Embedded FCM Distributor

You may want to embedded a FCM distributor to make notifications invisible for many users. Embedding a FCM Distributor is a solution : if the user doesn’t have another distributor installed, this one will be used.


You will need to add some code on your android project and host a FCM Rewrite proxy.


  • Add classpath 'com.google.gms:google-services:4.3.4' to your project level build.gradle.
  • Add id 'com.google.gms.google-services' and implementation 'com.github.UnifiedPush:android-embedded_fcm_distributor:{VERSION}' to your app level build.gradle.
  • Add the google-services.json file from firebase to your app directory.
  • Add the receiver to your code:

val handlerFCM = object: GetEndpointHandler {
    override fun getEndpoint(context: Context?, token: String, instance: String): String {
        // This returns the endpoint of your FCM Rewrite-Proxy
        return "https://<your.domain.tld>/FCM?instance=$instance&token=$token"

class EmbeddedDistrib: EmbeddedDistributorReceiver(handlerFCM) {}
  • Declare it on your Manifest:
        <receiver android:enabled="true"  android:name=".EmbeddedDistrib" android:exported="false">
                <action android:name="org.unifiedpush.android.distributor.REGISTER"/>
                <action android:name="org.unifiedpush.android.distributor.UNREGISTER"/>

FCM Rewrite Proxy

As a developer, if you’re using the FCM added version of the libraries, you will need a rewrite proxy for FCM-fallback for users who don’t have a UnifiedPush Distributor. It is close to the ususally needed gateway to FCM or trusted server

The rewrite proxy can be done in many ways, here are some.


location /FCM {
        local json=require("cjson")
        local args = ngx.req.get_uri_args()
        local token = args["token"]
        local instance = args["instance"]
        local req = ngx.req.get_body_data()
        local newreq =  { ["to"] = token, ["data"] = { ["body"] = req, ["instance"] = instance } }
        local body = json.encode(newreq)

    proxy_set_header		Authorization key=<YOUR FCM KEY>;
    proxy_set_header		Content-Type application/json;
    proxy_pass			https://fcm.googleapis.com/fcm/send;
    proxy_set_header            Host fcm.googleapis.com;

    # Force https
    if ($scheme = http) {
        rewrite ^ https://$server_name$request_uri? permanent;


Golang Rewrite Proxy is a program can be installed to run as a rewrite proxy for FCM.

Traffic from /FCM on any reverse proxy (for TLS) can be proxied to it. The following is an example for Nginx.

location  /FCM {
        proxy_pass  ;