Issue 8

0. Introduction

Welcome to issue 8 of the Chicken Gazette!

1. The Hatching Farm - New Eggs & The Egg Repository

It has been a good week for the egg repository, although it was one in a long time which did not have any new eggs. We mainly saw a few bug fix releases (getopt-long 1.9, dict 1.4, pstk 1.1 and colorize 0.3), as well as some releases introducing new features:

linenoise 0.4 Christian Kellermann added the handy procedure make-linenoise-port . This makes linenoise a viable alternative to the readline egg to be used as the current-input-port in csi . libsvm 0.2 Peter Lane's new egg has already been bumped to version 0.2 making Chicken the first programming language which allows you to be honest and humble about your programming skills by means of the newly introduced make-problem procedure. hyde 0.10 The latest release of the website compiler powering the Chicken Gazette adds a few handy features, including on-demand re-compilation for hyde serve (see the change log for more).

2. The Core - Bleeding Edge Development

Core development has been pretty quiet this week with only a little activity on the experimental branch. The most visible change is the addition of a blob literal syntax by Felix Winkelmann.

3. Chicken Talk

John Gabriele pointed out a few problems with the code colorization on the wiki which have been addressed and fixed by Peter Bex and Moritz Heidkamp. Thanks John!

Christian Kellermann suggested to try the relatively new DVCS fossil by giving a quick introduction, a few useful links as well as providing a fossil clone of the chicken-core git repository for us to play with. Definitely worth checking out!

Most importantly, Peter Bex appealed to all egg authors to document their undocumented eggs. He was even kind enough to compile a list of affected eggs. Fellow egg authors, let's remedy those gaps!

4. Omelette Recipes - Tips and Tricks

This week I'd like to direct your attention at our web server Spiffy. Its feature set is comparable to that of the Apache HTTP Server or lighttpd, although it doesn't sport as many extension modules (yet). While that may seem intimidating at first, it actually isn't: Since Spiffy is a Scheme web server, no idiosyncratic configuration file format is needed to set it up, all you need is a few s-exprs to get going! Let's start with a simple example:

( use spiffy ) ( vhost-map ` ( ( ( * any ) . , ( lambda ( continue ) ( send-response body: "hey there!

" headers: ' ( ( content-type text/plain ) ) ) ) ) ) ) ( start-server port: 12345 )

Alright, what does that mean? The vhost-map thing may look a little odd at first. It is necessary because Spiffy has been built from the ground up to support virtual hosting. The vhost-map parameter is just an alist of hostnames to handlers. Hostnames are given as regular expressions (either traditional or SREs). In the example we just define a handler for (* any) , i.e. we use the same handler for all hostnames.

The handler procedure is called whenever a request for the matching hostname is to be handled. In the example, we always send a static plain text response regardless of what the request was using the convenience function send-response (let's ignore the continue argument for the moment). Execute the code using csi to make Spiffy listen on TCP port 12345. Try it like this:

$ curl 'http://localhost:12345/' hey there!

Or with a more complex URI, inspecting the response headers:

$ curl -D - 'http://localhost:12345/foo/bar?baz' HTTP/1.1 200 OK Content-Type: text/plain Server: Spiffy/4.8 (Running on Chicken 4.6.0) Content-Length: 11 Date: Mon, 18 Oct 2010 13:06:39 GMT hey there!

Very well! Now, usually a handler would inspect the current-request parameter (which holds an intarweb request record representing the currently handled request) to determine how to respond. Let's try to change our handler so that it only sends "hey there" when the path /hey is requested. Otherwise, we'd like to serve files from a certain directory (say /var/www ) or, if no such file exists, send a 404 response. This is how it can be done:

( use spiffy uri-common intarweb ) ( root-path "/var/www" ) ( vhost-map ` ( ( ( * any ) . , ( lambda ( continue ) ( if ( equal? ( uri-path ( request-uri ( current-request ) ) ) ' ( / "hey" ) ) ( send-response body: "hey there!

" headers: ' ( ( content-type text/plain ) ) ) ( continue ) ) ) ) ) ) ( start-server port: 12345 )

As you can see, we now need intarweb and uri-common to be able to inspect current-request . We also set the root-path which is akin do Apache's DocumentRoot directive. Since it is a paramter, it can be easily altered by handlers using paramterize . The handler itself is only slightly more complicated now: We check whether current-request 's uri-path is (/ "hey") ( uri-common 's way of representing the path /hey ) and if so just send the response as before. For any other path we call the continue procedure which is passed to our handler. This tells Spiffy "I am done with that request, please pass control on to the next handler". As it happens, the next handler is Spiffy's file system handler which will just take the uri-path , check whether it exists under the current root-path and then delivers the file. If the path doesn't exist, a 404 response is sent.

If you need more control over the response, you might want to augment current-response (which is, of course, an intarweb response record) directly instead of using send-response .

Spiffy ships a few more useful handlers which you can easily integrate into your own application. There's also an egg providing a directory listing handler as well as several eggs that may help you creating more advanced applications such as spiffy-request-vars, spiffy-cookies, spiffy-uri-match and http-session.

For real-world uses check out the Spiffy based image gallery application phoghorn, qwiki (the wiki software powering the Chicken wiki) and, of course, the infamous awful web framework.

You should now hopefully be able to create your own web applications with Chicken. Have fun!

5. About the Chicken Gazette

The Gazette is produced weekly by a volunteer from the Chicken community. The latest issue can be found at http://gazette.call-cc.org or you can follow it in your feed reader at http://gazette.call-cc.org/feed.atom. If you'd like to write an issue, check out the instructions and come and find us in #chicken on Freenode!