TCP/P Socket blocking serial connection - c

Question

I have a program that is supposed to both read a serial port and from tcp/ip socket simultaneously.
However, I only can see the serial information when I receive a message via socket. I believe that it has something to do with blocking/nonblocking of the accept() method. However, I have been unsuccessful in figuring out how to add flags to it.
Anyone have any ideas?
Do I have to rewrite the whole thing or can I just add a flag?
int main(int argc, char *argv[]) {
int list_s; /* listening socket */
int conn_s; /* connection socket */
short int port; /* port number */
struct sockaddr_in servaddr; /* socket address structure */
char buffer[MAX_LINE]; /* character buffer */
char *endptr; /* for strtol() */
/* Get port number from the command line, and
* set to default port if no arguments were supplied */
if ( argc == 2 ) {
port = strtol(argv[1], &endptr, 0);
if ( *endptr ) {
fprintf(stderr, "ECHOSERV: Invalid port number.\n");
exit(EXIT_FAILURE);
}
}
else if ( argc < 2 ) {
port = ECHO_PORT;
}
else {
fprintf(stderr, "ECHOSERV: Invalid arguments.\n");
exit(EXIT_FAILURE);
}
/* Create the listening socket */
if ( (list_s = socket(AF_INET, SOCK_STREAM, 0)) < 0 ) {
fprintf(stderr, "ECHOSERV: Error creating listening socket.\n");
exit(EXIT_FAILURE);
}
/* Set all bytes in socket address structure to
* zero, and fill in the relevant data members */
memset(&servaddr, 0, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
servaddr.sin_port = htons(port);
/* Bind our socket addresss to the
* listening socket, and call listen() */
if ( bind(list_s, (struct sockaddr *) &servaddr, sizeof(servaddr)) < 0 ) {
fprintf(stderr, "ECHOSERV: Error calling bind()\n");
exit(EXIT_FAILURE);
}
if ( listen(list_s, LISTENQ) < 0 ) {
fprintf(stderr, "ECHOSERV: Error calling listen()\n");
exit(EXIT_FAILURE);
}
/* Enter an infinite loop to respond
* to client requests and echo input */
int result = 0;
int portID = -1;
char *device = "/dev/ttyUSB1";
int rate = convertRate("115200");
char parity = convertParity("N");
int databits = convertDatabits("8");
int stopbits = convertStopbits("1");
portID = posixComOpen(device,rate,parity,databits,stopbits);
while ( 1 ) {
char input = 0;
while(posixComDataReady(portID) && posixComRead(portID, &input)) {
printf("%c", input);
} //while
/* Write character to Vex */
if(posixComWrite(portID, 'x') < 0)
printf("POSIX: Error Writing char %c",'x');
/* Wait for a connection, then accept() it */
if ( (conn_s = accept(list_s, NULL, NULL) ) < 0 ) {
fprintf(stderr, "ECHOSERV: Error calling accept()\n");
exit(EXIT_FAILURE);
}
/* Retrieve an input line from the connected socket
* then simply write it back to the same socket. */
Readline(conn_s, buffer, MAX_LINE-1);
printf("Netbook got a TCP/IP message: %s\n", buffer);
char* sendMessage = "Thanks for the message!";
Writeline(conn_s,sendMessage , strlen(sendMessage));
/* Close the connected socket */
if ( close(conn_s) < 0 ) {
fprintf(stderr, "ECHOSERV: Error calling close()\n");
exit(EXIT_FAILURE);
}
}//while
return 0;
}

Answer 1

You're right, the problem is that accept blocks until there is a new connection.
I don't know how serial connections work, but you might want to look at the select function, which allows you to wait on several different file descriptors, and respond to them when there is data on the other end.
Here's an example of how to use select for sockets: Server Example