 

                     if (eTagList.FirstOrDefault(e => e.Equals(eTag)) != null)

                     {

                         Response.Headers.Add("ETag", eTagValue);

+                        _logger.LogInformation(Log.Format(Resources.Controllers.UserAvatarController.LogGetReturnNotModify, ("Username", username)));

                         return StatusCode(StatusCodes.Status304NotModified);

                     }

                 }

@@ -86,12 +98,13 @@ namespace Timeline.Controllers
                 var avatarInfo = await _service.GetAvatar(username);

                 var avatar = avatarInfo.Avatar;

 

+                _logger.LogInformation(Log.Format(Resources.Controllers.UserAvatarController.LogGetReturnData, ("Username", username)));

                 return File(avatar.Data, avatar.Type, new DateTimeOffset(avatarInfo.LastModified), eTag);

             }

             catch (UserNotExistException e)

             {

-                _logger.LogInformation(e, $"Attempt to get a avatar of a non-existent user failed. Username: {username} .");

-                return NotFound(new CommonResponse(ErrorCodes.Get_UserNotExist, "User does not exist."));

+                _logger.LogInformation(e, Log.Format(Resources.Controllers.UserAvatarController.LogGetUserNotExist, ("Username", username)));

+                return NotFound(new CommonResponse(ErrorCodes.Http.UserAvatar.Get.UserNotExist, _localizer["ErrorGetUserNotExist"]));

             }

         }

 

@@ -99,18 +112,18 @@ namespace Timeline.Controllers
         [Authorize]

         [RequireContentType, RequireContentLength]

         [Consumes("image/png", "image/jpeg", "image/gif", "image/webp")]

-        public async Task<IActionResult> Put(string username)

+        public async Task<IActionResult> Put([FromRoute][Username] string username)

         {

-            var contentLength = Request.ContentLength.Value;

+            var contentLength = Request.ContentLength!.Value;

             if (contentLength > 1000 * 1000 * 10)

-                return BadRequest(new CommonResponse(ErrorCodes.Put_Content_TooBig,

-                    "Content can't be bigger than 10MB."));

+                return BadRequest(ContentErrorResponse.TooBig(_localizerFactory, "10MB"));

 

             if (!User.IsAdministrator() && User.Identity.Name != username)

             {

-                _logger.LogInformation($"Attempt to put a avatar of other user as a non-admin failed. Operator Username: {User.Identity.Name} ;  Username To Put Avatar: {username} .");

+                _logger.LogInformation(Log.Format(Resources.Controllers.UserAvatarController.LogPutForbid,

+                    ("Operator Username", User.Identity.Name), ("Username To Put Avatar", username)));

                 return StatusCode(StatusCodes.Status403Forbidden,

-                    new CommonResponse(ErrorCodes.Put_Forbid, "Normal user can't change other's avatar."));

+                    new CommonResponse(ErrorCodes.Http.UserAvatar.Put.Forbid, _localizer["ErrorPutForbid"]));

             }

 

             try

@@ -119,13 +132,11 @@ namespace Timeline.Controllers
                 var bytesRead = await Request.Body.ReadAsync(data);

 

                 if (bytesRead != contentLength)

-                    return BadRequest(new CommonResponse(ErrorCodes.Put_Content_UnmatchedLength_Less,

-                        $"Content length in header is {contentLength} but actual length is {bytesRead}."));

+                    return BadRequest(ContentErrorResponse.UnmatchedLength_Smaller(_localizerFactory));

 

                 var extraByte = new byte[1];

                 if (await Request.Body.ReadAsync(extraByte) != 0)

-                    return BadRequest(new CommonResponse(ErrorCodes.Put_Content_UnmatchedLength_Bigger,

-                        $"Content length in header is {contentLength} but actual length is bigger than that."));

+                    return BadRequest(ContentErrorResponse.UnmatchedLength_Bigger(_localizerFactory));

 

                 await _service.SetAvatar(username, new Avatar

                 {

@@ -133,43 +144,57 @@ namespace Timeline.Controllers
                     Type = Request.ContentType

                 });

 

-                _logger.LogInformation($"Succeed to put a avatar of a user. Username: {username} ; Mime Type: {Request.ContentType} .");

+                _logger.LogInformation(Log.Format(Resources.Controllers.UserAvatarController.LogPutSuccess,

+                    ("Username", username), ("Mime Type", Request.ContentType)));

                 return Ok();

             }

             catch (UserNotExistException e)

             {

-                _logger.LogInformation(e, $"Attempt to put a avatar of a non-existent user failed. Username: {username} .");

-                return BadRequest(new CommonResponse(ErrorCodes.Put_UserNotExist, "User does not exist."));

+                _logger.LogInformation(e, Log.Format(Resources.Controllers.UserAvatarController.LogPutUserNotExist, ("Username", username)));

+                return BadRequest(new CommonResponse(ErrorCodes.Http.UserAvatar.Put.UserNotExist, _localizer["ErrorPutUserNotExist"]));

             }

-            catch (AvatarDataException e)

+            catch (AvatarFormatException e)

             {

-                _logger.LogInformation(e, $"Attempt to put a avatar of a bad format failed. Username: {username} .");

-                return BadRequest(new CommonResponse(ErrorCodes.From(e.Error), "Bad format."));

+                var (code, message) = e.Error switch

+                {

+                    AvatarFormatException.ErrorReason.CantDecode =>

+                        (ErrorCodes.Http.UserAvatar.Put.BadFormat_CantDecode, _localizer["ErrorPutBadFormatCantDecode"]),

+                    AvatarFormatException.ErrorReason.UnmatchedFormat =>

+                       (ErrorCodes.Http.UserAvatar.Put.BadFormat_UnmatchedFormat, _localizer["ErrorPutBadFormatUnmatchedFormat"]),

+                    AvatarFormatException.ErrorReason.BadSize =>

+                       (ErrorCodes.Http.UserAvatar.Put.BadFormat_BadSize, _localizer["ErrorPutBadFormatBadSize"]),

+                    _ =>

+                        throw new Exception(Resources.Controllers.UserAvatarController.ExceptionUnknownAvatarFormatError)

+                };

+

+                _logger.LogInformation(e, Log.Format(Resources.Controllers.UserAvatarController.LogPutUserBadFormat, ("Username", username)));

+                return BadRequest(new CommonResponse(code, message));

             }

         }

 

         [HttpDelete("users/{username}/avatar")]

         [Authorize]

-        public async Task<IActionResult> Delete([FromRoute] string username)

+        public async Task<IActionResult> Delete([FromRoute][Username] string username)

         {

             if (!User.IsAdministrator() && User.Identity.Name != username)

             {

-                _logger.LogInformation($"Attempt to delete a avatar of other user as a non-admin failed. Operator Username: {User.Identity.Name} ;  Username To Put Avatar: {username} .");

+                _logger.LogInformation(Log.Format(Resources.Controllers.UserAvatarController.LogPutUserBadFormat,

+                    ("Operator Username", User.Identity.Name), ("Username To Delete Avatar", username)));

                 return StatusCode(StatusCodes.Status403Forbidden,

-                    new CommonResponse(ErrorCodes.Delete_Forbid, "Normal user can't delete other's avatar."));

+                    new CommonResponse(ErrorCodes.Http.UserAvatar.Delete.Forbid, _localizer["ErrorDeleteForbid"]));

             }

 

             try

             {

                 await _service.SetAvatar(username, null);

 

-                _logger.LogInformation($"Succeed to delete a avatar of a user. Username: {username} .");

+                _logger.LogInformation(Log.Format(Resources.Controllers.UserAvatarController.LogDeleteSuccess, ("Username", username)));

                 return Ok();

             }

             catch (UserNotExistException e)

             {

-                _logger.LogInformation(e, $"Attempt to delete a avatar of a non-existent user failed. Username: {username} .");

-                return BadRequest(new CommonResponse(ErrorCodes.Delete_UserNotExist, "User does not exist."));

+                _logger.LogInformation(e, Log.Format(Resources.Controllers.UserAvatarController.LogDeleteNotExist, ("Username", username)));

+                return BadRequest(new CommonResponse(ErrorCodes.Http.UserAvatar.Delete.UserNotExist, _localizer["ErrorDeleteUserNotExist"]));

             }

         }

     }

diff --git a/Timeline/Entities/UserAvatar.cs b/Timeline/Entities/UserAvatar.cs
index d47bb28b..3b5388aa 100644
--- a/Timeline/Entities/UserAvatar.cs
+++ b/Timeline/Entities/UserAvatar.cs
@@ -11,6 +11,7 @@ namespace Timeline.Entities
         public long Id { get; set; }

 

         [Column("data")]

+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Performance", "CA1819:Properties should not return arrays", Justification = "This is data base entity.")]

         public byte[]? Data { get; set; }

 

         [Column("type")]

diff --git a/Timeline/ErrorCodes.cs b/Timeline/ErrorCodes.cs
index 0b325e27..5e7f003a 100644
--- a/Timeline/ErrorCodes.cs
+++ b/Timeline/ErrorCodes.cs
@@ -17,10 +17,17 @@
 

                 public static class Header // cc = 01

                 {

-                    public const int Missing_ContentType = 10010101; // dd = 01

-                    public const int Missing_ContentLength = 10010102; // dd = 02

-                    public const int Zero_ContentLength = 10010103; // dd = 03

-                    public const int BadFormat_IfNonMatch = 10010104; // dd = 04

+                    public const int Missing_ContentType = 10000101; // dd = 01

+                    public const int Missing_ContentLength = 10000102; // dd = 02

+                    public const int Zero_ContentLength = 10000103; // dd = 03

+                    public const int BadFormat_IfNonMatch = 10000104; // dd = 04

+                }

+

+                public static class Content // cc = 02

+                {

+                    public const int TooBig = 1000201;

+                    public const int UnmatchedLength_Smaller = 10030202;

+                    public const int UnmatchedLength_Bigger = 10030203;

                 }

             }

         }

diff --git a/Timeline/Filters/ContentHeaderAttributes.cs b/Timeline/Filters/ContentHeaderAttributes.cs
index 14685a01..e3d4eeb2 100644
--- a/Timeline/Filters/ContentHeaderAttributes.cs
+++ b/Timeline/Filters/ContentHeaderAttributes.cs
@@ -1,16 +1,20 @@
 using Microsoft.AspNetCore.Mvc;

 using Microsoft.AspNetCore.Mvc.Filters;

+using Microsoft.Extensions.DependencyInjection;

+using Microsoft.Extensions.Localization;

 using Timeline.Models.Http;

 

 namespace Timeline.Filters

 {

     public class RequireContentTypeAttribute : ActionFilterAttribute

     {

+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Design", "CA1062:Validate arguments of public methods")]

         public override void OnActionExecuting(ActionExecutingContext context)

