Content Negotiation

[seanmonstar]

Provide a content-negotiation filter with these objectives:

• User can chain together serializers, choosing what formats can be output.
• Serializers include content-type headers
• The filter checks for "best" serializer using the request's accept header.
• Wrapped filters can return either T: Serialize, or Negotiate(Response<T: Serialize>), which will automatically be serialized by the "best" format.

Example:

let negotiation = warp::reply::with::negotiate()
    .format(json)
    .format(xml);

let list = warp::path("todos")
    .and_then(|| DB::load_todos());
let one = path!("todos" / u64)
    .and_then(|id| Db::get_todo(id));

let api = list.or(one)
    .with(negotiate);

[carllerche]

I would be interested in hearing more about how you specify a serializer implementation, at what point does the serialization happen, etc...

[genbattle]

I recommended #668 be closed in favor of this feature, with the intention that content-negotiation filtering is somehow integrated into existing filters like warp::filters::body::json that currently do their own limited content negotiation.

Ideally there would be a way to override/extend the content negotiation to make it more or less permissive. In this particular case I wanted to add support for application/vnd.api+json which uses a Structured Syntax Name Suffix to specify that the content is, in fact, json. The simplest fix would be allowing overriding a existing content-negotiation filters in the chain with a new one, but there may be a more nuanced way to support composition of content-negotiation filters.