How to specify multipart/form-data request body in path macro?

[mrf7777]

I was looking at the latest path attribute macro documentation on docs.rs (utoipa-3.4.4) but could not find how to specify that a function could accept a request body with data with content type multipart/form-data.

For context, I am using utoipa to generate an OpenAPI spec to generate a typescript client to talk to my rust web server running actix-web. I intend to use multipart/form-data to upload a single file from the browser. I have considered trying to make an endpoint on my actix-web server to accept a raw file, but I struggle with annotating (with utoipa) the fact that multiple specific types of files can be uploaded and I have to resort to application/octet-stream to catch all file/content types and then use sniffing to deduce the content type uploaded. An endpoint that takes multipart/form-data would allow me to inspect the content type of the uploaded content easily.

[juhaku]

I belive it should be doable with something like this definition:

#[utoipa::path(
    request_body(content = WhatEverStruct, description = "Multipart file", content_type = "multipart/form-data"),
)]

[mrf7777]

And I guess that the WhatEverStruct will specify the expected keys of the form data passed to the function? I am using actix-multipart to represent that content struct but I think that there is an issue open for implementing this: #740. So, is there a manual way to specify the expected keys in the request body or elsewhere?

[juhaku]

The WhatEverStruct must implement ToSchema trait and so there are couple of options to choose from.

1. Is to use a general type, like Value or Object. These will render as "typeless" types e.g. Object will be the OpenAPI's type: object and Value is the JSON value indicating OpenAPI's "Any" type that can basically accept anything. With these of course then there will not be any fields generated in the docs but should make the compiler happy.
2. Would be to implement the ToSchema for the WhatEverStruct by the means possible e.g. using a "new type" pattern. More insight here: Could not resolve reference: /components/schemas/PathBuf does not exist in document #656 and here Component from external crate #507 (comment).