#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <string.h>#include <errno.h>#include <limits.h>		// for PIPE_BUF#include <signal.h>#include <sys/types.h>#include <sys/stat.h>#define BUFFER_SIZE	PIPE_BUFint global_exit_flag = 0;void parent_process_main(int fd);void child_process_main(int fd);void signal_handler(int s);int main(int argc, char **argv){  int fds[2];  //int pipe(int fildes[2]);  if (pipe(fds) < 0)  {    fprintf(stderr, "Create a pipe failed: %s\n", strerror(errno));    exit(1);  }  fprintf(stdout, "write endpoint: %d\n", fds[1]);  fprintf(stdout, "read endpoint: %d\n", fds[0]);  pid_t pid;  //pid_t fork(void);  if ((pid = fork()) < 0)  {    fprintf(stderr, "fork() failed: %s\n", strerror(errno));    exit(1);  }  else if (pid == 0)  {    // XXX: child process, close write endpoint    close(fds[1]);    child_process_main(fds[0]);    exit(0);  }  else  {    // XXX: parent process, close read endpoint    close(fds[0]);    parent_process_main(fds[1]);  }  close(fds[0]);  close(fds[1]);  return 0;}void parent_process_main(int fd){  char buffer[BUFFER_SIZE];  ssize_t written;  ssize_t offset = 0;  int length;  signal(SIGINT, signal_handler);  signal(SIGTERM, signal_handler);  //char *fgets(char *s, int size, FILE * stream);  while (fgets(buffer, BUFFER_SIZE, stdin))  {    length = strlen(buffer);    offset = 0;    while (offset < length)    {    again:      //ssize_t write(int fd, const void *buf, size_t count);      if ((written = write(fd, buffer + offset, length - offset)) < 0)      {	if (errno == EINTR)	{	  fprintf(stdout, "[%d]Got a signal, retry.\n", getpid());	  goto again;	}	else	{	  fprintf(stderr, "[%d]write() failed: %s\n", getpid(), strerror(errno));	  // FIXME: 	  exit(1);	}      }      else      {	offset += written;      }    }    fprintf(stdout, "[%d]written %d bytes to pipe.\n", getpid(), length);    if (global_exit_flag)    {      break;    }  }  fprintf(stdout, "[%d]out of fetch string from stdin.\n", getpid());}void child_process_main(int fd){  char buffer[BUFFER_SIZE];  ssize_t n;  for (;;)  {  again:    //ssize_t read(int fd, void *buf, size_t count);    if ((n = read(fd, buffer, BUFFER_SIZE)) < 0)    {      if (errno == EINTR)      {	goto again;      }      fprintf(stderr, "[%d]read() failed: %s\n", getpid(), strerror(errno));      // FIXME:      exit(1);    }    else if (n == 0)    {      struct stat s;      // FIXME: check return value      //int fstat(int filedes, struct stat *buf);      fstat(fd, &s);      if ((S_ISFIFO(s.st_mode)))      {	fprintf(stdout, "[%d]The write endpoint is closed, exiting ...\n", getpid());	exit(0);      }    }    else    {      fprintf(stdout, "%s", buffer);    }  }}void signal_handler(int s){  fprintf(stdout, "Caught signal %d, exiting...\n", s);  global_exit_flag = 1;}