Using Varbinary(max) And UPDATE .WRITE To Store Data In A Streaming Fashion

I have the following table:

CREATE TABLE [dbo].[IntegrationMessages]
(
[MessageId] [int] IDENTITY(1,1) NOT NULL,
[MessagePayload] [varbinary](max) NOT NULL,
)


I call the following insertmessage stored proc from a c# class that reads a file.

ALTER PROCEDURE [dbo].[InsertMessage]
@MessageId int OUTPUT
AS
BEGIN


INSERT INTO [dbo].[IntegrationMessages]
( MessagePayload )
VALUES
( 0x0 )

SELECT @MessageId = @@IDENTITY

END


The c# class then opens a filestream, reads bytes into a byte [] and calls UpdateMessage stored proc in a while loop to chunk the data into the MessagePayload column.


ALTER PROCEDURE [dbo].[UpdateMessage]
@MessageId int
,@MessagePayload varbinary(max)

AS
BEGIN


UPDATE [dbo].[IntegrationMessages]
SET
MessagePayload.WRITE(@MessagePayload, NULL, 0)
WHERE
MessageId = @MessageId


END



My problem is that I am always ending up with a 0x0 value prepended in my data. So far I have not found a way to avoid this issue. I have tried making the MessagePayload column NULLABLE but .WRITE does not work with columns that are NULLABLE.

My column contains the following:
0x0043555354317C...
but it should really contain
0x43555354317C...


My goal is to be able to store an exact copy of the data I read from the file.

Here is my c# code:

public void TestMethod1()
{
int bufferSize = 64;
byte[] inBuffer = new byte[bufferSize];
int bytesRead = 0;

byte[] outBuffer;

DBMessageLogger logger = new DBMessageLogger();

FileStream streamCopy =
new FileStream(@"C:vsProjectsSandboxBTSMessageLoggerInSACustomer3Rows.txt", FileMode.Open);

try
{
while ((bytesRead = streamCopy.Read(inBuffer, 0, bufferSize)) != 0)
{
outBuffer = new byte[bytesRead];

Array.Copy(inBuffer, outBuffer, bytesRead);

string inText = Encoding.UTF8.GetString(outBuffer);

Debug.WriteLine(inText);





//This calls the UpdateMessage stored proc
logger.LogMessageContentToDb(outBuffer);
}
}
catch (Exception ex)
{
// Do not fail the pipeline if we cannot archive
// Just log the failure to the event log
}
}