IPC Broker

VyomaOS apps don’t communicate directly. All messages flow through the supervisor’s IPC broker, which intercepts stdout writes and routes them to the appropriate target.

Message Format

@<target>: <message>

Apps write this to stdout. The supervisor strips the @sender: prefix before delivering to the target app’s stdin.

Routing Modes

Unicast

Send a message to a specific app by name:

println!("@calculator: compute 2+2");

The target app receives compute 2+2 on stdin.

Broadcast

Send a message to all running apps:

println!("@broadcast: system shutting down");

Every running app receives system shutting down on stdin.

Reply

Reply to the last app that sent you a message:

println!("@reply: acknowledged");

The supervisor tracks the last sender per-app and routes the reply back.

Supervisor Commands

Send commands to the supervisor itself:

println!("@supervisor: list");
println!("@supervisor: ping");
println!("@supervisor: uptime");
println!("@supervisor: version");
println!("@supervisor: apps");
println!("@supervisor: focus shell");
println!("@supervisor: loglevel debug");
println!("@supervisor: kill old-app");

Supervisor Command Reference

Command	Response	Description
list	App name list	List all running apps
apps	App name list	Alias for list
ping	pong <timestamp>	Health check
uptime	Duration string	System uptime since boot
version	Version string	VyomaOS version
focus <name>	(none)	Switch keyboard focus to named app
loglevel <level>	(none)	Set per-app log level filter
kill <name>	(none)	Terminate the named app

Receiving Messages

Apps receive IPC messages on stdin, one line at a time:

use std::io::BufRead;

fn main() {
    let stdin = std::io::stdin();
    for line in stdin.lock().lines() {
        if let Ok(msg) = line {
            let msg = msg.trim();
            if msg.starts_with("VYOMA_INPUT:key:") {
                // Keyboard input
                let key = &msg[16..];
                handle_key(key);
            } else {
                // IPC message from another app
                handle_ipc(msg);
            }
        }
    }
}

Design Decisions

Why supervisor-mediated IPC?

• Security: The supervisor can log, audit, and rate-limit messages
• Simplicity: No shared memory, no sockets between apps, no complex synchronization
• Debuggability: All messages are visible in supervisor logs
• Capability enforcement: Only apps with stdio = true can participate in IPC

Why stdout/stdin?

• WASI Preview 2 guarantees stdin/stdout availability
• No custom host functions or WASI extensions needed
• Any language that can print a string can do IPC
• Easy to test apps outside VyomaOS (just pipe text)

Limitations

• Messages are single-line only (no embedded newlines)
• The target app must be running for delivery
• No message persistence or queuing — if the target is dead, the message is dropped
• No request/response correlation — apps must implement their own sequencing