Fix handling of input of type FormData for the Fetch client

[frazar]

Several open issues are caused by the multipart/form-data formatter trying to provide a simple API based on an input of type Object. However, Object can not express some of the typical use cases of a multipart request. On the other hand, FormData could.

One example (mentioned in #705 and #965) is sending a requested with multiple entries belonging to the same "key". Since a FormData object allows one key to be mapped to multiple values, one can simply do:

f = new FormData()
f.append('files', new Blob())
f.append('files', new Blob())
[...f.keys()] // This gives 2 entries, as expected

This is clearly not possible with an Object, where the key-value relationship is 1:1. #1000 tries to achieve this by automatically converting Array values to multiple FormData keys. However, I argue that it is not necessarily what the user wants, since they could either expect:

• that the array is sent as-is as a single FormData entry, or
• that each array is sent a separate FormData entries.

In principle, it is not so easy to infer which of the two is the one desired by the user.

Currently, however, inputs of type FormData are not correctly handled by the multipart/form-data formatter for the Fetch client, which tries to enumerate the keys using the Object.keys(...) construct:

swagger-typescript-api/templates/base/http-clients/fetch-http-client.ejs

Lines 107 to 108 in 325e308

	[ContentType.FormData]: (input: any) =>
	Object.keys(input || {}).reduce((formData, key) => {

Unfortunately, FormData returns an empty list when used through Object.keys()

f = new FormData()
f.append('files', new Blob())
f.append('files', new Blob())
Object.keys(f) // This gives an empty array!

This PR proposes a way to allow the user to directly supply a FormData, basically opting out of any smart formatting logic that might actually get in the way. In this way, the user takes responsibility for correctly managing the conversion.

I argue that the breaking change is minimal since any use of FormData is broken under the current API. Additionally, this would align with the logic for the Axios client, which already short-circuits the formatting for FormData inputs.

swagger-typescript-api/templates/base/http-clients/axios-http-client.ejs

Lines 81 to 82 in 325e308

	protected createFormData(input: Record<string, unknown>): FormData {
	if (input instanceof FormData) {

[Copilot]

Copilot reviewed 5 out of 25 changed files in this pull request and generated no comments.

Files not reviewed (20)

• templates/base/http-clients/fetch-http-client.ejs: Language not supported
• tests/spec/another-query-params/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/custom-extensions/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/defaultAsSuccess/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/defaultResponse/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/deprecated/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/dot-path-params/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/enumNamesAsValues/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/extractRequestBody/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/extractRequestParams/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/extractResponseBody/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/extractResponseError/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/jsAxios/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/moduleNameFirstTag/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/moduleNameIndex/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/on-insert-path-param/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/patch/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/responses/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/singleHttpClient/snapshots/basic.test.ts.snap: Language not supported
• tests/spec/sortTypes-false/snapshots/basic.test.ts.snap: Language not supported

[DmitryShcheklein]

How long will this fix stay open? The problem is actual 😤

[PavelPopovIPS]

Hi everyone, resolving this issue can be helpfull for nodejs projects.
Is there chance to check and approve changes?

[antonkharkhonov]

+1, I encountered the same problem. So far, I have been adding this early return manually each time after generating a new build. Therefore, it would be very helpful if this could be checked and merged.

[changeset-bot]

🦋 Changeset detected

Latest commit: 25e12e3

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
swagger-typescript-api	Patch

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