建立socket连接之后，编写c++函数接收客户端发来的post请求

在C++中，可以使用socket和HTTP协议库来实现接收客户端发来的POST请求。

首先，创建一个socket连接并监听客户端请求：

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>

int main() {
    // 创建socket
    int server_fd = socket(AF_INET, SOCK_STREAM, 0);
    
    // 绑定IP地址和端口号
    struct sockaddr_in server_addr;
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(8080); // 端口号
    server_addr.sin_addr.s_addr = INADDR_ANY;
    bind(server_fd, (struct sockaddr*)&server_addr, sizeof(server_addr));
    
    // 监听客户端请求
    listen(server_fd, 5);
    
    // 接收客户端请求
    struct sockaddr_in client_addr;
    socklen_t client_addrlen = sizeof(client_addr);
    int client_fd = accept(server_fd, (struct sockaddr*)&client_addr, &client_addrlen);
}

接下来，读取客户端发来的POST请求，并解析请求头和请求体：

#include <sstream>

// 读取数据
std::stringstream ss;
char buffer[1024];
int len;
while ((len = recv(client_fd, buffer, 1024, 0)) > 0) {
    ss << buffer;
}

std::string request = ss.str();
std::string request_header = request.substr(0, request.find("\r\n\r\n")); //请求头
std::string request_body = request.substr(request.find("\r\n\r\n") + 4); //请求体

根据HTTP协议规定，POST请求的请求体中通常包含表单数据，需要对其进行解析。这里可以使用第三方库来实现。

例如，使用cpp-httplib库：

#include "httplib.h"

// 解析请求体
httplib::Params params;
httplib::parse_multipart_formdata(request_body, "boundary", params);

最后，返回响应给客户端：

// 返回响应
std::string response_body = "Hello World!";
std::stringstream response;
response << "HTTP/1.1 200 OK\r\n";
response << "Content-Type: text/html; charset=UTF-8\r\n";
response << "Content-Length: " << response_body.length() << "\r\n";
response << "\r\n";
response << response_body;
send(client_fd, response.str().c_str(), response.str().length(), 0);

完整代码如下：

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include "httplib.h"

int main() {
    // 创建socket
    int server_fd = socket(AF_INET, SOCK_STREAM, 0);
    
    // 绑定IP地址和端口号
    struct sockaddr_in server_addr;
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(8080); // 端口号
    server_addr.sin_addr.s_addr = INADDR_ANY;
    bind(server_fd, (struct sockaddr*)&server_addr, sizeof(server_addr));
    
    // 监听客户端请求
    listen(server_fd, 5);
    
    // 接收客户端请求
    struct sockaddr_in client_addr;
    socklen_t client_addrlen = sizeof(client_addr);
    int client_fd = accept(server_fd, (struct sockaddr*)&client_addr, &client_addrlen);
    
    // 读取数据
    std::stringstream ss;
    char buffer[1024];
    int len;
    while ((len = recv(client_fd, buffer, 1024, 0)) > 0) {
        ss << buffer;
    }
    
    std::string request = ss.str();
    std::string request_header = request.substr(0, request.find("\r\n\r\n")); //请求头
    std::string request_body = request.substr(request.find("\r\n\r\n") + 4); //请求体
    
    // 解析请求体
    httplib::Params params;
    httplib::parse_multipart_formdata(request_body, "boundary", params);
    for (const auto& param : params) {
        std::cout << param.first << " = " << param.second << std::endl;
    }
    
    // 返回响应
    std::string response_body = "Hello World!";
    std::stringstream response;
    response << "HTTP/1.1 200 OK\r\n";
    response << "Content-Type: text/html; charset=UTF-8\r\n";
    response << "Content-Length: " << response_body.length() << "\r\n";
    response << "\r\n";
    response << response_body;
    send(client_fd, response.str().c_str(), response.str().length(), 0);
    
    // 关闭socket连接
    close(client_fd);
    close(server_fd);
    
    return 0;
}