ari - Golang Asterisk Rest Interface (ARI) library

This library allows you to easily access ARI in go applications. The Asterisk Rest Interface (https://wiki.asterisk.org/wiki/pages/viewpage.action?pageId=29395573) is an asynchronous API which allows you to access basic Asterisk objects for custom communications applications.

This project also includes some convenience wrappers for various tasks, found in /ext. These include go-idiomatic utilities for playing audio, IVRs, recordings, and other tasks which are tricky to coordinate nicely in ARI alone.

NOTE This version of ari requires Asterisk version 14 or later. If support is needed for version 13, please use v5 of ari.

Getting started

This library maintains semver, and APIs between major releases do change. We use GO111MODULE, so Go version 1.11 or later is required.

Version 5.x.x is the current version.

There is also a NATS-based ari-proxy which is designed to work with this client library. It can be found at PolyAI-LDN/ari-proxy.

Install with:

go get github.com/PolyAI-LDN/ari/v6

Features

Cloud-ready

All configuration options for the client can be sourced by environment variable, making it easy to build applications without configuration files. The default connection to Asterisk is set to localhost on port 8088, which should run on Kubernetes deployments without configuration.

The available environment variables (and defaults) are:

• ARI_APPLICATION (randomly-generated ID)
• ARI_URL (http://localhost:8088/ari)
• ARI_WSURL (ws://localhost:8088/ari/events)
• ARI_WSORIGIN (http://localhost/)
• ARI_USERNAME (none)
• ARI_PASSWORD (none)

If using ari-proxy, the process is even easier.

Resource Keys

In order to facilitate the construction of ARI systems across many Asterisk instances, in version 4, we introduce the concept of Resource Keys. Previous versions expected a simple ID (string) field for the identification of a resource to ARI. This reflects how ARI itself operates. However, for systems with multiple Asterisk instances, more metadata is necessary in order to properly address a resource. Specifically, we need to know the Asterisk node. There is also the concept of a Dialog, which offers an orthogonal logical grouping of events which transcends nodes and applications. This is not meaningful in the native client, but other transports, such as the ARI proxy, may make use of this for alternative routing of events. This Key includes all of these data.

package ari

// Key identifies a unique resource in the system
type Key struct {
   // Kind indicates the type of resource the Key points to.  e.g., "channel",
   // "bridge", etc.
   Kind string   `json:"kind"`

   // ID indicates the unique identifier of the resource
   ID string `json:"id"`

   // Node indicates the unique identifier of the Asterisk node on which the
   // resource exists or will be created
   Node string `json:"node,omitempty"`

   // Dialog indicates a named scope of the resource, for receiving events
   Dialog string `json:"dialog,omitempty"`
}

At a basic level, when the specific Asterisk ID is not needed, a key can consist of a simple ID string:

  key := ari.NewKey(ari.ChannelKey, "myID")

For more interesting systems, however, we can declare the Node ID:

  key := ari.NewKey(ari.BridgeKey, "myID", ari.WithNode("00:01:02:30:40:50"))

We can also bind a dialog:

  key := ari.NewKey(ari.ChannelKey, "myID",
   ari.WithNode("00:01:02:30:40:50"),
   ari.WithDialog("privateConversation"))

We can also create a new key from an existing key. This allows us to easily copy the location information from the original key to a new key of a different resource. The location information is everything (including the Dialog) except for the key Kind and ID.

  brKey := key.New(ari.BridgeKey, "myBridgeID")

All ARI operations which accepted an ID for an operator now expect an *ari.Key instead. In many cases, this can be easily back-ported by wrapping IDs with ari.NewKey("channel", id).

Handles

Handles for all of the major entity types are available, which bundle in the tracking of resources with their manipulations. Every handle, at a minimum, internally tracks the resource's cluster-unique Key and the ARI client connection through which the entity is being interacted. Using a handle generally results in less and more readable code.

For instance, instead of calling:

ariClient.Channel().Hangup(channelKey, "normal")

you could just call Hangup() on the handle:

h.Hangup()

While the lower level direct calls have maintained fairly strict semantics to match the formal ARI APIs, the handles frequently provide higher-level, simpler operations. Moreover, most of the extensions (see below) make use of handles.

