Implement accept header parsing?

[glasser]

There doesn't seem to be a great Rust implementation of accept header parsing. Accept headers are basically a comma-separated list of media types, and so you'd think you can just split on comma and then parse each piece with a library like your library or the mime library.

But commas can exist inside quoted parameters, so this is technically incorrect.

There are several common implementations that get this wrong. It would be great if a library could just solve this once and for all, and since mime seems to be unmaintained, maybe your library could be that place?

[picoHz]

@glasser Thanks for your nice proposal!
I just added MediaTypeList.

[glasser]

@picoHz Thank you!

If you want to be really picking, quoted-strings do have a backslash-escaping mechanism which can escape double quotes: https://www.rfc-editor.org/rfc/rfc7230#section-3.2.6
But, say, the most popular npm Accept parser doesn't honor them either... presumably they are not common in practice.

[picoHz]

@glasser It's a good point. Backslash-escaping has been supported as of v0.19.8.

[maxcountryman]

@picoHz is it intentional that MediaTypeList does not do any sorting of MediaType based on implicit and explicit q parameters?

My expectation is that any implicit items remain in provided order and any explicit items are reordered in accordance with their relative q parameters.

For example, this would order audio/basic as the first item and then audio/* as the second:

Accept: audio/*; q=0.2, audio/basic

[picoHz]

@maxcountryman MediaTypeList is implemented as an iterator so the order cannot be changed.

[maxcountryman]

@picoHz is this meant to parse Accept in accordance with the spec? My read of the first comment here is that was the hope at least.

Without q parameter precedence ordering, I think this would fall short of what's required by the RFC.

[maxcountryman]

Without input from @picoHz it's unclear what the intent here is but regardless I've put together a parser for Accept that leverages this crate and implements headers::Header. Perhaps some folks here might find it useful. It's worth pointing out that there's some unfortunate duplication as the inner workings of MediaTypeList need to be adapted for MediaTypeBuf.