From 09b07992d4316899ee6878585622c0762588a82a Mon Sep 17 00:00:00 2001
From: 杨宇千 <crupest@outlook.com>
Date: Mon, 12 Aug 2019 16:14:57 +0800
Subject: Add username validator.

---
 Timeline/Services/UserService.cs | 73 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 71 insertions(+), 2 deletions(-)

(limited to 'Timeline/Services/UserService.cs')

diff --git a/Timeline/Services/UserService.cs b/Timeline/Services/UserService.cs
index 28218612..50aa4187 100644
--- a/Timeline/Services/UserService.cs
+++ b/Timeline/Services/UserService.cs
@@ -3,6 +3,7 @@ using Microsoft.Extensions.Caching.Memory;
 using Microsoft.Extensions.Logging;
 using System;
 using System.Linq;
+using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 using Timeline.Entities;
 using Timeline.Models;
@@ -102,6 +103,74 @@ namespace Timeline.Services
         public long RequiredVersion { get; private set; }
     }
 
+    /// <summary>
+    /// Thrown when username is of bad format.
+    /// </summary>
+    [Serializable]
+    public class UsernameBadFormatException : Exception
+    {
+        public UsernameBadFormatException(string username, string message) : base(message) { Username = username; }
+        public UsernameBadFormatException(string username, string message, Exception inner) : base(message, inner) { Username = username; }
+        protected UsernameBadFormatException(
+          System.Runtime.Serialization.SerializationInfo info,
+          System.Runtime.Serialization.StreamingContext context) : base(info, context) { }
+
+        /// <summary>
+        /// Username of bad format.
+        /// </summary>
+        public string Username { get; private set; }
+    }
+
+    public class UsernameValidator
+    {
+        public const int MaxLength = 26;
+        public const string RegexPattern = @"^[a-zA-Z0-9_][a-zA-Z0-9-_]*$";
+
+        private readonly Regex _regex = new Regex(RegexPattern);
+
+        /// <summary>
+        /// Validate a username.
+        /// </summary>
+        /// <param name="username">The username. Can't be null.</param>
+        /// <param name="message">Set as error message if there is error. Or null if no error.</param>
+        /// <returns>True if validation passed. Otherwise false.</returns>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="username"/> is null.</exception>
+        public bool Validate(string username, out string message)
+        {
+            if (username == null)
+                throw new ArgumentNullException(nameof(username));
+
+            if (username.Length == 0)
+            {
+                message = "An empty string is not permitted.";
+                return false;
+            }
+
+            if (username.Length > 26)
+            {
+                message = $"Too long, more than 26 characters is not premitted, found {username.Length}.";
+                return false;
+            }
+
+            foreach ((char c, int i) in username.Select((c, i) => (c, i)))
+                if (char.IsWhiteSpace(c))
+                {
+                    message = $"A whitespace is found at {i} . Whitespace is not permited.";
+                    return false;
+                }
+
+            var match = _regex.Match(username);
+            if (!match.Success)
+            {
+                message = "Regex match failed.";
+                return false;
+            }
+
+            message = null;
+            return true;
+        }
+    }
+
     public interface IUserService
     {
         /// <summary>
@@ -144,14 +213,14 @@ namespace Timeline.Services
 
         /// <summary>
         /// Create or modify a user with given username.
-        /// Return <see cref="PutUserResult.Created"/> if a new user is created.
-        /// Return <see cref="PutUserResult.Modified"/> if a existing user is modified.
+        /// Username must be match with [a-zA-z0-9-_].
         /// </summary>
         /// <param name="username">Username of user.</param>
         /// <param name="password">Password of user.</param>
         /// <param name="administrator">Whether the user is administrator.</param>
         /// <returns>Return <see cref="PutResult.Created"/> if a new user is created.
         /// Return <see cref="PutResult.Modified"/> if a existing user is modified.</returns>
+        /// <exception cref="UsernameBadFormatException">Thrown when <paramref name="username"/> is of bad format.</exception>
         /// <exception cref="ArgumentNullException">Thrown when <paramref name="username"/> or <paramref name="password"/> is null.</exception>
         Task<PutResult> PutUser(string username, string password, bool administrator);
 
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