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node2dm

A node.js server for sending push notifications to Google's C2DM push notification server. Written by Instagram to support our Android application, and inspired by statsd's protocol.

Setting up

Copy the provided exampleConfig.js into a config.js file, and follow the instructions in the file to fill out your application's Google account credentials. Then just run:

node node2dm.js /path/to/config/file

A sample upstart script is included for easy deployment on Ubuntu.

Pushing a message

Messages are pushed to the service using simple UDP datagrams, separated by a colon; here's what our Python application server code looks roughly like:

c2dm_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
encoded_payload = '%s:%s:%s' % (
    device_token,
    collapse_key,
    simplejson.encode(c2dm_payload)
)
c2dm_socket.sendto(encoded_payload,
                         (c2dm_server, c2dm_port))

As you can see from the example, the datagram looks as follows:

device_token:collapse_key:json_encoded_payload

We chose UDP because we wanted to minimize latency between our application servers and the node2dm service, and don't have hard delivery requirements for push notifications.

Rate limits / errors

node2dm handles a variety of errors that may be passed back from the C2DM service:

  • 401: Will force a re-authentication with the C2DM service
  • 503: Will back off, respecting the Retry-After header
  • QuotaExceeded: In this case, your application has exceeded Google's quota for pushes for the day. node2dm will write out a quota.lock file and quit itself
  • DeviceQuotaExceeded: You're sending too many pushes to this device; node2dm will blacklist this token for an hour before trying to send any more messages
  • InvalidRegistration/NotRegistered: Something's wrong with this device token; node2dm will drop the message
  • MessageTooBig: node2dm will drop this message

Bad token callbacks

node2dm supports a simple webhook-like callback on a bad token error from Google. To set it up, configure serverCallbackHost / serverCallbackPort / serverCallbackPath / serverCallbackSharedSecret in your config.js, and you should start receive POST requests with this payload:

device_token (the offending device token)
message_body (the body of the message that was being attempted; can be useful if you need to match something back up on your end)
shared_secret (the serverCallbackSharedSecret, can match up on your end to make sure it's the right server sending you a ping)

Getting stats

node2dm comes with a simple, telnet-able stats function. To use it:

> echo "stats" | nc localhost 8121
uptime: 226 seconds
messages_sent: 20583
messages_in_queue: 0
backing_off: false
total_errors: 9
rate_limited_tokens: 0
logged_in_to_c2dm: true
token_age: 221
memory_rss: 88793088
memory_heapTotal: 11075584
memory_heapUsed: 3658300

Contributing

The project is BSD-licensed; please fork and submit a pull request for any improvements you'd like to see in node2dm.