REST2 Public Beta and Request for Comment

It is my great pleasure to announce the official public beta of RT::Extension::REST2. REST2 is a fundamental rearchitecting of our REST API, which is a set of web services that allows external applications to retrieve and update information in RT. REST2 will let developers build richer and more robust integrations with the other services and applications that your team uses. It is the culmination of four years of work from five engineers, and was driven by the feedback of countless end-users and integration authors.

RT's existing REST API has served its users well throughout the years. REST was added to RT back in 2002 for the 2.1 release series. This was years before AJAX took off thanks to Gmail, and several more years still before Ruby on Rails was first published. At the time, Internet Explorer 6 was still hot off the presses. Needless to say, since then the landscape of the web has changed dramatically. Though RT was an early adopter of REST, back when it looked like SOAP and WSDL were poised to dominate the space, we appreciate that it became time to start anew. The primary consumer is no longer the "rt" command-line application; it is robust integrations with other services and applications.

REST2 was architected for the modern web. It fulfills level 3 of the Richardson Maturity Model. (REST 1.0, on the other hand, meets only level 1). This means that RT expects proper HTTP methods (GET, POST, PUT, DELETE), it provides the full range of HTTP status codes, and RT takes advantage of many HTTP headers in requests and responses (including ETag, If-Modified-Since, etc). We also publish hypermedia controls, which lets your client application explore RT's API dynamically. REST2 has first-class support for JSON which was far and away the most frequent feature request. REST2 was also designed to be extensible. Expect to see additional endpoints and hypermedia materialize as you install extensions.

We are also today releasing a new RT::Authen::Token extension which lets users generate application-specific authentication tokens. This not only makes it easier to get your REST2 application up and running, but it improves security. Your users no longer share their login password, and have the ability revoke an individual application's access.

RT::Extension::REST2 is compatible with RT 4.2.4 and later. You can install it (and RT::Authen::Token, which is compatible with RT 4.2.5 and later) using the ordinary extension installation process. We've also included our REST2 tutorial documentation below to help you hit the ground running.

Finally, while we believe REST2 now provides a stable foundation and a useful set of features—including support for new features in 4.4 like assets, SLA, and custom roles—it is not complete. We are releasing it today to get it into your hands and to hear from you, the developer community, about the features you'd like us to implement next. Please visit our forum thread on REST2 and let us know, either by replying, or just liking an existing message, what you need. All is fair game: anything from additional endpoints such as for articles, to XML support, to additional hypermedia controls, to novel authentication methods, and so on.

We look forward to seeing what you build!

(header photo CC BY Groman123)

REST2 Tutorial

To make it easier to authenticate to REST2, we recommend installing RT::Authen::Token. Visit "Logged in as Username" → Settings → Auth Tokens. Create an Auth Token, give it any description (such as "REST2 with curl"). Make note of the authentication token it provides to you.

For other authentication options see REST2's documentation on Authentication Methods.

Authentication

Run the following in a terminal, filling in XX_TOKEN_XX from the auth token above and XX_RT_URL_XX with the URL for your RT instance.

curl -H 'Authorization: token XX_TOKEN_XX' 'XX_RT_URL_XX/REST/2.0/queues/all'

This does an authenticated request (using the Authorization HTTP header with type token) for all of the queues you can see. You should see a response, typical of search results, like this:

{
   "total" : 1,
   "count" : 1,
   "page" : 1,
   "per_page" : 20,
   "items" : [
      {
         "type" : "queue",
         "id" : "1",
         "_url" : "XX_RT_URL_XX/REST/2.0/queue/1"
      }
   ]
}

This format is JSON, which is a format for which many programming languages provide libraries for parsing and generating.

(If you instead see a response like {"message":"Unauthorized"} that indicates RT couldn't process your authentication token successfully; make sure the word token appears between Authorization: and the auth token that RT provided to you)

You can request one of the provided _urls to get more information about that queue.

curl -H 'Authorization: token XX_TOKEN_XX' 'XX_QUEUE_URL_XX'

This will give a lot of information, like so:

{
   "id" : 1,
   "Name" : "General",
   "Description" : "The default queue",
   "Lifecycle" : "default",
   ...
   "CustomFields" : {},
   "_hyperlinks" : [
      {
         "id" : "1",
         "ref" : "self",
         "type" : "queue",
         "_url" : "XX_RT_URL_XX/REST/2.0/queue/1"
      },
      {
         "ref" : "history",
         "_url" : "XX_RT_URL_XX/REST/2.0/queue/1/history"
      },
      {
         "ref" : "create",
         "type" : "ticket",
         "_url" : "XX_RT_URL_XX/REST/2.0/ticket?Queue=1"
      }
   ],
}

Of particular note is the _hyperlinks key, which gives you a list of related resources to examine (following the HATEOAS principle). For example an entry with a ref of history lets you examine the transaction log for a record. You can implement your REST API client knowing that any other hypermedia link with a ref of history has the same meaning, regardless of whether it's the history of a queue, ticket, asset, etc.

