#include <arpa/inet.h>#include <errno.h>#include <poll.h>#include <stdio.h>#include <stdlib.h>#include <string.h>#include <sys/socket.h>#include <unistd.h> static int write_all(int fd, const void *data, size_t length) {    const unsigned char *cursor = data;     while (length > 0) {        ssize_t written = write(fd, cursor, length);        if (written < 0 && errno == EINTR)            continue;        if (written <= 0)            return -1;        cursor += written;        length -= (size_t)written;    }    return 0;} static int connect_ipv4(const char *host, const char *port_string) {    char *end = NULL;    long port = strtol(port_string, &end, 10);    struct sockaddr_in address;    int fd;     if (end == port_string || *end != '\0' || port <= 0 || port > 65535) {        errno = EINVAL;        return -1;    }    memset(&address, 0, sizeof(address));    address.sin_family = AF_INET;    address.sin_port = htons((unsigned short)port);    if (inet_pton(AF_INET, host, &address.sin_addr) != 1) {        errno = EINVAL;        return -1;    }    fd = socket(AF_INET, SOCK_STREAM, 0);    if (fd < 0)        return -1;    if (connect(fd, (struct sockaddr *)&address, sizeof(address)) < 0) {        int saved_errno = errno;        close(fd);        errno = saved_errno;        return -1;    }    return fd;} static int proxy_stdio(int socket_fd) {    int input_open = 1;    unsigned char buffer[16384];     for (;;) {        struct pollfd poll_fds[2] = {            { .fd = STDIN_FILENO, .events = input_open ? POLLIN : 0 },            { .fd = socket_fd, .events = POLLIN },        };        int ready;        do {            ready = poll(poll_fds, 2, -1);        } while (ready < 0 && errno == EINTR);        if (ready < 0)            return -1;         if (input_open && (poll_fds[0].revents & (POLLIN | POLLHUP))) {            ssize_t length = read(STDIN_FILENO, buffer, sizeof(buffer));            if (length < 0 && errno == EINTR)                continue;            if (length < 0)                return -1;            if (length == 0) {                input_open = 0;                if (shutdown(socket_fd, SHUT_WR) < 0 && errno != ENOTCONN)                    return -1;            } else if (write_all(socket_fd, buffer, (size_t)length) < 0) {                return -1;            }        }         if (poll_fds[1].revents & (POLLIN | POLLHUP)) {            ssize_t length = read(socket_fd, buffer, sizeof(buffer));            if (length < 0 && errno == EINTR)                continue;            if (length < 0)                return -1;            if (length == 0)                return 0;            if (write_all(STDOUT_FILENO, buffer, (size_t)length) < 0)                return -1;        }        if (poll_fds[0].revents & (POLLERR | POLLNVAL)) {            errno = EIO;            return -1;        }        if (poll_fds[1].revents & (POLLERR | POLLNVAL)) {            errno = EIO;            return -1;        }    }} static int proxy_fdpass(int socket_fd) {    char marker = 'F';    struct iovec iov = { .iov_base = &marker, .iov_len = 1 };    union {        struct cmsghdr align;        unsigned char bytes[CMSG_SPACE(sizeof(int))];    } control;    struct msghdr message;    struct cmsghdr *header;     memset(&message, 0, sizeof(message));    memset(&control, 0, sizeof(control));    message.msg_iov = &iov;    message.msg_iovlen = 1;    message.msg_control = control.bytes;    message.msg_controllen = sizeof(control.bytes);    header = CMSG_FIRSTHDR(&message);    header->cmsg_level = SOL_SOCKET;    header->cmsg_type = SCM_RIGHTS;    header->cmsg_len = CMSG_LEN(sizeof(int));    memcpy(CMSG_DATA(header), &socket_fd, sizeof(socket_fd));    return sendmsg(STDOUT_FILENO, &message, 0) == 1 ? 0 : -1;} int main(int argc, char **argv) {    int socket_fd;    int result;     if (argc != 4 ||        (strcmp(argv[1], "stdio") != 0 && strcmp(argv[1], "fdpass") != 0)) {        fprintf(stderr, "usage: ssh_proxy_helper {stdio|fdpass} HOST PORT\n");        return 2;    }    socket_fd = connect_ipv4(argv[2], argv[3]);    if (socket_fd < 0) {        perror("ssh_proxy_helper connect");        return 1;    }    result = strcmp(argv[1], "fdpass") == 0 ?        proxy_fdpass(socket_fd) : proxy_stdio(socket_fd);    if (result < 0)        perror("ssh_proxy_helper");    close(socket_fd);    return result == 0 ? 0 : 1;}