Adapt multipart/form-data request to curl with image and json in the same request - bash

Question

I need to rewrite this curl request extracted from the browser to execute it from bash, it is a multipart/form-data that combines the upload of an image together with a json in the same request, I have carried out several tests substituting the raw data for two -F but the server responds with error.
What would be the correct way?
I also fail to understand the key that is next to WebKitFormBoundary is a value that seems random, is it just a separator? can i use anything?
I have removed the headers that I considered irrelevant
curl 'https://localhost' \
-H 'Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryXXXXXXXXXXXXXXXX'
-H 'Accept: */*' \
--data-raw $'------WebKitFormBoundaryXXXXXXXXXXXXXXXX\r\nContent-Disposition: form-data; name="image"; filename="image.jpg"\r\nContent-Type: image/jpeg\r\n\r\n\r\n------WebKitFormBoundaryXXXXXXXXXXXXXXXX\r\nContent-Disposition: form-data; name="item"; filename="blob"\r\nContent-Type: application/json\r\n\r\n{"item1":"xxxx","item2":"yyyy"}\r\n------WebKitFormBoundaryXXXXXXXXXXXXXXXX--\r\n' \
Thanks

Answer 1

I also fail to understand the key that is next to WebKitFormBoundary is a value that seems random, is it just a separator? can i use anything?
yes and yes and practically speaking yes. it's supposed to be a random-guaranteed-unique string used as separator to signal start and end of forms.. if you know beforehand that none of your uploads contains the string stackoverflow, you could use Content-Type: multipart/form-data; boundary=stackoverflow for example (but this may break if you upload a file actually containing the string stackoverflow !), but you should let curl generate that string automatically, rather than specifying it yourself, curl will auto-generate a string that is practically guaranteed to be unique.
I have removed the headers that I considered irrelevant
... if you guessed wrong, the server may give you an error for missing a required header. assuimg that you didn't make any mistakes in removing irrelevant headers though, i think it's
curl 'https://localhost'\
--form "image=#image.jpg;type=image/jpeg"\
--form "item=#blob;type=application/json"
the request generated by that command is roghly:
POST / HTTP/1.1
Host: localhost
User-Agent: curl/7.81.0
Accept: */*
Content-Length: 359
Content-Type: multipart/form-data; boundary=------------------------7d0262831ce8f248
--------------------------7d0262831ce8f248
Content-Disposition: form-data; name="image"; filename="image.jpg"
Content-Type: image/jpeg
image.jpg content
--------------------------7d0262831ce8f248
Content-Disposition: form-data; name="item"; filename="blob"
Content-Type: application/json
["json lol"]
--------------------------7d0262831ce8f248--
as you can see above, Accept: */* is curl's default accept-header anyway, so there's no need to specify it, and curl auto-generated the boundary ------------------------7d0262831ce8f248 so there's no need to manually specify a boundary either.