pigeon: use const reference for std::string parameter (#19886)

old-commit-hash: b1660cf585278a65ec439ad8152cc8969797001a

selfdrive/boardd/pigeon.cc

@@ -89,7 +89,7 @@ void PandaPigeon::set_baud(int baud) {
   panda->usb_write(0xe4, 1, baud/300);
 }
 
-void PandaPigeon::send(std::string s) {
+void PandaPigeon::send(const std::string &s) {
   int len = s.length();
   const char * dat = s.data();
 
@@ -180,7 +180,7 @@ void TTYPigeon::set_baud(int baud){
   assert(tcflush(pigeon_tty_fd, TCIOFLUSH) == 0);
 }
 
-void TTYPigeon::send(std::string s) {
+void TTYPigeon::send(const std::string &s) {
   int len = s.length();
   const char * dat = s.data();
 

selfdrive/boardd/pigeon.h

@@ -13,7 +13,7 @@ class Pigeon {
 
   void init();
   virtual void set_baud(int baud) = 0;
-  virtual void send(std::string s) = 0;
+  virtual void send(const std::string &s) = 0;
   virtual std::string receive() = 0;
   virtual void set_power(bool power) = 0;
 };
@@ -24,7 +24,7 @@ public:
   ~PandaPigeon();
   void connect(Panda * p);
   void set_baud(int baud);
-  void send(std::string s);
+  void send(const std::string &s);
   std::string receive();
   void set_power(bool power);
 };
@@ -37,7 +37,7 @@ public:
   ~TTYPigeon();
   void connect(const char* tty);
   void set_baud(int baud);
-  void send(std::string s);
+  void send(const std::string &s);
   std::string receive();
   void set_power(bool power);
 };