Add support for simulators running on a different host than the PX4 instance

ROMFS/px4fmu_common/init.d-posix/rcS

@@ -220,7 +220,21 @@ dataman start
 # only start the simulator if not in replay mode, as both control the lockstep time
 if ! replay tryapplyparams
 then
-	simulator start -c $simulator_tcp_port
+  # Check if PX4_SIM_HOSTNAME environment variable is empty
+  # If empty check if PX4_SIM_HOST_ADDR environment variable is empty
+  # If both are empty use localhost for simulator
+  if [ -z "${PX4_SIM_HOSTNAME}" ]; then
+    if [ -z "${PX4_SIM_HOST_ADDR}" ]; then
+      echo "PX4 SIM HOST: localhost"
+      simulator start -c $simulator_tcp_port
+    else
+      echo "PX4 SIM HOST: $PX4_SIM_HOST_ADDR"
+      simulator start -t $PX4_SIM_HOST_ADDR $simulator_tcp_port 
+    fi
+  else
+    echo "PX4 SIM HOST: $PX4_SIM_HOSTNAME"
+    simulator start -h $PX4_SIM_HOSTNAME $simulator_tcp_port 
+  fi
 fi
 load_mon start
 battery_simulator start

src/modules/simulator/simulator.cpp

@@ -69,6 +69,7 @@ int Simulator::start(int argc, char *argv[])
 	_instance = new Simulator();
 
 	if (_instance) {
+
 		if (argc == 5 && strcmp(argv[3], "-u") == 0) {
 			_instance->set_ip(InternetProtocol::UDP);
 			_instance->set_port(atoi(argv[4]));
@@ -80,11 +81,21 @@ int Simulator::start(int argc, char *argv[])
 		}
 
 		if (argc == 6 && strcmp(argv[3], "-t") == 0) {
+			PX4_INFO("Simulator using TCP on remote host %s port %s", argv[4], argv[5]);
+			PX4_WARN("Please ensure port %s is not blocked by a firewall.", argv[5]);
 			_instance->set_ip(InternetProtocol::TCP);
 			_instance->set_tcp_remote_ipaddr(argv[4]);
 			_instance->set_port(atoi(argv[5]));
 		}
 
+		if (argc == 6 && strcmp(argv[3], "-h") == 0) {
+			PX4_INFO("Simulator using TCP on remote host %s port %s", argv[4], argv[5]);
+			PX4_WARN("Please ensure port %s is not blocked by a firewall.", argv[5]);
+			_instance->set_ip(InternetProtocol::TCP);
+			_instance->set_hostname(argv[4]);
+			_instance->set_port(atoi(argv[5]));
+		}
+
 		_instance->run();
 
 		return 0;
@@ -102,6 +113,7 @@ static void usage()
 	PX4_INFO("Connect using UDP: simulator start -u udp_port");
 	PX4_INFO("Connect using TCP: simulator start -c tcp_port");
 	PX4_INFO("Connect to a remote server using TCP: simulator start -t ip_addr tcp_port");
+	PX4_INFO("Connect to a remote server via hostname using TCP: simulator start -h hostname tcp_port");
 }
 
 __BEGIN_DECLS

src/modules/simulator/simulator.h

@@ -123,6 +123,7 @@ public:
 
 	void set_ip(InternetProtocol ip) { _ip = ip; }
 	void set_port(unsigned port) { _port = port; }
+	void set_hostname(std::string hostname) { _hostname = hostname; }
 	void set_tcp_remote_ipaddr(char *tcp_remote_ipaddr) { _tcp_remote_ipaddr = tcp_remote_ipaddr; }
 
 #if defined(ENABLE_LOCKSTEP_SCHEDULER)
@@ -206,6 +207,8 @@ private:
 
 	InternetProtocol _ip{InternetProtocol::UDP};
 
+	std::string _hostname{""};
+
 	char *_tcp_remote_ipaddr{nullptr};
 
 	double _realtime_factor{1.0};		///< How fast the simulation runs in comparison to real system time

src/modules/simulator/simulator_mavlink.cpp

@@ -45,7 +45,9 @@
 #include <conversion/rotation.h>
 #include <mathlib/mathlib.h>
 
+#include <arpa/inet.h>
 #include <errno.h>
+#include <netdb.h>
 #include <netinet/in.h>
 #include <netinet/tcp.h>
 #include <poll.h>
@@ -731,8 +733,19 @@ void Simulator::run()
 
 	if (_tcp_remote_ipaddr != nullptr) {
 		_myaddr.sin_addr.s_addr = inet_addr(_tcp_remote_ipaddr);
+
+	} else if (!_hostname.empty()) {
+		/* resolve hostname */
+		struct hostent *host;
+		host = gethostbyname(_hostname.c_str());
+		memcpy(&_myaddr.sin_addr, host->h_addr_list[0], host->h_length);
+
+		char ip[30];
+		strcpy(ip, (char *)inet_ntoa((struct in_addr)_myaddr.sin_addr));
+		PX4_INFO("Resolved host '%s' to address: %s", _hostname.c_str(), ip);
 	}
 
+
 	if (_ip == InternetProtocol::UDP) {
 
 		if ((_fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {