HTTP服务器

1. 项目背景和技术特点

实现目的

从移动端到浏览器，HTTP 协议无疑是打开互联网应用窗口的重要协议，其在网络应用层中的地位不可撼动，是能准确区分前后台的重要协议。

完善对HTTP协议的理论学习，从零开始完成WEB服务器开发。

采用 CS 模型，编写支持中小型应用的HTTP服务器，井结合MySQL。

该项目可以帮助我们从技术上理解上网输入网站URL到关闭浏览器到所有操作中的技术细节。

HTTP基础知识，这里就不再赘述了

技术特点

• Linux 网络编程 TCP/IP协议、socket流式套接、http协议。
• 多线程技术
• cgi 技术
• shell 脚本
• 线程池

开发环境

• centos7
• vim gcc/g++ Makefile

2. 代码结构和实现思路

TcpServer

先实现HTTP的底层协议TCP的代码，也就是完成基本的网络套接字代码。实现成单例模式以供上层调用。

//TcpServer.hpp
#pragma once
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include #define BACK_LOG 5class TcpServer
{
private:int _port;int _listen_sock;TcpServer(int port) : _port(port), _listen_sock(-1){}TcpServer(const TcpServer& ts) = delete;TcpServer operator=(const TcpServer& ts) = delete;static TcpServer* _svr;
public:static TcpServer* GetInstance(int port);void InitServer();void Socket();void Bind();void Listen();~TcpServer(){}
};
TcpServer* TcpServer::_svr = nullptr;

HttpServer

HttpServer类实现调用TcpServer单例，并进入事件循环。

#pragma once
#include 
#include 
#include "TcpServer.hpp"
#include "Protocol.hpp"#define PORT 8080class HttpServer
{
private:int _port;TcpServer* _tcp_svr;bool _stop;public:HttpServer(int port = PORT) : _port(port), _tcp_svr(nullptr), _stop(false){}void InitServer() {_tcp_svr = TcpServer::GetInstance(_port);}void Loop();~HttpServer(){}
};

接下来就是，读取请求，分析请求，构建响应并返回。

Protocol

定制HTTP请求和响应的协议。接着就是EndPoint类实现HTTP读取解析响应等一系列函数。

struct HttpRequest
{std::string _request_line;std::vector _request_headers;std::string _blank;std::string _request_body;std::string _method;std::string _uri;std::string _version;std::string _path;std::string _query;struct stat _resoucre_stat;bool _cgi = false;std::unordered_map _header_kvs;
};struct HttpResponse
{std::string _status_line;std::vector _response_headers;std::string _blank = LINE_BREAK;std::string response_body;int _status_code = OK; int _resource_fd = -1;
};

class EndPoint
{
private:int _sock;HttpRequest _http_request;HttpResponse _http_response;private:void RecvHttpRequestLine();void RecvHttpRequestHeadler();void ParseHttpRequestLine();void ParseHttpRequestHeadler();void RecvParseHttpRequestBody();int ProcessCgi();int ProcessWebPage();public:EndPoint(int sock) : _sock(sock) {}void RecvHttpRequest(){RecvHttpRequestLine();RecvHttpRequestHeadler();}void ParseHttpRequest(){ParseHttpRequestLine();ParseHttpRequestHeadler();RecvParseHttpRequestBody();}void BuildHttpResponse();void SendHttpResponse();~EndPoint(){}
};

读取和解析请求

当前请求时，我们以行为单位。

从各大平台发来的数据的行分隔符各有不同，我们要做的是兼容所有情况，也就是我们要自行实现读取一行数据的接口。

void EndPoint::RecvHttpRequestLine()
{std::string& line = _http_request._request_line;Util::ReadLine(_sock, &line);line.resize(line.size() - 1);
}
void EndPoint::RecvHttpRequestHeadler()
{std::string line;while (true) // 读到空行，读取结束{Util::ReadLine(_sock, &line);if (line == "\n") {_http_request._blank = line; // 将空行放到blank中break;}line.resize(line.size() - 1);_http_request._request_headers.push_back(std::move(line));line.clear();}
}void EndPoint::ParseHttpRequestLine()
{std::stringstream ss(_http_request._request_line);ss >> _http_request._method >> _http_request._uri >> _http_request._version;
}
void EndPoint::ParseHttpRequestHeadler()
{for (auto& header : _http_request._request_headers)_http_request._header_kvs.insert(Util::GetKV(header, ": "));
}
void EndPoint::RecvParseHttpRequestBody()
{auto& method = _http_request._method;auto& headers_map = _http_request._header_kvs;auto& body = _http_request._request_body;auto iter = headers_map.find("Content-Length");if (iter == headers_map.end())return;else_http_request._content_length = stoi(iter->second);Util::ReadLine(_sock, &body);body.resize(body.size() - 1);
}

