SNTP - wall-clock time via SNTP

Layer: L7 Application · Build flags: PC_ENABLE_NTP

What this example teaches

An ESP32 boots with no idea what time it is. pc_ntp_begin(tz) starts the ESP-IDF SNTP client (the first sync lands a few seconds later), and pc_ntp_http_date() formats the current time as an RFC 7231 date string - the same format HTTP Date/Last-Modified headers use. GET /time returns it, or 503 until the first sync completes.

Start the client, then format on demand.

pc_ntp_begin("UTC0"); // POSIX TZ string; set your zone for local time

char date[40];
if (pc_ntp_http_date(date, sizeof(date)) == 0) {  // 0 = not synced yet
    server.send(slot_id, 503, "text/plain", "Time not synced yet");
    return;
}
server.send(slot_id, 200, "text/plain", date);

pc_ntp_http_date() returns 0 until the clock is set, so the handler can distinguish "no time yet" from a real value and answer 503 in the meantime. The TZ argument is a POSIX TZ string ("UTC0", "EST5EDT", "CET-1CEST", ...) so the formatted time can be local.

Build and run

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

curl http://<ip>/time   # 503 for the first few seconds, then an RFC 7231 date

Annotated source

The complete sketch (SNTP.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_NTP 1
 
#include "protocore.h"
#include "network_drivers/physical/physical.h"
#include "services/ntp_service.h"
 
static const char *SSID = "YOUR_SSID";
static const char *PASSWORD = "YOUR_PASSWORD";
 
PC server;
 
void handle_time(uint8_t slot_id, HttpReq *req)
{
    (void)req;
    char date[40];
    if (pc_ntp_http_date(date, sizeof(date)) == 0) // 0 -> clock not set yet
    {
        server.send(slot_id, 503, "text/plain", "Time not synced yet");
        return;
    }
    server.send(slot_id, 200, "text/plain", date);
}
 
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));
 
    server.on("/time", HttpMethod::HTTP_GET, handle_time);
    server.begin(80);
 
    pc_ntp_begin("UTC0"); // POSIX TZ string; set your zone for local time
}
 
void loop()
{
    server.handle();
}