add check for characteristic max_len

Author: hathach

libraries/Bluefruit52Lib/examples/custom_hrm/custom_hrm.ino

@@ -130,11 +130,11 @@ void setupHRM(void)
   //    B6:7    = UINT16 - RR Internal (1/1024 second resolution)
   hrmc.setProperties(CHR_PROPS_NOTIFY);
   hrmc.setPermission(SECMODE_OPEN, SECMODE_NO_ACCESS);
-  hrmc.setMaxLen(8);
+  hrmc.setMaxLen(2);
   hrmc.start();
 
   // Set the characteristic to use 8-bit values, with the sensor connected and detected
-  uint8_t hrmdata[2] = { 0b00000110, 0x40 };
+  uint8_t hrmdata[2] = { 0b00000000, 0x40 };
   hrmc.write(hrmdata, 2);
 
   // Configure the Body Sensor Location characteristic

libraries/Bluefruit52Lib/src/BLECharacteristic.cpp

@@ -355,9 +355,12 @@ err_t BLECharacteristic::write(const char   * str)
 
 err_t BLECharacteristic::write(const uint8_t* data, int len, uint16_t offset)
 {
+  // could not exceed max len
+  uint16_t actual_len = min16(len, _max_len);
+
   ble_gatts_value_t value =
   {
-      .len     = (uint16_t) len,
+      .len     = (uint16_t) actual_len,
       .offset  = offset,
       .p_value = (uint8_t*) data
   };
@@ -388,7 +391,7 @@ err_t BLECharacteristic::write(uint8_t  num)
 
 bool BLECharacteristic::notifyEnabled(void)
 {
-  VERIFY( _properties.notify );
+  VERIFY( _properties.notify && Bluefruit.connected() );
   uint16_t cccd;
   ble_gatts_value_t value =
   {
@@ -409,14 +412,15 @@ err_t BLECharacteristic::notify(const uint8_t* data, int len, uint16_t offset)
   // Whether Txbuf available or not we still update the chars'value
   (void) Bluefruit.txbuf_get(100);
 
-  uint16_t len16 = (uint16_t) len;
+  // could not exceed max len
+  uint16_t actual_len = min16(len, _max_len);
 
   ble_gatts_hvx_params_t hvx_params =
   {
       .handle = _handles.value_handle,
       .type   = BLE_GATT_HVX_NOTIFICATION,
       .offset = offset,
-      .p_len  = &len16,
+      .p_len  = &actual_len,
       .p_data =  (uint8_t*) data,
   };