Receive Upstream Messages

When FCM receives an upstream messaging call from a client app, it generates the necessary XMPP stanza for sending the upstream message. FCM adds the category and from fields, and then sends a stanza like the following to the app server:

<message id="">
  <gcm xmlns="google:mobile:data">
  {
      "category":"com.example.yourapp", // to know which app sent it
      "data":
      {
          "hello":"world",
      },
      "message_id":"m-123",
      "from":"REGID"
  }
  </gcm>
</message>

Sending an ACK message

In response to an upstream message like the above, the app server must use the same connection to send an ACK message containing the unique message ID. If FCM does not receive an ACK, it may retry sending the message to the app server.

<message id="">
  <gcm xmlns="google:mobile:data">
  {
      "to":"REGID",
      "message_id":"m-123"
      "message_type":"ack"
  }
  </gcm>
</message>

See the XMPP Connection Server Reference for more information about upstream message syntax.

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