This module is a promise-based client ('inbound' event socket) and server ('outbound' event socket) for FreeSwitch, written entirely in Javascript with no dependencies on the libesl library.

This module is actively maintained and used in production systems.

This is version 11, a new major version of esl. It introduces TypeScript support, and gets rid of binding to this.

Overview

Client mode

This mode of operation is called "inbound" (to FreeSwitch) in the Event Socket FreeSwitch documentation. A client can be used to trigger calls asynchronously (for example in a click-to-dial application). A client can also be used to monitor events for known UUIDs or other fields (see the .filter(header,value) method).

Server mode

A server will handle calls sent to it using the socket diaplan application (called "outbound" mode in the Event Socket Outbound FreeSwitch documentation). The server is available at a pre-defined port which the socket dialplan application will specify.

Client Usage

The following code does the equivalent of fs_cli -x: it connects to the Event Socket, runs a single command, then disconnects.

import { FreeSwitchClient, once } from 'esl'

const client = new FreeSwitchClient({
  port: 8021
})

const fs_command = async (cmd) => {
  const p = once(client,'connect')
  await client.connect()
  const [ call ] = await p
  const res = await call.api(cmd)
  await call.exit();
  await client.end();
}

fs_command("reloadxml");

Generally speaking though, the client might reconnect multiple times, and your code should handle reconnections:

import { FreeSwitchClient, once } from 'esl'

const client = new FreeSwitchClient({
  port: 8021
})

client.on('connect', (call) => {
  // Do something here with the API
})

Constructor options

The FreeSwitchClient constructor takes a single argument, an options object with the following fields:

• host: defaults to 127.0.0.1
• port: defaults to 8021
• password: defaults to ClueCon
• logger: defaults to the console object

Methods

The FreeSwitchClient class has the following methods.

connect()

This method triggers the connection to FreeSWITCH.

The client will automatically reconnect if FreeSWITCH crashes or the connection is lost.

async end()

This methods closes the connection to FreeSWITCH and prevents further attempts.

Returns a Promise.

Events

The FreeSwitchClient class may emit the following events.

error (error)

Sent when an error is reported.

connect (current_call : FreeSwitchResponse)

Sent when connecting to FreeSWITCH. Might be sent multiple times in case disconnections happen.

reconnecting (retry: number)

Sent when disconnected from FreeSWITCH. The retry value indicates how long the client will wait until reconnecting to FreeSWITCH.

warning (data)

Sent by the underlying socket when a socket-level warning is triggered.

end

Sent when the end() method is called.

Server Usage

You can connect to an Event Socket server from the FreeSwitch XML dialplan, Notice the syntax to specify more than one server if desired.

<action application="set" data="socket_resume=true"/>
<action application="socket" data="127.0.0.1:7000|127.0.0.1:7001 async full"/>
<action application="respond" data="500 socket failure"/>

Another option is to configure a inbound profile to directly use the socket. This bypasses the XML dialplan; instead, an inline dialplan is used.

<profile name="my-sofia-profile">
  <settings>
    <param name="dialplan" value="inline:'socket:127.0.0.1:7000|127.0.0.1:7001 async full'"/>

Here is a simplistic event server:

import { FreeSwitchServer } from 'esl'

const server = new FreeSwitchServer()

server.on('connection', (call) => {
  const res = await call.command('playback', 'voicemail/vm-hello')
  const foo = res.body.variable_foo
  await call.hangup() // hang-up the call
  await call.exit()   // tell FreeSwitch we're disconnecting
})

await server.listen({ port: 7000 })

Constructor options

The FreeSwitchServer constructor takes a single argument, an options object with the following fields:

• all_events: boolean, defaults to true; indicates whether the FreeSwitchResponse object should request all events from FreeSWITCH (the default), or only the ones required to process commands (all_events:false). Note that the default will negatively impact performance of both FreeSWITCH and your application; it however provides the simplest onboarding.

• my_events: boolean, defaults to true; indicates whether the FreeSwitchResponse object should filter on the Unique-ID of the call. This is generally what one wants, there is generally no reason to set this to false. (If you want to monitor system-wide events you should probably use a FreeSwitchClient instance.)

• logger: defaults to the console object

Methods

The FreeSwitchClient class has the following methods.

async listen(options)

This method starts accepting connection from FreeSWITCH.

The options are the same as for server.listen in the Node.js net package: port, host, backlog, …

Returns a Promise.

async close()

This methods closes the connection to FreeSWITCH and prevents further attempts.

Returns a Promise.

async getConnectionCount()

This method returns a Promise for the number of currently opened connections.

const count = await server.getConnectionCount()
console.log(`There are ${count} connections left opened.)

