fetch time from ntp server

src/main.cpp

@@ -6,6 +6,7 @@
 #include "update.h"
 #include "bme280.h"
 #include "config.h"
+#include "time.h"
 
 #ifndef SERIAL_BAUD
 #define SERIAL_BAUD 74880
@@ -71,6 +72,7 @@ void setup()
     //
     bme280_init();
 
+    uweather_time_init();
     uweather_update_init();
 
 }
@@ -79,5 +81,6 @@ void loop()
 {
     uweather_web_handle();
     uweather_update_handle();
+    uweather_time_handle();
     delay(10);
 }

src/time.cpp

@@ -0,0 +1,118 @@
+#include <time.h>
+#include <Arduino.h>
+#include <WiFiUdp.h>
+#include <ESP8266WiFi.h>
+#include "config.h"
+
+#define LOCAL_NTP_PORT 2390
+#define NTP_RETRY_INTERVAL 300000
+#define DEFAULT_NTP_HOST "time.nist.gov"
+#define NTP_PACKET_SIZE 48
+
+enum state { INIT, SENT, IDLE, NO_HOST} ntp_state;
+byte packet_buffer[NTP_PACKET_SIZE]; // NTP timestamp is in the first 48 bytes
+WiFiUDP udp;
+unsigned long time_offset = 0;
+unsigned long ntp_timestamp = 0;
+unsigned long retry_at = 0;
+IPAddress host;
+
+const char* ntp_get_hostname()
+{
+    const char* host_in_cfg = (const char*) Config._data.ntp_host;
+    if (host_in_cfg[0] == '\0') {
+        return DEFAULT_NTP_HOST;
+    }
+    return host_in_cfg;
+}
+
+void uweather_time_init()
+{
+    ntp_state = state::INIT;
+    time_offset = 0;
+    ntp_timestamp = 0;
+    retry_at = 0;
+    udp.begin(LOCAL_NTP_PORT);
+}
+
+void uweather_time_handle()
+{
+    switch (ntp_state) {
+        case state::INIT: 
+        {
+            if (!WiFi.isConnected())
+                return;
+
+            // resolve ntp hostname
+            const char* hostname = ntp_get_hostname();
+            if (!WiFi.hostByName(hostname, host)) {
+                ntp_state = state::NO_HOST;
+                Serial.printf("Unable to resolve ntp host: %s\n", hostname);
+                retry_at = millis() + NTP_RETRY_INTERVAL;
+                break;
+            }
+
+            // send packet to ntp server
+            Serial.printf("Sending ntp packet to %s\n", hostname);
+            memset(packet_buffer, 0, NTP_PACKET_SIZE);
+            packet_buffer[0] = 0b11100011; // LI, Version, Mode
+            packet_buffer[1] = 0;
+            packet_buffer[2] = 6;
+            packet_buffer[3] = 0xEC;
+            packet_buffer[12] = 49;
+            packet_buffer[13] = 0x4E;
+            packet_buffer[14] = 49;
+            packet_buffer[15] = 52;
+            udp.beginPacket(host, 123);
+            udp.write(packet_buffer, NTP_PACKET_SIZE);
+            udp.endPacket();
+            ntp_state = state::SENT;
+        }
+
+        case state::SENT:
+        {
+            int cb = udp.parsePacket();
+            if (!cb) break;
+            udp.read(packet_buffer, NTP_PACKET_SIZE);
+            unsigned long high = word(packet_buffer[40], packet_buffer[41]);
+            unsigned long low = word(packet_buffer[42], packet_buffer[43]);
+            unsigned long secs = (high << 16 | low) - 2208988800UL; // subtract 70 years from time
+            time_offset = millis();
+            ntp_timestamp = secs;
+            ntp_state = state::IDLE;
+            Serial.printf("Received NTP response, current timestamp is %lu\n", secs);
+        }
+        case state::IDLE:
+            break;
+
+        case state::NO_HOST:
+            if (millis() > retry_at) {
+                state::INIT;
+            }
+            break;
+        default:
+            break;
+    }
+}
+
+bool has_timestamp()
+{
+    return ntp_timestamp > 0;
+}
+
+void set_timestamp(unsigned long ts)
+{
+    time_offset = millis() / 1000;
+    ntp_timestamp = ts;
+}
+
+unsigned long timestamp(unsigned long milliseconds)
+{
+    if (!has_timestamp()) return 0;
+    return (milliseconds / 1000) - time_offset + ntp_timestamp;
+}
+
+unsigned long current_timestamp()
+{
+    return timestamp(millis());
+}

src/time.h

@@ -0,0 +1,10 @@
+#ifndef _UWEATHER_NTP_H_
+#define _UWEATHER_NTP_H_
+
+void uweather_time_init();
+void uweather_time_handle();
+
+unsigned long timestamp(unsigned long);
+unsigned long current_timestamp();
+
+#endif /** End _UWEATHER_NTP_H_ include guard */

src/web.cpp

@@ -6,6 +6,7 @@
 #include <QueryString.h>
 #include "config.h"
 #include "version.h"
+#include "time.h"
 
 /**
  * How long to wait after the OK to shutdown before no longer
@@ -80,13 +81,19 @@ void handle_firmware(HttpRequest& req, HttpResponse& res)
 
 void handle_weather_current(HttpRequest& req, HttpResponse& res)
 {
-  char buff[3][10] = {};
+  char buff[4][10] = {};
+  unsigned long now = current_timestamp();
   dtostrf(BME.readTemperature(), 2, 1, buff[0]);
   dtostrf(BME.readPressure(), 2, 1, buff[1]);
   dtostrf(BME.readHumidity(), 2, 1, buff[2]);
+  if (now) {
+    sprintf(buff[3], "%d", now);
+  } else {
+    strcpy(buff[3], "null");
+  }
   Serial.printf("temp= %s, pres= %s, hum=%s\r\n", buff[0], buff[1], buff[2]);
   res.headers.set("Content-Type", "application/json");
-  content.printf("{\"time\": null, \"temperature\": %s, \"pressure\": %s, \"humidity\": %s}", buff[0], buff[1], buff[2]);
+  content.printf("{\"time\": %s, \"temperature\": %s, \"pressure\": %s, \"humidity\": %s}", buff[3], buff[0], buff[1], buff[2]);
 }
 
 // Handle WiFi Scan