Implement multipart body support in sttp stub

[urieli]

Multipart support was never added to the stub:

tapir/server/sttp-stub-server/src/main/scala/sttp/tapir/server/stub/SttpRequestBody.scala

Line 49 in abeb5d7

throw new IllegalArgumentException("Stub cannot handle multipart bodies")

This makes it impossible to test endpoints with multipart bodies.

Originally posted by @adamw in #3895 (comment)

[adamw]

/bounty $500

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Attempt	Started (GMT+0)	Solution
🟢 @asr2003	Oct 16, 2024, 12:59:11 PM	WIP
🟢 @rathi-dev	Oct 17, 2024, 8:45:21 AM	WIP
🟢 @abdelfetah18	Oct 24, 2024, 1:15:25 PM	#4117

[asr2003]

Hey @adamw! I’d love to take a crack at adding multipart body support to the sttp stub. Here’s what I am thinking for the approach:

Right now, the code throws an exception for MultipartBody. My idea is to properly parse multipart bodies instead of the exception. I will iterate over the parts, handling text and files and convert them into something Tapir can understand like RawBodyType.MultipartBody.Part. Once we can parse the multipart, I think we can update toRaw to return the proper raw value. So when the body type is RawBodyType.MultipartBody, it will grab the parsed parts and wrap them in RawValue[Seq[RawBodyType.MultipartBody.Part]]

I will also create some test cases that include multipart bodies with both text and file parts.

Does this sound good? I will get started and push a PR soon if all looks good to you! With this,
/attempt #3902

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[adamw]

@asr2003 Hey, great to see your interest in the issue! :) I'm not sure doing full multipart serialisation & parsing will be necessary (unless I'm missing something), but maybe it will be enough to remain on a higher level. I think a great start would be to create (failing) tests which would demonstrate how people might use the feature: either directly via sttp-client, or by interpreting the endpoint as a client. This should probably be an extension to the existing testsuite. Then we might work out what exactly is missing to make this work.

[rathi-dev]

/attempt #3902

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• Cancel my attempt

[adamw]

As we are getting first PRs for the bounties, I've published our "How to prepare a good PR" guide. I should have probably done this right away, sorry! :)

[abdelfetah18]

/attempt #3902

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• Cancel my attempt

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