add characteristic isFixedLen()

Author: hathach

libraries/Bluefruit52Lib/src/BLECharacteristic.cpp

@@ -127,6 +127,11 @@ uint16_t BLECharacteristic::getMaxLen(void)
   return _max_len;
 }
 
+bool BLECharacteristic::isFixedLen(void)
+{
+  return _attr_meta.vlen == 0;
+}
+
 void BLECharacteristic::setFixedLen(uint16_t fixed_len)
 {
   if ( fixed_len )

libraries/Bluefruit52Lib/src/BLECharacteristic.h

@@ -101,6 +101,7 @@ class BLECharacteristic
     void setBuffer(void* buf, uint16_t bufsize);
 
     uint16_t getMaxLen(void);
+    bool isFixedLen(void);
 
     /*------------- Descriptors -------------*/
     void setUserDescriptor(const char* descriptor); // aka user descriptor