Bridge an incoming socket to a serial port.

serial_bridge.c

#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
#include <sys/select.h>
#include <sys/ioctl.h>
#include <errno.h>

int main(int argc,char** argv)
{
  struct termios tio;
  struct termios stdio;
  struct termios old_stdio;
  int tty_fd;
    
  tcgetattr(STDOUT_FILENO,&old_stdio);
    
  memset(&stdio,0,sizeof(stdio));
  stdio.c_iflag=0;
  stdio.c_oflag=0;
  stdio.c_cflag=0;
  stdio.c_lflag=0;
  stdio.c_cc[VMIN]=1;
  stdio.c_cc[VTIME]=0;
  tcsetattr(STDOUT_FILENO,TCSANOW,&stdio);
  tcsetattr(STDOUT_FILENO,TCSAFLUSH,&stdio);
  fcntl(STDIN_FILENO, F_SETFL, O_NONBLOCK);       // make the reads non-blocking
    
  memset(&tio,0,sizeof(tio));
  tio.c_iflag=0;
  tio.c_oflag=0;
  tio.c_cflag=CS8|CREAD|CLOCAL;           // 8n1, see termios.h for more information
  tio.c_lflag=0;
  tio.c_cc[VMIN]=1;
  tio.c_cc[VTIME]=5;
    
  cfsetospeed(&tio,B19200);
  cfsetispeed(&tio,B19200);

  tty_fd=open(argv[1], O_RDWR | O_NONBLOCK);
  if(tty_fd <= 0)
    {
      perror("ERROR: couldn't open device");
      exit(1);
    }
    
  tcsetattr(tty_fd,TCSANOW,&tio);
    
    
  while(1)
    {
      // Set timeout
      struct timeval tv;
      tv.tv_sec = 0;
      tv.tv_usec = 250000;

      // Add file descriptors to be monitored
      fd_set rd_set;
      fd_set err_set;
      FD_ZERO(&rd_set);
      FD_ZERO(&err_set);
      int fd = -1;
      int maxfd = -1;
        
      fd = STDIN_FILENO;
      FD_SET(fd, &rd_set);
      FD_SET(fd, &err_set);
      if(fd > maxfd) maxfd = fd;
        
      fd = tty_fd;
      FD_SET(fd, &rd_set);
      FD_SET(fd, &err_set);
      if(fd > maxfd) maxfd = fd;
        
      int rc = select(maxfd+1, &rd_set, NULL, &err_set, &tv);
        
      // Check for errors
      if(FD_ISSET(tty_fd, &err_set))
	break;
      if(FD_ISSET(STDIN_FILENO, &err_set))
	break;

      // We read some data
      if(rc > 0)
        {
	  char buffer[1024];
            
	  if(FD_ISSET(tty_fd, &rd_set))
            {
	      ssize_t nread = read(tty_fd, buffer, sizeof(buffer));
	      if(nread > 0)
		write(STDOUT_FILENO,buffer,nread);
	      else if(nread < 0)
		break;
            }
            
	  if(FD_ISSET(STDIN_FILENO, &rd_set))
            {
	      ssize_t nread = read(STDIN_FILENO, buffer, sizeof(buffer));
	      if(nread > 0)
                {
		  int i;
		  for(i=0; i<nread; i++)
                    {
		      // Add a small inter-character delay
		      write(tty_fd,&(buffer[i]),1);
		      usleep(5000);
                    }
                }
	      else if(nread < 0)
		break;
            }
        }
      else if(rc < 0)
        {
	  if(errno != EINTR)
            {
	      // continue on EINTR
	      break;
            }
        }
    }

  close(tty_fd);
  tcsetattr(STDOUT_FILENO,TCSANOW,&old_stdio);
    
  perror("ERROR: closed");
  exit(1);
    
  return EXIT_SUCCESS;
}