Optimizations to ByteBufferStream and SingleChunkBuffer.

Author: rstam

src/MongoDB.Bson/IO/ByteBufferStream.cs

@@ -361,19 +361,19 @@ public override ArraySegment<byte> ReadCStringBytes()
             ThrowIfDisposed();
             ThrowIfEndOfStream(1);
 
-            var startPosition = _position;
-            var nullPosition = FindNullByte();
-            var length = nullPosition - startPosition;
-
-            var segment = _buffer.AccessBackingBytes(startPosition);
-            if (segment.Count >= length)
+            var segment = _buffer.AccessBackingBytes(_position);
+            var index = Array.IndexOf<byte>(segment.Array, 0, segment.Offset, segment.Count);
+            if (index != -1)
             {
-                _position = nullPosition + 1; // advance over null byte
+                var length = index - segment.Offset;
+                _position += length + 1; // advance over the null byte
                 return new ArraySegment<byte>(segment.Array, segment.Offset, length); // without the null byte
             }
             else
             {
-                var cstring = ReadBytes(length + 1); // read null byte also
+                var nullPosition = FindNullByte();
+                var length = nullPosition - _position;
+                var cstring = ReadBytes(length + 1); // advance over the null byte
                 return new ArraySegment<byte>(cstring, 0, length); // without the null byte
             }
         }

src/MongoDB.Bson/IO/SingleChunkBuffer.cs

@@ -35,7 +35,7 @@ public sealed class SingleChunkBuffer : IByteBuffer
         /// <param name="chunk">The chuns.</param>
         /// <param name="length">The length.</param>
         /// <param name="isReadOnly">Whether the buffer is read only.</param>
-        internal SingleChunkBuffer(IBsonChunk chunk, int length, bool isReadOnly = false)
+        public SingleChunkBuffer(IBsonChunk chunk, int length, bool isReadOnly = false)
         {
             if (chunk == null)
             {
@@ -103,7 +103,8 @@ public ArraySegment<byte> AccessBackingBytes(int position)
                 throw new ArgumentOutOfRangeException("position");
             }
 
-            return new ArraySegment<byte>(_chunk.Bytes.Array, _chunk.Bytes.Offset + position, _length - position);
+            var segment = _chunk.Bytes;
+            return new ArraySegment<byte>(segment.Array, segment.Offset + position, _length - position);
         }
 
         /// <inheritdoc/>
@@ -120,7 +121,8 @@ public void Clear(int position, int count)
             }
             EnsureIsWritable();
 
-            Array.Clear(_chunk.Bytes.Array, _chunk.Bytes.Offset + position, count);
+            var segment = _chunk.Bytes;
+            Array.Clear(segment.Array, segment.Offset + position, count);
         }
 
         /// <inheritdoc/>
@@ -159,7 +161,8 @@ public byte GetByte(int position)
                 throw new ArgumentOutOfRangeException("position");
             }
 
-            return _chunk.Bytes.Array[_chunk.Bytes.Offset + position];
+            var segment = _chunk.Bytes;
+            return segment.Array[segment.Offset + position];
         }
 
         /// <inheritdoc/>
@@ -183,7 +186,8 @@ public void GetBytes(int position, byte[] destination, int offset, int count)
                 throw new ArgumentOutOfRangeException("count");
             }
 
-            Buffer.BlockCopy(_chunk.Bytes.Array, _chunk.Bytes.Offset + position, destination, offset, count);
+            var segment = _chunk.Bytes;
+            Buffer.BlockCopy(segment.Array, segment.Offset + position, destination, offset, count);
         }
 
         /// <inheritdoc/>
@@ -221,7 +225,8 @@ public void SetByte(int position, byte value)
             }
             EnsureIsWritable();
 
-            _chunk.Bytes.Array[_chunk.Bytes.Offset + position] = value;
+            var segment = _chunk.Bytes;
+            segment.Array[segment.Offset + position] = value;
         }
 
         /// <inheritdoc/>
@@ -246,7 +251,8 @@ public void SetBytes(int position, byte[] source, int offset, int count)
             }
             EnsureIsWritable();
 
-            Buffer.BlockCopy(source, offset, _chunk.Bytes.Array, _chunk.Bytes.Offset + position, count);
+            var segment = _chunk.Bytes;
+            Buffer.BlockCopy(source, offset, segment.Array, segment.Offset + position, count);
         }
 
         // private methods