johngb / gcm

Google Cloud Messaging for application servers implemented using the Go programming language.

gcm

This is a modified version of the gcm library @alexjlockwood with some changes suggested by @timehop. However the message responses are quite different as the original library didn't make it feasible to distinguish between different GCM error responses, and didn't handle the 'Retry-After' headers that Google say are mandatory (or they may block your account).

The Android SDK provides a nice convenience library (com.google.android.gcm.server) that greatly simplifies the interaction between Java-based application servers and Google's GCM servers. However, Google has not provided much support for application servers implemented in languages other than Java, specifically those written in the Go programming language. The gcm package helps to fill in this gap, providing a simple interface for sending GCM messages and automatically retrying requests in case of service unavailability.

Documentation: http://godoc.org/github.com/johngb/gcm

Getting Started

To install gcm, use go get:

go get github.com/johngb/gcm

Import gcm with the following:

import "github.com/johngb/gcm"

Sample Usage

Here is a quick sample illustrating how to send a message to the GCM server:

package main

import (
	"fmt"
	"net/http"

	"github.com/johngb/gcm"
)

func main() {
	// Create the message to be sent.
	data := map[string]interface{}{"score": "5x1", "time": "15:10"}
	regIDs := []string{"4", "8", "15", "16", "23", "42"}
	msg := gcm.NewMessage(data, regIDs...)

	// Create a Sender to send the message.
	sender := &gcm.Sender{ApiKey: "sample_api_key"}

	// Send the message and receive the response after at most two retries.
	response, httpErr := sender.Send(msg, 2)
	if httpErr.Err != nil {
		switch httpErr.StatusCode{
		case http.StatusBadRequest:
			...
			// handle bad requests as needed
		case http.StatusInternalServerError
			...
			// handle internal server errors as needed, keeping to the httpErr.RetryAfter if you retry
		...
		}
		fmt.Println("Failed to send message:", err)
		return
	}

	/* ... */
}

Note for Google AppEngine users

If your application server runs on Google AppEngine, you must import the appengine/urlfetch package and create the Sender as follows:

package sample

import (
	"appengine"
	"appengine/urlfetch"

	"github.com/johngb/gcm"
)

func handler(w http.ResponseWriter, r *http.Request) {
	c := appengine.NewContext(r)
	client := urlfetch.Client(c)
	sender := &gcm.Sender{ApiKey: "sample_api_key", HTTP: client}

	/* ... */
}