Herman J. Radtke III

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Using the Nickel.rs Router Macro

Written by Herman J. Radtke III on 05 Jan 2015

The nickel.rs Web Application Framework for Rust is inspired by the popular node.js express framework. The stated goal of the nickel.rs framework is to show people that it can be easy to write web servers using a sytems language like Rust. I have been using the framework to create hypermredia examples using my hal-rs library.

One of the downsides to a systems language like Rust is the verbosity of the syntax. Someone used to writing in Python or Ruby may be in for quite a shock. I started really feeling this when writing route handlers used by nickel. Here is the simple example from the docs:

fn a_handler (_request: &Request, response: &mut Response) { 
    response.send("hello world"); 
}

server.get("/", a_handler);

Notice the _request variable has a leading underscore. This tells the compiler not to throw a warning if this variable is unused. If you do decided to use _request later on, then you need to remember to change the variable name to request. You also need to make a name for the function so it can be referenced in the call to server.get. This sort of boilerplate stuff is not what I want to spend time worrying about. What I really want is a nice looking DSL to describe my routes.

After some perusing of the provided examples in nickel.rs, I discovered the router! macro. We can use the router! macro to get a DSL-like syntax for routing. Here is the same example above using the router! macro:

router! {
    get "/" => |request, response| {
        response.send("hello world");
    }
}

When we use the router! macro, it expands into the same Rust code as in our first example. We don’t have to think of a name for the function, worry about type of request or response or or type out the server.get line. If you want to see the router! macro used in a real world example, check out the index response from my hal-rs-demo web server. The code for the router! macro is here.

The jury is still out on whether or not nickel.rs, or even Rust itself, will be suitable for creating web servers that serve up API responses and HTML to clients. I like many things about Rust though, so I will continue to find out.