构建和返回响应

如果是GET方法获取资源路径，并进行一系列的检查判断。根据请求资源的类型设置CGI处理，如果是POST方法直接设置CGI。

void EndPoint::BuildHttpResponse()
{auto& code = _http_response._status_code;auto& path = _http_request._path;auto& rsrc_st = _http_request._resoucre_stat;// 排除非法请求if (_http_request._method != "GET" && _http_request._method != "POST") {LOG(WARNING) << "bad request invaild method\n";code = BAD_REQUEST;goto END;}if (_http_request._method == "GET") {size_t pos = _http_request._uri.find('?');if (pos != std::string::npos) {Util::CutString(_http_request._uri, &path, &_http_request._query, pos);_http_request._cgi = true; // 带参一定用cgi}else path = _http_request._uri;// 检查资源路径path = WEB_ROOT + path; // 拼接web根目录前缀if (path.back() == '/')path += HOME_PAGE; // 拼接默认访问资源后缀//判断资源路径是否合法if (stat(path.c_str(), &rsrc_st) == 0) {if (S_ISDIR(rsrc_st.st_mode)) {path += "/" + HOME_PAGE;stat(path.c_str(), &rsrc_st);}if (rsrc_st.st_mode & S_IXUSR ||rsrc_st.st_mode & S_IXGRP ||rsrc_st.st_mode & S_IXOTH)_http_request._cgi = true;}else {LOG(WARNING) << "require " << path + " resource not found\n";code = NOT_FOUND;goto END;}}else if (_http_request._method == "POST") {_http_request._cgi = true;path = WEB_ROOT + _http_request._uri;}else {}// 处理请求if (_http_request._cgi == true) {code = ProcessCgi();     // 执行cgi请求，程序运行结果放到response_body中if (code == OK)LOG(INFO) << "cgi process executed success\n";code = ProcessWebPage(); // 讲cgi结果构建网页返回}else {code = ProcessWebPage(); // 返回静态网页if (code == OK)LOG(INFO) << "send " + path + " success\n";}
}

发送响应就是简单的将构建好的响应返回给对端即可。

void EndPoint::SendHttpResponse()
{send(_sock, _http_response._status_line.c_str(), _http_response._status_line.size(), 0);for (auto& header : _http_response._response_headers) {header += LINE_BREAK;send(_sock, header.c_str(), header.size(), 0);}send(_sock, _http_response._blank.c_str(), _http_response._blank.size(), 0);if (_http_request._cgi) {auto& body = _http_response.response_body;int total = 0;while (total < body.size()) {ssize_t s = send(_sock, body.c_str() + total, body.size() - total, 0);if (s == 0) break;total += s;}}else {sendfile(_sock, _http_response._resource_fd, 0, _http_request._resrc_stat.st_size);close(_http_response._resource_fd);}LOG(INFO) << "send http response success\n";
}

处理静态和非静态请求

构建普通网页响应。

int ProcessNonCgi()
{_http_response._resource_fd = open(_http_request._path.c_str(), O_RDONLY); if (_http_response._resource_fd < 0)return NOT_FOUND;auto& line = _http_response._status_line;auto& code = _http_response._status_code;line = HTTP_VERSION + " " + std::to_string(code) + " " + Util::Code2Desc(code) + LINE_BREAK;auto& stat = _http_request._resoucre_stat;auto& path = _http_request._path;std::string content_type_header = "Content-Type: " + Util::Suffix2Type(GetSuffix(path));std::string content_length_header = "Content-Length: " + std::to_string(stat.st_size);std::string content_language_header = "Content-Language: zh-cn";_http_response._response_headers.push_back(content_type_header);_http_response._response_headers.push_back(content_length_header);_http_response._response_headers.push_back(content_language_header);return OK;
}