         {

             if (context.HttpContext.Request.ContentType == null)

             {

-                context.Result = new BadRequestObjectResult(CommonResponse.MissingContentType());

+                var localizerFactory = context.HttpContext.RequestServices.GetRequiredService<IStringLocalizerFactory>();

+                context.Result = new BadRequestObjectResult(HeaderErrorResponse.MissingContentType(localizerFactory));

             }

         }

     }

@@ -30,17 +34,20 @@ namespace Timeline.Filters
 

         public bool RequireNonZero { get; set; }

 

+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Design", "CA1062:Validate arguments of public methods")]

         public override void OnActionExecuting(ActionExecutingContext context)

         {

             if (context.HttpContext.Request.ContentLength == null)

             {

-                context.Result = new BadRequestObjectResult(CommonResponse.MissingContentLength());

+                var localizerFactory = context.HttpContext.RequestServices.GetRequiredService<IStringLocalizerFactory>();

+                context.Result = new BadRequestObjectResult(HeaderErrorResponse.MissingContentLength(localizerFactory));

                 return;

             }

 

             if (RequireNonZero && context.HttpContext.Request.ContentLength.Value == 0)

             {

-                context.Result = new BadRequestObjectResult(CommonResponse.ZeroContentLength());

+                var localizerFactory = context.HttpContext.RequestServices.GetRequiredService<IStringLocalizerFactory>();

+                context.Result = new BadRequestObjectResult(HeaderErrorResponse.ZeroContentLength(localizerFactory));

                 return;

             }

         }

diff --git a/Timeline/Helpers/LanguageHelper.cs b/Timeline/Helpers/LanguageHelper.cs
new file mode 100644
index 00000000..b0156b8b
--- /dev/null
+++ b/Timeline/Helpers/LanguageHelper.cs
@@ -0,0 +1,12 @@
+using System.Linq;

+

+namespace Timeline.Helpers

+{

+    public static class LanguageHelper

+    {

+        public static bool AreSame(this bool firstBool, params bool[] otherBools)

+        {

+            return otherBools.All(b => b == firstBool);

+        }

+    }

+}

diff --git a/Timeline/Helpers/Log.cs b/Timeline/Helpers/Log.cs
index 8deebf1d..68c975fa 100644
--- a/Timeline/Helpers/Log.cs
+++ b/Timeline/Helpers/Log.cs
@@ -3,26 +3,6 @@ using System.Text;
 

 namespace Timeline.Helpers

 {

-    // TODO! Remember to remove this after refactor.

-    public static class MyLogHelper

-    {

-        public static KeyValuePair<string, object> Pair(string key, object value) => new KeyValuePair<string, object>(key, value);

-

-        public static string FormatLogMessage(string summary, params KeyValuePair<string, object>[] properties)

-        {

-            var builder = new StringBuilder();

-            builder.Append(summary);

-            foreach (var property in properties)

-            {

-                builder.AppendLine();

-                builder.Append(property.Key);

-                builder.Append(" : ");

-                builder.Append(property.Value);

-            }

-            return builder.ToString();

-        }

-    }

-

     public static class Log

     {

         public static string Format(string summary, params (string, object?)[] properties)

diff --git a/Timeline/Models/Http/Common.cs b/Timeline/Models/Http/Common.cs
index c741837a..39ddddd9 100644
--- a/Timeline/Models/Http/Common.cs
+++ b/Timeline/Models/Http/Common.cs
@@ -5,46 +5,74 @@ namespace Timeline.Models.Http
 {

     public class CommonResponse

     {

-        public static CommonResponse InvalidModel(string message)

+        internal static CommonResponse InvalidModel(string message)

         {

             return new CommonResponse(ErrorCodes.Http.Common.InvalidModel, message);

         }

 

-        public static CommonResponse MissingContentType()

+        public CommonResponse()

         {

-            return new CommonResponse(ErrorCodes.Http.Common.Header.Missing_ContentType, "Header Content-Type is required.");

+

         }

 

-        public static CommonResponse MissingContentLength()

+        public CommonResponse(int code, string message)

         {

-            return new CommonResponse(ErrorCodes.Http.Common.Header.Missing_ContentLength, "Header Content-Length is missing or of bad format.");

+            Code = code;

+            Message = message;

         }

 

-        public static CommonResponse ZeroContentLength()

+        public int Code { get; set; }

+        public string? Message { get; set; }

+    }

+

+    internal static class HeaderErrorResponse

+    {

+        internal static CommonResponse MissingContentType(IStringLocalizerFactory localizerFactory)

         {

-            return new CommonResponse(ErrorCodes.Http.Common.Header.Zero_ContentLength, "Header Content-Length must not be 0.");

+            var localizer = localizerFactory.Create("Models.Http.Common");

+            return new CommonResponse(ErrorCodes.Http.Common.Header.Missing_ContentType, localizer["HeaderMissingContentType"]);

         }

 

-        public static CommonResponse BadIfNonMatch()

+        internal static CommonResponse MissingContentLength(IStringLocalizerFactory localizerFactory)

         {

-            return new CommonResponse(ErrorCodes.Http.Common.Header.BadFormat_IfNonMatch, "Header If-Non-Match is of bad format.");

+            var localizer = localizerFactory.Create("Models.Http.Common");

+            return new CommonResponse(ErrorCodes.Http.Common.Header.Missing_ContentLength, localizer["HeaderMissingContentLength"]);

         }

 

-        public CommonResponse()

+        internal static CommonResponse ZeroContentLength(IStringLocalizerFactory localizerFactory)

         {

+            var localizer = localizerFactory.Create("Models.Http.Common");

+            return new CommonResponse(ErrorCodes.Http.Common.Header.Zero_ContentLength, localizer["HeaderZeroContentLength"]);

+        }

 

+        internal static CommonResponse BadIfNonMatch(IStringLocalizerFactory localizerFactory)

+        {

+            var localizer = localizerFactory.Create("Models.Http.Common");

+            return new CommonResponse(ErrorCodes.Http.Common.Header.BadFormat_IfNonMatch, localizer["HeaderBadIfNonMatch"]);

         }

+    }

 

-        public CommonResponse(int code, string message)

+    internal static class ContentErrorResponse

+    {

+        internal static CommonResponse TooBig(IStringLocalizerFactory localizerFactory, string maxLength)

         {

-            Code = code;

-            Message = message;

+            var localizer = localizerFactory.Create("Models.Http.Common");

+            return new CommonResponse(ErrorCodes.Http.Common.Content.TooBig, localizer["ContentTooBig", maxLength]);

         }

 

-        public int Code { get; set; }

-        public string? Message { get; set; }

+        internal static CommonResponse UnmatchedLength_Smaller(IStringLocalizerFactory localizerFactory)

+        {

+            var localizer = localizerFactory.Create("Models.Http.Common");

+            return new CommonResponse(ErrorCodes.Http.Common.Content.UnmatchedLength_Smaller, localizer["ContentUnmatchedLengthSmaller"]);

+        }

+        internal static CommonResponse UnmatchedLength_Bigger(IStringLocalizerFactory localizerFactory)

+        {

+            var localizer = localizerFactory.Create("Models.Http.Common");

+            return new CommonResponse(ErrorCodes.Http.Common.Content.UnmatchedLength_Bigger, localizer["ContentUnmatchedLengthBigger"]);

+        }

     }

 

+

     public class CommonDataResponse<T> : CommonResponse

     {

         public CommonDataResponse()

@@ -87,13 +115,13 @@ namespace Timeline.Models.Http
         internal static CommonPutResponse Create(IStringLocalizerFactory localizerFactory)

         {

             var localizer = localizerFactory.Create("Models.Http.Common");

-            return new CommonPutResponse(0, localizer["ResponsePutCreate"], true);

+            return new CommonPutResponse(0, localizer["PutCreate"], true);

         }

 

         internal static CommonPutResponse Modify(IStringLocalizerFactory localizerFactory)

         {

             var localizer = localizerFactory.Create("Models.Http.Common");

-            return new CommonPutResponse(0, localizer["ResponsePutModify"], false);

+            return new CommonPutResponse(0, localizer["PutModify"], false);

 

         }

     }

@@ -124,13 +152,13 @@ namespace Timeline.Models.Http
         internal static CommonDeleteResponse Delete(IStringLocalizerFactory localizerFactory)

         {

             var localizer = localizerFactory.Create("Models.Http.Common");

-            return new CommonDeleteResponse(0, localizer["ResponseDeleteDelete"], true);

+            return new CommonDeleteResponse(0, localizer["DeleteDelete"], true);

         }

 

         internal static CommonDeleteResponse NotExist(IStringLocalizerFactory localizerFactory)

         {

             var localizer = localizerFactory.Create("Models.Models.Http.Common");

-            return new CommonDeleteResponse(0, localizer["ResponseDeleteNotExist"], false);

+            return new CommonDeleteResponse(0, localizer["DeleteNotExist"], false);

         }

     }

 }

diff --git a/Timeline/Resources/Controllers/UserAvatarController.Designer.cs b/Timeline/Resources/Controllers/UserAvatarController.Designer.cs
new file mode 100644
index 00000000..e6eeb1e8
--- /dev/null
+++ b/Timeline/Resources/Controllers/UserAvatarController.Designer.cs
@@ -0,0 +1,171 @@
+//------------------------------------------------------------------------------

+// <auto-generated>

+//     This code was generated by a tool.

+//     Runtime Version:4.0.30319.42000

+//

+//     Changes to this file may cause incorrect behavior and will be lost if

+//     the code is regenerated.

+// </auto-generated>

+//------------------------------------------------------------------------------

+

+namespace Timeline.Resources.Controllers {

+    using System;

+    

+    

+    /// <summary>

+    ///   A strongly-typed resource class, for looking up localized strings, etc.

+    /// </summary>

+    // This class was auto-generated by the StronglyTypedResourceBuilder

+    // class via a tool like ResGen or Visual Studio.

+    // To add or remove a member, edit your .ResX file then rerun ResGen

+    // with the /str option, or rebuild your VS project.

+    [global::System.CodeDom.Compiler.GeneratedCodeAttribute("System.Resources.Tools.StronglyTypedResourceBuilder", "16.0.0.0")]

+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

+    [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]

+    internal class UserAvatarController {

+        

+        private static global::System.Resources.ResourceManager resourceMan;

+        

+        private static global::System.Globalization.CultureInfo resourceCulture;

+        

+        [global::System.Diagnostics.CodeAnalysis.SuppressMessageAttribute("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]

+        internal UserAvatarController() {

+        }

+        

+        /// <summary>

+        ///   Returns the cached ResourceManager instance used by this class.

