Hi, I'm not sure if you found a solution for your problem but the following sample will upload a file named 'hello.txt' with the contents 'Hello!!':
Headers:
'Content-Type': 'multipart/form-data; boundary=uploadboundary'
Body:
--uploadboundary
Content-Disposition: form-data; name="filename"
hello.txt
--uploadboundary
Content-Disposition: form-data; name="file"; filename="hello.txt"
Hello!!
--uploadboundary--