WebSockets
After mastering Server-Sent Events for one-way communication, Batman realized he needed something more powerful. When Commissioner Gordon wanted to chat with him in real-time during crisis situations, Batman needed bidirectional communication.
"SSE is great for pushing updates to my dashboard," Batman thought, "but I need two-way communication for coordinating with my allies!"
To handle real-time bidirectional communication, Batman learned how to work with WebSockets. He created a WebSocket class and wrapped it around his Robyn app:
Request
from robyn import Robyn, jsonify, WebSocket
app = Robyn(__file__)
websocket = WebSocket(app, "/web_socket")
@websocket.on("message")
def connect():
return "Hello world, from ws"
@websocket.on("close")
def close():
return "Goodbye world, from ws"
@websocket.on("connect")
def message():
return "Connected to ws"
Optional Return Values
Batman discovered that WebSocket handlers don't always need to return a value. Sometimes, he just wanted to process a message or perform an action without sending a response back to the client.
"Not every message needs a reply," Batman realized. "Sometimes I just need to log data or trigger an action."
WebSocket handlers (connect, message, and close) can optionally return a string. If no value is returned (or None is returned), no message will be sent to the client.
Optional Returns
from robyn import Robyn, WebSocket
app = Robyn(__file__)
websocket = WebSocket(app, "/web_socket")
@websocket.on("connect")
async def connect():
# No return needed - just log the connection
print("Client connected")
@websocket.on("message")
def message(ws, msg):
# Process message without responding
process_analytics(msg)
# No return statement needed
@websocket.on("close")
async def close():
# Explicitly return None - no message sent
cleanup_resources()
return None
For sending a message to the client, Batman used the sync_send_to method.
Request
@websocket.on("message")
def message(ws, msg, global_dependencies) -> str:
websocket_id = ws.id
ws.sync_send_to(websocket_id, "This is a message to self")
return ""
For sending a message to the client in async manner, Batman used the async_send_to method.
Request
@websocket.on("message")
async def message(ws, msg, global_dependencies) -> str:
websocket_id = ws.id
await ws.async_send_to(websocket_id, "This is a message to self")
return ""
For sending broadcast messages, Batman used the sync_broadcast method.
Request
@websocket.on("message")
def message(ws, msg, global_dependencies) -> str:
websocket_id = ws.id
ws.sync_broadcast("This is a message to self")
return ""
For sending broadcast messages in async style, Batman used the async_broadcast method.
Request
@websocket.on("message")
async def message(ws, msg, global_dependencies) -> str:
websocket_id = ws.id
await ws.async_broadcast("This is a message to self")
return ""
Robyn also showed Batman to work with query params.
Request
@websocket.on("message")
async def message(ws, msg, global_dependencies) -> str:
websocket_id = ws.id
if (ws.query_params.get("name") == "gordon" and ws.query_params.get("desg") == "commissioner"):
ws.sync_broadcast("Gordon authorized to login!")
return ""
To programmatically close a WebSocket connection from the server side, Batman learned to use the close() method:
The close() method does the following:
- Sends a close message to the client.
- Removes the client from the WebSocket registry.
- Closes the WebSocket connection.
This method is useful for scenarios where you need to programmatically end a WebSocket connection based on certain conditions or events on the server side.
Request
@websocket.on("message")
def message(ws, msg):
if msg == "disconnect":
ws.close()
return "Closing connection"
return "Message received"
What's next?
As the codebase grew, Batman wanted to onboard the justice league to help him manage the application.
Robyn told him about the different ways he could scale his application, and how to use views and subrouters to make his code more readable.