support `filename*`

[xgjhlws]

Is it possiable to support field filename* ?

https://datatracker.ietf.org/doc/html/rfc6266#section-5

[xgjhlws]

Because C# has encoded filename to base64.When C# send multipart request to Rust, it can not parse filename correctly.

[xgjhlws]

In C#, send request like this:

In Rust, can only receive like this:

[SergioBenitez]

Sure, I don't see why we can't do this. Happy to accept a PR.

[soundslocke]

I'm working with an Axum application (holiday coding 🎄 🎉) and hit a similar issue as this when a client sent name*= as an "extended" content disposition field instead of name=.

I'm thinking it may not be correct behavior for clients to set extended field names but some definitely do this. See RFC 7578 Section 4.2 and this rationale.

I'm also thinking it's okay to be permissive about it on the server side. I dove down the rabbit hole and tackled parsing extended fields (i.e. name*= and filename*=) as well as a TODO comment that had been left in the parsing code to handle fields in a case-insensitive way.

I added tests for the new functionality, fixed a Cargo conditional compilation warning, and moved things from constants.rs to content_disposition.rs. Hopefully that all makes sense.

See my branch here: master...soundslocke:multer:extended-content-disposition-field-parsing

Would you still be happy to have a PR for this @SergioBenitez?