HTTP - TCP实现HTTP GET请求 （2）

我们尝试用TCP来实现HTTP GET

基本TCP通信

首先写一段TCP通信的例子。这是一些测试代码，不要看代码质量，我们目的只是验证。

服务器：

先写个服务器，这里用了select。

// SelectServer.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <winsock2.h>
#include "boost/timer.hpp"
#pragma comment(lib,"ws2_32.lib")
#define  PORT  1688

bool InitAndListen(SOCKET &sListen)
{
WSADATA wsaData;
sockaddr_in local;
WORD version=MAKEWORD(2,0);
int ret=WSAStartup(version,&wsaData);
if(ret != 0)
{
printf("WASStarup failed/n");
return 0;
}

local.sin_family=AF_INET;
local.sin_addr.s_addr=INADDR_ANY;
local.sin_port=htons((u_short)PORT);

//Initial socket
sListen=socket(AF_INET,SOCK_STREAM,0);
if(sListen == INVALID_SOCKET)
{
printf("Initial socket failed/n");
return 0;
}

//Bind socket
if(bind(sListen,(sockaddr*)&local,sizeof(local))!=0)
{
printf("Bind socket failed/n");
return 0;
}

//Listen socket
if(listen(sListen,10)!=0)
{
printf("Listen socket failed");
return 0;
}
return 1;
}

void RunService()
{
SOCKET sListen;
if(InitAndListen(sListen) == 0)
{
return;
}
printf("Server wait for client connect...\n");
fd_set fdSocket;
FD_ZERO(&fdSocket);

//Add the listen socket to FD_set : fdSocket
FD_SET(sListen,&fdSocket);

while (true)
{
//assign the fdSocket to fdRead to select
fd_set fdRead = fdSocket;
timeval t;
t.tv_sec = 2;
t.tv_usec = 1;

boost::timer elapsed;
int nRet = select(NULL,&fdRead,NULL,NULL,NULL);//设置timeout为NULL,那么select会一直等下去,最多支持64个

printf("select elapsed: %f s\n", elapsed.elapsed());

if (nRet <= 0)
{
printf("select failed/n");
break;
}

for(int i=0;i<(int)fdSocket.fd_count;i++)
{
//check whether the socket is set
if(FD_ISSET(fdSocket.fd_array[i],&fdRead))
{
//New connect come
if(fdSocket.fd_array[i] == sListen)
{
sockaddr_in addrRemote;
int nAddrLen=sizeof(addrRemote);
SOCKET sNew=::accept(sListen,(sockaddr*)&addrRemote,&nAddrLen);
FD_SET(sNew,&fdSocket);//Put it to fdSocket sets
printf("Client %s connected\n",inet_ntoa(addrRemote.sin_addr));
}
else
{
char buffer[1024];
memset(buffer,0,1024);
int nRecev = recv(fdSocket.fd_array[i],buffer,
1024,0);

if (nRecev > 0)
{
printf("Received Client Msg:%s\n",buffer);

//echo back
::send(fdSocket.fd_array[i],buffer,
strlen(buffer),0);
}
else
{
printf("client disconnected\n");
//Close the socket and clear from the sets
closesocket(fdSocket.fd_array[i]);
FD_CLR(fdSocket.fd_array[i],&fdSocket);
}

}
}
}
}

}

int _tmain(int argc, _TCHAR* argv[])
{
RunService();
return 0;
}

这个服务器很简单，就是收到客户连接，如果客户有数据发过来，就再发回去。

客户端：

int Test1()
{
WSADATA wsaData;
int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
if (iResult != NO_ERROR) {
wprintf(L"WSAStartup function failed with error: %d\n", iResult);
return 1;
}
//----------------------
// Create a SOCKET for connecting to server
SOCKET ConnectSocket;
ConnectSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (ConnectSocket == INVALID_SOCKET) {
wprintf(L"socket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}
//----------------------
// The sockaddr_in structure specifies the address family,
// IP address, and port of the server to be connected to.
sockaddr_in clientService;
clientService.sin_family = AF_INET;
clientService.sin_addr.s_addr = inet_addr("127.0.0.1");
clientService.sin_port = htons(1688);

