azure sql database – Moving PDF files from a SQL Server Table to Blob Storage

I am trying to move PDF files from the Azure SQL Server database table to Blob Storage and running into some trouble.

I am trying to use the SQL Server stored procedure sp_invoke_external_rest_endpoint to accomplish this task. The issue is it is converting my file to Unicode before transmitting:

Here is my code

DECLARE @bytes VARBINARY(MAX) = NULL;
DECLARE @fileName VARCHAR(MAX) = NULL;

SELECT TOP 1 @bytes = Bytes, @fileName = FileName
FROM #TempPdf
OPTION(RECOMPILE);

DECLARE @response VARCHAR(MAX) = NULL;
DECLARE @storageContainerUrl VARCHAR(MAX) = 'https://mystorage.blob.core.windows.net/testing-pdfs/';

DECLARE @url VARCHAR(MAX) = CONCAT(@storageContainerUrl, @fileName);
DECLARE @payload VARCHAR(MAX) = @bytes;
DECLARE @payloadLength INT = DATALENGTH(@payload);

DECLARE @headers VARCHAR(1000) = JSON_OBJECT
(
        'content-length': @payloadLength,
        'x-ms-content-length': CAST(@payloadLength AS VARCHAR(20)),
        'content-type': 'application/x-www-form-urlencoded',
        'Accept': 'application/xml',
        'x-ms-blob-type': 'BlockBlob'
);

SELECT
@bytes AS Bytes,
DATALENGTH(@bytes) AS BytesLength,
@payload AS Payload,
DATALENGTH(@payload) AS PayloadLength;

EXEC sp_invoke_external_rest_endpoint
    @url = @url,
    @method = 'PUT',
    @headers = @headers,
    @payload = @payload,
    @credential="MyCredentials",
    @response = @response OUTPUT;

SELECT CAST(@response AS XML) AS Response;

The data length of both the bytes(VARBINARY(MAX)) and payload(VARCHAR(MAX)) is 88,698, which is correct for this PDF. However, when I look at the size in Blob Storage it is 127KiB, which is larger than 87Ki it should be.

I believe it doing this because sp_invoke_external_rest_endpoint parameter @payload is a NVARCHAR(MAX), so it’s converting my 8-bit variable to Unicode, which is causing file corruption.

Is there a way to use sp_invoke_external_rest_endpoint without file corruption or an alternative way of doing this in a stored procedure?

If all else fails, I will just have to accomplish this using C# and create some type of temporary job.

Thanks!