Another ref you'll see in _hyperlinks is create, with a type of ticket. This of course gives you the URL to create tickets in this queue. Importantly, if your user does not have the CreateTicket permission in this queue, then REST2 would simply not include this hyperlink in its response to your request. This allows you to dynamically adapt your client's behavior to its presence or absence, just like the web version of RT does.

Creating Tickets

Let's use the _url from the create hyperlink with type ticket.

To create a ticket is a bit more involved, since it requires providing a different HTTP verb (POST instead of GET), a Content-Type header (to tell REST2 that your content is JSON instead of, say, XML), and the fields for your new ticket such as Subject. Here is the curl invocation, wrapped to multiple lines for readability.

curl -X POST
     -H "Content-Type: application/json"
     -d '{ "Subject": "hello world" }'
     -H 'Authorization: token XX_TOKEN_XX'
        'XX_TICKET_CREATE_URL_XX'

If successful, that will provide output like so:

{
    "_url" : "XX_RT_URL_XX/REST/2.0/ticket/20",
    "type" : "ticket",
    "id"   : "20"
}

(REST2 also produces the status code of 201 Created with a Location header of the new ticket, which you may choose to use instead of the JSON response)

We can fetch that _url to continue working with this newly-created ticket. Request the ticket like so (make sure to include the -i flag to see response's HTTP headers).

curl -i -H 'Authorization: token XX_TOKEN_XX' 'XX_TICKET_URL_XX'

You'll first see that there are many hyperlinks for tickets, including one for each Lifecycle action you can perform, history, comment, correspond, etc. Again these adapt to whether you have the appropriate permissions to do these actions.

Additionally you'll see an ETag header for this record, which can be used for conflict avoidance. We'll first try updating this ticket with an invalid ETag to see what happens.

Updating Tickets

For updating tickets we use the PUT verb, but otherwise it looks much like a ticket creation.

curl -X PUT
     -H "Content-Type: application/json"
     -H "If-Match: invalid-etag"
     -d '{ "Subject": "trial update" }'
     -H 'Authorization: token XX_TOKEN_XX'
        'XX_TICKET_URL_XX'

You'll get an error response like {"message":"Precondition Failed"} and a status code of 412. If you examine the ticket, you'll also see that its Subject was not changed. This is because the If-Match header advises the server to make changes if and only if the ticket's ETag matches what you provide. Since it differed, the server refused the request and made no changes.

Now, try the same request by replacing the value invalid-etag in the If-Match request header with the real ETag you'd received when you requested the ticket previously. You'll then get a JSON response like:

["Ticket 1: Subject changed from 'hello world' to 'trial update'"]

which is a list of messages meant for displaying to an end-user.

If you GET the ticket again, you'll observe that the ETag header now has a different value, indicating that the ticket itself has changed. This means if you were to retry the PUT update with the previous (at the time, expected) ETag you would instead be rejected by the server with Precondition Failed.

You can use ETag and If-Match headers to avoid race conditions such as two people updating a ticket at the same time. Depending on the sophistication of your client, you may be able to automatically retry the change by incorporating the changes made on the server (for example adding time worked can be automatically be recalculated).

You may of course choose to ignore the ETag header and not provide If-Match in your requests; RT doesn't require its use.

Summary

RT's REST2 API provides the tools you need to build robust and dynamic integrations. Tools like ETag/If-Match allow you to avoid conflicts such as two people taking a ticket at the same time. Using JSON for all data interchange avoids problems caused by parsing text. Hypermedia links inform your client application of what the user has the ability to do.

Careful readers will see that, other than our initial entry into the system, we did not generate any URLs. We only followed links, just like you do when browsing a website on your computer. We've better decoupled the client's implementation from the server's REST API. Additionally, this system lets you be informed of new capabilities in the form of additional hyperlinks.

Using these tools and principles, REST2 will help you build rich, robust, and powerful integrations with the other applications and services that your team uses.

Shawn Moore

Share this post: