Client: Multipart upload doesn't work with some servers #5157
Description
When Ktor sends a multipart form request, the name= field isn't quoted, which differs from the standard FormData behavior. Even though the standard didn't say they must be quoted strings, many server frameworks (e.g. elysia) expect it to be quoted, which causes elysia to ignore the field entirely.
Packet capture: Note that the FormData sent name="photo" while Ktor sent name=photo
JS Fetch FormData
POST /upload HTTP/1.1
x-instant-key: meowmeow
Content-Type: multipart/form-data; boundary=-WebkitFormBoundary074b68ff41eb4ad0bc81501198ed9954
Connection: keep-alive
User-Agent: Bun/1.2.21
Accept: */*
Host: localhost:3000
Accept-Encoding: gzip, deflate, br, zstd
Content-Length: 9409403
---WebkitFormBoundary074b68ff41eb4ad0bc81501198ed9954
Content-Disposition: form-data; name="id"
test-252
---WebkitFormBoundary074b68ff41eb4ad0bc81501198ed9954
Content-Disposition: form-data; name="owner_key"
1234
---WebkitFormBoundary074b68ff41eb4ad0bc81501198ed9954
Content-Disposition: form-data; name="photo"; filename="./UWU01721.JPG"
Content-Type: application/octet-stream
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Ktor
POST /upload HTTP/1.1
Host: 172.16.0.212:3000
Content-Length: 14279723
x-instant-key: meowmeow
Accept: application/json
Accept-Charset: UTF-8
User-Agent: ktor-client
Content-Type: multipart/form-data; boundary=-748f4c8e-19eb394f-6d6c679e-74278686658a4a8c701fae79636dfd85372e904c-4
---748f4c8e-19eb394f-6d6c679e-74278686658a4a8c701fae79636dfd85372e904c-4
Content-Disposition: form-data; name=id
Content-Length: 36
e662d915-3ed6-4042-baca-861630ab65bc
---748f4c8e-19eb394f-6d6c679e-74278686658a4a8c701fae79636dfd85372e904c-4
Content-Disposition: form-data; name=owner_key
Content-Length: 4
1234
---748f4c8e-19eb394f-6d6c679e-74278686658a4a8c701fae79636dfd85372e904c-4
Content-Disposition: form-data; name=photo; filename=UWU01955.JPG
Content-Type: image/jpeg
Content-Length: 14166893
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