//----------------------
// Connect to server.
iResult = connect(ConnectSocket, (SOCKADDR *) & clientService, sizeof (clientService));
if (iResult == SOCKET_ERROR) {
wprintf(L"connect function failed with error: %ld\n", WSAGetLastError());
iResult = closesocket(ConnectSocket);
if (iResult == SOCKET_ERROR)
wprintf(L"closesocket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}

wprintf(L"Connected to server.\n");

char buf[] = "hello world.abc";
send(ConnectSocket, buf, sizeof(buf), 0);

char received[100] = {0};
int r = recv(ConnectSocket, received, 100, 0);

iResult = closesocket(ConnectSocket);
if (iResult == SOCKET_ERROR) {
wprintf(L"closesocket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}

WSACleanup();
}

很简单的客户端代码，往服务器发一些数据，再接收服务器的数据。

先运行服务端，在运行客户端，就会得到一下结果：



我们可以看到客户端收到了服务端的数据，其实就是客户端自己发给服务端的数据hello world.abc

这就是一个很简单的TCP通信例子。

如果配合前面介绍的，我们可以知道，当客户端发送数据"hello world.abc"的时候，send函数内部会加上TCP头，然后网络层会加上IP头，然后数据链路层会加上以太网头。

最终在物理网路上传播的数据类似：以太网头 + IP头 + TCP头 + 用户层数据（hello world.abc）。当然如果用户层数据多的话，一帧放不下，还会分片传播。

当服务器从网卡上收到数据的时候，就是反过来，从数据链路层=》网络层=》传输层=》应用层，一步一步把头给去掉，最终得到数据hello world.abc

应用层协议

到底什么是应用层协议呢？

我们上面的例子是没有什么意义的。假如我们的场景是用户登录，那么客户端就需要发送用户名和密码。怎么发呢？

简单点，我们约定好，客户端发上来的就是格式： 用户名;密码。也就是中间用分号隔开。

那么当服务器收到的时候就知道用分号来分割字符串，得到用户名和密码。

这就是一个自定义协议。

所谓协议，其实就是通信双方事先约定好的一些规则。

当然上面的协议只是一个例子，很傻的。

实际应用不太会用这么啥的办法，协议总是要尽可能定义的完善，通用。比如HTTP, FTP等，都是常见的协议。

HTTP协议

有关HTTP协议，可以查看RFC文档，里面有具体的定义，这里只是用TCP自己模拟一下HTTP访问。

以百度为例，先抓包看看浏览器访问百度的时候到底发送了什么数据包。我这里使用soapui来看：



可以很清楚的看到左边的HTTP GET 请求。

那么我们可以把刚才的代码改一下：

int Test2()
{
WSADATA wsaData;
int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
if (iResult != NO_ERROR) {
wprintf(L"WSAStartup function failed with error: %d\n", iResult);
return 1;
}
//----------------------
// Create a SOCKET for connecting to server
SOCKET ConnectSocket;
ConnectSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (ConnectSocket == INVALID_SOCKET) {
wprintf(L"socket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}
//----------------------
// The sockaddr_in structure specifies the address family,
// IP address, and port of the server to be connected to.
sockaddr_in clientService;
clientService.sin_family = AF_INET;
clientService.sin_addr.s_addr = inet_addr("115.239.211.112");

clientService.sin_port = htons(80);

//----------------------
// Connect to server.
iResult = connect(ConnectSocket, (SOCKADDR *) & clientService, sizeof (clientService));
if (iResult == SOCKET_ERROR) {
wprintf(L"connect function failed with error: %ld\n", WSAGetLastError());
iResult = closesocket(ConnectSocket);
if (iResult == SOCKET_ERROR)
wprintf(L"closesocket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}

wprintf(L"Connected to server.\n");

char buf[] = "GET / HTTP/1.1\r\n"
"Accept-Encoding: gzip,deflate\r\n"
"Host: www.baidu.com\r\n"
"Connection: Keep-Alive\r\n"
"User-Agent: Apache-HttpClient/4.1.1 (java 1.5)\r\n\r\n"
;

send(ConnectSocket, buf, sizeof(buf), 0);

char received[1000] = {0};
int r = recv(ConnectSocket, received, 1000, 0);

iResult = closesocket(ConnectSocket);
if (iResult == SOCKET_ERROR) {
wprintf(L"closesocket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}

WSACleanup();
}

这里没有写DNS解析，所以直接用百度的ip（ping一下就知道）。

115.239.211.112

上面这个就是ping得到的百度ip，那么大家都知道HTTP服务的监听端口是80，所以改成80.

