websocket-bidirectional — full-duplex WebSocket with PAGI::Context

Send and receive at the same time. After accepting, the handler runs two concurrent branches on one connection:

• incoming — echo each client message back, uppercased.
• outgoing — push an unsolicited server tick every second.

You see the server's ticks interleaved with echoes of whatever you type — both directions live at once.

This is the same demo as the raw-protocol examples/18-bidirectional-websocket in the PAGI distribution, rewritten with PAGI::Context to show how much it folds away.

What PAGI::Context gives you here

One object ($ctx) wraps $scope/$receive/$send and hands you exactly the pieces a bidirectional handler needs:

| PAGI::Context | does | |---|---| | $ctx->each_text(sub {...}) | the receive-loop, returned as a Future that completes when the client disconnects — no manual websocket.connect/receive/disconnect handling | | $ctx->send_text_if_connected(...) | a send that becomes a no-op once the socket is closing, so the concurrent send-loop never races the teardown (no eval, no guards) | | $ctx->is_connected | a clean loop guard | | $ctx->accept | the handshake |

Compare with the raw version, which spells out the websocket.connect → websocket.accept handshake, the websocket.receive/websocket.disconnect dispatch, and its own helper to race without cancelling $receive.

The two branches are joined with Future->wait_any: a client disconnect ends incoming, and wait_any then cancels the idle outgoing tick-loop. (That cancel is the right call here because the losers are our own branches — unlike a receive-multiplex, where the raced future is the live $receive that must not be cancelled.)

Run

pagi-server --app examples/websocket-bidirectional/app.pl --port 5000

From an uninstalled checkout, add the dist libs:

perl -I /path/to/PAGI-Server/lib -I /path/to/PAGI-Tools/lib \
  /path/to/PAGI-Server/bin/pagi-server \
  --app examples/websocket-bidirectional/app.pl --port 5000

Test

Use a WebSocket-aware client — not curl or socat, which can't do the WebSocket Upgrade handshake or frame masking. With websocat:

websocat ws://localhost:5000/
# server tick #1          <- arrives on its own every second
hello                     <- you type this
you said: HELLO           <- echoed back, uppercased
# server tick #2

...or a browser console, nothing to install:

let ws = new WebSocket('ws://localhost:5000/');
ws.onmessage = e => console.log(e.data);
ws.onopen    = () => ws.send('hello');

The tick lines keep arriving whether or not you type — that's the outgoing branch running concurrently with the incoming one.