Building blocks

In this chapter we’ll create routes, we’ll serve local files and we’ll run more than one web app in the same running image.

We’ll use those libraries:

(ql:quickload '("hunchentoot" "easy-routes" "djula" "spinneret"))

We will use the Hunchentoot web server, but we should say a few words about Clack too.

Hunchentoot is

a web server and at the same time a toolkit for building dynamic websites. As a stand-alone web server, Hunchentoot is capable of HTTP/1.1 chunking (both directions), persistent connections (keep-alive), and SSL. It provides facilities like automatic session handling (with and without cookies), logging, customizable error handling, and easy access to GET and POST parameters sent by the client.

It is a software written by Edi Weitz (author of the “Common Lisp Recipes” book, of the ubiquitous cl-ppcre library and much more), it is used and proven solid. One can achieve a lot with it, but sometimes with more friction than with a traditional web framework. For example, dispatching a route by the HTTP method is a bit convoluted, one must write a function for the :uri parameter that does the check, when it is a built-in keyword in other frameworks. We will use the easy-routes library for that.

Clack is

a web application environment for Common Lisp inspired by Python’s WSGI and Ruby’s Rack.

Also written by a prolific lisper (E. Fukamachi), it actually uses Hunchentoot by default as the server, but thanks to its pluggable architecture one can use another web server, like the asynchronous Woo, built on the libev event loop, maybe “the fastest web server written in any programming language”©.

We’ll cite also Wookie, an asynchronous HTTP server, and its companion library cl-async, for general purpose, non-blocking programming in Common Lisp, built on libuv, the backend library in Node.js.

Clack being more recent and less documented, and Hunchentoot a “de-facto standard”, we’ll concentrate on the latter for this guide. Your contributions to add support for Clack are of course welcome.

Web frameworks build upon web servers and can provide facilities for common activities in web development, like a templating system, access to a database, session management, or facilities to build a REST api (those are all easy to do from a bare bones Hunchentoot, as you will see). Caveman is the most popular as per the GitHub stars, but not the most capable. Snooze is maybe the most downloaded Common Lisp web server. In this guide we will learn how to use Hunchentoot, with some light libraries on top.

In the end, we will introduce Weblocks. It is a venerable Common Lisp web framework that permits to write ajax-based dynamic web applications without writing any JavaScript, nor writing some lisp that would transpile to JavaScript, thanks to its components-based architecture. It is seeing an extensive rewrite and update since 2017. We present it in more details in the “Isomorphic web frameworks” appendix.

For a full list of libraries for the web, please see the awesome-cl list #network-and-internet and Cliki.