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Stubbing HTTP services in Clojure

stub-http

I recently had the need to stub HTTP endpoints in Clojure. I needed something that could do this on the HTTP level since in one case I was integrating with a Java library that used Apache HTTP Client under the covers and another that used Axis 2. I tried searching for such a library in Clojure and even asked on stackoverflow but I couldn’t find any. In the Java ecosystem we have for example mockwebserver and while I probably could use this, its API is a bit cumbersome to use from Clojure. So my first reaction was to create a small wrapper library on top of mockwebserver. But mockwebserver brings with it quite a lot of dependencies and is a bit too focused on mocking than what I typically require when writing these kind of tests. I wanted a library that acted more like a fake or stub (see this article for a discussion on terminology) with fewer dependencies so I decided to base it on nanohttpd instead. The project is called (simply) Stub HTTP and is available on github and clojars.

Example

This example demonstrates how to use the with-routes! macro of Stub HTTP (there’s also a start! function if you prefer that) with clojure test and clj-http-lite. This example returns the json document { "hello" : "world" } if the request path matches “/something”:

This starts the stub server on a free random port and shuts it down automatically after the assertion. As you can see we supply a map as argument to with-routes! followed by a body. The map is referred to as a route map which consists of entries made up by a request specification (key) and a response specification (value). If you look closely you’ll see that we make a request to resource (str uri "/something") where uri is a property generated and exposed by the macro and points to the root path of the server (for example http://localhost:31212). There are other ways of constructing the request- and response specification, for example:

In this example we match only a GET request that has path equal to /something that also has a query parameter name=value and if so we return a response body that is constructed from a header supplied with the request. For more information please refer to the wiki.

Recordings

When stubbing an HTTP endpoint it can be useful to see which request generated which response and what these requests and responses actually looked like. For this reason Stub HTTP records all requests and its associated response. This can be retrieved from the routes atom available in the server record exposed by the macro. For example:

The routes atom consists of a vector of maps that (among other things) contains the “recordings” in the :recordings key:

This means that each route has zero to many recordings that matched the request specification of that route. The request has the following schema:

and the response is defined like this:

The server instance (from which routes where extracted in the example above) contains the convenience functions called recorded-requests and recorded-responses that allows you to get all recorded requests and/or responses for this server instance. For example:

See this link for more info.

Summary

While there are great alternative solutions in the Clojure space such as clj-http-fake and ring-mock they target a specific library and doesn’t work on the HTTP level. In some cases this is not enough and you need to be able to easily create fake/stub HTTP resources in your tests. Stub HTTP is my humble attempt to make it easy to do exactly this. So hopefully this library can become useful for someone in the same situation as myself. Comments, issues, pull requests or other kinds of feedback is of course welcome. Happy testing 🙂

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