Add support to Print::printf for printing from flash

cores/esp8266/Print.cpp

@@ -63,6 +63,53 @@ size_t Print::printf(const char *format, ...) {
     return len;
 }
 
+size_t Print::printf(const __FlashStringHelper * format, ...) {
+  va_list arg;
+  va_start(arg, format);
+  PGM_P p = reinterpret_cast<PGM_P>(format);
+  char temp[64];
+  char* buffer = temp;
+  size_t len = vsnprintf_P(temp, sizeof(temp), p, arg);
+  va_end(arg);
+  if (len > sizeof(temp) - 1) {
+      buffer = new char[len + 1];
+      if (!buffer) {
+          return 0;
+      }
+      va_start(arg, format);
+      vsnprintf_P(buffer, len + 1, p, arg);
+      va_end(arg);
+  }
+  len = write((const uint8_t*) buffer, len);
+  if (buffer != temp) {
+      delete[] buffer;
+  }
+  return len;
+}
+
+size_t Print::printf_P(PGM_P format, ...) {
+    va_list arg;
+    va_start(arg, format);
+    char temp[64];
+    char* buffer = temp;
+    size_t len = vsnprintf_P(temp, sizeof(temp), format, arg);
+    va_end(arg);
+    if (len > sizeof(temp) - 1) {
+        buffer = new char[len + 1];
+        if (!buffer) {
+            return 0;
+        }
+        va_start(arg, format);
+        vsnprintf_P(buffer, len + 1, format, arg);
+        va_end(arg);
+    }
+    len = write((const uint8_t*) buffer, len);
+    if (buffer != temp) {
+        delete[] buffer;
+    }
+    return len;
+}
+
 size_t Print::print(const __FlashStringHelper *ifsh) {
     PGM_P p = reinterpret_cast<PGM_P>(ifsh);
 

cores/esp8266/Print.h

@@ -64,6 +64,8 @@ class Print {
         }
 
         size_t printf(const char * format, ...)  __attribute__ ((format (printf, 2, 3)));
+        size_t printf(const __FlashStringHelper * format, ...);
+        size_t printf_P(PGM_P format, ...) __attribute__((format(printf, 2, 3)));
         size_t print(const __FlashStringHelper *);
         size_t print(const String &);
         size_t print(const char[]);