Use Pieces.Length for NumberOfPieces calculation

#48

Author: Krusen

BencodeNET.Tests/Torrents/TorrentTests.cs

@@ -192,20 +192,17 @@ public void TotalSize_UnknownFileMode_IsZero()
 
         [Theory]
         [AutoMockedData]
-        public void NumberOfPieces_ShouldBeTotalSizeDividedByPieceSizeRoundedUp(long fileSize, long pieceSize)
+        public void NumberOfPieces_ShouldBePiecesLengthDividedByPieceSizeRoundedUp(int piecesByteCount, long pieceSize)
         {
-            var expected = (int)Math.Ceiling((double) fileSize/pieceSize);
+            var expected = (int)Math.Ceiling((double) piecesByteCount/pieceSize);
 
             var torrent = new Torrent
             {
-                File = new SingleFileInfo
-                {
-                    FileSize = fileSize
-                },
+                Pieces = new byte[piecesByteCount],
                 PieceSize = pieceSize
             };
 
-            torrent.TotalSize.Should().Be(fileSize);
+            torrent.Pieces.Length.Should().Be(piecesByteCount);
             torrent.NumberOfPieces.Should().Be(expected);
         }
 

BencodeNET/Torrents/Torrent.cs

@@ -164,7 +164,7 @@ public virtual string DisplayName
         /// 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; }
+        public virtual byte[] Pieces { get; set; } = new byte[0];
 
         /// <summary>
         /// Gets or sets <see cref="Pieces"/> from/to a hex string (without dashes), e.g. 1C115D26444AEF2A5E936133DCF8789A552BBE9F[...].
@@ -218,7 +218,9 @@ public virtual long TotalSize
         /// <summary>
         /// The total number of file pieces.
         /// </summary>
-        public virtual int NumberOfPieces => (int)Math.Ceiling((double)TotalSize / PieceSize);
+        public virtual int NumberOfPieces => Pieces != null
+            ? (int) Math.Ceiling((double) Pieces.Length / PieceSize)
+            : 0;
 
         /// <summary>
         /// Converts the torrent to a <see cref="BDictionary"/>.