B4R Code Snippet Firebase Push Messages (FCM)

This code uses rHttpUtils2 to send push messages. It is equivalent to the B4J/A/i code posted here: https://www.b4x.com/android/forum/t...s-firebase-cloud-messaging-fcm.67716/#content

- #StackBufferSize should be set to 500+.
- The title and body messages are not escaped. You will need to manually escape the messages if they include quotes.

#Region Project Attributes
   #AutoFlushLogs: True
   #CheckArrayBounds: True
   #StackBufferSize: 2000
#End Region

Sub Process_Globals
   Public Serial1 As Serial
   Private API_KEY() As Byte = "cccccccccc:APA91bH-y-L-I6jIyfxWvbM4cccccccccccBz-j-Vm1TIpAXmp1dE4p0WYQb2Z0Iq3JqXk-6Ek60RV3vucENceCrVo4VJwIVmHrq1Ktb2P9zCPxnDhT_DjDfV9o__wA51nhR4-uyxiLhcwg"
   Private wifi As ESP8266WiFi
End Sub

Private Sub AppStart
   If wifi.Connect2("TP-LINK_D577", "xxxxxxxxx") Then
       Log("Connected to router.")
       Log("Failed to connect to router.")
   End If
   'send the android message
   SendMessage("general", "This is the title", "This is the body")
End Sub

Sub JobDone (jr As JobResult)
   Log("JobDone: ", jr.JobName)
   Log("Success: ", jr.Success)
   If jr.JobName = "ios_general" Then
     'send the ios message
     SendMessage("ios_general", "This is the title", "This is the body")
   End If
End Sub

Private Sub SendMessage(Topic() As Byte, Title() As Byte, Body() As Byte)
   Dim bc As ByteConverter
   Dim buffer(300) As Byte 'must be large enough to hold the message payload
   Dim raf As RandomAccessFile
   raf.Initialize(buffer, True)
   WriteBytes(raf, "{""data"":{""title"":""")
   WriteBytes(raf, Title)
   WriteBytes(raf, """,""body"":""")
   WriteBytes(raf, Body)
   WriteBytes(raf, """}")
   'end of data
   WriteBytes(raf, ",""to"":""\/topics\/")
   WriteBytes(raf, Topic)
   WriteBytes(raf, """")
   WriteBytes(raf, ",""priority"": 10")
   If bc.StartsWith(Topic, "ios_") Then
     WriteBytes(raf, ",""notification"": {""title"": """)
     WriteBytes(raf, Title)
     WriteBytes(raf, """,""body"":""")
     WriteBytes(raf, Body)
     WriteBytes(raf, """, ""sound"": ""default""}")
   End If
   WriteBytes(raf, "}")
   HttpJob.AddHeader("Authorization", JoinBytes(Array("key=".GetBytes, API_KEY)))
   HttpJob.AddHeader("Content-Type", "application/json")
   Log("stack: ", StackBufferUsage, ", buffer size:", raf.CurrentPosition)
   HttpJob.Post("https://fcm.googleapis.com/fcm/send", bc.SubString2(buffer, 0, raf.CurrentPosition))
End Sub

Private Sub WriteBytes(raf As RandomAccessFile, Data() As Byte)
   raf.WriteBytes(Data, 0, Data.Length, raf.CurrentPosition)
End Sub

Depends on rHttpUtils2 module (add it with Project - Add existing module): https://www.b4x.com/android/forum/threads/module-rhttputils2-http-client.74785/#content
Also depends on: rESP8266WiFi and rRandomAccessFile.
It should be simple to convert it to use rEthernet instead of rESP8266WiFi.
Last edited:


Licensed User
Longtime User
The part for wifi connection is missing from the code above in appstart :
If wifi.Connect("link") Then
        Log("Connected to router")
        Log("Failed to connect")
    End If


Active Member
Licensed User
Longtime User
Dear friends,
How do we use FCM with a GSM/GPRS module like SIM800?