然后发送的数据是：

GET http://www.baidu.com/ HTTP/1.1
Accept-Encoding: gzip,deflate
Host: www.baidu.com
Connection: Keep-Alive
User-Agent: Apache-HttpClient/4.1.1 (java 1.5)

而这个就是HTTP协议的header。这个就是实现约定好的规则，服务器和客户端都遵守。

运行一下：



得到了服务器的返回。当然这里只是傻傻的收固定的字节，实际上是应该根据HTTP协议把所有的数据收完的。这里只是例子，无所谓。

所以说，HTTP是应用层协议，它是基于TCP协议实现（听说也有基于UDP的，但是少见）。

HTTP一般是无状态的，也就是收到服务器的响应就断开连接了，实际上这也只是HTTP协议的一种规定而已。

实际上，我们不太可能自己用TCP去实现HTTP，像这种通用的协议，别人早就实现好了，拿来用就行，我们所要知道的是HTTP到底是怎么回事，怎么来的。

至于HTTP的具体细节，查看RFC文档就行了，像什么GET, POST, PUT, DELETE, KEEP-ALIVE, CHUNKED等等。

附

服务器代码：

// SelectServer.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <winsock2.h>
#include "boost/timer.hpp"
#pragma comment(lib,"ws2_32.lib")
#define  PORT  1688

bool InitAndListen(SOCKET &sListen)
{
WSADATA wsaData;
sockaddr_in local;
WORD version=MAKEWORD(2,0);
int ret=WSAStartup(version,&wsaData);
if(ret != 0)
{
printf("WASStarup failed/n");
return 0;
}

local.sin_family=AF_INET;
local.sin_addr.s_addr=INADDR_ANY;
local.sin_port=htons((u_short)PORT);

//Initial socket
sListen=socket(AF_INET,SOCK_STREAM,0);
if(sListen == INVALID_SOCKET)
{
printf("Initial socket failed/n");
return 0;
}

//Bind socket
if(bind(sListen,(sockaddr*)&local,sizeof(local))!=0)
{
printf("Bind socket failed/n");
return 0;
}

//Listen socket
if(listen(sListen,10)!=0)
{
printf("Listen socket failed");
return 0;
}
return 1;
}

void RunService()
{
SOCKET sListen;
if(InitAndListen(sListen) == 0)
{
return;
}
printf("Server wait for client connect...\n");
fd_set fdSocket;
FD_ZERO(&fdSocket);

//Add the listen socket to FD_set : fdSocket
FD_SET(sListen,&fdSocket);

while (true)
{
//assign the fdSocket to fdRead to select
fd_set fdRead = fdSocket;
timeval t;
t.tv_sec = 2;
t.tv_usec = 1;

boost::timer elapsed;
int nRet = select(NULL,&fdRead,NULL,NULL,NULL);//设置timeout为NULL,那么select会一直等下去,最多支持64个

printf("select elapsed: %f s\n", elapsed.elapsed());

if (nRet <= 0)
{
printf("select failed/n");
break;
}

for(int i=0;i<(int)fdSocket.fd_count;i++)
{
//check whether the socket is set
if(FD_ISSET(fdSocket.fd_array[i],&fdRead))
{
//New connect come
if(fdSocket.fd_array[i] == sListen)
{
sockaddr_in addrRemote;
int nAddrLen=sizeof(addrRemote);
SOCKET sNew=::accept(sListen,(sockaddr*)&addrRemote,&nAddrLen);
FD_SET(sNew,&fdSocket);//Put it to fdSocket sets
printf("Client %s connected\n",inet_ntoa(addrRemote.sin_addr));
}
else
{
char buffer[1024];
memset(buffer,0,1024);
int nRecev = recv(fdSocket.fd_array[i],buffer,
1024,0);

if (nRecev > 0)
{
printf("Received Client Msg:%s\n",buffer);

