B4A Library WebSocket Client Library

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This library allows you to create WebSocket connections with servers that support WebSockets.
It is based on this open source project: http://autobahn.ws/android/#

The main benefit of this library is that you can use it to communicate with B4J WebApp solutions.

The attached example includes a class named WebSocketHandler. With this class you can send events to the server and the server can send events to the device.


The server code is very simple:
Sub Class_Globals
   Private ws As WebSocket
   Private timer1 As Timer
End Sub

Public Sub Initialize

End Sub

Private Sub WebSocket_Connected (WebSocket1 As WebSocket)
   ws = WebSocket1
   timer1.Initialize("timer1", 1000)
   timer1.Enabled = True
End Sub

Sub Timer1_Tick
'This method will raise the event on the device
   ws.RunFunction("ServerTime", Array As Object(DateTime.Time(DateTime.Now)))
End Sub

'event from the device
Sub Device_Message(Params As Map)
   Log("Device message: " & Params.Get("message"))
End Sub

Private Sub WebSocket_Disconnected
   timer1.Enabled = False
End Sub

Sending events to the server

WebSocketHandler.SendEventToServer takes the event name (not prefix in this case) and the data. The data is a Map that is converted to a JSON string. Note that the event name must include an underscore.

Sub btnSend_Click
   Dim data As Map
   data.Put("message", EditText1.Text)
   wsh.SendEventToServer("Device_Message", data)
End Sub

Receiving events from the server

Sub wsh_ServerTime(Params As List)
   'example of a server push message
   lblServerTime.Text = "Server Time: " & Params.Get(0)
End Sub

The sub name in this case is made of the prefix set in the Initialize method and the event name as received from the server. There should be a single parameter which is a List.

How to run this example?

You need the latest version of B4J: http://www.basic4ppc.com/android/b4j.html
Download and run the server example.
You will need to open the firewall port (51042).

Set the address in the client code to match the server address.


v2.11: New Headers Map that can be used to add headers to the upgrade request (https://www.b4x.com/android/forum/threads/websocketclient-authorization.116574/#post-729213)
v2.10: New BinaryMessage event and SendBinary method.
v2.01: Fixes an issue with ssl disconnections that can throw the network on main thread exception.

v2.00: Based on the latest version of autobahn-java: https://github.com/crossbario/autobahn-java
Adds support for SSL connections (wss://) including using custom trust managers (mainly to accept self signed certificates).
SSL support is problematic on devices prior to Android 5. To support Android 4+ devices you need to update the security provider: https://www.b4x.com/android/forum/threads/ssl-websocket-client.88472/page-2#post-560044


  • ServerExample.zip
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  • ClientExample.zip
    8.3 KB · Views: 2,761
  • WebSocket.zip
    39.6 KB · Views: 796
Last edited:


Active Member
Licensed User
v2.10: New BinaryMessage event and SendBinary method.

Is there a possibility of getting some code samples of using these methods and events?
The samples in Post #1 are dated 2014



Staff member
Licensed User
1. Binary messages are not relevant when communicating with B4J servers. Most WebSocket servers send and receive text messages so it is not a commonly used feature. It was requested by one of the forum members so I've added it.
2. The usage is very simple:

Sub WebSocket1_BinaryMessage (Data() As Byte)
 Log("Binary message received.")
 'work with Data.
End Sub


Active Member
Licensed User
Binary messages are not relevant when communicating with B4J servers.

Okay, I see.
And thinking more about it, I don't really see a need for it in my situation.



Licensed User
I'm trying to use the latest version 2.1 of WebSocket library but compilation keeps failing with this error message:

B4A Version: 9.00
Parsing code. (0.02s)
Building folders structure. (0.03s)
Compiling code. (0.07s)
Compiling layouts code. (0.00s)
Organizing libraries. (0.00s)
Generating R file. (0.17s)
Compiling generated Java code. Error
B4A line: 81
javac 1.8.0_211
src\mydomain\torrentsmanager\torrentsmanager.java:204: error: cannot find symbol
symbol: method SendBinary(byte[])
location: variable _websocketconnection1 of type WebSocketWrapper

The offending code is:

Sub DownloadQueue1_Ready
   Dim NextIncompleteTorrent As TorrentMeta=DownloadQueue1.GetNextIncompleteTorrent
   If NextIncompleteTorrent.IsInitialized Then
       Dim NotifyCompletePacket() As Byte=Array As Byte(Starter.COMMAND_NOTIFY_COMPLETE)
   End If

End Sub

I've cleaned the project and restarted the b4a IDE but still compilation fails.
The b4a IDE shows i have version 2.1, and if i open the WebSocket.jar file in Java Decompiler i see the SendBinary(Data() As Byte) method exists in the wrapper.

What am i doing wrong?
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