System.IO.MemoryStream.ReadAsync C# (CSharp) Method

        public override Task<int> ReadAsync(Byte[] buffer, int offset, int count, CancellationToken cancellationToken)
        {
            if (buffer == null)
            {
                throw new ArgumentNullException(nameof(buffer), SR.ArgumentNull_Buffer);
            }
            if (offset < 0)
            {
                throw new ArgumentOutOfRangeException(nameof(offset), SR.ArgumentOutOfRange_NeedNonNegNum);
            }
            if (count < 0)
            {
                throw new ArgumentOutOfRangeException(nameof(count), SR.ArgumentOutOfRange_NeedNonNegNum);
            }
            if (buffer.Length - offset < count)
            {
                throw new ArgumentException(SR.Argument_InvalidOffLen);
            }

            return ReadAsyncImpl(buffer, offset, count, cancellationToken);
        }

        public async Task WritesMessage()
        {
            MemoryStream outputStream = new MemoryStream();

            MessageWriter messageWriter = 
                new MessageWriter(
                    outputStream,
                    this.messageSerializer);

            // Write the message and then roll back the stream to be read
            // TODO: This will need to be redone!
            await messageWriter.WriteMessage(Message.Event("testEvent", null));
            outputStream.Seek(0, SeekOrigin.Begin);

            string expectedHeaderString =
                string.Format(
                    Constants.ContentLengthFormatString,
                    ExpectedMessageByteCount);

            byte[] buffer = new byte[128];
            await outputStream.ReadAsync(buffer, 0, expectedHeaderString.Length);

            Assert.Equal(
                expectedHeaderString,
                Encoding.ASCII.GetString(buffer, 0, expectedHeaderString.Length));

            // Read the message
            await outputStream.ReadAsync(buffer, 0, ExpectedMessageByteCount);

            Assert.Equal(
                TestEventString,
                Encoding.UTF8.GetString(buffer, 0, ExpectedMessageByteCount));

            outputStream.Dispose();
        }