how do you stop a zip file upload to s3 having the headers appended

Hi,

I have a test step which uploads a file to Amazon s3 using a PUT. i have attached the zip file to my test step and chosen not to cache it. When I run the test step the file is padded out with extra headers that i do not want, for example:

PUT  <amazon stuff>
Accept-Encoding: gzip,deflate
Content-Type: multipart/form-data; boundary="----=_Part_33_1379518672.1495112195626"
MIME-Version: 1.0
Content-Length: 2033
Host: <amazon bits>
Connection: Keep-Alive
User-Agent: Apache-HttpClient/4.1.1 (java 1.5)

------=_Part_33_1379518672.1495112195626
Content-Type: application/zip; name=test.zip
Content-Transfer-Encoding: binary
Content-Disposition: form-data; name="test.zip"; filename="test.zip"

<the zip content> 

creates a file on s3, all good... but when i try and unzip the file it is a "corrupted archive", if i open the file in notepad it contains the 

Content-Type: application/zip; name=test.zip
Content-Transfer-Encoding: binary
Content-Disposition: form-data; name="test.zip"; filename="test.zip"

at the top of the file which it shouldn't