readn

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ssize_t readn(int fd, void *buf, size_t count) {
    size_t nleft;
    size_t nread;
    char *ptr;
    ptr = buf;
    nleft = count;
    while (nleft > 0) {
        nread = read(fd, ptr, nleft);
        if (nread < 0) {
            if (errno == EINTR) {
                nread = 0;
            } else {
                return -1;
            }
        } else if (nread == 0) {
            break;
        }
        nleft -= nread;
        ptr += nread;
    }
    return count - nleft;
}
ssize_t writen(int fd, const void *buf, size_t count) {
    size_t nleft;
    size_t nwritten;
    const char *ptr;
    ptr = buf;
    nleft = count;
    while (nleft > 0) {
        nwritten = write(fd, ptr, nleft);
        if (nwritten <= 0) {
            if (nwritten < 0 && nwritten == EINTR) {
                nwritten = 0;
            } else {
                return -1;
            }
        }
        nleft -= nwritten;
        ptr += nwritten;
    }
    return count;
}