time: import IANA timezone definitions, expose SNTP API

cores/esp8266/Arduino.h

@@ -275,10 +275,13 @@ long secureRandom(long);
 long secureRandom(long, long);
 long map(long, long, long, long, long);
 
-extern "C" void configTime(long timezone, int daylightOffset_sec,
-    const char* server1, const char* server2 = nullptr, const char* server3 = nullptr);
+void configTime(int timezone, int daylightOffset_sec, const char* server1,
+    const char* server2 = nullptr, const char* server3 = nullptr);
 
-#endif
+void configTime(const char* tz, const char* server1,
+    const char* server2 = nullptr, const char* server3 = nullptr);
+
+#endif // __cplusplus
 
 #include "pins_arduino.h"
 

cores/esp8266/time.cpp

@@ -16,6 +16,7 @@
  *
  */
 
+#include <stdlib.h>
 #include <time.h>
 #include <sys/time.h>
 #include <sys/reent.h>
@@ -55,25 +56,12 @@ static void setServer(int id, const char* name_or_ip)
 {
     if (name_or_ip)
     {
-        //TODO: check whether server is given by name or IP
+        // per current configuration,
+        // lwIP can receive an IP address or a fqdn
         sntp_setservername(id, (char*) name_or_ip);
     }
 }
 
-
-void configTime(int timezone_sec, int daylightOffset_sec, const char* server1, const char* server2, const char* server3)
-{
-    sntp_stop();
-
-    setServer(0, server1);
-    setServer(1, server2);
-    setServer(2, server3);
-
-    sntp_set_timezone_in_seconds(timezone_sec);
-    sntp_set_daylight(daylightOffset_sec);
-    sntp_init();
-}
-
 int clock_gettime(clockid_t unused, struct timespec *tp)
 {
     (void) unused;
@@ -108,4 +96,33 @@ int _gettimeofday_r(struct _reent* unused, struct timeval *tp, void *tzp)
     return 0;
 }
 
-};
+}; // extern "C"
+
+void configTime(int timezone_sec, int daylightOffset_sec, const char* server1, const char* server2, const char* server3)
+{
+    sntp_stop();
+
+    setServer(0, server1);
+    setServer(1, server2);
+    setServer(2, server3);
+
+    sntp_set_timezone_in_seconds(timezone_sec);
+    sntp_set_daylight(daylightOffset_sec);
+    sntp_init();
+}
+
+void configTime(const char* tz, const char* server1, const char* server2, const char* server3)
+{
+    sntp_stop();
+
+    setServer(0, server1);
+    setServer(1, server2);
+    setServer(2, server3);
+
+    char tzram[strlen_P(tz) + 1];
+    memcpy_P(tzram, tz, sizeof(tzram));
+    setenv("TZ", tzram, 1/*overwrite*/);
+    tzset();
+
+    sntp_init();
+}