+        /// </summary>

+        [global::System.ComponentModel.EditorBrowsableAttribute(global::System.ComponentModel.EditorBrowsableState.Advanced)]

+        internal static global::System.Resources.ResourceManager ResourceManager {

+            get {

+                if (object.ReferenceEquals(resourceMan, null)) {

+                    global::System.Resources.ResourceManager temp = new global::System.Resources.ResourceManager("Timeline.Resources.Controllers.UserAvatarController", typeof(UserAvatarController).Assembly);

+                    resourceMan = temp;

+                }

+                return resourceMan;

+            }

+        }

+        

+        /// <summary>

+        ///   Overrides the current thread's CurrentUICulture property for all

+        ///   resource lookups using this strongly typed resource class.

+        /// </summary>

+        [global::System.ComponentModel.EditorBrowsableAttribute(global::System.ComponentModel.EditorBrowsableState.Advanced)]

+        internal static global::System.Globalization.CultureInfo Culture {

+            get {

+                return resourceCulture;

+            }

+            set {

+                resourceCulture = value;

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Unknown AvatarDataException.ErrorReason value..

+        /// </summary>

+        internal static string ExceptionUnknownAvatarFormatError {

+            get {

+                return ResourceManager.GetString("ExceptionUnknownAvatarFormatError", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Attempt to delete a avatar of other user as a non-admin failed..

+        /// </summary>

+        internal static string LogDeleteForbid {

+            get {

+                return ResourceManager.GetString("LogDeleteForbid", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Attempt to delete a avatar of a non-existent user failed..

+        /// </summary>

+        internal static string LogDeleteNotExist {

+            get {

+                return ResourceManager.GetString("LogDeleteNotExist", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Succeed to delete a avatar of a user..

+        /// </summary>

+        internal static string LogDeleteSuccess {

+            get {

+                return ResourceManager.GetString("LogDeleteSuccess", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Attempt to get a avatar with If-None-Match in bad format..

+        /// </summary>

+        internal static string LogGetBadIfNoneMatch {

+            get {

+                return ResourceManager.GetString("LogGetBadIfNoneMatch", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Returned full data for a get avatar attempt..

+        /// </summary>

+        internal static string LogGetReturnData {

+            get {

+                return ResourceManager.GetString("LogGetReturnData", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Returned NotModify for a get avatar attempt..

+        /// </summary>

+        internal static string LogGetReturnNotModify {

+            get {

+                return ResourceManager.GetString("LogGetReturnNotModify", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Attempt to get a avatar of a non-existent user failed..

+        /// </summary>

+        internal static string LogGetUserNotExist {

+            get {

+                return ResourceManager.GetString("LogGetUserNotExist", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Attempt to put a avatar of other user as a non-admin failed..

+        /// </summary>

+        internal static string LogPutForbid {

+            get {

+                return ResourceManager.GetString("LogPutForbid", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Succeed to put a avatar of a user..

+        /// </summary>

+        internal static string LogPutSuccess {

+            get {

+                return ResourceManager.GetString("LogPutSuccess", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Attempt to put a avatar of a bad format failed..

+        /// </summary>

+        internal static string LogPutUserBadFormat {

+            get {

+                return ResourceManager.GetString("LogPutUserBadFormat", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Attempt to put a avatar of a non-existent user failed..

+        /// </summary>

+        internal static string LogPutUserNotExist {

+            get {

+                return ResourceManager.GetString("LogPutUserNotExist", resourceCulture);

+            }

+        }

+    }

+}

diff --git a/Timeline/Resources/Controllers/UserAvatarController.en.resx b/Timeline/Resources/Controllers/UserAvatarController.en.resx
new file mode 100644
index 00000000..cf92ae6d
--- /dev/null
+++ b/Timeline/Resources/Controllers/UserAvatarController.en.resx
@@ -0,0 +1,144 @@
+<?xml version="1.0" encoding="utf-8"?>

+<root>

+  <!-- 

+    Microsoft ResX Schema 

+    

+    Version 2.0

+    

+    The primary goals of this format is to allow a simple XML format 

+    that is mostly human readable. The generation and parsing of the 

+    various data types are done through the TypeConverter classes 

+    associated with the data types.

+    

+    Example:

+    

+    ... ado.net/XML headers & schema ...

+    <resheader name="resmimetype">text/microsoft-resx</resheader>

+    <resheader name="version">2.0</resheader>

+    <resheader name="reader">System.Resources.ResXResourceReader, System.Windows.Forms, ...</resheader>

+    <resheader name="writer">System.Resources.ResXResourceWriter, System.Windows.Forms, ...</resheader>

+    <data name="Name1"><value>this is my long string</value><comment>this is a comment</comment></data>

+    <data name="Color1" type="System.Drawing.Color, System.Drawing">Blue</data>

+    <data name="Bitmap1" mimetype="application/x-microsoft.net.object.binary.base64">

+        <value>[base64 mime encoded serialized .NET Framework object]</value>

+    </data>

+    <data name="Icon1" type="System.Drawing.Icon, System.Drawing" mimetype="application/x-microsoft.net.object.bytearray.base64">

+        <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>

+        <comment>This is a comment</comment>

+    </data>

+                

+    There are any number of "resheader" rows that contain simple 

+    name/value pairs.

+    

+    Each data row contains a name, and value. The row also contains a 

+    type or mimetype. Type corresponds to a .NET class that support 

+    text/value conversion through the TypeConverter architecture. 

+    Classes that don't support this are serialized and stored with the 

+    mimetype set.

+    

+    The mimetype is used for serialized objects, and tells the 

+    ResXResourceReader how to depersist the object. This is currently not 

+    extensible. For a given mimetype the value must be set accordingly:

+    

+    Note - application/x-microsoft.net.object.binary.base64 is the format 

+    that the ResXResourceWriter will generate, however the reader can 

+    read any of the formats listed below.

+    

+    mimetype: application/x-microsoft.net.object.binary.base64

+    value   : The object must be serialized with 

+            : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter

+            : and then encoded with base64 encoding.

+    

+    mimetype: application/x-microsoft.net.object.soap.base64

+    value   : The object must be serialized with 

+            : System.Runtime.Serialization.Formatters.Soap.SoapFormatter

+            : and then encoded with base64 encoding.

+

+    mimetype: application/x-microsoft.net.object.bytearray.base64

+    value   : The object must be serialized into a byte array 

+            : using a System.ComponentModel.TypeConverter

+            : and then encoded with base64 encoding.

+    -->

+  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">

+    <xsd:import namespace="http://www.w3.org/XML/1998/namespace" />

+    <xsd:element name="root" msdata:IsDataSet="true">

+      <xsd:complexType>

+        <xsd:choice maxOccurs="unbounded">

+          <xsd:element name="metadata">

+            <xsd:complexType>

+              <xsd:sequence>

+                <xsd:element name="value" type="xsd:string" minOccurs="0" />

+              </xsd:sequence>

+              <xsd:attribute name="name" use="required" type="xsd:string" />

+              <xsd:attribute name="type" type="xsd:string" />

+              <xsd:attribute name="mimetype" type="xsd:string" />

+              <xsd:attribute ref="xml:space" />

+            </xsd:complexType>

+          </xsd:element>

+          <xsd:element name="assembly">

+            <xsd:complexType>

+              <xsd:attribute name="alias" type="xsd:string" />

+              <xsd:attribute name="name" type="xsd:string" />

+            </xsd:complexType>

+          </xsd:element>

+          <xsd:element name="data">

+            <xsd:complexType>

+              <xsd:sequence>

+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />

+                <xsd:element name="comment" type="xsd:string" minOccurs="0" msdata:Ordinal="2" />

+              </xsd:sequence>

+              <xsd:attribute name="name" type="xsd:string" use="required" msdata:Ordinal="1" />

+              <xsd:attribute name="type" type="xsd:string" msdata:Ordinal="3" />

+              <xsd:attribute name="mimetype" type="xsd:string" msdata:Ordinal="4" />

+              <xsd:attribute ref="xml:space" />

+            </xsd:complexType>

+          </xsd:element>

+          <xsd:element name="resheader">

+            <xsd:complexType>

+              <xsd:sequence>

+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />

+              </xsd:sequence>

+              <xsd:attribute name="name" type="xsd:string" use="required" />

+            </xsd:complexType>

+          </xsd:element>

+        </xsd:choice>

+      </xsd:complexType>

+    </xsd:element>

+  </xsd:schema>

+  <resheader name="resmimetype">

+    <value>text/microsoft-resx</value>

+  </resheader>

+  <resheader name="version">

+    <value>2.0</value>

+  </resheader>

+  <resheader name="reader">

+    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>

+  </resheader>

+  <resheader name="writer">

+    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>

+  </resheader>

+  <data name="ErrorDeleteForbid" xml:space="preserve">

+    <value>Normal user can't delete other's avatar.</value>

+  </data>

+  <data name="ErrorDeleteUserNotExist" xml:space="preserve">

+    <value>User does not exist.</value>

+  </data>

+  <data name="ErrorGetUserNotExist" xml:space="preserve">

+    <value>User does not exist.</value>

+  </data>

+  <data name="ErrorPutBadFormatBadSize" xml:space="preserve">

+    <value>Image is not a square.</value>

+  </data>

+  <data name="ErrorPutBadFormatCantDecode" xml:space="preserve">

+    <value>Decoding image failed.</value>

+  </data>

+  <data name="ErrorPutBadFormatUnmatchedFormat" xml:space="preserve">

+    <value>Image format is not the one in header.</value>

+  </data>

+  <data name="ErrorPutForbid" xml:space="preserve">

+    <value>Normal user can't change other's avatar.</value>

+  </data>

+  <data name="ErrorPutUserNotExist" xml:space="preserve">

+    <value>User does not exist.</value>

+  </data>

+</root>
\ No newline at end of file
diff --git a/Timeline/Resources/Controllers/UserAvatarController.resx b/Timeline/Resources/Controllers/UserAvatarController.resx
new file mode 100644
index 00000000..58860c83
--- /dev/null
+++ b/Timeline/Resources/Controllers/UserAvatarController.resx
@@ -0,0 +1,156 @@
+<?xml version="1.0" encoding="utf-8"?>

+<root>

+  <!-- 

+    Microsoft ResX Schema 

+    

+    Version 2.0

+    

+    The primary goals of this format is to allow a simple XML format 

+    that is mostly human readable. The generation and parsing of the 

+    various data types are done through the TypeConverter classes 

+    associated with the data types.

+    

+    Example:

+    

+    ... ado.net/XML headers & schema ...

