Content negotiation

So far, the contacts service supports only the JSON format, and thus works only with media-type application/json. Let's assume our service has to offer data in different formats, for example, both JSON and XML. Then, the consumer needs to explicitly define the data format they need. The best way to carry out content negotiation in REST has been a very debatable subject for a long time.

In his famous discussion on implementing content negotiation correctly, Roy Fielding states:

"All important must have URIs."

However, that leaves a gap on how to expose the same resource in a different data format, so Roy continues:

"Agent-driven negotiation is far more effective, but there was a huge disagreement between myself and the chair of the HTTP working group and my original agent-driven design for HTTP/1.1 was effectively buried in committee. To do negotiation right, the client needs to be aware of all the alternatives and what it should use as a bookmark....