Push notification from custom server

Introduction

This can be done using 2 methods with HTTP Post request, With Firebase admin SDK running on your server. Here I will discuss both of them.

Firebase Cloud Messaging HTTP Protocol

From your server request to the the link below to send the notification with some request parameters

https://fcm.googleapis.com/fcm/send

While requesting add headers as follows

Authorization    key=<Your_key_from_the_console>
Content-Type     application/json

The body of the request varies

{
  "to" : <tokens or the topic>,
  "notification" : {
    "title":"This is a test title",
    "body":"This is the body"
  },
  "data": {
      //whatever key value payer you need to send  
  }
}

The to parameters takes Array of tokens like

["token1","token2",..........]

or a single token like

"token"

or a topic name starting with /topic/ like

"/topic_name/"

For multiple topic use conditions using || and && operators like

"/topic_name/ && /topic2/"

Using Admin SDK(Node js)

At first initilize the firebase sdk and admin SDK

const functions = require('firebase-functions');
const admin = require('firebase-admin');

admin.initializeApp({
  credential: admin.credential.cert({
        //your admin credential certificate generated from the console. Follow this [link][1].
    }),
  databaseURL: "https:///<PROJECT_NAME>.firebaseio.com"
});

Create a payload JSON string as in the first example.

var payload = {
              notification: {
                title: "Title of the notification,
                body: "Body of the notification",
              },
              data:{
                //required key value pair
              }
            };

Then call different send methods to send the notification.

For Topic

admin.messaging().sendToTopic("/topic/", payload)
              .then(function(response) {
                console.log("Successfully sent message:", response);
              })
              .catch(function(error) {
                console.log("Error sending message:", error);
              });
            });

For device

admin.messaging().sendToDevice(token, payload).then(response=>{
                       response.results.forEach((result, index) => {
                        const error = result.error;
                        if (error) {
                          console.error('Failure sending notification to', tokens, error);
                        } else{
                          console.log('Sucessfully sent to '+tokens);
                        }
                      });