原理

HTTP代理服务器中能够提供一种HTTP CONNECT代理服务，能够允许用户建立TCP连接到任何端口。通过CONNECT方法穿透代理的实现方法为：
CONNECT代理服务器的代理端口（如：8080）；如果成功返回就可以按照正常的Socket进行通讯。当然在此之前需要先获得代理相关的信息。
如何获取HTTP代理相关信息
程序中是通过读取注册表来获取计算机HTTP代理相关信息的，在注册表的\\Software\\Microsoft\\Windows\\CurrentVersion\\Internet Settings键值下就保存着HTTP代理服务器及端口等信息，
根据该键值下的ProxyEnable值可以判断是否有HTTP代理，没有代理的情况下ProxyEnable值为0。
当然一般情况下程序去中访问该键值可能是受限的，所有就需要获取到访问令牌不受限制的UserSid，使用该UserSid去读取HTTP代理信息。

1char tmpBuffer[128] = { 0 };
2	::sprintf(tmpBuffer, "CONNECT %s:%d HTTP/1.1\r\nUser-Agent: Mozilla/4.0\r\nConnection: Keep-Alive\r\n\r\n", ip.c_str(), port);
3	Send(tmpBuffer, strlen(tmpBuffer));
4	Receive(tmpBuffer, sizeof(tmpBuffer));

实现

头文件

1#pragma once
2
3#include <string>
4#include <vector>
5
6using namespace std;
7
8class addrinfo;
9
10class CHttpProxy
11{
12public:
13	CHttpProxy(std::string ip, unsigned short port)
14		:m_proxyIp(ip), m_proxyPort(port), m_socket(-1)
15	{}
16
17	~CHttpProxy(void);
18
19	void ConnectProxyServer();
20	void ConnectServer(std::string ip, unsigned short port);
21
22	bool Send(const char* buf, int len);
23	int Receive(char* buf, int bufLen);
24
25	int GetSocket()
26	{
27		return m_socket;
28	}
29private:
30	std::string m_proxyIp;
31	addrinfo* m_addrinfo = nullptr;
32	unsigned short m_proxyPort;
33	int m_socket;
34};

实现

1#include "HttpProxy.h"
2#include <string.h>
3
4#include <time.h>
5#ifdef WIN32
6#include <WS2tcpip.h>
7#else 
8#include <unistd.h>
9#include <netdb.h> 
10#include <arpa/inet.h>
11#include <sys/types.h>          /* See NOTES */
12#include <sys/socket.h>
13#include <netinet/in.h>  
14#define INVALID_SOCKET -1
15#endif
16
17CHttpProxy::~CHttpProxy(void)
18{
19	if (m_addrinfo)
20	{
21		freeaddrinfo(m_addrinfo);
22	}
23}
24void CHttpProxy::ConnectProxyServer()
25{
26	struct sockaddr_in addr;
27	m_socket = socket(AF_INET, SOCK_STREAM, 0);
28	if (m_socket == INVALID_SOCKET)
29	{
30		throw CException("Error on creating socket fd");
31	}
32	
33	addrinfo inAddrInfo = { 0 };
34	inAddrInfo.ai_family = AF_INET;
35	inAddrInfo.ai_socktype = SOCK_STREAM;
36
37	std::string strPort = std::to_string(m_proxyPort);
38	if (getaddrinfo(m_proxyIp.c_str(), strPort.c_str(), &inAddrInfo, &m_addrinfo) != 0) // error occurs
39	{
40		throw CException("Error on calling getadrrinfo().");
41	}
42
43	if (connect(m_socket, m_addrinfo->ai_addr, m_addrinfo->ai_addrlen))
44	{
45		throw CException("Error on calling connect().");
46	}
47}
48
49void CHttpProxy::ConnectServer(std::string ip, unsigned short port)
50{
51	if (m_socket == INVALID_SOCKET)
52	{
53		throw CException("Invalid socket fd");
54	}
55	char tmpBuffer[128] = { 0 };
56	::sprintf(tmpBuffer, "CONNECT %s:%d HTTP/1.1\r\nUser-Agent: Mozilla/4.0\r\nConnection: Keep-Alive\r\n\r\n", ip.c_str(), port);
57	Send(tmpBuffer, strlen(tmpBuffer));
58	Receive(tmpBuffer, sizeof(tmpBuffer));
59
60	int mj, mi, code;
61	::sscanf(tmpBuffer, "HTTP/%d.%d %d", &mj, &mi, &code);
62	if (code != 200)
63	{
64		throw CException("http connect emial server faild");
65	}
66}
67
68int CHttpProxy::Receive(char* buf, int bufLen)
69{
70	return recv(m_socket, buf, bufLen, 0);
71}
72
73bool CHttpProxy::Send(const char* buf, int len)
74{
75	long ilen = len;
76	int sendCnt = 0;
77	int ret;
78
79	while (sendCnt < ilen)
80	{
81		if ((ret = send(m_socket, buf + sendCnt, ilen - sendCnt, 0)) == INVALID_SOCKET)
82		{
83			return false;
84		}
85		else
86		{
87			sendCnt += ret;
88		}
89	}
90
91	return true;
92}