C++ 手写 HTTP 服务器：从请求解析到响应构建全流程

响应报文

• 状态行：HTTP 版本、状态码（如 200 OK）、描述信息。
• 响应报头：说明返回数据类型、长度等。
• 空行：分隔元数据和数据内容。
• 响应正文：HTML、JSON 等资源内容。

HTTP 服务器实现

HTTP 服务器本质上仍是 TCP 服务器，核心在于解析请求并返回符合规范的响应。

核心流程

socket → bind → listen → accept ↓ 创建线程 ↓ read → 解析 → write

关键步骤解析

1. 读取请求 使用 read 函数从 socket 读取数据，通常缓冲区设为 1024 字节。

2. 解析请求行 利用 stringstream 分割首行，提取方法、URL 和版本。

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

3. 拼接文件路径 根据 URL 映射到本地文件系统。

std::string path;
if (url == "/" || url == "/index.html") path = "./wwwroot/index.html";
else path = "./wwwroot" + url;

4. 读取网页内容 使用 ifstream 读取文件内容。

std::ifstream in(path);
while (std::getline(in, line)) { content += line + "\n"; }

5. 构造响应 组装 HTTP 响应头和内容。

std::string response = "HTTP/1.0 200 OK\r\n";
response += "Content-Length: " + std::to_string(content.size()) + "\r\n";
response += "Content-Type: text/html\r\n";
response += "\r\n";
response += content;
write(sockfd, response.c_str(), response.size());

6. 处理 404 若文件未找到，返回 404 状态码及错误页面。

完整代码示例

Socket.hpp 封装 Socket 基础操作。

#include <iostream>
#include <string>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/stat.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;
    }
    bool Connect(uint16_t server_port, std::string server_ip) {
        struct sockaddr_in server;
        bzero(&server, sizeof server);
        server.sin_family = AF_INET;
        server.sin_port = htons(server_port);
        inet_pton(AF_INET, server_ip.c_str(), &server.sin_addr);
        if (connect(sockfd_, (struct sockaddr *)&server, sizeof(server)) < 0) return false;
        return true;
    }
    ~Socket() { close(sockfd_); }
private:
    int sockfd_;
};

HttpServer.cc 主逻辑实现。

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

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

class HttpServer;

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

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;
            ThreadData *td = new ThreadData(sockfd, this);
            pthread_t tid;
            pthread_create(&tid, nullptr, ThreadRun, td);
        }
    }
    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;
            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;
            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);
    }
    ~HttpServer() {}
private:
    Socket listenfd_;
    uint16_t port_;
    std::string ip_;
};

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;
}

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://49.232.193.163:8080/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://49.232.193.163:8080/index.html">回到首页</a>
</body>
</html>

GET 与 POST 的区别

GET 和 POST 是最常用的两种方法，主要区别在于参数传递位置。

GET 方法 参数拼接到 URL 之后，可见于地址栏，安全性较低。

<form action="..." method="GET">
<input type="text" name="user">
<input type="password" name="pass">
</form>

POST 方法 参数放在请求正文中，不可见，适合敏感数据传输。

<form action="..." method="POST">
<input type="text" name="user">
<input type="password" name="pass">
</form>

通过 TCP 通信到 HTTP 服务器的实现，我们理解了请求如何被解析、浏览器与服务器交互的本质，以及 GET 与 POST 的差异。HTTP 不再是黑盒，而是一个有规则的字符串协议。