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cURL and Your Rails 2 App

If you’re anything like me, you’ve used cURL to download a batch of MP3 files from the web, or to move a TAR file from one remote server to another. It might come as a surprise, then, that cURL is a full-featured HTTP client, which makes it perfect for interacting with RESTful web services like the ones encouraged by Rails 2. To illustrate, let’s create a small Rails app called ‘tv_show’:

rails tv_show
cd tv_show
script/generate scaffold character name:string action:string
rake db:migrate
script/server

Fire up your web browser and create a few characters. Once you’ve done that, open a new terminal window and try the following:

curl http://localhost:3000/characters.xml

You’ll get a nice XML representation of your characters:

<?xml version"1.0" encoding="UTF-8"?>
<characters type="array">
  <character>
    <id type="integer">1</id>
    <name>George Sr.</name>
    <action>goes to jail</action>
    <created-at type="datetime">2008-03-28T11:01:57-04:00</created-at>
    <updated-at type="datetime">2008-03-28T11:01:57-04:00</updated-at>
  </character>
  <character>
    <id type="integer">2</id>
    <name>Gob</name> 
    <action>rides a Segway</action>
    <created-at type="datetime">2008-03-28T11:02:07-04:00</created-at>
    <updated-at type="datetime">2008-03-28T11:02:12-04:00</updated-at>
  </character>
  <character>
    <id type="integer">3</id>
    <name>Tobias</name>
    <action>wears cutoffs</action>
    <created-at type="datetime">2008-03-28T11:02:20-04:00</created-at>
    <updated-at type="datetime">2008-03-28T11:02:20-04:00</updated-at>
  </character>
</characters>

You can retrieve the representation of a specific character by specifying his ID in the URL:

dce@roflcopter ~ > curl http://localhost:3000/characters/1.xml

<?xml version="1.0" encoding="UTF-8"?>
<character>
  <id type="integer">1</id>
  <name>George Sr.</name>
  <action>goes to jail</action>
  <created-at type="datetime">2008-03-28T11:01:57-04:00</created-at>
  <updated-at type="datetime">2008-03-28T11:01:57-04:00</updated-at>
</character>

To create a new character, issue a POST request, use the -X flag to specify the action, and the -d flag to define the request body:

curl -X POST -d "character[name]=Lindsay&character[action]=does+nothing" http://localhost:3000/characters.xml

Here’s where things get interesting: unlike most web browsers, which only support GET and POST, cURL supports the complete set of HTTP actions. If we want to update one of our existing characters, we can issue a PUT request to the URL of that character’s representation, like so:

curl -X PUT -d "character[action]=works+at+clothing+store" http://localhost:3000/characters/4.xml

If we want to delete a character, issue a DELETE request:

curl -X DELETE http://localhost:3000/characters/1.xml

For some more sophisticated uses of REST and Rails, check out rest-client and ActiveResource.


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