REST2 Public Beta and Request for Comment

(header photo CC BY Groman123)

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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)

Following Links

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.