+    <resheader name="resmimetype">text/microsoft-resx</resheader>

+    <resheader name="version">2.0</resheader>

+    <resheader name="reader">System.Resources.ResXResourceReader, System.Windows.Forms, ...</resheader>

+    <resheader name="writer">System.Resources.ResXResourceWriter, System.Windows.Forms, ...</resheader>

+    <data name="Name1"><value>this is my long string</value><comment>this is a comment</comment></data>

+    <data name="Color1" type="System.Drawing.Color, System.Drawing">Blue</data>

+    <data name="Bitmap1" mimetype="application/x-microsoft.net.object.binary.base64">

+        <value>[base64 mime encoded serialized .NET Framework object]</value>

+    </data>

+    <data name="Icon1" type="System.Drawing.Icon, System.Drawing" mimetype="application/x-microsoft.net.object.bytearray.base64">

+        <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>

+        <comment>This is a comment</comment>

+    </data>

+                

+    There are any number of "resheader" rows that contain simple 

+    name/value pairs.

+    

+    Each data row contains a name, and value. The row also contains a 

+    type or mimetype. Type corresponds to a .NET class that support 

+    text/value conversion through the TypeConverter architecture. 

+    Classes that don't support this are serialized and stored with the 

+    mimetype set.

+    

+    The mimetype is used for serialized objects, and tells the 

+    ResXResourceReader how to depersist the object. This is currently not 

+    extensible. For a given mimetype the value must be set accordingly:

+    

+    Note - application/x-microsoft.net.object.binary.base64 is the format 

+    that the ResXResourceWriter will generate, however the reader can 

+    read any of the formats listed below.

+    

+    mimetype: application/x-microsoft.net.object.binary.base64

+    value   : The object must be serialized with 

+            : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter

+            : and then encoded with base64 encoding.

+    

+    mimetype: application/x-microsoft.net.object.soap.base64

+    value   : The object must be serialized with 

+            : System.Runtime.Serialization.Formatters.Soap.SoapFormatter

+            : and then encoded with base64 encoding.

+

+    mimetype: application/x-microsoft.net.object.bytearray.base64

+    value   : The object must be serialized into a byte array 

+            : using a System.ComponentModel.TypeConverter

+            : and then encoded with base64 encoding.

+    -->

+  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">

+    <xsd:import namespace="http://www.w3.org/XML/1998/namespace" />

+    <xsd:element name="root" msdata:IsDataSet="true">

+      <xsd:complexType>

+        <xsd:choice maxOccurs="unbounded">

+          <xsd:element name="metadata">

+            <xsd:complexType>

+              <xsd:sequence>

+                <xsd:element name="value" type="xsd:string" minOccurs="0" />

+              </xsd:sequence>

+              <xsd:attribute name="name" use="required" type="xsd:string" />

+              <xsd:attribute name="type" type="xsd:string" />

+              <xsd:attribute name="mimetype" type="xsd:string" />

+              <xsd:attribute ref="xml:space" />

+            </xsd:complexType>

+          </xsd:element>

+          <xsd:element name="assembly">

+            <xsd:complexType>

+              <xsd:attribute name="alias" type="xsd:string" />

+              <xsd:attribute name="name" type="xsd:string" />

+            </xsd:complexType>

+          </xsd:element>

+          <xsd:element name="data">

+            <xsd:complexType>

+              <xsd:sequence>

+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />

+                <xsd:element name="comment" type="xsd:string" minOccurs="0" msdata:Ordinal="2" />

+              </xsd:sequence>

+              <xsd:attribute name="name" type="xsd:string" use="required" msdata:Ordinal="1" />

+              <xsd:attribute name="type" type="xsd:string" msdata:Ordinal="3" />

+              <xsd:attribute name="mimetype" type="xsd:string" msdata:Ordinal="4" />

+              <xsd:attribute ref="xml:space" />

+            </xsd:complexType>

+          </xsd:element>

+          <xsd:element name="resheader">

+            <xsd:complexType>

+              <xsd:sequence>

+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />

+              </xsd:sequence>

+              <xsd:attribute name="name" type="xsd:string" use="required" />

+            </xsd:complexType>

+          </xsd:element>

+        </xsd:choice>

+      </xsd:complexType>

+    </xsd:element>

+  </xsd:schema>

+  <resheader name="resmimetype">

+    <value>text/microsoft-resx</value>

+  </resheader>

+  <resheader name="version">

+    <value>2.0</value>

+  </resheader>

+  <resheader name="reader">

+    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>

+  </resheader>

+  <resheader name="writer">

+    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>

+  </resheader>

+  <data name="ExceptionUnknownAvatarFormatError" xml:space="preserve">

+    <value>Unknown AvatarDataException.ErrorReason value.</value>

+  </data>

+  <data name="LogDeleteForbid" xml:space="preserve">

+    <value>Attempt to delete a avatar of other user as a non-admin failed.</value>

+  </data>

+  <data name="LogDeleteNotExist" xml:space="preserve">

+    <value>Attempt to delete a avatar of a non-existent user failed.</value>

+  </data>

+  <data name="LogDeleteSuccess" xml:space="preserve">

+    <value>Succeed to delete a avatar of a user.</value>

+  </data>

+  <data name="LogGetBadIfNoneMatch" xml:space="preserve">

+    <value>Attempt to get a avatar with If-None-Match in bad format.</value>

+  </data>

+  <data name="LogGetReturnData" xml:space="preserve">

+    <value>Returned full data for a get avatar attempt.</value>

+  </data>

+  <data name="LogGetReturnNotModify" xml:space="preserve">

+    <value>Returned NotModify for a get avatar attempt.</value>

+  </data>

+  <data name="LogGetUserNotExist" xml:space="preserve">

+    <value>Attempt to get a avatar of a non-existent user failed.</value>

+  </data>

+  <data name="LogPutForbid" xml:space="preserve">

+    <value>Attempt to put a avatar of other user as a non-admin failed.</value>

+  </data>

+  <data name="LogPutSuccess" xml:space="preserve">

+    <value>Succeed to put a avatar of a user.</value>

+  </data>

+  <data name="LogPutUserBadFormat" xml:space="preserve">

+    <value>Attempt to put a avatar of a bad format failed.</value>

+  </data>

+  <data name="LogPutUserNotExist" xml:space="preserve">

+    <value>Attempt to put a avatar of a non-existent user failed.</value>

+  </data>

+</root>
\ No newline at end of file
diff --git a/Timeline/Resources/Controllers/UserAvatarController.zh.resx b/Timeline/Resources/Controllers/UserAvatarController.zh.resx
new file mode 100644
index 00000000..94de1606
--- /dev/null
+++ b/Timeline/Resources/Controllers/UserAvatarController.zh.resx
@@ -0,0 +1,144 @@
+<?xml version="1.0" encoding="utf-8"?>

+<root>

+  <!-- 

+    Microsoft ResX Schema 

+    

+    Version 2.0

+    

+    The primary goals of this format is to allow a simple XML format 

+    that is mostly human readable. The generation and parsing of the 

+    various data types are done through the TypeConverter classes 

+    associated with the data types.

+    

+    Example:

+    

+    ... ado.net/XML headers & schema ...

+    <resheader name="resmimetype">text/microsoft-resx</resheader>

+    <resheader name="version">2.0</resheader>

+    <resheader name="reader">System.Resources.ResXResourceReader, System.Windows.Forms, ...</resheader>

+    <resheader name="writer">System.Resources.ResXResourceWriter, System.Windows.Forms, ...</resheader>

+    <data name="Name1"><value>this is my long string</value><comment>this is a comment</comment></data>

+    <data name="Color1" type="System.Drawing.Color, System.Drawing">Blue</data>

+    <data name="Bitmap1" mimetype="application/x-microsoft.net.object.binary.base64">

+        <value>[base64 mime encoded serialized .NET Framework object]</value>

+    </data>

+    <data name="Icon1" type="System.Drawing.Icon, System.Drawing" mimetype="application/x-microsoft.net.object.bytearray.base64">

+        <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>

+        <comment>This is a comment</comment>

+    </data>

+                

+    There are any number of "resheader" rows that contain simple 

+    name/value pairs.

+    

+    Each data row contains a name, and value. The row also contains a 

+    type or mimetype. Type corresponds to a .NET class that support 

+    text/value conversion through the TypeConverter architecture. 

+    Classes that don't support this are serialized and stored with the 

+    mimetype set.

+    

+    The mimetype is used for serialized objects, and tells the 

+    ResXResourceReader how to depersist the object. This is currently not 

+    extensible. For a given mimetype the value must be set accordingly:

+    

+    Note - application/x-microsoft.net.object.binary.base64 is the format 

+    that the ResXResourceWriter will generate, however the reader can 

+    read any of the formats listed below.

+    

+    mimetype: application/x-microsoft.net.object.binary.base64

+    value   : The object must be serialized with 

+            : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter

+            : and then encoded with base64 encoding.

+    

+    mimetype: application/x-microsoft.net.object.soap.base64

+    value   : The object must be serialized with 

+            : System.Runtime.Serialization.Formatters.Soap.SoapFormatter

+            : and then encoded with base64 encoding.

+

+    mimetype: application/x-microsoft.net.object.bytearray.base64

+    value   : The object must be serialized into a byte array 

+            : using a System.ComponentModel.TypeConverter

+            : and then encoded with base64 encoding.

+    -->

+  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">

+    <xsd:import namespace="http://www.w3.org/XML/1998/namespace" />

+    <xsd:element name="root" msdata:IsDataSet="true">

+      <xsd:complexType>

+        <xsd:choice maxOccurs="unbounded">

+          <xsd:element name="metadata">

+            <xsd:complexType>

+              <xsd:sequence>

+                <xsd:element name="value" type="xsd:string" minOccurs="0" />

+              </xsd:sequence>

+              <xsd:attribute name="name" use="required" type="xsd:string" />

+              <xsd:attribute name="type" type="xsd:string" />

+              <xsd:attribute name="mimetype" type="xsd:string" />

+              <xsd:attribute ref="xml:space" />

+            </xsd:complexType>

+          </xsd:element>

+          <xsd:element name="assembly">

+            <xsd:complexType>

+              <xsd:attribute name="alias" type="xsd:string" />

+              <xsd:attribute name="name" type="xsd:string" />

+            </xsd:complexType>

+          </xsd:element>

+          <xsd:element name="data">

+            <xsd:complexType>

+              <xsd:sequence>

+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />

+                <xsd:element name="comment" type="xsd:string" minOccurs="0" msdata:Ordinal="2" />

+              </xsd:sequence>

+              <xsd:attribute name="name" type="xsd:string" use="required" msdata:Ordinal="1" />

+              <xsd:attribute name="type" type="xsd:string" msdata:Ordinal="3" />

+              <xsd:attribute name="mimetype" type="xsd:string" msdata:Ordinal="4" />

+              <xsd:attribute ref="xml:space" />

+            </xsd:complexType>

+          </xsd:element>

+          <xsd:element name="resheader">

+            <xsd:complexType>

+              <xsd:sequence>

+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />

+              </xsd:sequence>

+              <xsd:attribute name="name" type="xsd:string" use="required" />

+            </xsd:complexType>

+          </xsd:element>

+        </xsd:choice>

+      </xsd:complexType>

+    </xsd:element>

+  </xsd:schema>

+  <resheader name="resmimetype">

+    <value>text/microsoft-resx</value>

+  </resheader>

+  <resheader name="version">

+    <value>2.0</value>

+  </resheader>

+  <resheader name="reader">

+    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>

+  </resheader>

+  <resheader name="writer">

+    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>

+  </resheader>

+  <data name="ErrorDeleteForbid" xml:space="preserve">

+    <value>普通用户不能删除其他用户的头像。</value>

+  </data>

+  <data name="ErrorDeleteUserNotExist" xml:space="preserve">

+    <value>用户不存在。</value>

+  </data>

+  <data name="ErrorGetUserNotExist" xml:space="preserve">

+    <value>用户不存在。</value>

+  </data>

+  <data name="ErrorPutBadFormatBadSize" xml:space="preserve">

+    <value>图片不是正方形。</value>

+  </data>

+  <data name="ErrorPutBadFormatCantDecode" xml:space="preserve">

+    <value>解码图片失败。</value>

+  </data>

+  <data name="ErrorPutBadFormatUnmatchedFormat" xml:space="preserve">

+    <value>图片格式与请求头中指示的不一样。</value>

+  </data>

+  <data name="ErrorPutForbid" xml:space="preserve">

+    <value>普通用户不能修改其他用户的头像。</value>

+  </data>

+  <data name="ErrorPutUserNotExist" xml:space="preserve">

+    <value>用户不存在。</value>

+  </data>

+</root>
\ No newline at end of file
diff --git a/Timeline/Resources/Models/Http/Common.en.resx b/Timeline/Resources/Models/Http/Common.en.resx
index 40d44191..10407d76 100644
--- a/Timeline/Resources/Models/Http/Common.en.resx
+++ b/Timeline/Resources/Models/Http/Common.en.resx
@@ -117,16 +117,37 @@
   <resheader name="writer">

     <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>

   </resheader>

-  <data name="ResponseDeleteDelete" xml:space="preserve">

+  <data name="ContentTooBig" xml:space="preserve">

+    <value>Body is too big. It can't be bigger than {0}.</value>

+  </data>

+  <data name="ContentUnmatchedLengthBigger" xml:space="preserve">

+    <value>Actual body length is bigger than it in header.</value>

+  </data>

+  <data name="ContentUnmatchedLengthSmaller" xml:space="preserve">

+    <value>Actual body length is smaller than it in header.</value>

+  </data>

+  <data name="DeleteDelete" xml:space="preserve">

     <value>An existent item is deleted.</value>

   </data>

-  <data name="ResponseDeleteNotExist" xml:space="preserve">

+  <data name="DeleteNotExist" xml:space="preserve">

     <value>The item does not exist, so nothing is changed.</value>

   </data>

-  <data name="ResponsePutCreate" xml:space="preserve">

+  <data name="HeaderBadIfNonMatch" xml:space="preserve">

+    <value>Header If-Non-Match is of bad format.</value>

+  </data>

+  <data name="HeaderMissingContentLength" xml:space="preserve">

+    <value>Header Content-Length is missing or of bad format.</value>

+  </data>

+  <data name="HeaderMissingContentType" xml:space="preserve">

+    <value>Header Content-Type is required.</value>

+  </data>

+  <data name="HeaderZeroContentLength" xml:space="preserve">

+    <value>Header Content-Length must not be 0.</value>

+  </data>

+  <data name="PutCreate" xml:space="preserve">

     <value>A new item is created.</value>

   </data>

-  <data name="ResponsePutModify" xml:space="preserve">

+  <data name="PutModify" xml:space="preserve">

     <value>An existent item is modified.</value>

   </data>

 </root>
\ No newline at end of file
diff --git a/Timeline/Resources/Models/Http/Common.zh.resx b/Timeline/Resources/Models/Http/Common.zh.resx
index b6d955d9..528dc7ab 100644
--- a/Timeline/Resources/Models/Http/Common.zh.resx
+++ b/Timeline/Resources/Models/Http/Common.zh.resx
@@ -117,16 +117,37 @@
   <resheader name="writer">

     <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>

   </resheader>

-  <data name="ResponseDeleteDelete" xml:space="preserve">

+  <data name="ContentTooBig" xml:space="preserve">

+    <value>请求体太大。它不能超过{0}.</value>

+  </data>

+  <data name="ContentUnmatchedLengthBigger" xml:space="preserve">

+    <value>实际的请求体长度比头中指示的大。</value>

+  </data>

+  <data name="ContentUnmatchedLengthSmaller" xml:space="preserve">

+    <value>实际的请求体长度比头中指示的小。</value>

+  </data>

+  <data name="DeleteDelete" xml:space="preserve">

     <value>删除了一个项目。</value>

   </data>

-  <data name="ResponseDeleteNotExist" xml:space="preserve">

+  <data name="DeleteNotExist" xml:space="preserve">

     <value>要删除的项目不存在，什么都没有修改。</value>

   </data>

-  <data name="ResponsePutCreate" xml:space="preserve">

+  <data name="HeaderBadIfNonMatch" xml:space="preserve">

+    <value>头If-Non-Match格式不对。</value>

+  </data>

+  <data name="HeaderMissingContentLength" xml:space="preserve">

+    <value>头Content-Length缺失或者格式不对。</value>

+  </data>

+  <data name="HeaderMissingContentType" xml:space="preserve">

+    <value>缺少必需的头Content-Type。</value>

+  </data>

+  <data name="HeaderZeroContentLength" xml:space="preserve">

+    <value>头Content-Length不能为0。</value>

+  </data>

+  <data name="PutCreate" xml:space="preserve">

     <value>创建了一个新项目。</value>

   </data>

-  <data name="ResponsePutModify" xml:space="preserve">

+  <data name="PutModify" xml:space="preserve">

     <value>修改了一个已存在的项目。</value>

   </data>

 </root>
\ No newline at end of file
diff --git a/Timeline/Resources/Services/Exception.Designer.cs b/Timeline/Resources/Services/Exception.Designer.cs
index 24f6b8e6..ddf60f45 100644
--- a/Timeline/Resources/Services/Exception.Designer.cs
+++ b/Timeline/Resources/Services/Exception.Designer.cs
@@ -61,6 +61,51 @@ namespace Timeline.Resources.Services {
         }

         

         /// <summary>

+        ///   Looks up a localized string similar to Avartar is of bad format because {0}..

+        /// </summary>

+        internal static string AvatarFormatException {

+            get {

+                return ResourceManager.GetString("AvatarFormatException", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to image is not a square, aka, width is not equal to height.

+        /// </summary>

+        internal static string AvatarFormatExceptionBadSize {

+            get {

+                return ResourceManager.GetString("AvatarFormatExceptionBadSize", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to failed to decode image, see inner exception.

+        /// </summary>

+        internal static string AvatarFormatExceptionCantDecode {

+            get {

+                return ResourceManager.GetString("AvatarFormatExceptionCantDecode", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to unknown error.

+        /// </summary>

+        internal static string AvatarFormatExceptionUnknownError {

+            get {

+                return ResourceManager.GetString("AvatarFormatExceptionUnknownError", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to image&apos;s actual mime type is not the specified one.

+        /// </summary>

+        internal static string AvatarFormatExceptionUnmatchedFormat {

+            get {

+                return ResourceManager.GetString("AvatarFormatExceptionUnmatchedFormat", resourceCulture);

+            }

+        }

+        

+        /// <summary>

         ///   Looks up a localized string similar to The password is wrong..

         /// </summary>

         internal static string BadPasswordException {

diff --git a/Timeline/Resources/Services/Exception.resx b/Timeline/Resources/Services/Exception.resx
index 408c45a1..12bf9afb 100644
--- a/Timeline/Resources/Services/Exception.resx
+++ b/Timeline/Resources/Services/Exception.resx
@@ -117,6 +117,21 @@
   <resheader name="writer">

     <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>

   </resheader>

+  <data name="AvatarFormatException" xml:space="preserve">

+    <value>Avartar is of bad format because {0}.</value>

+  </data>

+  <data name="AvatarFormatExceptionBadSize" xml:space="preserve">

+    <value>image is not a square, aka, width is not equal to height</value>

+  </data>

+  <data name="AvatarFormatExceptionCantDecode" xml:space="preserve">

+    <value>failed to decode image, see inner exception</value>

+  </data>

+  <data name="AvatarFormatExceptionUnknownError" xml:space="preserve">

+    <value>unknown error</value>

+  </data>

+  <data name="AvatarFormatExceptionUnmatchedFormat" xml:space="preserve">

+    <value>image's actual mime type is not the specified one</value>

+  </data>

   <data name="BadPasswordException" xml:space="preserve">

     <value>The password is wrong.</value>

   </data>

diff --git a/Timeline/Resources/Services/UserAvatarService.Designer.cs b/Timeline/Resources/Services/UserAvatarService.Designer.cs
new file mode 100644
index 00000000..cabc9ede
--- /dev/null
+++ b/Timeline/Resources/Services/UserAvatarService.Designer.cs
@@ -0,0 +1,108 @@
+//------------------------------------------------------------------------------

+// <auto-generated>

+//     This code was generated by a tool.

+//     Runtime Version:4.0.30319.42000

+//

+//     Changes to this file may cause incorrect behavior and will be lost if

+//     the code is regenerated.

+// </auto-generated>

+//------------------------------------------------------------------------------

+

+namespace Timeline.Resources.Services {

+    using System;

+    

+    

+    /// <summary>

+    ///   A strongly-typed resource class, for looking up localized strings, etc.

+    /// </summary>

+    // This class was auto-generated by the StronglyTypedResourceBuilder

+    // class via a tool like ResGen or Visual Studio.

+    // To add or remove a member, edit your .ResX file then rerun ResGen

+    // with the /str option, or rebuild your VS project.

+    [global::System.CodeDom.Compiler.GeneratedCodeAttribute("System.Resources.Tools.StronglyTypedResourceBuilder", "16.0.0.0")]

+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]

+    [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]

+    internal class UserAvatarService {

+        

+        private static global::System.Resources.ResourceManager resourceMan;

+        

+        private static global::System.Globalization.CultureInfo resourceCulture;

+        

+        [global::System.Diagnostics.CodeAnalysis.SuppressMessageAttribute("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]

+        internal UserAvatarService() {

+        }

+        

+        /// <summary>

+        ///   Returns the cached ResourceManager instance used by this class.

