Add sntp-time-sync example

examples/sntp-time-sync/Makefile

@@ -0,0 +1,10 @@
+PROG ?= example
+
+all: $(PROG)
+	$(RUN) ./$(PROG) $(ARGS)
+
+$(PROG): main.c
+	$(CC) ../../mongoose.c -I../.. -W -Wall -DMG_ENABLE_LINES=1 $(CFLAGS) -o $(PROG) main.c
+
+clean:
+	rm -rf $(PROG) *.o *.dSYM *.gcov *.gcno *.gcda *.obj *.exe *.ilk *.pdb

examples/sntp-time-sync/main.c

@@ -0,0 +1,52 @@
+// Copyright (c) 2022 Cesanta Software Limited
+// All rights reserved
+//
+// Synchronize time with remote SNTP server
+// A working time() call is required by TLS, so an embedded device without
+// a clock that wants to use TLS, must sync time via SNTP.
+
+#include "mongoose.h"
+
+// The UNIX epoch of the boot time. Initially, we set it to 0.  But then after
+// SNTP response, we update it to the correct value, which will allow us to
+// use time(). Uptime in milliseconds is returned by mg_millis().
+static time_t s_boot_timestamp = 0;
+
+// SNTP client connection
+static struct mg_connection *s_sntp_conn = NULL;
+
+// On embedded systems, rename to time()
+time_t my_time(time_t *tp) {
+  time_t t = s_boot_timestamp + mg_millis() / 1000;
+  if (tp != NULL) *tp = t;
+  return t;
+}
+
+// SNTP client callback
+static void sfn(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
+  if (ev == MG_EV_SNTP_TIME) {
+    int64_t t = *(int64_t *) ev_data;
+    MG_INFO(("Got SNTP time: %lld ms from epoch", t));
+    s_boot_timestamp = (time_t) ((t - mg_millis()) / 1000);
+  } else if (ev == MG_EV_CLOSE) {
+    s_sntp_conn = NULL;
+  }
+  (void) fn_data, (void) c;
+}
+
+// Called every 5 seconds. Increase that for production case.
+static void timer_fn(void *arg) {
+  struct mg_mgr *mgr = (struct mg_mgr *) arg;
+  if (s_sntp_conn == NULL) s_sntp_conn = mg_sntp_connect(mgr, NULL, sfn, NULL);
+  if (s_sntp_conn != NULL) mg_sntp_request(s_sntp_conn);
+}
+
+int main(void) {
+  struct mg_mgr mgr;  // Event manager
+  mg_mgr_init(&mgr);  // Initialise event manager
+  mg_log_set("3");    // Set debug log level
+  mg_timer_add(&mgr, 5000, MG_TIMER_REPEAT | MG_TIMER_RUN_NOW, timer_fn, &mgr);
+  for (;;) mg_mgr_poll(&mgr, 300);  // Infinite event loop
+  mg_mgr_free(&mgr);                // Free manager resources
+  return 0;
+}

mongoose.c

@@ -342,7 +342,7 @@ static void mg_sendnsreq(struct mg_connection *c, struct mg_str *name, int ms,
     dnsc->c = mg_connect(c->mgr, dnsc->url, NULL, NULL);
     if (dnsc->c != NULL) {
       dnsc->c->pfn = dns_cb;
-      dnsc->c->is_hexdumping = 1;
+      // dnsc->c->is_hexdumping = 1;
     }
   }
   if (dnsc->c == NULL) {

src/dns.c

@@ -230,7 +230,7 @@ static void mg_sendnsreq(struct mg_connection *c, struct mg_str *name, int ms,
     dnsc->c = mg_connect(c->mgr, dnsc->url, NULL, NULL);
     if (dnsc->c != NULL) {
       dnsc->c->pfn = dns_cb;
-      dnsc->c->is_hexdumping = 1;
+      // dnsc->c->is_hexdumping = 1;
     }
   }
   if (dnsc->c == NULL) {