In general, when operating on longer lifetime entities (such as channels and bridges), it is easier to use handles wherever you can rather than tracking Keys and clients discretely.

Obtaining a Handle from a Key is very simple; just call the Get() operation on the resource interface appropriate to the key. The Get() operation is a local-only operation which does not interact with the Asterisk or ARI proxy at all, and it is thus quite efficient.

h := ariClient.Channel().Get(channelKey)

Staging resources

A common issue for ARI resources is making sure a subscription exists before events for that resource are sent. Otherwise, important events which occur too quickly can become lost. This results in a chicken-and-egg problem for subscriptions.

In order to address this common issue, resource handles creation operations now offer a StageXXXX variant, which returns the handle for the resource without actually creating the resource. Once all of the subscriptions are bound to this handle, the caller may call resource.Exec() in order to create the resource in Asterisk.

   h := NewChannelHandle(key, c, nil)

   // Stage a playback
   pb, err := h.StagePlay("myPlaybackID", "sound:tt-monkeys")
   if err != nil {
      return err
   }
   
   // Add a subscription to the staged playback
   startSub := pb.Subscribe(EventTypes.PlaybackStarted)
   defer startSub.Cancel()

   // Execute the staged playback
   pb.Exec()

   // Wait for something to happen
   select {
      case <-time.After(time.Second):
        fmt.Println("timeout waiting for playback to start")
        return errors.New("timeout")
      case <-startSub.Events():
        fmt.Println("playback started")
   }

Extensions

There are a number of extensions which wrap the lower-level operations in higher-level ones, making it easier to perform many common tasks.

AudioURI

Constructing Asterisk audio playback URIs can be a bit tedious, particularly for handling certain edge cases in digits and for constructing dates.

The audiouri package provides a number of routines to make the construction of these URIs simpler.

Bridgemon

Monitoring a bridge for events and data updates is not difficult, but it involves a lot of code and often makes several wasteful calls to obtain bridge data, particularly when accessing it on large bridges.

Bridgemon provides a cache and proxy for the bridge data and bridge events so that a user can simply Watch() for changes in the bridge state and efficiently retrieve the updated data without multiple requests.

It also shuts itself down automatically when the bridge it is monitoring is destroyed.

Play

Playback of media and waiting for (DTMF) responses therefrom is an incredibly common task in telephony. ARI provides many tools to perform these types of actions, but the asynchronous nature of the interface makes it fairly tedious to build these kinds of things.

In ext/play, there resides a tool for executing many common tasks surrounding media playback and response sequences. The core function, play.Play() plays, in sequence, a series of audio media URIs. It can be extended to expect and (optionally) wait for a DTMF response by supplying it with a Match function. There is a small convenience wrapper play.Prompt() which sets some common defaults for playbacks which expect a response.

The execution of a Play is configured by any number of option functions, which supply structured modifiers for the behaviour of the playback. You can even supply your own Match function for highly-customized matching.

Record

Making recordings is another complicated but common task for ARI applications. The ext/record, we provide a simple wrapper which facilitates many common recording-related operations inside a single recording Session wrapper.

Features include:

• record with or without a beep at the start
• listen for various termination types: hangup, dtmf, silence, timeout
• review, scrap, and save recordings upon completion
• retrieve the playback URI for the recording

Documentation and Examples

Go documentation is available at https://godoc.org/github.com/PolyAI-LDN/ari

Examples for helloworld, play, script, bridge, and record are available. Set your environment variables as described above (at minimum, ARI_USERNAME and ARI_PASSWORD) and run:

cd /_examples/helloworld
go run ./main.go

Other examples:

• stasisStart demonstrates a simple click-to-call announcer system
• stasisStart-nats demonstrates the same click-to-call using the NATS-based ARI proxy
• bridge demonstrates a simple conference bridge
• play demonstrates the use of the ext/play extension
• record demonstrates the use of the ext/record extension

The files in _ext/infra demonstrates the minimum necessary changes to the Asterisk configuration to enable the operation of ARI.

Tests

Run go test to verify

Contributing

Contributions welcomed. Changes with tests and descriptive commit messages will get priority handling.

License

Licensed under the Apache License, Version 2.0