diff options
Diffstat (limited to 'BackEnd/Timeline/Services/Data')
| -rw-r--r-- | BackEnd/Timeline/Services/Data/DataManager.cs | 138 | ||||
| -rw-r--r-- | BackEnd/Timeline/Services/Data/ETagGenerator.cs | 45 |
2 files changed, 183 insertions, 0 deletions
diff --git a/BackEnd/Timeline/Services/Data/DataManager.cs b/BackEnd/Timeline/Services/Data/DataManager.cs new file mode 100644 index 00000000..d9a4491d --- /dev/null +++ b/BackEnd/Timeline/Services/Data/DataManager.cs @@ -0,0 +1,138 @@ +using Microsoft.EntityFrameworkCore;
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Timeline.Entities;
+
+namespace Timeline.Services.Data
+{
+ /// <summary>
+ /// A data manager controlling data.
+ /// </summary>
+ /// <remarks>
+ /// Identical data will be saved as one copy and return the same tag.
+ /// Every data has a ref count. When data is retained, ref count increase.
+ /// When data is freed, ref count decease. If ref count is decreased
+ /// to 0, the data entry will be destroyed and no longer occupy space.
+ /// </remarks>
+ public interface IDataManager
+ {
+ /// <summary>
+ /// Saves the data to a new entry if it does not exist,
+ /// increases its ref count and returns a tag to the entry.
+ /// </summary>
+ /// <param name="data">The data. Can't be null.</param>
+ /// <returns>The tag of the created entry.</returns>
+ /// <exception cref="ArgumentNullException">Thrown when <paramref name="data"/> is null.</exception>
+ public Task<string> RetainEntry(byte[] data);
+
+ /// <summary>
+ /// Decrease the the ref count of the entry.
+ /// Remove it if ref count is zero.
+ /// </summary>
+ /// <param name="tag">The tag of the entry.</param>
+ /// <exception cref="ArgumentNullException">Thrown when <paramref name="tag"/> is null.</exception>
+ /// <remarks>
+ /// It's no-op if entry with tag does not exist.
+ /// </remarks>
+ public Task FreeEntry(string tag);
+
+ /// <summary>
+ /// Retrieve the entry with given tag. If not exist, returns null.
+ /// </summary>
+ /// <param name="tag">The tag of the entry.</param>
+ /// <returns>The data of the entry. If not exist, returns null.</returns>
+ /// <exception cref="ArgumentNullException">Thrown when <paramref name="tag"/> is null.</exception>
+ public Task<byte[]?> GetEntry(string tag);
+ }
+
+ public class DataManager : IDataManager
+ {
+ private readonly DatabaseContext _database;
+ private readonly IETagGenerator _eTagGenerator;
+
+ public DataManager(DatabaseContext database, IETagGenerator eTagGenerator)
+ {
+ _database = database;
+ _eTagGenerator = eTagGenerator;
+ }
+
+ public async Task<string> RetainEntry(byte[] data)
+ {
+ if (data == null)
+ throw new ArgumentNullException(nameof(data));
+
+ var tag = await _eTagGenerator.Generate(data);
+
+ var entity = await _database.Data.Where(d => d.Tag == tag).SingleOrDefaultAsync();
+
+ if (entity == null)
+ {
+ entity = new DataEntity
+ {
+ Tag = tag,
+ Data = data,
+ Ref = 1
+ };
+ _database.Data.Add(entity);
+ }
+ else
+ {
+ entity.Ref += 1;
+ }
+
+ await _database.SaveChangesAsync();
+
+ return tag;
+ }
+
+ public async Task FreeEntry(string tag)
+ {
+ if (tag == null)
+ throw new ArgumentNullException(nameof(tag));
+
+ var entity = await _database.Data.Where(d => d.Tag == tag).SingleOrDefaultAsync();
+
+ if (entity != null)
+ {
+ if (entity.Ref == 1)
+ {
+ _database.Data.Remove(entity);
+ }
+ else
+ {
+ entity.Ref -= 1;
+ }
+
+ await _database.SaveChangesAsync();
+ }
+ }
+
+ public async Task<byte[]?> GetEntry(string tag)
+ {
+ if (tag == null)
+ throw new ArgumentNullException(nameof(tag));
+
+ var entity = await _database.Data.Where(d => d.Tag == tag).Select(d => new { d.Data }).SingleOrDefaultAsync();
+
+ if (entity is null)
+ return null;
+
+ return entity.Data;
+ }
+ }
+
+ public static class DataManagerExtensions
+ {
+ /// <summary>
+ /// Try to get an entry and throw <see cref="DatabaseCorruptedException"/> if not exist.
+ /// </summary>
+ public static async Task<byte[]> GetEntryAndCheck(this IDataManager dataManager, string tag, string notExistMessage)
+ {
+ var data = await dataManager.GetEntry(tag);
+ if (data is null)
+ throw new DatabaseCorruptedException($"Can't get data of tag {tag}. {notExistMessage}");
+ return data;
+ }
+ }
+}
diff --git a/BackEnd/Timeline/Services/Data/ETagGenerator.cs b/BackEnd/Timeline/Services/Data/ETagGenerator.cs new file mode 100644 index 00000000..847c120b --- /dev/null +++ b/BackEnd/Timeline/Services/Data/ETagGenerator.cs @@ -0,0 +1,45 @@ +using System;
+using System.Security.Cryptography;
+using System.Threading.Tasks;
+
+namespace Timeline.Services.Data
+{
+ 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>
+ Task<string> Generate(byte[] source);
+ }
+
+ 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();
+ }
+
+ public Task<string> Generate(byte[] source)
+ {
+ if (source == null)
+ throw new ArgumentNullException(nameof(source));
+
+ return Task.Run(() => Convert.ToBase64String(_sha1.ComputeHash(source)));
+ }
+
+ private bool _disposed; // To detect redundant calls
+
+ public void Dispose()
+ {
+ if (_disposed) return;
+ _sha1.Dispose();
+ _disposed = true;
+ }
+ }
+}
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