Add variation of PPPClass::cmd()

libraries/PPP/src/PPP.cpp

@@ -757,6 +757,30 @@ String PPPClass::cmd(const char *at_command, int timeout) {
   return String(out);
 }
 
+bool PPPClass::cmd(const char *at_command, String &response, int timeout) {
+  PPP_CMD_MODE_CHECK(false);
+
+  char out[128] = {0};
+  esp_err_t err = _esp_modem_at(_dce, at_command, out, timeout);
+  response = String(out);
+
+  if (err != ESP_OK) {
+    log_e("esp_modem_at failed %d %s", err, esp_err_to_name(err));
+
+    if (err == ESP_FAIL && response.isEmpty()) {
+      response = "ERROR";
+    }
+
+    return false;
+  }
+
+  if (response.isEmpty()) {
+    response = "OK";
+  }
+
+  return true;
+}
+
 size_t PPPClass::printDriverInfo(Print &out) const {
   size_t bytes = 0;
   if (_dce == NULL || _mode == ESP_MODEM_MODE_DATA) {

libraries/PPP/src/PPP.h

@@ -73,11 +73,26 @@ class PPPClass : public NetworkInterface {
   }
 
   // Send AT command with timeout in milliseconds
+  // Function deprecated - kept for backward compatibility
+  // Function may return empty string in multiple cases:
+  // - When timeout occured;
+  // - When "OK" AT response was received;
+  // - When "ERROR" AT response was received.
+  // For more detailed return, usage of `bool PPPClass::cmd(at_command, response, timeout)` is recommended.
   String cmd(const char *at_command, int timeout);
   String cmd(String at_command, int timeout) {
     return cmd(at_command.c_str(), timeout);
   }
 
+  // Send AT command with timeout in milliseconds
+  // When PPP is not started or timeout occurs: Function returns false; response string is not modified
+  // When AT error response is received: Function returns false; response contains "ERROR" or detailed AT response
+  // When AT success response is received: Function returns true; response contains "OK" or detailed AT response
+  bool cmd(const char *at_command, String &response, int timeout);
+  bool cmd(String at_command, String &response, int timeout) {
+    return cmd(at_command.c_str(), response, timeout);
+  }
+
   // untested
   bool powerDown();
   bool reset();