The combination of Negroni and Gorilla MUX is a useful combination for buildng REST applications. However, there are some features I felt were necessary to be built on top. This has not been made into a separate project, and in fact I doubt that it needs to — the world doesn’t need more “frameworks” to add to the paralysis of choice. I think it would be better, instead, to go over some of these that may be of use, so I’ll do that here and in further blog entries.

This was borne out of some real cases at Romana; here I’ll show examples of some of these features in a real project.

Overview

At the core of it all is a Service interface, representing a REST service. It has an Initialize() method that would initialize a Negroni, add some middleware (we will see below) and set up Gorilla Mux Router using its Routes. Overall this part is a very thin layer on top of Negroni and Gorilla and can be easily seen from the above-linked source files. But there are some nice little features worth explaining in detail below.

In the below, we assume that the notions of Gorilla’s Routes and Handlers are understood.

Sort-of-strong-dynamic typing when consuming data

While we have to define our route handlers as taking interface{} as input, nonetheless, it would be nice if the handler received a struct it expects so it can cast it to the proper one and proceed, instead of each handler parsing the provided JSON payload.

To that end, we introduce a MakeMessage field in Route. As its godoc says, “This should return a POINTER to an instance which this route expects as an input”, but let’s illustrate what it means if it is confusing.

Let us consider a route handling an IP allocation request. The input it needs is an IPAMAddressRequest, and so we set its MakeMessage field to a function returning that, as in

func() interface{} {
    return &api.IPAMAddressRequest{}
}

Looks convoluted, right? But here is what happens:

The handlers of routes are not called directly, they are wrapped by wrapHandler() method, which will:

1. Call the above func() to create the pointer to IPAMAddressRequest
2. Use the unmarshaller (based on Content-Type) to unmarshal the body of the request into the above struct pointer.

Voila!

Rapid prototyping with hooks

Sometimes we prototype features outside of the Go-bases server — as we may be calling out to various CLI utilities (iptables, kubectl, etc), it is easier to first ensure the calls work as CLI or shell scripts, and iterate there. But for some demonstration/QA purposes we still would like to have this functionality available via a REST call to the main Romana service. Enter the hooks functionality.

A Route can specify a Hook field, which is a structure that defines:

• Which executable to run
• Whether to run it before or after the Route‘s Handler (When field)
• Optionally, a field where the hook’s output will be written (which can then be examined by the Handler if the When field is “before”). If not specified, the output will just be logged.

Hooks are specified in the Romana config, and are set up during service initialization (this is in keeping with the idea that no Go code needs to be modified for this prototyping exercise).

Then during a request, they are executed by the wrapHandler() method (it has been described above).

That’s it! And it allows for doing some work outside the server to et it right, and only then bother about adding the functionality into the server’s code.

If this doesn’t seem like that much, wait for further installments. There are several more useful features to come. This just sets the stage.