Can't reopen telnet session

[chekhovana]

Hello,

I'm facing the following problem: first telnet connection is established successfully:

$ telnet localhost 1137
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Connected to JSBSim server
JSBSim> quit
Closing connection
JSBSim> Connection closed by foreign host.

but the second attempt hangs without expected response, the output is:

$ telnet localhost 1137
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.

and nothing else. Is that the intended behaviour? I tried to skim through the source code and it seems that socket isn't closed completely on quit command. Adding extra line to FGfdmSocket::Close method fixes the issue:

original version:

jsbsim/src/input_output/FGfdmSocket.cpp

Lines 316 to 323 in b9bfc23

	void FGfdmSocket::Close(void)
	{
	#ifdef _WIN32
	closesocket(sckt_in);
	#else
	close(sckt_in);
	#endif
	}

modified version:

void FGfdmSocket::Close(void)
{
#ifdef _WIN32
  closesocket(sckt_in);
#else
  close(sckt_in);
#endif
  sckt_in = INVALID_SOCKET; // added line
}

But I'm not sure this is correct thing to do, as I'm extremely unexperienced both in c++ an sockets.

Any help would be appreciated.

[bcoconni]

Hi @chekhovana,

Indeed the method FGfdmSocket::Receive will not open a new socket if sckt_in != INVALID_SOCKET:

jsbsim/src/input_output/FGfdmSocket.cpp

Lines 245 to 264 in 3c7582e

	string FGfdmSocket::Receive(void)
	{
	char buf[1024];
	socklen_t len = sizeof(struct sockaddr_in);
	string data; // todo: should allocate this with a standard size as a
	// class attribute and pass as a reference?
	if (sckt_in == INVALID_SOCKET && Protocol == ptTCP) {
	sckt_in = accept(sckt, (struct sockaddr*)&scktName, &len);
	if (sckt_in != INVALID_SOCKET) {
	#ifdef _WIN32
	u_long NoBlock = 1;
	ioctlsocket(sckt_in, FIONBIO, &NoBlock);
	#else
	int flags = fcntl(sckt_in, F_GETFL, 0);
	fcntl(sckt_in, F_SETFL, flags | O_NONBLOCK);
	#endif
	send(sckt_in, "Connected to JSBSim server\n\rJSBSim> ", 36, 0);
	}
	}

So your suggestion looks good to me. Would you mind opening a pull request to update the code ?
Thanks for your contribution.

[chekhovana]

Hello @bcoconni

Thanks for your response, here's my pull request: #1078