Add NimBLEAttValue class. (#67)

This is a specialized container class to hold BLE attribute values.

- Removes the use of std::string previously used to store the values.
- Allows for setting/getting/notifying values from std::string, std::vector<uint8_t>, Arduino String, const char*, and uint8_t buffers.
- Has operators retrieve the value as std::string, Arduino String, std::vector<uint8_t>, uint8_t* or char pointers.
- Includes iterators and subscript/random access operator.
- Introduces a max length parameter to the creation of server characteristics/descriptors to limit the size of the memory footprint.
- Nearly Seamless integration with existing code.
- Adds a config option to enable/disable timestamp storage when the value is updated.
- Adds a config option to specify the initial size of the value container if not specified in the constructor.

src/NimBLERemoteCharacteristic.cpp

@@ -58,7 +58,6 @@ static const char* LOG_TAG = "NimBLERemoteCharacteristic";
     m_charProp           = chr->properties;
     m_pRemoteService     = pRemoteService;
     m_notifyCallback     = nullptr;
-    m_timestamp          = 0;
 
     NIMBLE_LOGD(LOG_TAG, "<< NimBLERemoteCharacteristic(): %s", m_uuid.toString().c_str());
  } // NimBLERemoteCharacteristic
@@ -414,15 +413,12 @@ NimBLEUUID NimBLERemoteCharacteristic::getUUID() {
  * @param [in] timestamp A pointer to a time_t struct to store the time the value was read.
  * @return The value of the remote characteristic.
  */
-std::string NimBLERemoteCharacteristic::getValue(time_t *timestamp) {
-    ble_npl_hw_enter_critical();
-    std::string value = m_value;
+NimBLEAttValue NimBLERemoteCharacteristic::getValue(time_t *timestamp) {
     if(timestamp != nullptr) {
-        *timestamp = m_timestamp;
+        *timestamp = m_value.getTimeStamp();
     }
-    ble_npl_hw_exit_critical(0);
 
-    return value;
+    return m_value;
 }
 
 
@@ -470,12 +466,12 @@ float NimBLERemoteCharacteristic::readFloat() {
  * @param [in] timestamp A pointer to a time_t struct to store the time the value was read.
  * @return The value of the remote characteristic.
  */
-std::string NimBLERemoteCharacteristic::readValue(time_t *timestamp) {
+NimBLEAttValue NimBLERemoteCharacteristic::readValue(time_t *timestamp) {
     NIMBLE_LOGD(LOG_TAG, ">> readValue(): uuid: %s, handle: %d 0x%.2x",
                          getUUID().toString().c_str(), getHandle(), getHandle());
 
     NimBLEClient* pClient = getRemoteService()->getClient();
-    std::string value;
+    NimBLEAttValue value;
 
     if (!pClient->isConnected()) {
         NIMBLE_LOGE(LOG_TAG, "Disconnected");
@@ -526,14 +522,11 @@ std::string NimBLERemoteCharacteristic::readValue(time_t *timestamp) {
         }
     } while(rc != 0 && retryCount--);
 
-    time_t t = time(nullptr);
-    ble_npl_hw_enter_critical();
+    value.setTimeStamp();
     m_value = value;
-    m_timestamp = t;
     if(timestamp != nullptr) {
-        *timestamp = m_timestamp;
+        *timestamp = value.getTimeStamp();
     }
-    ble_npl_hw_exit_critical(0);
 
     NIMBLE_LOGD(LOG_TAG, "<< readValue length: %d rc=%d", value.length(), rc);
     return value;
@@ -558,17 +551,17 @@ int NimBLERemoteCharacteristic::onReadCB(uint16_t conn_handle,
 
     NIMBLE_LOGI(LOG_TAG, "Read complete; status=%d conn_handle=%d", error->status, conn_handle);
 
-    std::string *strBuf = (std::string*)pTaskData->buf;
+    NimBLEAttValue *valBuf = (NimBLEAttValue*)pTaskData->buf;
     int rc = error->status;
 
     if(rc == 0) {
         if(attr) {
             uint16_t data_len = OS_MBUF_PKTLEN(attr->om);
-            if(((*strBuf).length() + data_len) > BLE_ATT_ATTR_MAX_LEN) {
+            if((valBuf->size() + data_len) > BLE_ATT_ATTR_MAX_LEN) {
                 rc = BLE_ATT_ERR_INVALID_ATTR_VALUE_LEN;
             } else {
                 NIMBLE_LOGD(LOG_TAG, "Got %u bytes", data_len);
-                (*strBuf) += std::string((char*) attr->om->om_data, data_len);
+                valBuf->append(attr->om->om_data, data_len);
                 return 0;
             }
         }
@@ -719,22 +712,33 @@ std::string NimBLERemoteCharacteristic::toString() {
 
 
 /**
- * @brief Write the new value for the characteristic.
- * @param [in] newValue The new value to write.
- * @param [in] response Do we expect a response?
- * @return false if not connected or cant perform write for some reason.
+ * @brief Write a new value to the remote characteristic from a std::vector<uint8_t>.
+ * @param [in] vec A std::vector<uint8_t> value to write to the remote characteristic.
+ * @param [in] response Whether we require a response from the write.
+ * @return false if not connected or otherwise cannot perform write.
  */
-bool NimBLERemoteCharacteristic::writeValue(const std::string &newValue, bool response) {
-    return writeValue((uint8_t*)newValue.c_str(), newValue.length(), response);
+bool NimBLERemoteCharacteristic::writeValue(const std::vector<uint8_t>& vec, bool response) {
+    return writeValue((uint8_t*)&vec[0], vec.size(), response);
 } // writeValue
 
 
 /**
- * @brief Write the new value for the characteristic from a data buffer.
+ * @brief Write a new value to the remote characteristic from a const char*.
+ * @param [in] char_s A character string to write to the remote characteristic.
+ * @param [in] response Whether we require a response from the write.
+ * @return false if not connected or otherwise cannot perform write.
+ */
+bool NimBLERemoteCharacteristic::writeValue(const char* char_s, bool response) {
+    return writeValue((uint8_t*)char_s, strlen(char_s), response);
+} // writeValue
+
+
+/**
+ * @brief Write a new value to the remote characteristic from a data buffer.
  * @param [in] data A pointer to a data buffer.
  * @param [in] length The length of the data in the data buffer.
  * @param [in] response Whether we require a response from the write.
- * @return false if not connected or cant perform write for some reason.
+ * @return false if not connected or otherwise cannot perform write.
  */
 bool NimBLERemoteCharacteristic::writeValue(const uint8_t* data, size_t length, bool response) {