基于 C++ 手写 HTTP 服务器：从请求解析到响应构建

1. Socket 封装

为了方便管理，我们通常封装一个 Socket 类来处理底层系统调用。

#include <iostream>
#include <string>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <cstring>

enum Err { SocketErr = 1, BindErr, ListenErr };

class Socket {
public:
    Socket() {}
    void Init() {
        sockfd_ = socket(AF_INET, SOCK_STREAM, 0);
        if (sockfd_ < 0) {
            std::cout << "socket fail!!!" << std::endl;
            exit(SocketErr);
        }
    }
    void Bind(uint16_t port, std::string ip) {
        struct sockaddr_in server;
        memset(&server, 0, sizeof server);
        server.sin_family = AF_INET;
        server.sin_port = htons(port);
        inet_pton(AF_INET, ip.c_str(), &server.sin_addr);
        if (bind(sockfd_, (struct sockaddr *)&server, sizeof server) < 0) {
            std::cout << "bind fail" << std::endl;
            exit(BindErr);
        }
    }
    void Listen() {
        if (listen(sockfd_, 10) < 0) {
            std::cout << "listen fail" << std::endl;
            exit(ListenErr);
        }
    }
    int Accept(uint16_t *client_port, std::string *client_ip) {
        struct sockaddr_in client;
        bzero(&client, sizeof client);
        socklen_t len = sizeof(client);
        int newfd = accept(sockfd_, (struct sockaddr *)&client, &len);
        if (newfd < 0) return -1;
        char ip[64];
        inet_ntop(AF_INET, &client.sin_addr, ip, sizeof ip);
        *client_port = ntohs(client.sin_port);
        *client_ip = ip;
        return newfd;
    }
    ~Socket() { close(sockfd_); }
private:
    int sockfd_;
};

2. 核心处理逻辑

在 HttpServer.cc 中，我们启动监听循环，接受连接后创建线程处理请求。

#include <iostream>
#include <unistd.h>
#include "Socket.hpp"
#include <fstream>
#include <vector>
#include <sstream>

const std::string wwwroot = "./wwwroot";

class HttpServer {
public:
    HttpServer(uint16_t port, std::string ip) : port_(port), ip_(ip) {}
    
    void Init() {
        listenfd_.Init();
        listenfd_.Bind(port_, ip_);
        listenfd_.Listen();
    }

    void start() {
        while (1) {
            uint16_t client_port;
            std::string client_ip;
            int sockfd = listenfd_.Accept(&client_port, &client_ip);
            if (sockfd < 0) continue;
            // 实际项目中建议使用线程池，此处演示基础多线程
            pthread_t tid;
            pthread_create(&tid, nullptr, ThreadRun, new ThreadData(sockfd, this));
        }
    }

    static void *ThreadRun(void *arg) {
        pthread_detach(pthread_self());
        ThreadData *td = (ThreadData *)arg;
        td->ts_->HttpHandler(td->sockfd_);
        delete td;
        return nullptr;
    }

    std::string ReadHtmlContent(std::string &htmlpath) {
        std::string content;
        std::ifstream in(htmlpath.c_str());
        if (!in.is_open()) return "404";
        std::string line;
        while (std::getline(in, line)) {
            content += line;
        }
        in.close();
        return content;
    }

    void HttpHandler(int sockfd) {
        char buffer[1024];
        ssize_t s = read(sockfd, buffer, sizeof buffer - 1);
        std::string request;
        if (s > 0) {
            buffer[s] = 0;
            std::cout << buffer << std::endl;
            request = buffer;

            // 解析请求行
            std::vector<std::string> req_header;
            while (!request.empty()) {
                ssize_t pos = request.find("\r\n", 0);
                if (pos == std::string::npos) break;
                std::string line = request.substr(0, pos);
                if (line.empty()) break;
                req_header.push_back(line);
                request.erase(0, pos + 2);
            }

            std::stringstream ss(req_header[0]);
            std::string method, url, http_version;
            ss >> method >> url >> http_version;

            // 拼接文件路径
            std::string path = url;
            if (path == "/" || path == "/index.html") {
                path = wwwroot + "/index.html";
            } else {
                path = wwwroot + url;
            }

            std::string text = ReadHtmlContent(path);
            std::string response;

            if (text == "404") {
                std::string body = "<h1>404 Not Found</h1>";
                response = "HTTP/1.0 404 Not Found\r\n";
                response += "Content-Length: " + std::to_string(body.size()) + "\r\n";
                response += "Content-Type: text/html\r\n";
                response += "\r\n";
                response += body;
            } else {
                response = "HTTP/1.0 200 OK\r\n";
                response += "Content-Length: " + std::to_string(text.size()) + "\r\n";
                response += "Content-Type: text/html\r\n";
                response += "\r\n";
                response += text;
            }
            write(sockfd, response.c_str(), response.size());
        }
        close(sockfd);
    }

private:
    Socket listenfd_;
    uint16_t port_;
    std::string ip_;
};

class ThreadData {
public:
    ThreadData(int sockfd, HttpServer *ts) : sockfd_(sockfd), ts_(ts) {}
    int sockfd_;
    HttpServer *ts_;
};

int main(int argc, char *argv[]) {
    uint16_t port = std::stoi(argv[2]);
    std::string ip = argv[1];
    HttpServer *svr = new HttpServer(port, ip);
    svr->Init();
    svr->start();
    return 0;
}

3. 静态资源示例

我们需要准备简单的 HTML 文件来测试。

index.html

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>index</title>
</head>
<body>
<h1>你是一个好人</h1>
<a href="http://localhost:8080/a/b/hello.html">下一页</a>
</body>
</html>

hello.html

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Hello World</title>
</head>
<body>
<h1>祝你幸福</h1>
<a href="http://localhost:8080/index.html">回到首页</a>
</body>
</html>

启动服务器后，在浏览器输入 http://ip:port/ 即可访问。

GET 与 POST 方法对比

HTTP 中最常用的两种方法是 GET 和 POST，它们的区别主要体现在参数传递的位置上。

GET 方法

GET 请求会将表单参数拼接到 URL 之后。

<form action="http://localhost:8080/login" method="GET">
    账号：<input type="text" name="user"><br>
    密码：<input type="password" name="pass"><br>
    <input type="submit" value="登录">
</form>

当提交敏感信息（如密码）时，URL 中会明文显示参数，存在安全隐患，且容易受长度限制。

POST 方法

POST 请求将参数放在请求正文（Body）中。

<form action="http://localhost:8080/login" method="POST">
    账号：<input type="text" name="user"><br>
    密码：<input type="password" name="pass"><br>
    <input type="submit" value="登录">
</form>

这种方式更适合传输大量数据或敏感信息，因为参数不会暴露在 URL 栏中。

总结

从 TCP 通信到亲手实现 HTTP 服务器，我们深入理解了以下关键点：

• 请求是如何被服务器解析的？
• 浏览器和服务器之间到底在'说什么'？
• GET 和 POST 的本质区别是什么？

HTTP 不再是黑盒，它只是一个遵循特定规则的字符串协议。掌握其底层原理，有助于我们在进行网络编程时更加游刃有余。