C语言中的Socks 5客户端

Question

我想使用 C 中的流套接字编写 socks 5 客户端。

这是我的代码：

/*
** client_socks.c -- a stream socket socks 5 client demo
*/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>

#include <arpa/inet.h>

#define PORT "9050" // the port client will be connecting to 

#define MAXDATASIZE 100 // max number of bytes we can get at once 

// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
    if (sa->sa_family == AF_INET) {
        return &(((struct sockaddr_in*)sa)->sin_addr);
    }

    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}

int main(int argc, char *argv[])
{
    int sockfd, numbytes;  
    char buf[MAXDATASIZE];
    struct addrinfo hints, *servinfo, *p;
    int rv;
    char s[INET6_ADDRSTRLEN];

    if (argc != 2) {
        fprintf(stderr,"usage: client hostname\n");
        exit(1);
    }

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;

    if ((rv = getaddrinfo(argv[1], PORT, &hints, &servinfo)) != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
        return 1;
    }

    // loop through all the results and connect to the first we can
    for(p = servinfo; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) == -1) {
            perror("client: socket");
            continue;
        }

        if (connect(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
            perror("client: connect");
            close(sockfd);
            continue;
        }

        break;
    }

    if (p == NULL) {
        fprintf(stderr, "client: failed to connect\n");
        return 2;
    }

    inet_ntop(p->ai_family, get_in_addr((struct sockaddr *)p->ai_addr), s, sizeof s);
    printf("client: connecting to %s\n", s);

    freeaddrinfo(servinfo); // all done with this structure

    /* Version 5, one method: no authentication */
    char buffer[256], *ptrBuff;
    ptrBuff = buffer;

    ptrBuff[0] = 5; // socks version
    ptrBuff[1] = 1;
    ptrBuff[2] = 0; // SOCKS_NOAUTH

    if (send(sockfd, ptrBuff, buffer-ptrBuff, 0) == -1)
                perror("send");

    if ((numbytes = recv(sockfd, buffer, MAXDATASIZE-1, 0)) == -1) {
        perror("recv");
        exit(1);
    }

    buffer[numbytes] = '\0';

    printf("client: received '%s'\n",buffer);

    close(sockfd);

    return 0;
}

但它不起作用 - 它正在写入：

client: connecting to 127.0.0.1 

等待，仅此而已

我还没有找到如何在 C 中执行此操作的真正有用的示例，因此我非常感谢您能给我的任何帮助。

如何实现auth和no auth方法？

新的更正代码：

/*
** client_proxy.c -- a stream socket socks 5 client demo
*/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>

#include <arpa/inet.h>

#define PORT "9050" // the port client will be connecting to 

#define MAXDATASIZE 100 // max number of bytes we can get at once 

// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
    if (sa->sa_family == AF_INET) {
        return &(((struct sockaddr_in*)sa)->sin_addr);
    }

    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}

int main(int argc, char *argv[])
{
    int sockfd, numbytes;  
    char buf[MAXDATASIZE];
    struct addrinfo hints, *servinfo, *p;
    int rv;
    char s[INET6_ADDRSTRLEN];

    if (argc != 2) {
        fprintf(stderr,"usage: client hostname\n");
        exit(1);
    }

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;

    if ((rv = getaddrinfo(argv[1], PORT, &hints, &servinfo)) != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
        return 1;
    }

    // loop through all the results and connect to the first we can
    for(p = servinfo; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) == -1) {
            perror("client: socket");
            continue;
        }

        if (connect(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
            perror("client: connect");
            close(sockfd);
            continue;
        }

        break;
    }

    if (p == NULL) {
        fprintf(stderr, "client: failed to connect\n");
        return 2;
    }

    inet_ntop(p->ai_family, get_in_addr((struct sockaddr *)p->ai_addr), s, sizeof s);
    printf("client: connecting to %s\n", s);

    freeaddrinfo(servinfo); // all done with this structure

    /* Version 5, one method: no authentication */
    char buffer[256], *ptrBuff, bufferf[256];
    ptrBuff = buffer;

    *(ptrBuff++) = 5; // socks version
    *(ptrBuff++) = 2;
    *(ptrBuff++) = 0x00; // no auth 
    *(ptrBuff++) = 0x02; // user pass auth

    if (send(sockfd, ptrBuff, buffer-ptrBuff, 0) == -1)
                perror("send");

    printf("sent\n");

    if ((numbytes = recv(sockfd, bufferf, MAXDATASIZE-1, 0)) == -1) {
        perror("recv");
        exit(1);
    }

    printf("client: received '%d'\n", bufferf[1]);

    close(sockfd);

    return 0;
}

我明白了：

client: connecting to 127.0.0.1
sent
client: received '97

每次收到的号码都不一样，怎么回事？

Answer 1

深入了解这段代码：

char buffer[256], *ptrBuff;
ptrBuff = buffer;

ptrBuff[0] = 5; // socks version
ptrBuff[1] = 1;
ptrBuff[2] = 0; // SOCKS_NOAUTH

if (send(sockfd, ptrBuff, buffer-ptrBuff, 0) == -1)
            perror("send");

您正在将len:buffer-ptrBuff 传递给发送函数。但是这些值（地址）是相同的地址，所以结果是0。

我猜，你想做的是

char buffer[256], *ptrBuff;
ptrBuff = buffer;

*(ptrBuff++) = 5; // socks version
*(ptrBuff++) = 1;
*(ptrBuff++) = 0; // SOCKS_NOAUTH

if (send(sockfd, ptrBuff, buffer-ptrBuff, 0) == -1)
            perror("send");

在这种情况下，ptrBuff 值（地址指向）在每次分配时递增，因此当调用 send 时，len (buffer-ptrBuff) 将是 3。

最后，您看到的是正确的，因为您没有向服务器端发送任何内容，并且客户端无法收到任何答复。所以recv 永远等待（阻塞模式）一个永远不会回答的答案。

Answer 2

ptrBuff = buffer;
..
 //stuff that does not modify ptrBuff
..
send(sockfd, ptrBuff, buffer-ptrBuff, 0) // ie. send nothing.

Answer 3

这个问题没有完全回答。

根据 RFC (https://datatracker.ietf.org/doc/html/rfc1928)，VER 和 NMETHODS 是十六进制值：

*(ptrBuff++) = 0x05; // socks version
*(ptrBuff++) = 0x02;

您真正的错误是缓冲区指向数据的开头，而ptrBuff 指向数据的结尾（因此，buffer-ptrBuff 是负值）。 那会更好：

if (send(sockfd, buffer, ptrBuff-buffer, 0) == -1)
            perror("send");