Update Torrent.Pieces property with null-check and multiple of 20 check

Author: Krusen

BencodeNET.Tests/AutoFixture/RepeatCountAttribute.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Reflection;
+using AutoFixture;
+using AutoFixture.Xunit2;
+
+namespace BencodeNET.Tests.AutoFixture
+{
+    [AttributeUsage(AttributeTargets.Parameter, AllowMultiple = false)]
+    public class RepeatCountAttribute : CustomizeAttribute
+    {
+        private int Count { get; }
+
+        public RepeatCountAttribute(int count)
+        {
+            Count = count;
+        }
+
+        public override ICustomization GetCustomization(ParameterInfo parameter)
+        {
+            return new RepeatCountCustomization(Count);
+        }
+    }
+}

BencodeNET.Tests/AutoFixture/RepeatCountCustomization.cs

@@ -0,0 +1,19 @@
+using AutoFixture;
+
+namespace BencodeNET.Tests.AutoFixture
+{
+    public class RepeatCountCustomization : ICustomization
+    {
+        private int Count { get;  }
+
+        public RepeatCountCustomization(int count)
+        {
+            Count = count;
+        }
+
+        public void Customize(IFixture fixture)
+        {
+            fixture.RepeatCount = Count;
+        }
+    }
+}

BencodeNET.Tests/Torrents/TorrentParserTests.cs

@@ -4,6 +4,7 @@
 using BencodeNET.IO;
 using BencodeNET.Objects;
 using BencodeNET.Parsing;
+using BencodeNET.Tests.AutoFixture;
 using BencodeNET.Torrents;
 using FluentAssertions;
 using NSubstitute;
@@ -202,16 +203,17 @@ public void Info_PieceLength_IsParsed(long pieceSize)
 
         [Theory]
         [AutoMockedData]
-        public void Info_Pieces_IsParsed(byte[] pieces)
+        public void Info_Pieces_IsParsed([RepeatCount(20)] byte[] pieces)
         {
             // Arrange
             ParsedData = ValidSingleFileTorrentData;
             var info = ParsedData.Get<BDictionary>(TorrentFields.Info);
             info[TorrentInfoFields.Pieces] = new BString(pieces);
+            pieces.Should().HaveCount(20);
 
             // Act
             var parser = new TorrentParser(BencodeParser);
-            var torrent = parser.Parse((BencodeReader)null);
+            var torrent = parser.Parse((BencodeReader) null);
 
             // Assert
             torrent.Pieces.Should().Equal(pieces);

BencodeNET.Tests/Torrents/TorrentTests.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Text;
+using AutoFixture.Xunit2;
 using BencodeNET.Exceptions;
 using BencodeNET.Objects;
 using BencodeNET.Torrents;
@@ -135,6 +136,27 @@ public void DisplayNameUtf8_UnknownFileMode_ThrowsBencodeException()
             act.Should().Throw<BencodeException>();
         }
 
+        [Theory]
+        [AutoMockedData]
+        public void Pieces_Setter_NullValue_ThrowsArgumentNullException([NoAutoProperties] Torrent torrent)
+        {
+            Action act = () => torrent.Pieces = null;
+
+            act.Should().ThrowExactly<ArgumentNullException>();
+        }
+
+        [Theory]
+        [AutoMockedData]
+        public void Pieces_Setter_NotMultipleOf20_ThrowsArgumentException([NoAutoProperties] Torrent torrent)
+        {
+            var pieces = new byte[] { 66, 115, 135, 19, 149, 125, 229, 85, 68, 117, 252, 185, 243, 247, 139, 38, 11, 37, 60 };
+            pieces.Should().NotHaveCount(20);
+
+            Action act = () => torrent.Pieces = pieces;
+
+            act.Should().ThrowExactly<ArgumentException>();
+        }
+
         [Fact]
         public void PiecesAsHexString_Get_ReturnsHexUppercaseWithoutDashes()
         {

BencodeNET/Torrents/Torrent.cs

@@ -177,13 +177,26 @@ public virtual string DisplayNameUtf8
         /// </summary>
         public virtual long PieceSize { get; set; }
 
-        // TODO: Split into list of 20-byte hashes and rename to something appropriate?
-
         /// <summary>
         /// A concatenation of all 20-byte SHA1 hash values (one for each piece).
         /// Use <see cref="PiecesAsHexString"/> to get/set this value as a hex string instead.
         /// </summary>
-        public virtual byte[] Pieces { get; set; } = Array.Empty<byte>();
+        public virtual byte[] Pieces
+        {
+            get => _pieces;
+            set
+            {
+                if (value is null)
+                    throw new ArgumentNullException(nameof(value), "Pieces array cannot be null.");
+
+                var remainder = value.Length % 20;
+                if (remainder is not 0)
+                    throw new ArgumentException($"Array size has to be a multiple of 20, but length was {value.Length}");
+
+                _pieces = value;
+            }
+        }
+        private byte[] _pieces = Array.Empty<byte>();
 
         /// <summary>
         /// Gets or sets <see cref="Pieces"/> from/to a hex string (without dashes), e.g. 1C115D26444AEF2A5E936133DCF8789A552BBE9F[...].