How to send JSON as part of multipart POST-request

Question

I have following POST-request form (simplified):

POST /target_page HTTP/1.1  
Host: server_IP:8080
Content-Type: multipart/form-data; boundary=AaaBbbCcc

--AaaBbbCcc
Content-Disposition: form-data; name="json" 
Content-Type: application/json

{ "param_1": "value_1", "param_2": "value_2"}

--AaaBbbCcc
Content-Disposition: form-data; name="file"; filename="..." 
Content-Type: application/octet-stream

<..file data..>
--AaaBbbCcc--

I try to send POST-request with requests:

import requests
import json

file = "C:\\Path\\To\\File\\file.zip"
url = 'http://server_IP:8080/target_page'


def send_request():
    headers = {'Content-type': 'multipart/form-data; boundary=AaaBbbCcc'}

    payload = { "param_1": "value_1", "param_2": "value_2"}

    r = requests.post(url, files={'json': (None, json.dumps(payload), 'application/json'), 'file': (open(file, 'rb'), 'application/octet-stream')}, headers=headers)

    print(r.content)

if __name__ == '__main__':
    send_request()

but it returns status 400 with following comment:

Required request part \'json\' is not present.
The request sent by the client was syntactically incorrect.

Please point on my mistake. What should I change to make it work?

Answer 1

You are setting the header yourself, including a boundary. Don't do this; requests generates a boundary for you and sets it in the header, but if you already set the header then the resulting payload and the header will not match. Just drop you headers altogether:

def send_request():
    payload = {"param_1": "value_1", "param_2": "value_2"}
    files = {
         'json': (None, json.dumps(payload), 'application/json'),
         'file': (os.path.basename(file), open(file, 'rb'), 'application/octet-stream')
    }

    r = requests.post(url, files=files)
    print(r.content)

Note that I also gave the file part a filename (the base name of the file path`).

For more information on multi-part POST requests, see the advanced section of the documentation.