Parse Accept Header

Question

Does anyone have any suggestions (or a regular expression) for parsing the HTTP Accept header?

I am trying to do some content-type negotiation in ASP.NET MVC. There doesn't seem to be a built in way (which is fine, because there are a lot of schools of thought here), but the parsing is not entirely trivial and I would rather not re-invent the wheel if someone has already done it well and is willing to share.

Answer 1

As of .NET 4.5 (I think—Microsoft have made info on framework versions < 4.5 rather obscure these days), you can use one of the the built in parsers from System.Net.Http.Headers:

public IOrderedEnumerable<MediaTypeWithQualityHeaderValue> GetMediaTypes(string headerValue) =>
    headerValue?.Split(',')
        .Select(MediaTypeWithQualityHeaderValue.Parse)
        .OrderByDescending(mt => mt.Quality.GetValueOrDefault(1));

Then you can do something like this:

var headerValue = "application/json, text/javascript, */*; q=0.01";
var mediaTypes = GetMediaTypes(headerValue);

Giving you a nice list of all the media types, where the preferred option is the first item. Here's a LINQPad Dump of the mediaTypes result from the example:

Hat tip to this answer, for getting me on the right track.