构建CGI响应。这是本项目的重难点。

线程首先首先创建子进程，将具体执行进程程序替换的任务交给子进程。

其次定制父子进程通信协议。

请求方法，GET方法的请求参数，报头中的正文大小几个变量都用环境变量导给子进程。POST方法的请求体使用管道导给子进程。

中个细节代码中有注释说明。

int ProcessCgi()
{auto& method = _http_request._method;auto& body = _http_request._request_body;auto& path = _http_request._path;auto& code = _http_response._status_code;// 构建两个管道，一个是父写子读，一个是父读子写，管道从父进程角度命名// parent output[1]  -->  output[0] child// parent  input[0]  <--  input[1]  childint input[2];  // 父读子写int output[2]; // 父写子读if (pipe(input) < 0 || pipe(output) < 0)return SVR_ERROR;pid_t pid = fork();if (pid == 0) /* child */ {close(input[0]);close(output[1]);int ret = setenv("METHOD", method.c_str(), 1); // 先导请求方法if (method == "GET") // 再导GET请求参数ret |= setenv("QUERY", _http_request._query.c_str(), 0); else if (method == "POST") // 再导正文大小ret |= setenv("CONTENT_LENGTH", std::to_string(body.size()).c_str(), 0); if (ret < 0)LOG(WARNING) << "set env failed, errno: " << errno << '\n';dup2(input[1], 1);dup2(output[0], 0);execl(_http_request._path.c_str(), _http_request._path.c_str(), nullptr);code = SVR_ERROR;exit(1);}else if (pid > 0) /* parent */ {close(input[1]);close(output[0]);if (_http_request._method == "POST") {auto& body = _http_request._request_body;int already = 0;while (already < body.size()) {ssize_t s = write(output[1], body.c_str() + already, body.size() - already);if (s == 0) break;already += s;}}int status = 0;pid_t ret = waitpid(pid, &status, 0);if (ret < 0)LOG(ERROR) << "parent process wait failed\n";code = SVR_ERROR;}close(input[0]);close(output[1]);return code;}else { /* pid < 0 */ LOG(ERROR) << "failed to create child process\n";return SVR_ERROR;}return code;
}

差错处理

在读取请求构建响应发送响应的过程中，都穿插着错误判断，并以HTTP响应状态码作为返回值。

在适当的地方goto END;，直接进行错误处理。错误处理利用得到的状态码构建错误响应，也就是返回错误网页，如404页面。

void BuildHttpResponse()
{// 排除非法请求if (_http_request._method != "GET" && _http_request._method != "POST"){LOG(WARNING) << "bad request invaild method\n";code = BAD_REQUEST;goto END;}//...// 差错处理END:if (code != OK){LOG(INFO) << "headler error begin, code: " << code << '\n';ErrorHelper(); // 构建错误响应}
}private:
void ErrorHelper()
{_http_request._cgi = false; // 错误处理，返回静态网页auto& code = _http_response._status_code;switch (code){case BAD_REQUEST:HeadlerWrong(PAGE_404);break;case NOT_FOUND:HeadlerWrong(PAGE_404); // 单独构建404页面break;case SVR_ERROR:HeadlerWrong(PAGE_404);break;case SVR_UNAVL:HeadlerWrong(PAGE_404);break;default:LOG(WARNING) << "unkown error code" << std::endl;break;}
}void HeadlerWrong(const std::string& wrong_page)
{_http_request._path = WEB_ROOT + '/' + wrong_page;stat(_http_request._path.c_str(), &_http_request._resoucre_stat);ProcessWebPage(); // 返回404页面
}int ProcessCgi()
{if (pid == 0) {//...}else if (pid > 0) { /* parent */// 获取子进程退出结果int status = 0;pid_t ret = waitpid(pid, &status, 0);if (ret == pid){// 管道读取子进程输出char ch = 0;while (read(input[0], &ch, 1))_http_response.response_body.push_back(ch); // 子进程输出放到响应体中//判断进程是否正常终止if (WIFEXITED(status)) {LOG(INFO) << "subprocess exited exit code: " << WEXITSTATUS(status) << '\n';if (WEXITSTATUS(status) != 0)code = BAD_REQUEST;} else {LOG(INFO) << "subprocess exited by signal: " << WIFEXITED(status) << '\n';code = BAD_REQUEST;}}else {LOG(ERROR) << "parent process wait failed\n";code = SVR_ERROR;}//...return code;}else /* pid < 0 */ {LOG(ERROR) << "failed to create child process\n";return SVR_ERROR;}return code;
}

引入线程池

任务队列中的任务类，设置回调方法，使任务体能够自行调用处理任务的函数。

class Task
{
private:int _sock;CallBack HandlerTask; // 设置回调 当队列中有任务时，调用回调让后端处理任务public:Task() {}Task(int sock) : _sock(sock) {}~Task() {}void ProcessTask() {HandlerTask(_sock);}
};

