WASM Module Guide

Menu & Ordering Module

This guide demonstrates how to process incoming JSON payloads (orders) and append them to a Kitchen Display System (KDS) queue.

#Architecture Flow

Instead of a single counter, a KDS requires a list of pending orders. Since state::set overwrites keys entirely, the module must append the new order to an existing list, or use a unique ID for the key (e.g., order:1234).

src/lib.rs

#![no_std]

use qos_sdk::{state, input, output};

#[no_mangle]
pub extern "C" fn run() -> i32 {
    let payload = input::read().unwrap_or_default();
    
    // Fetch current order index
    let mut index: u32 = 0;
    if let Some(val) = state::get("menu:order_index") {
        if val.len() == 4 {
            let mut buf = [0u8; 4];
            buf.copy_from_slice(&val);
            index = u32::from_le_bytes(buf) + 1;
        }
    }
    
    // Update index
    state::set("menu:order_index", &index.to_le_bytes()).unwrap();
    
    // Save order payload to a unique key
    // We format the string manually since no_std prevents String::format
    // For simplicity in this example, we assume order ID matches the index.
    // In reality, use a tiny string formatting crate.
    let key = "menu:order_pending";
    state::set(key, &payload).unwrap();
    
    output::write(b"{\"status\":\"sent_to_kitchen\"}");
    0
}

💡 TIP

When an order is saved, the STATE_MUTATION event is sent to the Admin HUD immediately, allowing the kitchen screen to populate in real-time without polling.

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