+        /// </summary>

+        [global::System.ComponentModel.EditorBrowsableAttribute(global::System.ComponentModel.EditorBrowsableState.Advanced)]

+        internal static global::System.Resources.ResourceManager ResourceManager {

+            get {

+                if (object.ReferenceEquals(resourceMan, null)) {

+                    global::System.Resources.ResourceManager temp = new global::System.Resources.ResourceManager("Timeline.Resources.Services.UserAvatarService", typeof(UserAvatarService).Assembly);

+                    resourceMan = temp;

+                }

+                return resourceMan;

+            }

+        }

+        

+        /// <summary>

+        ///   Overrides the current thread's CurrentUICulture property for all

+        ///   resource lookups using this strongly typed resource class.

+        /// </summary>

+        [global::System.ComponentModel.EditorBrowsableAttribute(global::System.ComponentModel.EditorBrowsableState.Advanced)]

+        internal static global::System.Globalization.CultureInfo Culture {

+            get {

+                return resourceCulture;

+            }

+            set {

+                resourceCulture = value;

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Data of avatar is null..

+        /// </summary>

+        internal static string ArgumentAvatarDataNull {

+            get {

+                return ResourceManager.GetString("ArgumentAvatarDataNull", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Type of avatar is null..

+        /// </summary>

+        internal static string ArgumentAvatarTypeNull {

+            get {

+                return ResourceManager.GetString("ArgumentAvatarTypeNull", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Database corupted! One of type and data of a avatar is null but the other is not..

+        /// </summary>

+        internal static string DatabaseCorruptedDataAndTypeNotSame {

+            get {

+                return ResourceManager.GetString("DatabaseCorruptedDataAndTypeNotSame", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Created an entry in user_avatars..

+        /// </summary>

+        internal static string LogCreateEntity {

+            get {

+                return ResourceManager.GetString("LogCreateEntity", resourceCulture);

+            }

+        }

+        

+        /// <summary>

+        ///   Looks up a localized string similar to Updated an entry in user_avatars..

+        /// </summary>

+        internal static string LogUpdateEntity {

+            get {

+                return ResourceManager.GetString("LogUpdateEntity", resourceCulture);

+            }

+        }

+    }

+}

diff --git a/Timeline/Resources/Services/UserAvatarService.resx b/Timeline/Resources/Services/UserAvatarService.resx
new file mode 100644
index 00000000..ab6389ff
--- /dev/null
+++ b/Timeline/Resources/Services/UserAvatarService.resx
@@ -0,0 +1,135 @@
+<?xml version="1.0" encoding="utf-8"?>

+<root>

+  <!-- 

+    Microsoft ResX Schema 

+    

+    Version 2.0

+    

+    The primary goals of this format is to allow a simple XML format 

+    that is mostly human readable. The generation and parsing of the 

+    various data types are done through the TypeConverter classes 

+    associated with the data types.

+    

+    Example:

+    

+    ... ado.net/XML headers & schema ...

+    <resheader name="resmimetype">text/microsoft-resx</resheader>

+    <resheader name="version">2.0</resheader>

+    <resheader name="reader">System.Resources.ResXResourceReader, System.Windows.Forms, ...</resheader>

+    <resheader name="writer">System.Resources.ResXResourceWriter, System.Windows.Forms, ...</resheader>

+    <data name="Name1"><value>this is my long string</value><comment>this is a comment</comment></data>

+    <data name="Color1" type="System.Drawing.Color, System.Drawing">Blue</data>

+    <data name="Bitmap1" mimetype="application/x-microsoft.net.object.binary.base64">

+        <value>[base64 mime encoded serialized .NET Framework object]</value>

+    </data>

+    <data name="Icon1" type="System.Drawing.Icon, System.Drawing" mimetype="application/x-microsoft.net.object.bytearray.base64">

+        <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>

+        <comment>This is a comment</comment>

+    </data>

+                

+    There are any number of "resheader" rows that contain simple 

+    name/value pairs.

+    

+    Each data row contains a name, and value. The row also contains a 

+    type or mimetype. Type corresponds to a .NET class that support 

+    text/value conversion through the TypeConverter architecture. 

+    Classes that don't support this are serialized and stored with the 

+    mimetype set.

+    

+    The mimetype is used for serialized objects, and tells the 

+    ResXResourceReader how to depersist the object. This is currently not 

+    extensible. For a given mimetype the value must be set accordingly:

+    

+    Note - application/x-microsoft.net.object.binary.base64 is the format 

+    that the ResXResourceWriter will generate, however the reader can 

+    read any of the formats listed below.

+    

+    mimetype: application/x-microsoft.net.object.binary.base64

+    value   : The object must be serialized with 

+            : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter

+            : and then encoded with base64 encoding.

+    

+    mimetype: application/x-microsoft.net.object.soap.base64

+    value   : The object must be serialized with 

+            : System.Runtime.Serialization.Formatters.Soap.SoapFormatter

+            : and then encoded with base64 encoding.

+

+    mimetype: application/x-microsoft.net.object.bytearray.base64

+    value   : The object must be serialized into a byte array 

+            : using a System.ComponentModel.TypeConverter

+            : and then encoded with base64 encoding.

+    -->

+  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">

+    <xsd:import namespace="http://www.w3.org/XML/1998/namespace" />

+    <xsd:element name="root" msdata:IsDataSet="true">

+      <xsd:complexType>

+        <xsd:choice maxOccurs="unbounded">

+          <xsd:element name="metadata">

+            <xsd:complexType>

+              <xsd:sequence>

+                <xsd:element name="value" type="xsd:string" minOccurs="0" />

+              </xsd:sequence>

+              <xsd:attribute name="name" use="required" type="xsd:string" />

+              <xsd:attribute name="type" type="xsd:string" />

+              <xsd:attribute name="mimetype" type="xsd:string" />

+              <xsd:attribute ref="xml:space" />

+            </xsd:complexType>

+          </xsd:element>

+          <xsd:element name="assembly">

+            <xsd:complexType>

+              <xsd:attribute name="alias" type="xsd:string" />

+              <xsd:attribute name="name" type="xsd:string" />

+            </xsd:complexType>

+          </xsd:element>

+          <xsd:element name="data">

+            <xsd:complexType>

+              <xsd:sequence>

+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />

+                <xsd:element name="comment" type="xsd:string" minOccurs="0" msdata:Ordinal="2" />

+              </xsd:sequence>

+              <xsd:attribute name="name" type="xsd:string" use="required" msdata:Ordinal="1" />

+              <xsd:attribute name="type" type="xsd:string" msdata:Ordinal="3" />

+              <xsd:attribute name="mimetype" type="xsd:string" msdata:Ordinal="4" />

+              <xsd:attribute ref="xml:space" />

+            </xsd:complexType>

+          </xsd:element>

+          <xsd:element name="resheader">

+            <xsd:complexType>

+              <xsd:sequence>

+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />

+              </xsd:sequence>

+              <xsd:attribute name="name" type="xsd:string" use="required" />

+            </xsd:complexType>

+          </xsd:element>

+        </xsd:choice>

+      </xsd:complexType>

+    </xsd:element>

+  </xsd:schema>

+  <resheader name="resmimetype">

+    <value>text/microsoft-resx</value>

+  </resheader>

+  <resheader name="version">

+    <value>2.0</value>

+  </resheader>

+  <resheader name="reader">

+    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>

+  </resheader>

+  <resheader name="writer">

+    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>

+  </resheader>

+  <data name="ArgumentAvatarDataNull" xml:space="preserve">

+    <value>Data of avatar is null.</value>

+  </data>

+  <data name="ArgumentAvatarTypeNull" xml:space="preserve">

+    <value>Type of avatar is null.</value>

+  </data>

+  <data name="DatabaseCorruptedDataAndTypeNotSame" xml:space="preserve">

+    <value>Database corupted! One of type and data of a avatar is null but the other is not.</value>

+  </data>

+  <data name="LogCreateEntity" xml:space="preserve">

+    <value>Created an entry in user_avatars.</value>

+  </data>

+  <data name="LogUpdateEntity" xml:space="preserve">

+    <value>Updated an entry in user_avatars.</value>

+  </data>

+</root>
\ No newline at end of file
diff --git a/Timeline/Services/AvatarFormatException.cs b/Timeline/Services/AvatarFormatException.cs
new file mode 100644
index 00000000..788eabb2
--- /dev/null
+++ b/Timeline/Services/AvatarFormatException.cs
@@ -0,0 +1,51 @@
+using System;

+using System.Globalization;

+

+namespace Timeline.Services

+{

+    /// <summary>

+    /// Thrown when avatar is of bad format.

+    /// </summary>

+    [Serializable]

+    public class AvatarFormatException : Exception

+    {

+        public enum ErrorReason

+        {

+            /// <summary>

+            /// Decoding image failed.

+            /// </summary>

+            CantDecode,

+            /// <summary>

+            /// Decoding succeeded but the real type is not the specified type.

+            /// </summary>

+            UnmatchedFormat,

+            /// <summary>

+            /// Image is not a square.

+            /// </summary>

+            BadSize

+        }

+

+        public AvatarFormatException() : base(MakeMessage(null)) { }

+        public AvatarFormatException(string message) : base(message) { }

+        public AvatarFormatException(string message, Exception inner) : base(message, inner) { }

+

+        public AvatarFormatException(Avatar avatar, ErrorReason error) : base(MakeMessage(error)) { Avatar = avatar; Error = error; }

+        public AvatarFormatException(Avatar avatar, ErrorReason error, Exception inner) : base(MakeMessage(error), inner) { Avatar = avatar; Error = error; }

+

+        protected AvatarFormatException(

+          System.Runtime.Serialization.SerializationInfo info,

+          System.Runtime.Serialization.StreamingContext context) : base(info, context) { }

+

+        private static string MakeMessage(ErrorReason? reason) =>

+            string.Format(CultureInfo.InvariantCulture, Resources.Services.Exception.AvatarFormatException, reason switch

+            {

+                ErrorReason.CantDecode => Resources.Services.Exception.AvatarFormatExceptionCantDecode,

+                ErrorReason.UnmatchedFormat => Resources.Services.Exception.AvatarFormatExceptionUnmatchedFormat,

+                ErrorReason.BadSize => Resources.Services.Exception.AvatarFormatExceptionBadSize,

+                _ => Resources.Services.Exception.AvatarFormatExceptionUnknownError

+            });

+

+        public ErrorReason? Error { get; set; }

+        public Avatar? Avatar { get; set; }

+    }

+}

diff --git a/Timeline/Services/DatabaseExtensions.cs b/Timeline/Services/DatabaseExtensions.cs
index a37cf05b..62b22f00 100644
--- a/Timeline/Services/DatabaseExtensions.cs
+++ b/Timeline/Services/DatabaseExtensions.cs
@@ -4,22 +4,27 @@ using System.Collections.Generic;
 using System.Linq;

 using System.Threading.Tasks;

 using Timeline.Entities;

+using Timeline.Models.Validation;

 

 namespace Timeline.Services

 {

-    public static class DatabaseExtensions

+    internal static class DatabaseExtensions

     {

         /// <summary>

         /// Check the existence and get the id of the user.

