HalClient is yet another ruby client library for HAL based web APIs. The goal is to provide an easy to use set of abstractions on top of HAL without completely hiding the HAL based API underneath. The areas of complication that HalClient seeks to simplify are
Unlike many other ruby HAL libraries HalClient does not attempt to abstract HAL away in favor of domain objects. Domain objects are great but HalClient leaves that to the application code.
CURIEs
CURIEd links are often misunderstood by new users of HAL. Dealing with them is not hard but it requires care to do correctly. Failure to implement CURIE support correctly will result in future breakage as services make minor syntactic changes to how they encode links. HalClient’s approach is to treat CURIEs as a purely over-the-wire encoding choice. Looking up links in HalClient is always done using the full link relation. This insulates clients from future changes by the server to the namespaces in the HAL representations.
Links are links
From the client perspective there is very little difference between embedded resources and remote links. The only difference is that dereferencing a remote link will take a lot longer. Servers are allowed to move links from the _links section to the _embedded section with impunity. Servers are also allow to put half of the targets of a particular rel in the _links section and the other half in the _embedded section. These choices are all semantically equivalent and therefor should not effect clients ability to function.
HalClient facilitates this by providing a single way to navigate links. The #related(rel) method provides a set of representations for all the resources linked via the specified relationship regardless of which section the links are specified. Clients don’t have to worry about the details or what idiosyncratic choices the server may be making today.
Templated links
Templated links are a powerful feature of HAL but they can be a little challenging to work with in a uniform way. HalClient’s philosophy is that the template itself is rarely of interest. Therefore the #related method takes, as a second argument, as set of option with which to expand the template. The resulting full URL is used instantiate a new representation. This removes the burden of template management from the client and allows clients to treat templated links very similarly to normal links.
RFC6573 collections
Collections are a part of almost every application. HalClient provides built in support for collections implemented using the standard item, next, prev link relationships. The result is a Ruby Enumerable that can used just like your favor collections. The collection is lazily evaluated so it can be used even for very large collections.
Conclusion
If you are using HAL based web APIs I strongly encourage you to use a client library of some sort. The amount of resilience you will gain, and the amount of minutiae you will save yourself from will be well worth it. The Ruby community has a nice suite of HAL libraries whose level of abstraction ranges from ActiveRecord style ORM to very thin veneers over JSON parsing. HalClient tries to be somewhere in the middle. Exposing the API as designed while providing helpful commonly needed functionality to make the client application simpler and easier to implement and understand.
HalClient is under active development so expect to see even more functionality over time. Feedback and pull requests are, of course, greatly desired. We’d love to have your help and insight.