Events

The FreeSwitchServer class may emit the following events.

error (error)

Sent when an error is reported.

drop (data)

Sent when an incoming connection is dropped.

connection (call : FreeSwitchResponse, { headers, body, data, uuid })

Sent when FreeSWITCH connects to Node.js.

This event receives two parameters:

• the first one is a FreeSwitchResponse instance you will use to process the call;
• the second one contains data received during the initial connection.

Message tracing

Both FreeSwitchServer and FreeSwitchClient accept a logger option which must provide logger.debug, logger.info, and logger.error.

If logger.debug is not required, it can be set to an no-op function:

const logger = {
  debug: () => {},
  info: (...args) => console.info(...args),
  error: (...args) => console.error(...args)
}

FreeSwitchResponse

The FreeSwitchResponse class is the one you will interact most. It allows you to interact with FreeSWITCH using both low-level (Event Socket) commands and higher-level (API) commands.

The FreeSwitchResponse class extends EventEmitter.

Methods

ref() : string

Returns the unique identifier used internally to reference this instance.

async bgapi(command: string, timeout?: number ) : Promise<{ body: StringMap }>

Send a bgapi (background API) command to FreeSwitch and wait for completion. Different FreeSWITCH modules provide different commands, consult the documentation of each module to know which commands it provides. Inside the FreeSWITCH CLI use show api and show application to get the list of registered commands.

bgapi will wait until the commands completes before returning its Promise. This migh be multiple hours if the command initiates a call.

The timeout parameter has no default. If a timeout is not provided, the Promise might never get fulfilled.

Might thow FreeSwitchError.

async api(command: string, timeout?: number) : Promise<{ uuid: string, body: StringMap, headers: StringMap }>

Send an api command to FreeSwitch. Different FreeSWITCH modules provide different commands, consult the documentation of each module to know which commands it provides. Inside the FreeSWITCH CLI use show api and show application to get the list of registered commands.

Returns a Promise that is fulfilled as soon as FreeSwitch sends a reply. Requests are queued and each request is matched with the first-coming response, since there is no way to match between requests and responses.

On the FreeSWITCH side, api command block the Event Socket until they respond. This is probably not what you want if using FreeSwitchClient, you should use bgapi in that case.

Also use bgapi if you need to make sure responses are matched properly, since it provides the proper semantics.

The timeout defaults to the value of .default_send_timeout(), i.e. 10s.

Might thow FreeSwitchError.

command(app_name:string,app_arg:string) : SendResult

command_uuid(uuid:string,app_name:string,app_arg:string,timeout?:number) : SendResult

These methods are identical; you would typically use command in a FreeSwitchServer application, and command_uuid in a FreeSwitchClient application.

Execute a dialplan application synchronously — returns a Promise that completes when the command is completed (which may take hours).

// Send the command and wait for completion
await call.command('playback', '/tmp/example.wav')

execute(app_name:string,app_arg:string) : SendResult

execute_uuid(uuid:string,app_name:string,app_arg:string,loops?:number,event_uuid?:string) : SendResult

These methods are identical; you would typically use execute in a FreeSwitchServer application, and execute_uuid in a FreeSwitchClient application.

Execute a dialplan application asynchronously — does not wait for completion.

In most cases you probably want to use command or command_uuid instead of execute and execute_uuid.

// Send the command
await call.execute('playback', '/tmp/example.wav')

hangup(hangup_cause?:string) : SendResult

hangup_uuid(uuid:string,hangup_cause?:string) : SendResult

These methods are identical; you would typically use hangup in a FreeSwitchServer application, and hangup_uuid in a FreeSwitchClient application.

Hangs up the call.

unicast(args: {'local-ip':string, 'local-port':number, 'remote-ip':string, 'remote-port':number, transport:'tcp'|'udp', flags?:'native'}) : SendResult

unicast_uuid(uuid:string,args:{'local-ip':string, 'local-port':number, 'remote-ip':string, 'remote-port':number, transport:'tcp'|'udp', flags?:'native'}) : SendResult

These methods are identical; you would typically use unicast in a FreeSwitchServer application, and unicast_uuid in a FreeSwitchClient application.

Interface media with the specified IP and port.

• local-ip: default to 127.0.0.1
• local-port: default to 8025
• remote-ip: default to 127.0.0.1
• remote-port: default to 8026
• flags: native — do not transcode audio to/from the FreeSWITCH internal format (L16)

Methods for low-level interface

event_json(...events:string[]) : SendResult

Add the specified events to the list of events forwarded to Node.js.