         /// </summary>

         /// <param name="username">The username of the user.</param>

         /// <returns>The user id.</returns>

-        /// <exception cref="ArgumentException">Thrown if <paramref name="username"/> is null or empty.</exception>

+        /// <exception cref="ArgumentNullException">Thrown if <paramref name="username"/> is null.</exception>

+        /// <exception cref="UsernameBadFormatException">Thrown if <paramref name="username"/> is of bad format.</exception>

         /// <exception cref="UserNotExistException">Thrown if user does not exist.</exception>

-        public static async Task<long> CheckAndGetUser(DbSet<User> userDbSet, string username)

+        internal static async Task<long> CheckAndGetUser(DbSet<User> userDbSet, UsernameValidator validator, string username)

         {

-            if (string.IsNullOrEmpty(username))

-                throw new ArgumentException("Username is null or empty.", nameof(username));

+            if (username == null)

+                throw new ArgumentNullException(nameof(username));

+            var (result, messageGenerator) = validator.Validate(username);

+            if (!result)

+                throw new UsernameBadFormatException(username, messageGenerator(null));

 

             var userId = await userDbSet.Where(u => u.Name == username).Select(u => u.Id).SingleOrDefaultAsync();

             if (userId == 0)

diff --git a/Timeline/Services/ETagGenerator.cs b/Timeline/Services/ETagGenerator.cs
index e2abebdc..e518f01f 100644
--- a/Timeline/Services/ETagGenerator.cs
+++ b/Timeline/Services/ETagGenerator.cs
@@ -5,13 +5,20 @@ namespace Timeline.Services
 {

     public interface IETagGenerator

     {

+        /// <summary>

+        /// Generate a etag for given source.

+        /// </summary>

+        /// <param name="source">The source data.</param>

+        /// <returns>The generated etag.</returns>

+        /// <exception cref="ArgumentNullException">Thrown if <paramref name="source"/> is null.</exception>

         string Generate(byte[] source);

     }

 

-    public class ETagGenerator : IETagGenerator, IDisposable

+    public sealed class ETagGenerator : IETagGenerator, IDisposable

     {

         private readonly SHA1 _sha1;

 

+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Security", "CA5350:Do Not Use Weak Cryptographic Algorithms", Justification = "Sha1 is enough ??? I don't know.")]

         public ETagGenerator()

         {

             _sha1 = SHA1.Create();

@@ -19,15 +26,19 @@ namespace Timeline.Services
 

         public string Generate(byte[] source)

         {

-            if (source == null || source.Length == 0)

-                throw new ArgumentException("Source is null or empty.", nameof(source));

+            if (source == null)

+                throw new ArgumentNullException(nameof(source));

 

             return Convert.ToBase64String(_sha1.ComputeHash(source));

         }

 

+        private bool _disposed = false; // To detect redundant calls

+

         public void Dispose()

         {

+            if (_disposed) return;

             _sha1.Dispose();

+            _disposed = true;

         }

     }

 }

diff --git a/Timeline/Services/UserAvatarService.cs b/Timeline/Services/UserAvatarService.cs
index ecec5a31..4c65a0fa 100644
--- a/Timeline/Services/UserAvatarService.cs
+++ b/Timeline/Services/UserAvatarService.cs
@@ -10,54 +10,25 @@ using System.IO;
 using System.Linq;

 using System.Threading.Tasks;

 using Timeline.Entities;

+using Timeline.Helpers;

+using Timeline.Models.Validation;

 

 namespace Timeline.Services

 {

     public class Avatar

     {

-        public string Type { get; set; }

-        public byte[] Data { get; set; }

+        public string Type { get; set; } = default!;

+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Performance", "CA1819:Properties should not return arrays", Justification = "DTO Object")]

+        public byte[] Data { get; set; } = default!;

     }

 

     public class AvatarInfo

     {

-        public Avatar Avatar { get; set; }

+        public Avatar Avatar { get; set; } = default!;

         public DateTime LastModified { get; set; }

     }

 

     /// <summary>

-    /// Thrown when avatar is of bad format.

-    /// </summary>

-    [Serializable]

-    public class AvatarDataException : Exception

-    {

-        public enum ErrorReason

-        {

-            /// <summary>

-            /// Decoding image failed.

-            /// </summary>

-            CantDecode,

-            /// <summary>

-            /// Decoding succeeded but the real type is not the specified type.

-            /// </summary>

-            UnmatchedFormat,

-            /// <summary>

-            /// Image is not a square.

-            /// </summary>

-            BadSize

-        }

-

-        public AvatarDataException(Avatar avatar, ErrorReason error, string message) : base(message) { Avatar = avatar; Error = error; }

-        public AvatarDataException(Avatar avatar, ErrorReason error, string message, Exception inner) : base(message, inner) { Avatar = avatar; Error = error; }

-        protected AvatarDataException(

-          System.Runtime.Serialization.SerializationInfo info,

-          System.Runtime.Serialization.StreamingContext context) : base(info, context) { }

-

-        public ErrorReason Error { get; set; }

-        public Avatar Avatar { get; set; }

-    }

-

-    /// <summary>

     /// Provider for default user avatar.

     /// </summary>

     /// <remarks>

@@ -83,7 +54,7 @@ namespace Timeline.Services
         /// Validate a avatar's format and size info.

         /// </summary>

         /// <param name="avatar">The avatar to validate.</param>

-        /// <exception cref="AvatarDataException">Thrown when validation failed.</exception>

+        /// <exception cref="AvatarFormatException">Thrown when validation failed.</exception>

         Task Validate(Avatar avatar);

     }

 

@@ -94,16 +65,18 @@ namespace Timeline.Services
         /// </summary>

         /// <param name="username">The username of the user to get avatar etag of.</param>

         /// <returns>The etag.</returns>

-        /// <exception cref="ArgumentException">Thrown if <paramref name="username"/> is null or empty.</exception>

+        /// <exception cref="ArgumentNullException">Thrown if <paramref name="username"/> is null.</exception>

+        /// <exception cref="UsernameBadFormatException">Thrown if the <paramref name="username"/> is of bad format.</exception>

         /// <exception cref="UserNotExistException">Thrown if the user does not exist.</exception>

         Task<string> GetAvatarETag(string username);

 

         /// <summary>

-        /// Get avatar of a user. If the user has no avatar, a default one is returned.

+        /// Get avatar of a user. If the user has no avatar set, a default one is returned.

         /// </summary>

         /// <param name="username">The username of the user to get avatar of.</param>

         /// <returns>The avatar info.</returns>

-        /// <exception cref="ArgumentException">Thrown if <paramref name="username"/> is null or empty.</exception>

+        /// <exception cref="ArgumentNullException">Thrown if <paramref name="username"/> is null.</exception>

+        /// <exception cref="UsernameBadFormatException">Thrown if the <paramref name="username"/> is of bad format.</exception>

         /// <exception cref="UserNotExistException">Thrown if the user does not exist.</exception>

         Task<AvatarInfo> GetAvatar(string username);

 

@@ -112,38 +85,41 @@ namespace Timeline.Services
         /// </summary>

         /// <param name="username">The username of the user to set avatar for.</param>

         /// <param name="avatar">The avatar. Can be null to delete the saved avatar.</param>

-        /// <exception cref="ArgumentException">Throw if <paramref name="username"/> is null or empty.

-        /// Or thrown if <paramref name="avatar"/> is not null but <see cref="Avatar.Type"/> is null or empty or <see cref="Avatar.Data"/> is null.</exception>

+        /// <exception cref="ArgumentNullException">Throw if <paramref name="username"/> is null.</exception>

+        /// <exception cref="ArgumentException">Thrown if any field in <paramref name="avatar"/> is null when <paramref name="avatar"/> is not null.</exception>

+        /// <exception cref="UsernameBadFormatException">Thrown if the <paramref name="username"/> is of bad format.</exception>

         /// <exception cref="UserNotExistException">Thrown if the user does not exist.</exception>

-        /// <exception cref="AvatarDataException">Thrown if avatar is of bad format.</exception>

-        Task SetAvatar(string username, Avatar avatar);

+        /// <exception cref="AvatarFormatException">Thrown if avatar is of bad format.</exception>

+        Task SetAvatar(string username, Avatar? avatar);

     }

 

+    // TODO! : Make this configurable.

     public class DefaultUserAvatarProvider : IDefaultUserAvatarProvider

     {

-        private readonly IWebHostEnvironment _environment;

-

         private readonly IETagGenerator _eTagGenerator;

 

-        private byte[] _cacheData;

+        private readonly string _avatarPath;

+

+        private byte[] _cacheData = default!;

         private DateTime _cacheLastModified;

-        private string _cacheETag;

+        private string _cacheETag = default!;

 

+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Design", "CA1062:Validate arguments of public methods", Justification = "DI.")]

         public DefaultUserAvatarProvider(IWebHostEnvironment environment, IETagGenerator eTagGenerator)

         {

-            _environment = environment;

+            _avatarPath = Path.Combine(environment.ContentRootPath, "default-avatar.png");

             _eTagGenerator = eTagGenerator;

         }

 

         private async Task CheckAndInit()

         {

-            if (_cacheData != null)

-                return;

-

-            var path = Path.Combine(_environment.ContentRootPath, "default-avatar.png");

-            _cacheData = await File.ReadAllBytesAsync(path);

-            _cacheLastModified = File.GetLastWriteTime(path);

-            _cacheETag = _eTagGenerator.Generate(_cacheData);

+            var path = _avatarPath;

+            if (_cacheData == null || File.GetLastWriteTime(path) > _cacheLastModified)

+            {

+                _cacheData = await File.ReadAllBytesAsync(path);

+                _cacheLastModified = File.GetLastWriteTime(path);

+                _cacheETag = _eTagGenerator.Generate(_cacheData);

+            }

         }

 

         public async Task<string> GetDefaultAvatarETag()

@@ -175,17 +151,15 @@ namespace Timeline.Services
             {

                 try

                 {

-                    using (var image = Image.Load(avatar.Data, out IImageFormat format))

-                    {

-                        if (!format.MimeTypes.Contains(avatar.Type))

-                            throw new AvatarDataException(avatar, AvatarDataException.ErrorReason.UnmatchedFormat, "Image's actual mime type is not the specified one.");

-                        if (image.Width != image.Height)

-                            throw new AvatarDataException(avatar, AvatarDataException.ErrorReason.BadSize, "Image is not a square, aka, width is not equal to height.");

-                    }

+                    using var image = Image.Load(avatar.Data, out IImageFormat format);

+                    if (!format.MimeTypes.Contains(avatar.Type))

