Add NTP waitSet callback (#705)

Allows printing "."s or flashing an LED while NTP is waiting for sync.

docs/wifintp.rst

@@ -51,6 +51,24 @@ it is not already running.  Using this method, the above code becomes:
     void setClock() {
       NTP.begin("pool.ntp.org", "time.nist.gov");
       NTP.waitSet();
+      time_t now = time(nullptr);
+      struct tm timeinfo;
+      gmtime_r(&now, &timeinfo);
+      Serial.print("Current time: ");
+      Serial.print(asctime(&timeinfo));
+    }
+
+bool NTP.waitSet(void (\*cb)(), uint32_t timeout)
+-------------------------------------------------
+Allows for a callback that will be called every 1/10th of a second while waiting for
+NTP sync.  For example, using lambdas you can simply print "."s:"
+
+.. code :: cpp
+
+    void setClock() {
+      NTP.begin("pool.ntp.org", "time.nist.gov");
+      NTP.waitSet([]() { Serial.print("."); });
+      time_t now = time(nullptr);
       struct tm timeinfo;
       gmtime_r(&now, &timeinfo);
       Serial.print("Current time: ");

libraries/WiFi/examples/BearSSL_CertStore/BearSSL_CertStore.ino

@@ -57,13 +57,12 @@ void setClock() {
   NTP.begin("pool.ntp.org", "time.nist.gov");
 
   Serial.print("Waiting for NTP time sync: ");
-  time_t now = time(nullptr);
-  while (now < 8 * 3600 * 2) {
-    delay(500);
+  NTP.waitSet([]() {
     Serial.print(".");
-    now = time(nullptr);
-  }
+  });
   Serial.println("");
+
+  time_t now = time(nullptr);
   struct tm timeinfo;
   gmtime_r(&now, &timeinfo);
   Serial.print("Current time: ");

libraries/WiFi/examples/BearSSL_ServerClientCert/BearSSL_ServerClientCert.ino

@@ -164,13 +164,10 @@ void setClock() {
   NTP.begin("pool.ntp.org", "time.nist.gov");
 
   Serial.print("Waiting for NTP time sync: ");
-  time_t now = time(nullptr);
-  while (now < 8 * 3600 * 2) {
-    delay(500);
-    Serial.print(".");
-    now = time(nullptr);
-  }
+  NTP.waitSet([]() { Serial.print("."); } );
   Serial.println("");
+
+  time_t now = time(nullptr);
   struct tm timeinfo;
   gmtime_r(&now, &timeinfo);
   Serial.print("Current time: ");

libraries/WiFi/examples/BearSSL_Sessions/BearSSL_Sessions.ino

@@ -45,13 +45,12 @@ void setup() {
   NTP.begin("pool.ntp.org", "time.nist.gov");
 
   Serial.print("Waiting for NTP time sync: ");
-  time_t now = time(nullptr);
-  while (now < 8 * 3600 * 2) {
-    delay(500);
+  NTP.waitSet([]() {
     Serial.print(".");
-    now = time(nullptr);
-  }
+  });
   Serial.println("");
+
+  time_t now = time(nullptr);
   struct tm timeinfo;
   gmtime_r(&now, &timeinfo);
   Serial.print("Current time: ");

libraries/WiFi/examples/BearSSL_Validation/BearSSL_Validation.ino

@@ -22,16 +22,14 @@ const char *path = "/";
 
 // Set time via NTP, as required for x.509 validation
 void setClock() {
-  configTime(3 * 3600, 0, "pool.ntp.org", "time.nist.gov");
+  NTP.begin("pool.ntp.org", "time.nist.gov");
 
   Serial.print("Waiting for NTP time sync: ");
-  time_t now = time(nullptr);
-  while (now < 8 * 3600 * 2) {
-    delay(500);
+  NTP.waitSet([]() {
     Serial.print(".");
-    now = time(nullptr);
-  }
+  });
   Serial.println("");
+  time_t now = time(nullptr);
   struct tm timeinfo;
   gmtime_r(&now, &timeinfo);
   Serial.print("Current time: ");

libraries/WiFi/src/WiFiNTP.h

@@ -77,12 +77,19 @@ public:
     }
 
     bool waitSet(uint32_t timeout = 10000) {
+        return waitSet(nullptr, timeout);
+    }
+
+    bool waitSet(void (*cb)(), uint32_t timeout = 10000) {
         if (!running()) {
             begin("pool.ntp.org");
         }
         uint32_t start = millis();
         while ((time(nullptr) < 10000000) && (millis() - start < timeout)) {
-            delay(10);
+            delay(100);
+            if (cb) {
+                cb();
+            }
         }
         return time(nullptr) < 10000000;
     }