//echo back
::send(fdSocket.fd_array[i],buffer,
strlen(buffer),0);
}
else
{
printf("client disconnected\n");
//Close the socket and clear from the sets
closesocket(fdSocket.fd_array[i]);
FD_CLR(fdSocket.fd_array[i],&fdSocket);
}

}
}
}
}

}

int _tmain(int argc, _TCHAR* argv[])
{
RunService();
return 0;
}

客户端代码：

// TestSocket.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>
#include <string>
#pragma comment(lib, "ws2_32.lib")

using namespace std;

int Test1()
{
WSADATA wsaData;
int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
if (iResult != NO_ERROR) {
wprintf(L"WSAStartup function failed with error: %d\n", iResult);
return 1;
}
//----------------------
// Create a SOCKET for connecting to server
SOCKET ConnectSocket;
ConnectSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (ConnectSocket == INVALID_SOCKET) {
wprintf(L"socket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}
//----------------------
// The sockaddr_in structure specifies the address family,
// IP address, and port of the server to be connected to.
sockaddr_in clientService;
clientService.sin_family = AF_INET;
clientService.sin_addr.s_addr = inet_addr("127.0.0.1");
clientService.sin_port = htons(1688);

//----------------------
// Connect to server.
iResult = connect(ConnectSocket, (SOCKADDR *) & clientService, sizeof (clientService));
if (iResult == SOCKET_ERROR) {
wprintf(L"connect function failed with error: %ld\n", WSAGetLastError());
iResult = closesocket(ConnectSocket);
if (iResult == SOCKET_ERROR)
wprintf(L"closesocket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}

wprintf(L"Connected to server.\n");

char buf[] = "hello world.abc";
send(ConnectSocket, buf, sizeof(buf), 0);

char received[100] = {0};
int r = recv(ConnectSocket, received, 100, 0);

iResult = closesocket(ConnectSocket);
if (iResult == SOCKET_ERROR) {
wprintf(L"closesocket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}

WSACleanup();
}

int Test2()
{
WSADATA wsaData;
int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
if (iResult != NO_ERROR) {
wprintf(L"WSAStartup function failed with error: %d\n", iResult);
return 1;
}
//----------------------
// Create a SOCKET for connecting to server
SOCKET ConnectSocket;
ConnectSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (ConnectSocket == INVALID_SOCKET) {
wprintf(L"socket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}
//----------------------
// The sockaddr_in structure specifies the address family,
// IP address, and port of the server to be connected to.
sockaddr_in clientService;
clientService.sin_family = AF_INET;
clientService.sin_addr.s_addr = inet_addr("115.239.211.112");

clientService.sin_port = htons(80);

//----------------------
// Connect to server.
iResult = connect(ConnectSocket, (SOCKADDR *) & clientService, sizeof (clientService));
if (iResult == SOCKET_ERROR) {
wprintf(L"connect function failed with error: %ld\n", WSAGetLastError());
iResult = closesocket(ConnectSocket);
if (iResult == SOCKET_ERROR)
wprintf(L"closesocket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}

wprintf(L"Connected to server.\n");

char buf[] = "GET / HTTP/1.1\r\n"
"Accept-Encoding: gzip,deflate\r\n"
"Host: www.baidu.com\r\n"
"Connection: Keep-Alive\r\n"
"User-Agent: Apache-HttpClient/4.1.1 (java 1.5)\r\n\r\n"
;

send(ConnectSocket, buf, sizeof(buf), 0);

char received[2000] = {0};
int r = recv(ConnectSocket, received, 2000, 0);

iResult = closesocket(ConnectSocket);
if (iResult == SOCKET_ERROR) {
wprintf(L"closesocket function failed with error: %ld\n", WSAGetLastError());
WSACleanup();
return 1;
}

WSACleanup();
}

int main(int argc, char **argv)
{

Test2();

return 0;
}