HTTP 웹 서버를 직접 구현하여 프로토콜 스펙을 이해해보자!

public class WebServer {
    private static final Logger log = LoggerFactory.getLogger(WebServer.class);
    private static final int DEFAULT_PORT = 8080;

    public static void main(String args[]) throws Exception {
        int port = 0;
        if (args == null || args.length == 0) {
            port = DEFAULT_PORT;
        } else {
            port = Integer.parseInt(args[0]);
        }

        // 서버소켓을 생성한다. 웹서버는 기본적으로 8080번 포트를 사용한다.
        try (ServerSocket listenSocket = new ServerSocket(port)) {
            log.info("Web Application Server started {} port.", port);

            Socket connection; // Socket: 클라이언트와의 연결을 담당. 클라이언트가 연결될 때 까지 (요청이 들어올 때 까지) 대기한다.
            while ((connection = listenSocket.accept())  != null) {
            	// 요청이 들어오면 해당 요청을, 즉 Socket을 RequestHandler 에 전달하면서 요청에 대한 처리를 위임한다.
                RequestHandler requestHandler = new RequestHandler(connection);
                requestHandler.start(); // 요청 처리 시작
            }
        }
    }
}

public class RequestHandler extends Thread {
    private static final Logger log = LoggerFactory.getLogger(RequestHandler.class);
    DataBase dataBase = new DataBase();

    private Socket connection;

    public RequestHandler(Socket connectionSocket) {
        this.connection = connectionSocket;
    }

    public void run() {
        log.debug("New Client Connect! Connected IP : {}, Port : {}", connection.getInetAddress(),
                connection.getPort());

        try (InputStream in = connection.getInputStream();
			 OutputStream out = connection.getOutputStream()) {

         	// TODO: 사용자 요청에 대한 처리는 여기서 구현된다.

         } catch(IOException e) {
			log.error(e.getMessage());
         }
    }

    private void response200Header(DataOutputStream dos, int lengthOfBodyContent) {
    	try {
            dos.writeBytes("HTTP/1.1 200 OK \r\n");
            dos.writeBytes("Content-Type: text/html;charset=utf-8\r\n");
            dos.writeBytes("Content-Length: " + lengthOfBodyContent + "\r\n");
            dos.writeBytes("\r\n");
        } catch (IOException e) {
            log.error(e.getMessage());
        }
    }
}

POST /user/create HTTP/1.1  // (1) 요청 라인(Request Line)
HOST: localhost:8080  // (2) 요청 헤더(Request Header)
Connection-Length: 59
Content-Type: application/x-wwww-form-unlencoded
Accept: */*

userId=msung99&password=password  // (3) 요청 본문(Request Body)

HTTP/1.1 200 OK  // (1) 상태 라인(Status Line)
Content-Type: text/html;charset=utf-8  // (2) 응답 헤더(Response Header)
Content-Length: 20

<h1>Hello World!</h1> // (3) 응답 본문(Response Body)

public void run() {
	log.debug("New Client Connect! Connected IP : {}, Port : {}", connection.getInetAddress(),
    	connection.getPort());

     try (InputStream in = connection.getInputStream(); OutputStream out = connection.getOutputStream()) {
          DataOutputStream dos = new DataOutputStream(out);
          BufferedReader br = new BufferedReader(
							    new InputStreamReader(in, "UTF-8"));//(1)
          String line = br.readLine(); // (2)
          log.debug("request line : {}", line);

           if(line == null) {
           		return;
           }

           String[] tokens = line.split(" "); //  (3)
           while(!line.equals("")) { // (4)
             	line = br.readLine();
                log.debug("header : {}", line);
           }

           byte[] body = Files.readAllBytes(
           			new File("./webapp" + tokens[1]).toPath()); // (5)
           response200Header(dos, body.length);
           responseBody(dos, body);
      } catch (IOException e) {
      		log.error(e.getMessage());
      }
}

http://localhost:8080/user/create?userId=msung99&password=msung1234&name=minsung&email=msung99@gmail.com

public void run() {
	log.debug("New Client Connect! Connected IP : {}, Port : {}", connection.getInetAddress(),
    connection.getPort());

     try (InputStream in = connection.getInputStream(); OutputStream out = connection.getOutputStream()) {
     	DataOutputStream dos = new DataOutputStream(out);
        BufferedReader br = new BufferedReader(new InputStreamReader(in, "UTF-8"));
        String line = br.readLine();
        log.debug("request line : {}", line);

        if(line == null) {
        	return;
        }

        String[] tokens = line.split(" ");

        while(!line.equals("")) {
        	line = br.readLine();
            log.debug("header : {}", line);
        }

