mod_push_appserver

Simple and extendable app server for XMPP push notifications as defined in XEP-0357.

The app server is implemented as a module for the Prosody XMPP server.

Currently, only push notifications to Apple's APNS and Google's FCM are implemented, but other push services can easily be added in a separate module.

Requirements

Prosody trunk/0.12 or later.
Lua 5.1, 5.2 or 5.3
Installed luasec Lua library version 0.5 (Debian package: lua-sec) or higher.
Installed cqueues Lua library (Debian package: lua-cqueues).
Installed lua-http Lua library (Debian package: lua-http).

Installation

Just check out the repository somewhere and point prosody at this directory using plugin_paths in its main config file.
For example: plugin_paths = { "/usr/local/lib/mod_push_appserver" }.

Then add the submodule you need (for example mod_push_appserver_apns or mod_push_appserver_fcm) to the enabled modules of a specific virtual host or component.

See this configuration example for APNS if you want to load the needed submodule as component:

Component "push.example.org" "push_appserver_apns"
	push_appserver_debugging = false
	push_appserver_apns_sandbox = false
	push_appserver_apns_collapse_pushes = false
	push_appserver_apns_push_priority = "auto"
	push_appserver_apns_mutable_content = true
	push_appserver_apns_cert = "/etc/prosody/apns_normal.crt"
	push_appserver_apns_key = "/etc/prosody/apns_normal.key"
	push_appserver_apns_topic = "my.app.bundle.id"

Component "voip-push.example.org" "push_appserver_apns"
	push_appserver_debugging = false
	push_appserver_apns_sandbox = false
	push_appserver_apns_collapse_pushes = false
	push_appserver_apns_push_priority = "voip"
	push_appserver_apns_cert = "/etc/prosody/apns_voip.crt"
	push_appserver_apns_key = "/etc/prosody/apns_voip.key"
	push_appserver_apns_topic = "my.app.bundle.id"

If you want to have only one component host supporting APNS and FCM you can use the following:

Component "push.example.org" "push_appserver"
	modules_enabled = {
		"push_appserver_fcm";
		"push_appserver_apns";
	}
	push_appserver_debugging = false
	push_appserver_fcm_key = "someFCMkey"
	push_appserver_apns_sandbox = false
	push_appserver_apns_collapse_pushes = false
	push_appserver_apns_push_priority = "voip"
	push_appserver_apns_cert = "/etc/prosody/apns_voip1.crt"
	push_appserver_apns_key = "/etc/prosody/apns_voip1.key"
	push_appserver_apns_topic = "my.app.bundle.id"

Or only use FCM:

Component "fcm-push.example.org" "push_appserver_fcm"
	push_appserver_debugging = false
	push_appserver_fcm_key = "myFCMkey"

Usage notes (configuration)

For chat apps using VoIP pushes to APNS, the priority should be set to high. The alert text can be ignored in this case (if you only want to wakeup your device). For normal push notifications, the priorities high and silent are supported. The configured alert text (push_appserver_apns_push_alert) is ignored for silent pushes.

For pushes to FCM the priorities high and normal are supported with normal priorities being delayed while the device is in doze mode. Pushes having priority high are always delivered, even in doze mode, thus should be used for chat apps.

Configuration options (mod_push_appserver)

push_appserver_debugging (boolean)
Make /push_appserver/v1/settings HTTP endpoint available. Default: false.
This setting will also make http forms available at all POST HTTP endpoints for easier manual testing of your setup by simply using your browser of choice.
push_appserver_rate_limit (number)
Allow only one request everey N seconds. Default: 5.
The throttle will always space out incoming requests by this timeframe and make sure that the last request of a burst will always be handled at the beginning of the next timeframe (the first request of a burst will be handled immediately, all other requests in between the first and the last one will be ignored completely).
This should mitigate some DOS attacks.
push_appserver_store_plugin (string)
Set this to the store plugin to use, currently available: cached, uncached.
Use the uncached store to deactivate local caching of device tokens and node settings.
This is useful if you are using an SQL storage backend and this backend is replicated across several servers in an HA- or loadbalancing-setup.
Default: cached.
push_appserver_store_params (table)
Set this to anything you want to pass to the storage plugin.
The two default implementations cached, uncached don't take any params.
Default: nil.

