DirectBuffer - Support ArraySegment for underlying array (#878)

* DirectBuffer - Support ArraySegment for backing storage * fix comments

Author: guigzzz

csharp/sbe-dll/DirectBuffer.cs

@@ -64,6 +64,25 @@ public DirectBuffer(byte* pBuffer, int bufferLength, BufferOverflowDelegate buff
  Wrap(pBuffer, bufferLength);
  }
 
+ /// <summary>
+ /// Attach a view to a buffer owned by external code
+ /// </summary>
+ /// <param name="buffer">byte buffer</param>
+ public DirectBuffer(ArraySegment<byte> buffer) : this(buffer, null)
+ {
+ }
+
+ /// <summary>
+ /// Attach a view to a buffer owned by external code
+ /// </summary>
+ /// <param name="buffer">byte buffer</param>
+ /// <param name="bufferOverflow">delegate to allow reallocation of buffer</param>
+ public DirectBuffer(ArraySegment<byte> buffer, BufferOverflowDelegate bufferOverflow)
+ {
+ this.bufferOverflow = bufferOverflow;
+ Wrap(buffer);
+ }
+
  /// <summary>
  /// Creates a DirectBuffer that can later be wrapped
  /// </summary>
@@ -114,6 +133,24 @@ public void Wrap(byte* pBuffer, int bufferLength)
  _needToFreeGCHandle = false;
  }
 
+ /// <summary>
+ /// Recycles an existing <see cref="DirectBuffer"/> from a byte buffer owned by external code
+ /// </summary>
+ /// <param name="buffer">buffer of bytes</param>
+ public void Wrap(ArraySegment<byte> buffer)
+ {
+ if (buffer == null) throw new ArgumentNullException(nameof(buffer));
+
+ FreeGCHandle();
+
+ // pin the buffer so it does not get moved around by GC, this is required since we use pointers
+ _pinnedGCHandle = GCHandle.Alloc(buffer.Array, GCHandleType.Pinned);
+ _needToFreeGCHandle = true;
+
+ _pBuffer = ((byte*)_pinnedGCHandle.AddrOfPinnedObject().ToPointer()) + buffer.Offset;
+ _capacity = buffer.Count;
+ }
+
  /// <summary>
  /// Capacity of the underlying buffer
  /// </summary>

csharp/sbe-tests/DirectBufferTests.cs

@@ -66,6 +66,40 @@ public void ConstructFromNativeBuffer()
  }
  }
 
+ [TestMethod]
+ public void ConstructFromByteArray()
+ {
+ var buffer = new byte[16];
+
+ const int value = 5;
+ const int index = 0;
+ 
+ using (var directBuffer = new DirectBuffer(buffer))
+ {
+ directBuffer.Int64PutLittleEndian(index, value);
+ Assert.AreEqual(value, buffer[index]);
+ }
+ }
+
+ [TestMethod]
+ public void ConstructFromArraySegment()
+ {
+ const int value = 5;
+ const int index = 0;
+ const int offset = 512;
+ const int size = 1024;
+
+ var bigBuffer = new byte[size];
+ var buffer = new ArraySegment<byte>(bigBuffer, offset, size - offset);
+ 
+ using (var directBuffer = new DirectBuffer(buffer))
+ {
+ directBuffer.Int64PutLittleEndian(index, value);
+ Assert.AreEqual(value, bigBuffer[offset + index]);
+ Assert.AreEqual(value, buffer.AsSpan<byte>()[index]);
+ }
+ }
+
  [TestMethod]
  public void Recycle()
  {