This module provides functions to interact with the Firebase Cloud Messaging (FCM) API for sending messages, subscribing/unsubscribing devices to/from topics, and handling multicast messages.

Subscribes a device or multiple devices to an FCM topic.

• accessToken (string): Access token generated by Google JWT.
• registrationTokenOrTokens (string|string[]): A token or array of registration tokens for the devices to subscribe to the topic.
• topic (string): The topic to which to subscribe.

Returns a promise fulfilled with the server's response after the device(s) have been subscribed to the topic.

Unsubscribes a device or multiple devices from an FCM topic.

• accessToken (string): Access token generated by Google JWT.
• registrationTokenOrTokens (string|string[]): A device registration token or an array of device registration tokens to unsubscribe from the topic.
• topic (string): The topic from which to unsubscribe.

Returns a promise fulfilled with the server's response after the device(s) have been unsubscribed from the topic.

Sends a message via FCM.

• projectId (string): Project ID assigned in Firebase.
• accessToken (string): Access token generated by Google JWT.
• message (Message): The message payload.
• dryRun (boolean): Whether to send the message in the dry-run (validation only) mode.

Returns a promise fulfilled with a unique message ID string after the message has been successfully handed off to the FCM service for delivery.

Sends a multicast message to all specified device tokens.

• projectId (string): Project ID assigned in Firebase.
• accessToken (string): Access token generated by Google JWT.
• message (MulticastMessage): A multicast message containing an array of device tokens.
• dryRun (boolean): Whether to send the message in the dry-run (validation only) mode.

Returns a promise fulfilled with an object representing the result of the send operation.

Sends each message in the given array via Firebase Cloud Messaging.

• projectId (string): Project ID assigned in Firebase.
• accessToken (string): Access token generated by Google JWT.
• messages (Message[]): A non-empty array containing up to 500 messages.
• dryRun (boolean): Whether to send the messages in the dry-run (validation only) mode.

Returns a promise fulfilled with an object representing the result of the send operation.

Payload for sending messages via FCM.

{
  data?: { [key: string]: string };
  notification?: Notification;
  android?: AndroidConfig;
  webpush?: WebpushConfig;
  apns?: ApnsConfig;
  fcmOptions?: FcmOptions;
}

For more details, refer to the Firebase Admin Node SDK Messaging API documentation.

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File                         | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s       
-----------------------------|---------|----------|---------|---------|-------------------------
All files                    |   80.64 |     62.5 |   89.65 |   80.48 |                         
 app                         |    75.8 |       50 |   92.85 |    75.4 |                         
  messagin-error-internal.js |   51.85 |       50 |     100 |   51.85 | 11,14-17,24,35-36,42-49 
  messaging.js               |   94.28 |       50 |   91.66 |   94.11 | 124-126                 
 constants                   |     100 |      100 |     100 |     100 |                         
  apiConstants.js            |     100 |      100 |     100 |     100 |                         
  errorConstants.js          |     100 |      100 |     100 |     100 |                         
 util                        |   84.74 |    81.25 |   86.66 |   84.74 |                         
  apiRequest.js              |   33.33 |      100 |       0 |   33.33 | 4-7                     
  helper.js                  |      75 |      100 |     100 |      75 | 5                       
  request.js                 |   87.23 |       75 |   88.88 |   87.23 | 39,45,71-77,93          
  validator.js               |     100 |      100 |     100 |     100 |                         
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