[BUG][TYPESCRIPT-FETCH] Fix #23998: Form data requests with mime type parameters use URLSearchParams instead of FormData

[MarcelKonrad]

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Fixes #23998. A description and a guide on how to reproduce the issue can be found there.

@TiFu @taxpon @sebastianhaas @kenisteward @Vrolijkx @macjohnny @topce @akehir @petejohansonxo @amakhrov @davidgamero @mkusaka @joscha @dennisameling

---

Summary by cubic

Fixes incorrect detection of multipart form data in typescript-fetch when MIME parameters are present, so requests now use FormData instead of URLSearchParams. Fixes #23998.

• Bug Fixes
  • In canConsumeForm, replace strict equality with startsWith('multipart/form-data') to handle content types like multipart/form-data; charset=UTF-8.

^{Written for commit 9a9ca47. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 20 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="samples/client/petstore/typescript-fetch/builds/allOf-nullable/runtime.ts">

<violation number="1" location="samples/client/petstore/typescript-fetch/builds/allOf-nullable/runtime.ts:372">
P2: MIME type detection in `canConsumeForm` is case-sensitive, which violates RFC 2045/7231 case-insensitivity rules for media types. Mixed-case `multipart/form-data` values (e.g., `Multipart/Form-Data`) will incorrectly bypass FormData selection.</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

P2: MIME type detection in canConsumeForm is case-sensitive, which violates RFC 2045/7231 case-insensitivity rules for media types. Mixed-case multipart/form-data values (e.g., Multipart/Form-Data) will incorrectly bypass FormData selection.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At samples/client/petstore/typescript-fetch/builds/allOf-nullable/runtime.ts, line 372:

<comment>MIME type detection in `canConsumeForm` is case-sensitive, which violates RFC 2045/7231 case-insensitivity rules for media types. Mixed-case `multipart/form-data` values (e.g., `Multipart/Form-Data`) will incorrectly bypass FormData selection.</comment>

<file context>
@@ -369,7 +369,7 @@ export function mapValues(data: any, fn: (item: any) => any) {
 export function canConsumeForm(consumes: Consume[]): boolean {
     for (const consume of consumes) {
-        if ('multipart/form-data' === consume.contentType) {
+        if (consume.contentType?.startsWith('multipart/form-data') == true) {
             return true;
         }
</file context>

[macjohnny]

thanks for the fix!

[macjohnny]

@MarcelKonrad please update the samples

[MarcelKonrad]

Thanks, @macjohnny, for the review. I re-ran the scripts of the PR template, but there were no changed files. The CI error indicates an issue with the TypeScript version, which is unrelated to this PR.