#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/select.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#define FIFO_IN  "/tmp/pipe.in"
#define FIFO_OUT "/tmp/pipe.out"

#define FALSE 0
#define TRUE  1

typedef int bool;

void openpipes(void);
void closepipes(void);
int startpipe(char *name, bool inputpipe);
void endpipe(char *name, int fd);

int infd;
int outfd;
int count = 0;

int main(void)
{
    int nsel;
    bool done = FALSE;
    char const *msg = "You sent: ";
    int mlen = strlen(msg);
    fd_set readfds;
    FD_ZERO(&readfds);

    openpipes();

    do {
	FD_SET(infd, &readfds);
	do {
	    nsel = select(infd + 1, &readfds, 0, 0, 0);
	} while (nsel == -1 && (errno == EINTR || errno == EAGAIN));

	if (nsel == -1) {
	    perror("select");
	    exit(4);
	}

	if (FD_ISSET(infd, &readfds)) {
	    char buf[100] = "You sent: ";
	    int status;
	    int count = 0;
	    strcpy(buf, msg);
	    while ((status = read(infd, buf + mlen, sizeof(buf) - mlen - 1))) {
		if (status > 0) {
		    buf[mlen + status] = '\0';
		    if (write(outfd, buf, strlen(buf)) < 0) {
			if (buf[mlen + status - 1] == '\n')
			    buf[mlen + status - 1] = '\0';
			fprintf(stderr, "Error sending message: '%s': %s\n",
				buf, strerror(errno));
		    }
		    if (strncasecmp(buf + mlen, "quit", 4) == 0)
			done = TRUE;
		} else if (errno == EAGAIN) {
		    /* Nothing to read, continue */
		    break;
		} else {
		    /* An error occurred, bail out */
		    perror("read");
		    done = TRUE;
		    break;
		}
	    }
	    if (!done) {
		sleep(3);
		closepipes();
		openpipes();
		errno = 0;
	    }
	}
    } while (!done);

    closepipes();
    return 0;
}


void openpipes(void)
{
    fprintf(stderr, "%d) Opening pipes\n", ++count);

    infd = startpipe(FIFO_IN, TRUE);
    if (infd == -1)
	exit(1);

    outfd = startpipe(FIFO_OUT, FALSE);
    if (outfd == -1)
	exit(2);

    if (fcntl(outfd, F_SETFL, O_NONBLOCK) < 0) {
	fprintf(stderr, "Could not set flags on pipe %s: %s\n",
		FIFO_OUT, strerror(errno));
	exit(3);
    }
}


void closepipes()
{
    fprintf(stderr, "%d) Closing pipes\n", count);

    endpipe(FIFO_IN, infd);
    endpipe(FIFO_OUT, outfd);
}


int startpipe(char *name, bool inputpipe)
{
    static bool stalepipe = FALSE;
    int fd;

    if (access(name, F_OK) == 0) {
	if (inputpipe) {
	    /* Let's see whether we have a stale pipe */
	    fd = open(name, O_WRONLY | O_NONBLOCK);
	    if (fd >= 0) {
		/* pipe exists and is used by another process */
		close(fd);
	    } else if (errno == ENXIO) {
		/* No process is reading from the other end */
		stalepipe = TRUE;
		endpipe(name, -1);
	    }
	} else if (stalepipe) {
	    endpipe(name, -1);
	    stalepipe = FALSE;
	}
	if (access(name, F_OK) == 0) {
	    fprintf(stderr, "Pipe %s already exists and is in use.\n", name);
	    return -1;
	}
    }

    if (mkfifo(name, 0600) < 0) {
	fprintf(stderr, "Could not create pipe %s: %s\n",
		name, strerror(errno));
	return -1;
    }

    fd = open(name, inputpipe ? (O_RDONLY | O_NONBLOCK) : O_RDWR);

    if (fd < 0) {
	fprintf(stderr, "Could not open pipe %s: %s\n",
		name, strerror(errno));
	endpipe(name, -1);
	return -1;
    }

    return fd;
}


void endpipe(char *name, int fd)
{
    if (fd >= 0 && close(fd) < 0)
	fprintf(stderr, "Could not close pipe %s: %s\n",
		name, strerror(errno));

    if (remove(name) < 0)
	fprintf(stderr, "Could not remove pipe %s: %s\n",
		name, strerror(errno));
}