HATEOAS: absolute or relative URLs?

Question

In designing a RESTful Web Service using HATEOAS, what are the pros and cons of showing a link as a complete URL ("http://server:port/application/customers/1234") vs. just the path ("/application/customers/1234")?

Answer 1

The only real difference would seem to be that it's easier for clients if they are consuming absolute URIs instead of having to construct them from the relative version. Of course, that difference would be enough to sway me to do the absolute version.

Answer 2

It depends on who is writing the client code. If you are writing the client and server then it doesn't make much difference. You will either suffer the pain of building the URLs on the client or on the server.

However, if you are building the server and you expect other people to write client code then they will love you much more if you provide complete URIs. Resolving relative URIs can be a bit tricky. First how you resolve them depends on the media-type returned. Html has the base tag, Xml can have xml:base tags in every nested element, Atom feeds could have a base in the feed and a different base in the content. If you don't provide your client with explicit information about the base URI then they have to get the base URI from the request URI, or maybe from the Content-Location header! And watch out for that trailing slash. The base URI is determined by ignoring all characters to the right of the last slash. This means that trailing slash is now very significant when resolving relative URIs.

The only other issue that does require a small mention is document size. If you are returning a large list of items where each item may have multiple links, using absolute URLs can add a significant amount of bytes to your entity if you do not compress the entity. This is a perf issue and you need to decide if it is significant on a case by case basis.