Configuration options (mod_push_appserver_apns)

push_appserver_apns_cert (string)
Path to your APNS push certificate in PEM format.
push_appserver_apns_key (string)
Path to your APNS push certificate key in PEM format.
push_appserver_apns_topic (string)
The APNS push topic to use (should be your app's bundle id).
push_appserver_apns_capath (string)
Path to CA certificates directory. Default: "/etc/ssl/certs" (Debian and Ubuntu use this path for the system CA store).
push_appserver_apns_ciphers (string)
Ciphers to use when establishing a tls connection. Default: ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256
push_appserver_apns_sandbox (boolean)
Use apns sandbox api endpoint if true, production endpoint otherwise. Default: true.
push_appserver_apns_collapse_pushes (boolean)
Instruct Apple to collapse queued pushes into one single push (true), or keep them separated (false).
Setting this to false allows to get more background time for your app when sending multiple pushes in a row (this can be subject to implementation changes by Apple, though). Default: false.
push_appserver_apns_mutable_content (boolean)
Mark high prio pushes as mutable content (only has a meaningful effect if push_appserver_apns_push_priority is set to "high" or "auto"). Default: true.
push_appserver_apns_push_ttl (number)
TTL for push notification in seconds. Default: 4*7*24*3600 (that means 4 weeks from now).
push_appserver_apns_push_priority (string)
Value "high" for high priority pushes always triggering a visual indication on the user's phone, "silent" for silent pushes that can be delayed or not delivered at all but don't trigger a visual indication, voip for voip pushes and "auto" to let the appserver automatically decide between "high" and "silent" based on the presence of "last-message-body" in the push summary received from the XMPP server. Default: "auto".
NOTE 1 (iOS >= 13): Apple decided for iOS >= 13 to not allow silent voip pushes anymore. Use "high" or "auto" on this systems and set push_appserver_apns_mutable_content to true. Then use a Notification Service Extension in your app to log in into your XMPP account in the background, retrieve the acutal stanzas and replace the notification with a useful one before the dummy notification sent by this appserver hits the screen.
NOTE 2 (iOS >= 10 and < 13): if you have VoIP capabilities in your app "silent" pushes will become reliable and always wake up your app without triggering any visual indications on the user's phone. In VoIP mode your app can decide all by itself if it wants to show a notification to the user or not by simply logging into the XMPP account in the backround and retrieving the stanzas that triggered the push.
You have to use voip if you want to send voip pushes (all iOS versions).

Configuration options (mod_push_appserver_fcm)

push_appserver_fcm_key (string)
Your FCM push credentials (can be found in FCM dashboard under Settings --> Cloud Messaging --> Server key).
push_appserver_fcm_capath (string)
Path to CA certificates directory. Default: "/etc/ssl/certs" (Debian and Ubuntu use this path for the system CA store).
push_appserver_fcm_ciphers (string)
Ciphers to use when establishing a tls connection. Default: ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256
push_appserver_fcm_push_ttl (number)
TTL for push notification in seconds, can be 4 weeks at max. Default: nil (that means 4 weeks).
push_appserver_fcm_push_priority (string)
Value "high" for high priority pushes that wake up the device even when in doze mode or "normal" for normal pushes that can be delayed. Default: "high".

API (register device etc.)

This appserver implements XEP-0357 commands for sending actual push notifications. Additionally XEP-0357 requires a device to be registered on the appserver but does not dictate how this should be done.

Therefore this appserver provides two different APIs to register a (new) device on the appserver. Just use the one more convenient to you.

XEP-0050 Ad-Hoc Command API

This API resembles more or less what Conversations is doing, but with some small differences:

the command is named "v1-register-push" instead of "register-push-gcm"
the device id field is called "node" instead of "device-id"
the new field "type" was added. This can be used to specify the push type just as it is done using the http based API.
unregistering a device is not done at all in Conversations, but this appserver supports it via the v1-unregister-push command

This Gist demonstrates the changes needed to Conversations to use this appserver instead of inputmice's p2. See XEP-0050 for more info regarding Ad-Hoc Commands in general.

Keep in mind that the registration/unregistration commands sent to this appserver are routed through the user's xmpp server. This exposes the raw APNS/FCM push token and device id to the user's xmpp server. Use the HTTP API if you don't like this (HTTP will expose the user's IP, though).

Example XMPP flow for registering a device:

<iq to="push.example.org" id="MyID-6465" type="set">
	<command xmlns="http://jabber.org/protocol/commands" node="v1-register-push" action="execute">
		<x xmlns="jabber:x:data" type="submit">
		<field type='hidden' var='FORM_TYPE'>
			<value>https://github.com/tmolitor-stud-tu/mod_push_appserver/#v1-register-push</value>
		</field>
		<field var="type">
			<value>fcm</value>
		</field>
		<field var="node">
			<value>static device id like ANDROID_ID OR some stable iOS id</value>
		</field>
		<field var="token">
			<value>dynamic token obtained from FirebaseInstanceId_InstanceId OR apns token</value>
		</field>
		</x>
	</command>
</iq>

<iq to="[email protected]/res1" from="push.example.org" type="result" id="MyID-6465">
	<command xmlns="http://jabber.org/protocol/commands" status="complete" node="v1-register-push" sessionid="1559985918910">
		<x xmlns="jabber:x:data" type="form">
			<field type="jid-single" var="jid">
				<value>push.example.org</value>
			</field>
			<field type="text-single" var="node">
				<value>echoed back static device id</value>
			</field>
			<field type="text-single" var="secret">
				<value>some arbitrary hash-like value</value>
			</field>
		</x>
	</command>
</iq>

The two values node and secret are needed for registering push on the XMPP server afterwards, see example 9 in XEP-0357, section 5.

