How to send JSON as part of multipart POST-request

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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?

python-requests http-post multipartform-data python json
2 Answers

In case if someone searches ready to use method to transform python dicts to multipart-form data structures here is a simple gist example to do such transformation:

{"some": ["balls", "toys"], "field": "value", "nested": {"objects": "here"}}
    ->
{"some[0]": "balls", "some[1]": "toys", "field": "value", "nested[objects]": "here"}

To send some data you may want to use the multipartify method from this gist like this:

import requests  # library for making requests

payload = {
    "person": {"name": "John", "age": "31"},
    "pets": ["Dog", "Parrot"],
    "special_mark": 42,
}  # Example payload

requests.post("https://example.com/", files=multipartify(payload))

To send same data along with any file (as OP wanted) you may simply add it like this:

converted_data = multipartify(payload)
converted_data["attachment[0]"] = ("file.png", b'binary-file', "image/png")

requests.post("https://example.com/", files=converted_data)

Note, that attachment is a name defined by server endpoint and may vary. Also attachment[0] indicates that it is first file in you request - this is also should be defined by API documentation.

user_61706760
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