The class ODataMessageWriter in Microsoft.Data.OData.dll, v5.6.1.0 accepts constructors that take IODataRequestMessage requestMessage as well as IODataResponseMessage responseMessage. The question is when to use one or the other.
I'm implementing a OData service by hand using ODataMessageWriter, and I'd like to get the headers of my response correct based on the headers in the request... but there seems to require a lot of manual coding to get all the headers right (accept, content-type, DataServiceVersion, etc)... Am I missing something?
If the HTTP message you're writing is a response message (i.e., from the server), then you'll use IODataResponseMessage. If you're constructing a message from a client, you'll use IODataRequestMessage. It sounds like you're writing a server, so you should be using IODataResponseMessage when creating writers and IODataRequestMessage when creating readers.
You're right that there's a lot of work involved when using ODataLib directly. ODataLib is great when you want/need to write your own server and need a component that knows how to serialize the OData payload format. If you don't need such a high degree of control over your server, I'd recommend using ASP.Net Web API's OData implementation, which actually uses ODataLib under the hood.
Having said that, ODataLib can figure the Content-Type to respond with if you give it the Accept header from the request. You just need to call SetContentType on the writer settings:
var settings = new ODataMessageWriterSettings();
settings.SetContentType(
"application/json;q=.4, text/html", // Accept
"iso-8859-5, unicode-1-1;q=0.8" // Accept-Charset
);