When a client asks for the resource it can specify the representation of that
resource that it wants, such as JSON or XML etc. This is done by providing an
Accept header with the various MIME types or resources that the client can
process.
Content negotiation is used by Crest to serialize the .NET objects returned by the route methods into a format understood by the client.
By default, responses can be sent in JSON format or XML format but this can
easily be extended. If the Accept header is not present then the system
defaults in the value application/json and processes the response in the
normal manner.
The media types are checked in order of their weight (the q parameter), with
higher values being checked first to see if any of the serializers can produce
that type. If no suitable serializer can be found for any of the media types
in the Accept header then a 406 No Content will be sent back to the client.
There are two main interfaces that the system uses: one for performing the
serialization (IContentConverter) and one for determining which serializer to
use (IContentConverterFactory).
The default factory gets all implementations of the IContentConverter
interface injected in to the constructor and checks what MIME types they can
handle, using the Priority as a tie-breaker if two serializers can produce the
same type. The MIME type returned can also specify the weight of the mapping,
allowing it to act as a fall-back if another serializer is not found. For
example, if ConverterA returns application/type;q=0.5 and ConverterB
return application/type then ConverterB would be used for application/type
even if ConverterA has a higher priority.
Note: If the client specifies any type (*/*), the serializer with the
highest priority will be used.