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to the Digium folks for it.
As an example of what this is good for, select the endpoints:Endpoint resources
item, press the GET button beside /endpoints, and you will see the screen shown in
Figure 19-3.
Figure 19-3. Get endpoints
Well, go ahead—press the “Try it out!” button.
Note the "id" of the channel in the wscat session, which you’ll want to copy for use
in the Swagger UI (you’ll see several lines of JSON output relating to the call).
Perform the following actions on the channel using the Swagger UI interface: POST:
Answer (answer the channel), POST: hold (place the call on hold), DELETE: hold
(take the call off hold). Note what happens to the channel in each case.
Use of this Swagger UI is also documented over at the Asterisk wiki.
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Chapter 19: Asterisk REST Interface
This will greatly simplify your development and testing process.
OK, that’s the quick start. Let’s dive in deeper to ARI.
The Building Blocks of ARI
There are three components that work together to deliver ARI:
• The RESTful interface, through which the external application communicates
with Asterisk.
• A WebSocket that passes information back to the external application from
Asterisk (in JSON format).
• The Stasis() dialplan application, which connects control of a channel to the
external application.
REST
The term RESTful stems from Representational State Transfer (REST), which is an
architectural model for web services (as opposed to, say, a protocol). The term REST‐
ful has commonly come to refer to any API that provides interaction through URLs,
with data represented in JSON format.4 So, anything that is “RESTful” is supposed to
adhere to the constraints of REST, but in practice may be implemented as a looser
interpretation (which, if it gets the job done, may indeed be good enough).
WebSocket
The WebSocket connection is the mechanism that performs the communication
between the internals of Asterisk and the RESTful interface. In Asterisk, events may
happen that the client did not initiate, and the WebSocket allows Asterisk to signal
those changes to the client.
Asterisk’s built-in HTTP server potentially provides other services across a web inter‐
face. For example, WebRTC also connects through the web server. If you are making
changes or adding new services, make sure you not only test the item you’re working
on, but also other services running through the same server, to ensure you haven’t
inadvertently misconfigured something else.
4 Strictly speaking, REST is far more than that, but as a practical matter, these days it seems not uncommon to
assume that a REST API will be URL and JSON-based, simply because so many such services are presented in
those formats.
The Building Blocks of ARI
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Stasis
The Stasis Message Bus allows the core of Asterisk to communicate events with other
modules and components. It is mostly internal to Asterisk; however, in the case of
ARI, a dialplan application named Stasis() allows the dialplan to pass call control to
your external ARI application.
The Stasis() application itself is required in order to signal to the dialplan that call
control is to be passed to the external program via ARI.
As of Asterisk 16, it is no longer necessary to write dialplan code to define a connec‐
tion from an incoming channel to your ARI client application. Many developers in
the Asterisk community write all their call control logic in external applications, and
having to code up a few lines of dialplan just to pass channels to their app was seen as
kludgy and confusing. They requested (and developed) a mechanism whereby Aster‐
isk will create automatic dialplan to handle this function.
When the API is instantiated, the application reference in the URL—for example, our
app zarniwoop—will trigger the automatic creation of a dialplan context named
according to the app name (in this case, [stasis-zarniwoop]), including an exten‐
sion that pattern matches everything. This extension will then pass all calls arriving in
that context to Stasis(zarniwoop). You will need to associate your channels with the
correct context (context=stasis-zarniwoop) in your PJSIP (or other channel) con‐
figuration tables, at which point calls to those channels will automatically be connec‐
ted through Stasis() to the client application.
If all this seems confusing, there’s no reason you need to stop using actual dialplan to