+                        throw new AvatarFormatException(avatar, AvatarFormatException.ErrorReason.UnmatchedFormat);

+                    if (image.Width != image.Height)

+                        throw new AvatarFormatException(avatar, AvatarFormatException.ErrorReason.BadSize);

                 }

                 catch (UnknownImageFormatException e)

                 {

-                    throw new AvatarDataException(avatar, AvatarDataException.ErrorReason.CantDecode, "Failed to decode image. See inner exception.", e);

+                    throw new AvatarFormatException(avatar, AvatarFormatException.ErrorReason.CantDecode, e);

                 }

             });

         }

@@ -203,6 +177,8 @@ namespace Timeline.Services
 

         private readonly IETagGenerator _eTagGenerator;

 

+        private readonly UsernameValidator _usernameValidator;

+

         public UserAvatarService(

             ILogger<UserAvatarService> logger,

             DatabaseContext database,

@@ -215,13 +191,14 @@ namespace Timeline.Services
             _defaultUserAvatarProvider = defaultUserAvatarProvider;

             _avatarValidator = avatarValidator;

             _eTagGenerator = eTagGenerator;

+            _usernameValidator = new UsernameValidator();

         }

 

         public async Task<string> GetAvatarETag(string username)

         {

-            var userId = await DatabaseExtensions.CheckAndGetUser(_database.Users, username);

+            var userId = await DatabaseExtensions.CheckAndGetUser(_database.Users, _usernameValidator, username);

 

-            var eTag = (await _database.UserAvatars.Where(a => a.UserId == userId).Select(a => new { a.ETag }).SingleAsync()).ETag;

+            var eTag = (await _database.UserAvatars.Where(a => a.UserId == userId).Select(a => new { a.ETag }).SingleOrDefaultAsync())?.ETag;

             if (eTag == null)

                 return await _defaultUserAvatarProvider.GetDefaultAvatarETag();

             else

@@ -230,54 +207,57 @@ namespace Timeline.Services
 

         public async Task<AvatarInfo> GetAvatar(string username)

         {

-            var userId = await DatabaseExtensions.CheckAndGetUser(_database.Users, username);

+            var userId = await DatabaseExtensions.CheckAndGetUser(_database.Users, _usernameValidator, username);

 

-            var avatar = await _database.UserAvatars.Where(a => a.UserId == userId).Select(a => new { a.Type, a.Data, a.LastModified }).SingleAsync();

+            var avatarEntity = await _database.UserAvatars.Where(a => a.UserId == userId).Select(a => new { a.Type, a.Data, a.LastModified }).SingleOrDefaultAsync();

 

-            if ((avatar.Type == null) != (avatar.Data == null))

+            if (avatarEntity != null)

             {

-                _logger.LogCritical("Database corupted! One of type and data of a avatar is null but the other is not.");

-                throw new DatabaseCorruptedException();

-            }

+                if (!LanguageHelper.AreSame(avatarEntity.Data == null, avatarEntity.Type == null))

+                {

+                    var message = Resources.Services.UserAvatarService.DatabaseCorruptedDataAndTypeNotSame;

+                    _logger.LogCritical(message);

+                    throw new DatabaseCorruptedException(message);

+                }

 

-            if (avatar.Data == null)

-            {

-                var defaultAvatar = await _defaultUserAvatarProvider.GetDefaultAvatar();

-                defaultAvatar.LastModified = defaultAvatar.LastModified > avatar.LastModified ? defaultAvatar.LastModified : avatar.LastModified;

-                return defaultAvatar;

-            }

-            else

-            {

-                return new AvatarInfo

+                if (avatarEntity.Data != null)

                 {

-                    Avatar = new Avatar

+                    return new AvatarInfo

                     {

-                        Type = avatar.Type,

-                        Data = avatar.Data

-                    },

-                    LastModified = avatar.LastModified

-                };

+                        Avatar = new Avatar

+                        {

+                            Type = avatarEntity.Type!,

+                            Data = avatarEntity.Data

+                        },

+                        LastModified = avatarEntity.LastModified

+                    };

+                }

             }

+            var defaultAvatar = await _defaultUserAvatarProvider.GetDefaultAvatar();

+            if (avatarEntity != null)

+                defaultAvatar.LastModified = defaultAvatar.LastModified > avatarEntity.LastModified ? defaultAvatar.LastModified : avatarEntity.LastModified;

+            return defaultAvatar;

         }

 

-        public async Task SetAvatar(string username, Avatar avatar)

+        public async Task SetAvatar(string username, Avatar? avatar)

         {

             if (avatar != null)

             {

-                if (string.IsNullOrEmpty(avatar.Type))

-                    throw new ArgumentException("Type of avatar is null or empty.", nameof(avatar));

                 if (avatar.Data == null)

-                    throw new ArgumentException("Data of avatar is null.", nameof(avatar));

+                    throw new ArgumentException(Resources.Services.UserAvatarService.ArgumentAvatarDataNull, nameof(avatar));

+                if (avatar.Type == null)

+                    throw new ArgumentException(Resources.Services.UserAvatarService.ArgumentAvatarTypeNull, nameof(avatar));

             }

 

-            var userId = await DatabaseExtensions.CheckAndGetUser(_database.Users, username);

-

-            var avatarEntity = await _database.UserAvatars.Where(a => a.UserId == userId).SingleAsync();

+            var userId = await DatabaseExtensions.CheckAndGetUser(_database.Users, _usernameValidator, username);

+            var avatarEntity = await _database.UserAvatars.Where(a => a.UserId == userId).SingleOrDefaultAsync();

 

             if (avatar == null)

             {

-                if (avatarEntity.Data == null)

+                if (avatarEntity == null || avatarEntity.Data == null)

+                {

                     return;

+                }

                 else

                 {

                     avatarEntity.Data = null;

@@ -285,18 +265,29 @@ namespace Timeline.Services
                     avatarEntity.ETag = null;

                     avatarEntity.LastModified = DateTime.Now;

                     await _database.SaveChangesAsync();

-                    _logger.LogInformation("Updated an entry in user_avatars.");

+                    _logger.LogInformation(Resources.Services.UserAvatarService.LogUpdateEntity);

                 }

             }

             else

             {

                 await _avatarValidator.Validate(avatar);

-                avatarEntity.Type = avatar.Type;

+                var create = avatarEntity == null;

+                if (create)

+                {

+                    avatarEntity = new UserAvatar();

+                }

+                avatarEntity!.Type = avatar.Type;

                 avatarEntity.Data = avatar.Data;

                 avatarEntity.ETag = _eTagGenerator.Generate(avatar.Data);

                 avatarEntity.LastModified = DateTime.Now;

+                if (create)

+                {

+                    _database.UserAvatars.Add(avatarEntity);

+                }

                 await _database.SaveChangesAsync();

-                _logger.LogInformation("Updated an entry in user_avatars.");

+                _logger.LogInformation(create ?

+                    Resources.Services.UserAvatarService.LogCreateEntity

+                    : Resources.Services.UserAvatarService.LogUpdateEntity);

             }

         }

     }

@@ -308,7 +299,7 @@ namespace Timeline.Services
             services.TryAddTransient<IETagGenerator, ETagGenerator>();

             services.AddScoped<IUserAvatarService, UserAvatarService>();

             services.AddSingleton<IDefaultUserAvatarProvider, DefaultUserAvatarProvider>();

-            services.AddSingleton<IUserAvatarValidator, UserAvatarValidator>();

+            services.AddTransient<IUserAvatarValidator, UserAvatarValidator>();

         }

     }

 }

diff --git a/Timeline/Services/UserService.cs b/Timeline/Services/UserService.cs
index d706d05e..f1317856 100644
--- a/Timeline/Services/UserService.cs
+++ b/Timeline/Services/UserService.cs
@@ -272,7 +272,7 @@ namespace Timeline.Services
                     Name = username,

                     EncryptedPassword = _passwordService.HashPassword(password),

                     RoleString = UserRoleConvert.ToString(administrator),

-                    Avatar = UserAvatar.Create(DateTime.Now)

+                    Avatar = null

                 };

                 await _databaseContext.AddAsync(newUser);

                 await _databaseContext.SaveChangesAsync();

diff --git a/Timeline/Timeline.csproj b/Timeline/Timeline.csproj
index 0ba34471..519a802d 100644
--- a/Timeline/Timeline.csproj
+++ b/Timeline/Timeline.csproj
@@ -49,6 +49,11 @@
         <AutoGen>True</AutoGen>

         <DependentUpon>TokenController.resx</DependentUpon>

       </Compile>

+      <Compile Update="Resources\Controllers\UserAvatarController.Designer.cs">

+        <DesignTime>True</DesignTime>

+        <AutoGen>True</AutoGen>

+        <DependentUpon>UserAvatarController.resx</DependentUpon>

+      </Compile>

       <Compile Update="Resources\Controllers\UserController.Designer.cs">

         <DesignTime>True</DesignTime>

         <AutoGen>True</AutoGen>

@@ -69,6 +74,11 @@
         <AutoGen>True</AutoGen>

         <DependentUpon>Exception.resx</DependentUpon>

       </Compile>

+      <Compile Update="Resources\Services\UserAvatarService.Designer.cs">

+        <DesignTime>True</DesignTime>

+        <AutoGen>True</AutoGen>

+        <DependentUpon>UserAvatarService.resx</DependentUpon>

+      </Compile>

       <Compile Update="Resources\Services\UserService.Designer.cs">

         <DesignTime>True</DesignTime>

         <AutoGen>True</AutoGen>

@@ -97,6 +107,10 @@
       <EmbeddedResource Update="Resources\Controllers\TokenController.en.resx">

         <Generator></Generator>

       </EmbeddedResource>

+      <EmbeddedResource Update="Resources\Controllers\UserAvatarController.resx">

+        <Generator>ResXFileCodeGenerator</Generator>

+        <LastGenOutput>UserAvatarController.Designer.cs</LastGenOutput>

+      </EmbeddedResource>

       <EmbeddedResource Update="Resources\Controllers\UserController.resx">

         <Generator>ResXFileCodeGenerator</Generator>

         <LastGenOutput>UserController.Designer.cs</LastGenOutput>

@@ -116,6 +130,10 @@
         <Generator>ResXFileCodeGenerator</Generator>

         <LastGenOutput>Exception.Designer.cs</LastGenOutput>

       </EmbeddedResource>

+      <EmbeddedResource Update="Resources\Services\UserAvatarService.resx">

+        <Generator>ResXFileCodeGenerator</Generator>

+        <LastGenOutput>UserAvatarService.Designer.cs</LastGenOutput>

+      </EmbeddedResource>

       <EmbeddedResource Update="Resources\Services\UserService.resx">

         <Generator>ResXFileCodeGenerator</Generator>

         <LastGenOutput>UserService.Designer.cs</LastGenOutput>