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This software provides an Erlang client for Google Cloud Messaging.

What you can do with gcm-erlang:

Using gcm-erlang you can:

  1. start several gen_servers representing different GCM applications defined by different GCM API keys
  2. send notification messages to Android mobile devices registered to your specific application and registered to GCM using a specific registration id

So far gcm-erlang does only provide support for JSON messages since GCM does not allow to send multicast messages using plain text.

How to compile:

The first thing you have to do is to compile all the Erlang files using rebar.

$ ./rebar get-deps compile

How to use with rebar:

You can use gcm_app as a dependency in your rebar.config:

{deps , [
    {gcm, ".*", {git, "https://github.com/pdincau/gcm-erlang.git", {tag, "1.0.0"}}}

How to run tests:

./rebar compile && ./rebar skip_deps=true eunit && ./run-dialyzer.sh

How to run the application gcm-erlang:

Once all the Erlang files are compiled you can start the application gcm-erlang. This application depends on other applications so it is mandatory to start them as well.

$ erl -pa deps/*/ebin -pa ebin
1> application:start(inets).
2> application:start(jsx).
3> ssl:start().
4> application:start(gcm).

How to start/stop different gen_servers under application gcm-erlang (one for each GCM application):

While gcm-erlang is running you can start several supervised gen_servers, one for each GCM application. Every gen_server is defined by an atom used internally for registration and by a GCM API key.

3> gcm:start(foo, "myapikey").
4> gcm:start(bar, "myotherapikey").
5> gcm:start(baz, "mylastapikey").

You can stop a gen_server representing a GCM Application using:

6> gcm:stop(foo).

How to send a GCM message using from a specific GCM application:

At any time you can send a GCM message to one or more mobile devices by calling:

7> gcm:push(RegisteredName, RegIds, Message).

or by calling:

7> gcm:sync_push(RegisteredName, RegIds, Message).

Where RegistereName is the atom used during registration, RegIds is a list (max 1000 elements) of Registration Ids specified as Erlang binaries (e.g., <<"APA91bHun4MxP5egoKMwt2KZFBaFUH-1RYqx...">>) and Message is an Erlang term representing the data you want to send to the device.

The JSON message is built using jsx in the module gcm.erl and in the end will have the following form:

  "registration_ids" : ["APA91bHun4MxP5egoKMwt2KZFBaFUH-1RYqx..."],
  "data" : {
    "message" : "a message"
  "time_to_live" : 3600,
  "collapse_key" : "your_update"

You can send this message using:

8> gcm:push(RegisteredName, RegIds, [{<<"data">>, [
8>     {<<"message">>, <<"a message">>}
8> ]}, {<<"time_to_live">>,3600}, {<<"collapse_key">>,<<"your_update">>}]).

or simply:

8> gcm:push(RegisteredName, RegIds, [{<<"data">>, [
8>     {<<"message">>, <<"a message">>}
8> ]}]).

gcm-erlang will push the message for you to Google Cloud Messaging servers and will parse the JSON provided as result.

In order to understand errors see: Interpreting an error response.


Some of the concepts I used for building this Erlang application are based on this blog post and on this Erlang application for APN.

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