Feature request: Fallible extractor filter

[jakajancar]

For example:

fn user(db: Db) -> impl Filter<Extract = (UserId,)> + Clone {
    // ...
}

It internally calls e.g. warp::header() but then connects to the database which might fail. If such a filter just rejects, other peer filters will still be attempted (perhaps attempting the same database query 10 times).

What is the best practice for filters like this?