System.Net.WebConnectionStream.BeginRead C# (CSharp) Method

		public override IAsyncResult BeginRead (byte [] buffer, int offset, int size,
							AsyncCallback cb, object state)
		{
			if (!isRead)
				throw new NotSupportedException ("this stream does not allow reading");

			if (buffer == null)
				throw new ArgumentNullException ("buffer");

			int length = buffer.Length;
			if (offset < 0 || length < offset)
				throw new ArgumentOutOfRangeException ("offset");
			if (size < 0 || (length - offset) < size)
				throw new ArgumentOutOfRangeException ("size");

			lock (locker) {
				pendingReads++;
				pending.Reset ();
			}

			WebAsyncResult result = new WebAsyncResult (cb, state, buffer, offset, size);
			if (totalRead >= contentLength) {
				result.SetCompleted (true, -1);
				result.DoCallback ();
				return result;
			}
			
			int remaining = readBufferSize - readBufferOffset;
			if (remaining > 0) {
				int copy = (remaining > size) ? size : remaining;
				Buffer.BlockCopy (readBuffer, readBufferOffset, buffer, offset, copy);
				readBufferOffset += copy;
				offset += copy;
				size -= copy;
				totalRead += copy;
				if (size == 0 || totalRead >= contentLength) {
					result.SetCompleted (true, copy);
					result.DoCallback ();
					return result;
				}
				result.NBytes = copy;
			}

			if (cb != null)
				cb = cb_wrapper;

			if (contentLength != Int32.MaxValue && contentLength - totalRead < size)
				size = contentLength - totalRead;

			if (!read_eof) {
				result.InnerAsyncResult = cnc.BeginRead (request, buffer, offset, size, cb, result);
			} else {
				result.SetCompleted (true, result.NBytes);
				result.DoCallback ();
			}
			return result;
		}