By default this module already executes call.event_json('CHANNEL_EXECUTE_COMPLETE', 'BACKGROUND_JOB'), or, with the all_events flag of FreeSwitchServer, call.event_json('ALL').

call.event_json('CHANNEL_HANGUP_COMPLETE','DTMF')

nixevent(...events:string[]) : SendResult

Remove the specified events from the list of events forwarded to Node.js.

Removing CHANNEL_EXECUTE_COMPLETE and BACKGROUND_JOB will break command/command_uuid and bgapi, respectively.

noevents() : SendResult

Stop receiving events.

Using this method will prevent command/command_uuid and bgapi from working.

filter(header:string, value:string) : SendResult

Add an event filter for the specified event header and value.

filter_delete(header:string, value:string) : SendResult

Remove an event filter for the specified event header and value.

sendevent(event_name:string, args:StringMap) : SendResult

Enqueue an event in the FreeSWITCH event queue.

Requires the full flag when sending to FreeSwitchServer.

linger() : SendResult

Used in server mode, requests FreeSwitch to not close the socket as soon as the call is over, allowing us to do some post-processing on the call (mainly, receiving call termination events).

By default, FreeSwitchServer with call exit() for you after 4 seconds. You must capture the cleanup_linger event if you want to handle things differently.

log(level:number) : SendResult

Enable logging on the socket, optionally setting the log level.

nolog() : SendResult

Disable logging.

sendmsg(command:string,args:StringMap) : SendResult

sendmsg_uuid(uuid:string,command:string,args:StringMap) : SendResult

Send a message on the socket.

The command is one of the low-level call-command documented for the Event Socket interface.

In most cases you should use one of the provided methods (api, bgapi, etc.) rather than try to implement this.

send(command: string, args?: StringMap, timeout?: number ) : SendResult

Write a command to the Event Socket and wait for the (low-level) reply.

In most cases you should use one of the provided methods (api, bgapi, etc.) rather than try to implement this.

Events

The FreeSwitchResponse class may emit different events.

FreeSWITCH events

By default in FreeSwitchServer, all_events is true and your code will receive the different events for the call.

You might also activate additional events in FreeSwitchClient using the event_json() method.

The event callback will receive a single argument, an object with two fields:

• headers: the headers of the Event Socket event
• body: the content sent by FreeSWITCH

Both are Object.

import { FreeSwitchServer } from 'esl'

const server = new FreeSwitchServer()

server.on('connection', (call) => {
  // Only triggered once. `onceAsync` returns a Promise and might throw.
  call.onceAsync('CHANNEL_ANSWER').then( function ({headers,body}) {
    console.log('Call was answered');
  });
  // Might be triggered multiple times.
  call.on('CHANNEL_ANSWER', function({headers,body}) {
    console.log('Call was answered');
  });
  // By default `all_events` is true and we do not need to use `event_json`.
})

await server.listen({ port: 7000 })

'socket.close'

Emitted when the underlying network socket is closed.

'socket.error' (err:Error)

Emitted when the unerlying network socket has an error.

'socket.write' (err:Error)

Emitted when a write on the underlying network socket has an error.

'socket.end' (err:Error)

Emitted when the underlying socket was terminated due to an error.

'error.missing-content-type' (err:FreeSwitchMissingContentTypeError)

Emitted when FreeSWITCH did not provide a Content-Type header.

Should normally not happen, most probably a bug in FreeSWITCH if this happens.

'error.unhandled-content-type' (err:FreeSwitchUnhandledContentTypeError)

Emitted when the parser received an unsupported Content-Type header from FreeSWITCH.

Should normally not happen, report these as bug!

'error.invalid-json' (err:Error)

Emitted when the JSON received from FreeSWITCH could not be parsed.

'error.missing-event-name' (err:FreeSwitchMissingEventNameError)

Emitted when the FreeSWITCH response could be parsed but no Event-Name is found.

'cleanup_linger'

Emitted when you activated .linger() and it's time for your code to call .exit().

'freeswitch_log_data' (data:{ headers: StringMap, body: string })

Emitted when you activated .log() and a log event is received.

'freeswitch_disconnect_notice'

Emitted by FreeSWITCH to indicate imminent disconnection of the socket.

'freeswitch_rude_rejection'

Undocumented rejection from FreeSWITCH.

Install

Add the module to your project using npm, yarn, pnpm.

npm install esl

Examples

The test suite provides many examples.

Support

Please use GitHub issues for community support.

Commercial support is available as well from the maintainer.

Migrating from earlier versions

• creating client and server now uses new and the FreeSwitchClient, FreeSwitchServer classes
• this is no longer used; the call object is passed as a parameter.