enum { BUF_SIZE = 256 };

ssize_t write2(int fd, char * buf, size_t size) {
    ssize_t tmp = write(fd, buf, size);
    if (tmp <= 0) {
        exit(0);
    }
    return tmp;
}

ssize_t read2(int fd, char * buf, size_t size) {
    ssize_t tmp = read(fd, buf, size);
    if (tmp <= 0) {
        exit(0);
    }
    return tmp;
}

int add_overflow(unsigned a, unsigned b) {
    int tmp;
    return ((int)a != a) || ((int)b != b) || __builtin_sadd_overflow(a, b, &tmp);
}

void ignore_handler(int sig) {
    ;
}

void usr1_handler(int sig) {
    exit(0);
}

void term_handler(int sig) {
    kill(-getpid(), SIGUSR1);
    while (wait(NULL) > 0) { ; }
    exit(0);
};

void process(int fd, const char * KEY, unsigned serial) {
    char buf[BUF_SIZE];
    strcpy(buf, KEY);
    strncat(buf, "\r\n", 3);
    write2(fd, buf, strlen(buf));
    sprintf(buf, "%u\r\n", serial);
    write2(fd, buf, strlen(buf));
    ssize_t size = read2(fd, buf, sizeof(buf));
    buf[size] = '\0';
    unsigned max = strtoul(buf, NULL, 10);
    write2(fd, buf, size);
    unsigned num;
    while (1) {
        size = read2(fd, buf, sizeof(buf));
        buf[size] = '\0';
        num = strtoul(buf, NULL, 10);
        if (num > max || add_overflow(num, serial)) {
            strcpy(buf, "-1\r\n");
            write2(fd, buf, 4);
            close(fd);
            return;
        }
        sprintf(buf, "%u\r\n", num + serial);
        write2(fd, buf, strlen(buf));
    }
}

int main(int argc, char ** argv) {
    signal(SIGTERM, term_handler);
    signal(SIGUSR1, ignore_handler);
    if (argc < 3) {
        return 1;
    }
    int fd = socket(PF_INET, SOCK_STREAM, 0);
    if (fd < 0) {
        perror("socket\n");
        return 1;
    }
    // magic
    int val = 1;
    setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
    setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &val, sizeof(val));

    struct sockaddr_in s1;
    s1.sin_family = AF_INET;
    s1.sin_port = htons(strtol(argv[1], NULL, 10));
    s1.sin_addr.s_addr = INADDR_ANY;
    int r = bind(fd, (struct sockaddr*) &s1, sizeof(s1));
    if (r < 0) {
        perror("bind\n");
        return 1;
    }
    // magic again
    listen(fd, 5);

    unsigned serial = 1;

    while (1) {
        while (waitpid(-1, NULL, WNOHANG) > 0) { ; }
        struct sockaddr_in s2;
        socklen_t slen = sizeof(s2);
        int fd2 = accept(fd, (struct sockaddr *) &s2, &slen);
        if (fd2 < 0) {
            continue;
        }
        pid_t pid = fork();
        if (pid < 0) {
            close(fd2);
            continue;
        }
        if (pid == 0) {
            signal(SIGUSR1, usr1_handler);
            process(fd2, argv[2], serial);
            exit(0);
        }
        close(fd2);
        ++serial;
    }
}