        String url = tokens[1];
        if(url.startsWith("/user/create")) {
        	int index = url.indexOf("?");
            String queryString = url.substring(index + 1);

            Map<String, String> params = HttpRequestUtils.parseQueryString(queryString);
            String userId = params.get("userId");
            String password = params.get("password");
            String name = params.get("name");
            String email = params.get("email");
            User user = new User(userId, password, name, email);
            // TODO: 추후 DB 구현 필요
         } else {
             byte[] body = Files.readAllBytes(new File("./webapp" + tokens[1]).toPath());
             response200Header(dos, body.length);
             responseBody(dos, body);
         }
     } catch (IOException e) {
         log.error(e.getMessage());
     }
}

<form name="question" method="post" action="/user/create"></form>

public void run() {
	log.debug("New Client Connect! Connected IP : {}, Port : {}", connection.getInetAddress(),
    connection.getPort());

     try (InputStream in = connection.getInputStream(); OutputStream out = connection.getOutputStream()) {
     	DataOutputStream dos = new DataOutputStream(out);
        BufferedReader br = new BufferedReader(new InputStreamReader(in, "UTF-8"));
        String line = br.readLine();
        log.debug("request line : {}", line);

        if(line == null) {
        	return;
        }

        String[] tokens = line.split(" ");
        int contentLength = 0; // (1)

        while(!line.equals("")) {
        	line = br.readLine();
            log.debug("header : {}", line);
            if(line.contains("Content-Length")) { // (2)
            	contentLength = getContentLength(line);
            }
        }

        String url = tokens[1];
        if(("/user/create".equals(url)) {
        	String body = IOUtils.readData(br, contentLength); // (3)

            // (4)
            Map<String, String> params = HttpRequestUtils.parseQueryString(body);
            String userId = params.get("userId");
            String password = params.get("password");
            String name = params.get("name");
            String email = params.get("email");
            User user = new User(userId, password, name, email);
            // TODO: 추후 DB 구현 필요
         } else {
             byte[] body = Files.readAllBytes(new File("./webapp" + tokens[1]).toPath());
             response200Header(dos, body.length);
             responseBody(dos, body);
         }
     } catch (IOException e) {
         log.error(e.getMessage());
     }
}

private int getContentLength(String line) {
	String[] headerTokens = line.split(":");
    return Integer.parseInt(headerTokens[1].trim());
}

HTTP/1.1 302 Found
Location: /index.html

String url = tokens[1];
if("/user/create".equals(url)) {
	String body = IOUtils.readData(br, contentLength);
    // ... (이전 구현 코드와 동일)
    response302Header(dos, "/index.html");
}
// ...

private void response302Header(DataOutputStream dos, String url) {
    try {
    	dos.writeBytes("HTTP/1.1 302 Found \r\n");
        dos.writeBytes("Location: " + url + "\r\n");
        dos.writeBytes("\r\n");
    } catch (IOException e) {
        log.error(e.getMessage());
	}
}

if("/user/create".equals(url)) {
    // ... (기존 로직과 동일)
    DataBase.addUser(user); // (1)
    response302Header(dos, "/index.html");
} else if("/user/login".equals(url)) {
	String body = IOUtils.readData(br, contentLength);

    Map<String, String> params = HttpRequestUtils.parseQueryString(body);
    User user = DataBase.findUserById(params.get("userId"));

    if(user == null) {
    	responseResource(out, "/user/login_failed.html");
        return;
    }

    if(user.getPassword().equals(params.get("password"))) {
    	response302LoginSuccess(dos);
    } else {
    	responseResource(out, "/user/login_failed.html");
	}
}

private void response302LoginSuccess(DataOutputStream dos) {
	try {
    	dos.writeBytes("HTTP/1.1 302 Found \r\n");
        dos.writeBytes("Set-Cookie: logined-true \r\n");
        dos.writeBytes("\r\n");
    } catch (IOException e) {
        log.error(e.getMessage());
    }
}

private void responseResource(OutputStream out, String url) throws IOException {
	DataOutputStream dos = new DataOutputStream(out);
    byte[] body = Files.readAllBytes(new File("./webapp" + url).toPath());
    response200Header(dos, body.length);
    responseBody(dos, body);
}