将HeaderRequest方法，构建成回调CallBack仿函数。

class CallBack
{
public:CallBack() {}~CallBack() {}public:void operator()(int sock) {EndPoint* ep = new EndPoint(sock);if (ep->RecvHttpRequest() && ep->ParseHttpRequest()) {ep->BuildHttpResponse();ep->SendHttpResponse();}else LOG(WARNING) << "recv http request failed\n";delete ep;}
};

设置线程池，并配备任务队列。

交给外部HTTPServer类向任务队列中添加accept接受到的任务。

自身设置TASK_NUM数量的线程来同步互斥地获取任务队列中的任务。

class ThreadPool
{
private:std::queue _task_queue;int _task_num;bool _stop;pthread_mutex_t _mtx;pthread_cond_t _cond;static ThreadPool* _thread_pool;private:ThreadPool() = default;ThreadPool(int num = TASK_NUM) : _task_num(num), _stop(false) {pthread_mutex_init(&_mtx, nullptr);pthread_cond_init(&_cond, nullptr);}ThreadPool(const ThreadPool&) = delete;public:static ThreadPool* GetInstance() {pthread_mutex_t lck = PTHREAD_MUTEX_INITIALIZER;if (_thread_pool == nullptr) {pthread_mutex_lock(&lck);if (_thread_pool == nullptr) {_thread_pool = new ThreadPool(TASK_NUM);_thread_pool->InitThreadPool();}pthread_mutex_unlock(&lck);}return _thread_pool;}void InitThreadPool() {for (int i = 0; i < _task_num; ++i) {pthread_t tid;if (pthread_create(&tid, nullptr, ThreadRoutine, (void*)_thread_pool) != 0) {LOG(FATAL) << "create pthread failed\n";exit(1);}}LOG(INFO) << "thread pool init success\n";}bool isEmpty() {return _task_queue.empty();}void Lock() {pthread_mutex_lock(&_mtx);}void Unlock() {pthread_mutex_unlock(&_mtx);}void ThreadWait() {pthread_cond_wait(&_cond, &_mtx);}void ThreadWakeup() {pthread_cond_signal(&_cond);}static void* ThreadRoutine(void* args) {ThreadPool* tp = (ThreadPool*)args;while (!tp->_stop) {tp->Lock();while (tp->isEmpty())tp->ThreadWait();Task task;tp->PopTask(&task);tp->Unlock();task.ProcessTask();}}void PushTask(const Task& task) {Lock();_task_queue.push(task);Unlock();ThreadWakeup();}void PopTask(Task* task) {*task = _task_queue.front();_task_queue.pop();}~ThreadPool() {pthread_mutex_destroy(&_mtx);pthread_cond_destroy(&_cond);}
};
ThreadPool* ThreadPool::_thread_pool = nullptr;

class HttpServer
{
private:int _port;TcpServer* _tcp_svr;ThreadPool* _thread_pool;bool _stop;public:HttpServer(int port = PORT) : _port(port), _tcp_svr(nullptr), _stop(false) {}~HttpServer() {}void InitServer() {signal(SIGPIPE, SIG_IGN); // 忽略SIGPIPE信号_tcp_svr = TcpServer::GetInstance(_port);_thread_pool = ThreadPool::GetInstance();}void Loop() {while (!_stop) {struct sockaddr_in peer;socklen_t len = sizeof(peer);int sock = accept(_tcp_svr->GetListenSock(), (struct sockaddr*)&peer, &len);if (sock < 0) continue;Task task(sock);_thread_pool->PushTask(task);}}
};

调用逻辑

3. 难点总结和项目扩展

对于CGI机制的理解和实现。

整个HTTP服务就是CGI程序和客户端沟通的桥梁，因为CGI程序与外界的输入输出都由HTTP服务器代理和转发。

通过子进程进程程序替换的方式，能够调用任意程序，且可以获得程序的运行结果和控制其输入输出。

项目扩展

• URL encode decode
• 数据库增删查改
• HTTP其他方法
• 配置文件化
• 301302转发

业务层面

• 实现在线计算器（日期转换等）
• 实现在线简历
• 实现博客系统

技术层面

• 支持HTTP1.1长连接（链接管理）
• 提高并发量和执行效率
• 支持redis
• 支持多机器业务转发负载均衡的代理功能