• Welcome
• User Guide

  Getting started

  Setting up Dragonfly

  Working locally

  The .htaccess file

  Routes

  Default routes

  Creating your own routes

  Templates

  Creating templates and views

  Handling errors using templates

  Important Globals

  $GET $POST $FILES $COOKIES

  DF_SELF DF_SELF_DIR DF_PAGE

  Plugins

  Using and creating plugins

  List of included plugins

  Changes

  Changes between versions

  API Reference

  Core API

  Dragonfly DB

  Dragonfly SMTP

• Examples

  Tables

  Generate tables from lists

  Feeds

  How to read feeds from other websites

  AJAX

  Some simple AJAX calls

  Twitter

  Using Twitter with Dragonfly

  SEO Experiments

  Experiments in SEO

  Useful information

  Dragonfly debugging information

• Code
• About

Handling Errors

What happens when a user visits the following link?

http://www.rundragonfly.com/bar

Go ahead and click it. I can wait.

Back already?

That was an error 404 page, the page that's displayed when all routes failed to match.

Generating Errors

Dragonfly uses the DF:display-error function to show these pages. You can too! Here's a quick example of how to use it:

(display-error 500)

Pretty simple huh?

The ERROR_TEMPLATE

By default Dragonfly does not show that fancy page you just saw, instead it stores a default (and boring) error template in the symbol DF:ERROR_TEMPLATE. It will use that to display all errors unless it can find an alternative.

For example, if this page didn't exist and no alternative 404 page was found, here's what you'd see:

How do you specify an alternative?

Custom Error Templates

Dragonfly will check inside VIEW_PATHS to see if a view with the error number exists. In other words, a call to (display-error 500) results in a check for:

(file? (Dragonfly:view-path "500"))

If it exists, it will be displayed instead of ERROR_TEMPLATE.

To see this site's 500 page, click here.

Checking the dragonfly.log

Dragonfly defines an error handler DF:error-handler, that's called whenever an error is generated (for example, by a call to throw-error). You can specify your own handler with a plugin.

The default handler makes use of Dragonfly's logging functions to log the stack-trace to the file specified by LOG_FILE_PATH in config.lsp, and then it will call (display-error 500).

If you don't want to publicly show the stack trace in your error 500 template, you don't have to. Just remember to check the log for it. You'll probably also want to setup a cron script roll over the log every now and then to prevent it from getting too large.

Dragonfly's logging facilities are defined dragonfly-framework/lib/log.lsp, check the api for more info.

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