Example XMPP flow for UNregistering a device:

<iq to="push.example.org" id="MyID-6446" type="set">
	<command xmlns="http://jabber.org/protocol/commands" node="v1-unregister-push" action="execute">
		<x xmlns="jabber:x:data" type="submit">
		<field type='hidden' var='FORM_TYPE'>
			<value>https://github.com/tmolitor-stud-tu/mod_push_appserver/#v1-unregister-push</value>
		</field>
		<field var="type">
			<value>fcm</value>
		</field>
		<field var="node">
			<value>static device id like ANDROID_ID OR some stable iOS id</value>
		</field>
		</x>
	</command>
</iq>

<iq to="[email protected]/res1" from="push.example.org" type="result" id="MyID-6446">
	<command xmlns="http://jabber.org/protocol/commands" status="complete" node="v1-unregister-push" sessionid="1559985918910">
		<x xmlns="jabber:x:data" type="form">
			<field type="jid-single" var="jid">
				<value>push.example.org</value>
			</field>
			<field type="text-single" var="node">
				<value>echoed back static device id</value>
			</field>
		</x>
	</command>
</iq>

HTTP API

All POST endpoints can be used via GET to get back a simple html page which allows you to manually test the endpoint behaviour in your browser, if the config option push_appserver_debugging is set to true (an error is returned otherwise). This config option should be false in production environments!

POST to http://<host>:5280/push_appserver/v1/register or https://<host>:5281/push_appserver/v1/register
POST data: type=<push type>&node=<device uuid>&token=<apns/fcm/etc. push token>
function: register device for push
result: text document separated by \n
- first line: OK, everything else (including ERROR) is specified as error condition if ok: 2nd line: XEP-0357 push node, 3rd line: XEP-0357 push secret
  if error: 2nd and subsequent lines: error description
POST to http://<host>:5280/push_appserver/v1/unregister or https://<host>:5281/push_appserver/v1/unregister
POST data: type=<push type>&node=<device uuid>
function: unregister device
result: text document separated by \n
- first line: OK, everything else (including ERROR) is specified as error condition
  if ok: 2nd line: XEP-0357 push node, 3rd line: XEP-0357 push secret
  if error: 2nd and subsequent lines: error description
POST to http://<host>:5280/push_appserver/v1/push or https://<host>:5281/push_appserver/v1/push
POST data: node=<device uuid>&secret=<secret obtained on register>
function: send push notification to device
result: text document separated by \n
- first line: OK, everything else (including ERROR) is specified as error condition
  if ok: 2nd line: XEP-0357 push node
  if error: 2nd and subsequent lines: error description
GET to http://<host>:5280/push_appserver/v1/settings or https://<host>:5281/push_appserver/v1/settings
function: get list of registered device UUIDs
result: html site listing all registered device UUIDS as links
GET to http://<host>:5280/push_appserver/v1/settings/<device uuid> or https://<host>:5281/push_appserver/v1/settings/<device uuid>
function: get internal data saved for this device UUID
result: HTML site listing all data (serialized Lua table using penlight's pl.pretty)
GET to http://<host>:5280/push_appserver/v1/health or https://<host>:5281/push_appserver/v1/health
function: get health status of module
result: html site containing the word RUNNING if the module is loaded properly (this GET-node is accessible even when push_appserver_debugging is set to false)

Implementation notes

mod_push_appserver and its submodules use events to communicate with each other. These events are documented here.

Interaction between mod_push_appserver and its submodules

mod_push_appserver triggers the event incoming-push-to-<push type> (currently only the types apns and fcm are supported). The event handler has to return true or an error description string for failed push attempts and false for successfull ones.
Returning nil will be handled as error!
The event data always includes the following keys:

origin
Prosody session the stanza came from (typically an s2s session).
settings
The registered push settings which are also available at the /push_appserver/v1/settings/<device uuid> HTTP endpoint in debug mode.
summary
The push summary (see XEP-0357 for more information)
stanza
The incoming push stanza (see XEP-0357 for more information).

Submodules (like mod_push_appserver_apns) can trigger the event unregister-push-token. The event data has to include the following keys:

token
The push token to invalidate (note: this is not the secret obtained by registering the device, but the raw token obtained from APNS, FCM etc.).
type
apns, fcm etc.
timestamp
The timestamp of the delete request. mod_push_appserver won't unregister the token if it was re-registered after this timestamp.

Example of internal data

{
  type = "apns",
  token = "DEADBEEFABCDEF0123456DEADBEEF112DEADBEEFABCDEF0123456DEADBEEF112",
  last_push_error = "2017-03-18T04:07:44Z",
  last_successful_push = "2017-03-18T03:54:24Z",
  registered = "2017-03-17T02:10:21Z",
  renewed = "2017-03-18T02:54:51Z",
  node = "E0FF1D8C-EB96-4E10-A912-F68B03FD8D3E",
  secret = "384e51b4b2d5e4758e5dc342b22dea9217212f2c4886e2a3dcf16f3eb0eb3807"
}

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