DeviceUuid - a stable MAC-derived device UUID

Layer: L7 Application · Build flags: PC_ENABLE_DEVICE_ID

What this example teaches

A fleet of identical firmware images needs a stable per-device identity. pc_device_uuid() derives a deterministic RFC 4122 v5 UUID from the chip's factory MAC: the same value on every boot, with no storage to wear out or provision. Use it for mDNS hostnames, MQTT client IDs, telemetry tags, and the like.

Compute once, reuse everywhere:

static char g_uuid[PC_UUID_STR_LEN];
pc_device_uuid(g_uuid);          // stable per-chip UUID string

PC_UUID_STR_LEN sizes the caller-owned buffer (no heap). Because it is derived (hashed from the MAC, not random) it is reproducible and needs no NVS. GET /id returns it as JSON.

Build and run

pio ci --board=esp32dev --project-option="framework=arduino" \
  --project-option="build_flags=-DPC_ENABLE_DEVICE_ID=1" \
  --lib="." examples/L7-Application/DeviceUuid/DeviceUuid.ino

curl http://<ip>/id   # {"uuid":"...."} - identical across reboots

Annotated source

The complete sketch (DeviceUuid.ino), reproduced verbatim with added explanatory comments:

// Copyright (C) 2026 Douglas Quigg (dstroy0) <dquigg123@gmail.com>
// SPDX-License-Identifier: AGPL-3.0-or-later
 
#define PC_ENABLE_DEVICE_ID 1
 
#include "protocore.h"
#include "network_drivers/physical/physical.h"
#include "services/system/device_id/device_id.h"
 
static const char *SSID = "YOUR_SSID";
static const char *PASSWORD = "YOUR_PASSWORD";
 
PC server;
static char g_uuid[PC_UUID_STR_LEN]; // caller-owned (no heap)
 
void setup()
{
    Serial.begin(115200);
    init_wifi_physical(SSID, PASSWORD);
    Serial.print("Connecting to WiFi");
    while (!wifi_ready())
    {
        delay(250);
        Serial.print('.');
    }
    uint32_t ip = pc_net_egress_ip(); // library egress IP (network byte order), no Arduino WiFi
    Serial.printf("IP: %u.%u.%u.%u\n", (unsigned)(ip & 0xFF), (unsigned)((ip >> 8) & 0xFF),
                  (unsigned)((ip >> 16) & 0xFF), (unsigned)((ip >> 24) & 0xFF));
 
    pc_device_uuid(g_uuid); // stable per-chip UUID (v5, derived from the MAC)
    Serial.printf("device UUID: %s\n", g_uuid);
 
    server.on("/id", HttpMethod::HTTP_GET, [](uint8_t id, HttpReq *) {
        char body[64];
        snprintf(body, sizeof(body), "{\"uuid\":\"%s\"}", g_uuid);
        server.send(id, 200, "application/json", body);
    });
    server.begin(80);
}
 
void loop()
{
    server.handle();
}