Rest Sharp - 406 Error - No match for accept header

Question

I'm getting a 406 error when trying to use RestSharp to post a request to a third-party application. I'm new to REST, so I have to admit I didn't even know you could add headers. I tried adding these, but I'm still getting the same issue:

    var client = new RestClient(myURL);            

    RestRequest request = new RestRequest("restAction", Method.POST);     

    request.AddHeader("Accept", "text/plain"); 
    request.AddHeader("Content-Type", "text/plain");

    request.AddParameter("parameter1", param1);
    request.AddParameter("parameter2", param2);

    var response = client.Execute(request);

From what I've read, this may be dealing with a header named "accept". Is that right?

Any idea what could be going on?

Answer 1

In general in HTTP, when a client makes a request to a server, it tells the server what kinds of formats it's prepared to understand (accept). This list of acceptable formats is what the Accept header is for. If the server can't respond using any of the media types in the Accept header, it will return a 406. Otherwise, it will indicate which media type it chose in the Content-Type header of the response. Putting "*/*" in the Accept header tells the server that the client can handle any response media type.

In my original comment to your question, I said that RestSharp looks like it's including "*" in the Accept header by default, but looking closer I see now that it's actually not. So, if you don't override the Accept header like you've done here, the default header value is "application/json","application/xml","text/json","text/x-json","text/javascript","text/xml", and it appears the server you're talking to doesn't speak any of these media types.

If the server you're working with doesn't speak json or xml, I don't think you can use RestSharp, unless you create your own deserializer. I'm not sure if you can do this from the public API or if you'd have to modify the source yourself and recompile it for you own needs.

Since you're still getting HTTP errors from the server, I would recommend taking RestSharp out of the equation for right now, and just speaking HTTP directly to the server until you actually get a correct response from the server. You can use a tool like Fiddler to make a HTTP requests directly. When you send the request (for now in the debugging stage), send an Accept header of "*/*" to get around the 406. Once you've figured out what media types the server can send back to you, you should change this back to being a media type you know you can read and you know the server can send.

It sounds like the main issue here is really just not knowing the protocol of the server. If there's any documentation on the service you're talking to, I would read that very carefully to figure out what media types it's prepared to respond with and how to craft the URLs that it expects.