#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>

int main(int argc, char *argv[])
{
    int pipes[2];
    int flags;
    long pipe_buf;
    size_t bufsize1, bufsize2, nitems;
    FILE *fp;
    char *bp;

    if (pipe(pipes) != 0) {
        fprintf(stderr, "error: could not create pipe\n");
        return 1;
    }

    flags = fcntl(pipes[1], F_GETFL, 0);
    flags |= O_NONBLOCK;
    fcntl(pipes[1], F_SETFL, flags);

    pipe_buf = fpathconf(pipes[1], _PC_PIPE_BUF);
    if (pipe_buf <= 0L) {
        printf("cannot test: unlimited pipe buffer\n");
        return 0;
    }

    bufsize1 = (size_t) pipe_buf + 16;
    bufsize2 = bufsize1 + 8;

    fp = fdopen(pipes[1], "w");
    if (fp == NULL) {
        fprintf(stderr, "error: could not reopen pipe\n");
        return 1;
    }

    setbuf(fp, (char *) NULL);

    bp = (char *) malloc(bufsize2);
    if (bp == NULL) {
        fprintf(stderr, "error: could not allocate memory\n");
        return 1;
    }

    while (write(pipes[1], bp, (unsigned) pipe_buf/2) == pipe_buf/2) ;
    read(pipes[0], bp, (unsigned) pipe_buf);

    /* here we go */
    nitems = fwrite((void *) bp, 1, (size_t) bufsize2, fp);
    if (nitems > 0) {
        printf("the write appeared to succeed\n");
    } else if (ferror(fp)) {
        if (errno == EAGAIN) {
            printf("the write failed; EAGAIN seen\n");
        } else {
            printf("the write failed; error: %s\n", strerror(errno));
        }
    } else {
        printf("something weird happened\n");
    }

    return 0;
}