HTTP(超文本传输协议)是一种客户端与服务端的传输协议，最早用于浏览器和服务器之间的通信，后来因为其使用灵活、方便等特点，广泛用于客户端与服务端的通信。文章将简单介绍HTTP协议，同时以C++方式分别实现HTTP GET、POST 请求
HTTP 请求报文
HTTP请求报文的一般格式由4部分组成：请求行、请求头部、空行、请求数据。如下图所示：
1.jpg
请求行：包含3部分内容：请求方法，URL，协议版本。形式如：GET /?aaa=1 HTTP/1.1。请求方法有GET、POST、HEAD、PUT、DELETE、OPTIONS等。URL指请求服务端的地址，可以是相对地址或域名形式的绝对地址。协议版本主要有HTTP/1.1 HTTP/1.0 HTTP/0.9，后面两种已很少使用了。
请求头部：以key/value形式成对表示头部参数，以英文冒号分隔。key名称的约定写法为Key，Key-Name，自定义key名称一般以“X-”开头。如php的声明“X-Powered-By:PHP/5.5.4-1”
空行：用来标识请求头部的数据已结束。
请求数据：可选项，这块内容只在POST方式下使用，作为POST的数据表示区域。使用这块内容，要在请求头部以Content-Length声明请求数据长度，以Content-Type声明请求数据类型。
HTTP POST请求
HTTP POST方式是把请求参数放到HTTP请求报文的请求数据中，为了让例子更容易看懂，仅保留HTTP Post关键参数，你还可以自定义一些参数，比如浏览器喜欢用的User-Agent，Accept，Connection等等
char *pHttpPost = "POST %s HTTP/1.1\r\n"
"Host: %s:%d\r\n"
"Content-Type: application/x-www-form-urlencoded\r\n"
"Content-Length: %d\r\n\r\n"
"%s";
char* addr = "http://localhost/post.php";
char* host = "127.0.0.1";
int port = 80;
char* msg = "aaa=1&bbb=2";
char strHttpPost[1024] = {0};
sprintf(strHttpPost, pHttpPost, addr, host, port, strlen(msg), msg);
//这里忽略掉了socket连接代码
send(sockClient, strHttpPost, strlen(strHttpPost), 0);
HTTP GET请求
HTTP GET方式是把请求参数放到HTTP请求报文的请求行URL中，所以请求行就是“GET /?aaa=1&bbb=2 HTTP/1.1\r\n”。URL最大长度通常浏览器取255，这和文件路径最大长度有关。虽然HTTP允许更大长度，但不建议怎么做，如果太长了，可以考虑换成POST方式
char *pHttpGet = "GET %s?%s HTTP/1.1\r\n"
"Host: %s:%d\r\n\r\n";
char* addr = "http://localhost/get.php";
char* host = "127.0.0.1";
int post = 80;
char* msg = "aaa=1&bbb=2";
char strHttpGet[1024] = {0};
sprintf(strHttpGet, pHttpGet, addr, msg, host, post);
//这里忽略掉了socket连接代码
send(sockClient, strHttpGet, strlen(strHttpGet), 0);
实现的HTTP
#include "HttpConnect.h"
#ifdef WIN32
#pragma comment(lib,"ws2_32.lib")
#endif
HttpConnect::HttpConnect()
{
#ifdef WIN32
//此处一定要初始化一下，否则gethostbyname返回一直为空
WSADATA wsa = { 0 };
WSAStartup(MAKEWORD(2, 2), &wsa);
#endif
}
HttpConnect::~HttpConnect()
{
}
void HttpConnect::socketHttp(std::string host, std::string request)
{
int sockfd;
struct sockaddr_in address;
struct hostent *server;
sockfd = socket(AF_INET,SOCK_STREAM,0);
address.sin_family = AF_INET;
address.sin_port = htons(80);
server = gethostbyname(host.c_str());
memcpy((char *)&address.sin_addr.s_addr,(char*)server->h_addr, server->h_length);
if(-1 == connect(sockfd,(struct sockaddr *)&address,sizeof(address))){
DBG <<"connection error!"<<std::endl;
return;
}
DBG << request << std::endl;
#ifdef WIN32
send(sockfd, request.c_str(),request.size(),0);
#else
write(sockfd,request.c_str(),request.size());
#endif
char buf[1024*1024] = {0};
int offset = 0;
int rc;
#ifdef WIN32
while(rc = recv(sockfd, buf+offset, 1024,0))
#else
while(rc = read(sockfd, buf+offset, 1024))
#endif
{
offset += rc;
}
#ifdef WIN32
closesocket(sockfd);
#else
close(sockfd);
#endif
buf[offset] = 0;
DBG << buf << std::endl;
}
void HttpConnect::postData(std::string host, std::string path, std::string post_content)
{
//POST请求方式
std::stringstream stream;
stream << "POST " << path;
stream << " HTTP/1.0\r\n";
stream << "Host: "<< host << "\r\n";
stream << "User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.3\r\n";
stream << "Content-Type:application/x-www-form-urlencoded\r\n";
stream << "Content-Length:" << post_content.length()<<"\r\n";
stream << "Connection:close\r\n\r\n";
stream << post_content.c_str();
socketHttp(host, stream.str());
}
void HttpConnect::getData(std::string host, std::string path, std::string get_content)
{
//GET请求方式
std::stringstream stream;
stream << "GET " << path << "?" << get_content;
stream << " HTTP/1.0\r\n";
stream << "Host: " << host << "\r\n";
stream <<"User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.3\r\n";
stream <<"Connection:close\r\n\r\n";
socketHttp(host, stream.str());
}
HttpConnect *http = new HttpConnect();
http->getData("127.0.0.1", "/login", "id=liukang&pw=123");
http->postData("127.0.0.1", "/login","id=liukang&pw=123");