multipart data POST using python requests: no multipart boundary was found

Question

I have a form-data as well as file to be sent in the same POST. For ex, {duration: 2000, file: test.wav}. I saw the many threads here on multipart/form-data posting using python requests. They were useful, especially this one.

My sample request is as below:

    files = {'file': ('wavfile', open(filename, 'rb'))}
    data = {'duration': duration}
    headers = {'content-type': 'multipart/form-data'}
    r = self.session.post(url, files=files, data=data, headers=headers)

But when I execute the above code, I get this error:

5:59:55.338 Dbg 09900 [DEBUG] Resolving exception from handler [null]: org.springframework.web.multipart.MultipartException: Could not parse multipart servlet request; nested exception is org.apache.commons.fileupload.FileUploadException: the request was rejected because no multipart boundary was found.

So my questions are: 1) How can I see the content of the request being sent? Couldn't use wireshark, its not across the network. 2) why is the boundary missing in the encoded data? Did I miss anything, please point out.

Ian Stapleton Cordasco · Accepted Answer · 2013-07-03 02:02:12Z

85

You should NEVER set that header yourself. We set the header properly with the boundary. If you set that header, we won't and your server won't know what boundary to expect (since it is added to the header). Remove your custom Content-Type header and you'll be fine.

answered Jul 3, 2013 at 2:02

Ian Stapleton Cordasco

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7 Comments

Dan Over a year ago

Hi, when I use postman to generate code it explicitly add that header but if I try if without the header it doesn't work. Perhaps you can spot my error / misunderstanding? stackoverflow.com/q/51141881/1011724

jmcgrath207 Over a year ago

to added to that I've had a requests session that was appending these headers. Once I removed it worked api_session.headers.update({"Content-Type": "application/json"})

RCross Over a year ago

Sorry, but that's not my experience. If I use curl, and don't set the Content-Type, it generates a Content-Type of Content-Type: multipart/form-data. When I try the same with Python Requests, it generates Content-Type: application/x-www-form-urlencoded which is wrong (and is rejected by the server I'm running the request against.

pdoherty926 Over a year ago

Who is "we" in this answer?

Ian Stapleton Cordasco Over a year ago

We referring to the maintainers of the requests library. The way it's authored, it needs to control this header. Specifying it yourself is documented as behaviour that should be avoided

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Anirban Kundu · Accepted Answer · 2015-10-28 05:49:10Z

17

Taking out the Content-Type header with explicit "multipart/form-data" worked!

answered Oct 28, 2015 at 5:49

Anirban Kundu

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1 Comment

semore_1267 Over a year ago

This is actually the correct answer for some reason. Using requests==2.26.0 and django-rest-framework==0.1.0. 8 years later. Imagine that

jeet.chanchawat · Accepted Answer · 2019-07-19 07:10:41Z

0

To specifically add boundary add following in header :

headers = {
    'content-type': 'multipart/form-data; boundary=ebf9f03029db4c2799ae16b5428b06bd'
}

answered Jul 19, 2019 at 7:10

jeet.chanchawat

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2 Comments

shacker Over a year ago

See Ian Stapletons' answer above - you should never do this manually.

jeet.chanchawat Over a year ago

removing "content-type" did-not worked for me, adding boundary did.

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