preface

What is a Socket? It is the cornerstone of computer network communication based on TCP/IP protocol. We can think of it abstractly as IP+ port number. Its essence is a programming interface (API), the encapsulation of TCP/IP. Understanding sockets helps us better understand the Http protocol.

1 Network Model

Network architecture models mainly include OSI reference model and TCP/IP five-layer model.We usually use the TCP/IP five-tier network model.

As shown in the figure, common network protocols at the application layer include Http, Https, and FTP. There are only two transport layers, TCP and UDP.

The mainstreamHttp1.1Also based on TCP to achieve persistent connection.

3 the Http message

HTTP request packets

Example: GET request

GET /test HTTP/1.1 Host: 192.168.62.248:8080 upgrade-insecure -Requests: 1 User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.128 Safari/537.36 Accept: text/html,application/xhtml+xml,application/xml; Q = 0.9, image/avif, image/webp image/apng, * / *; Q = 0.8, application/signed - exchange; v=b3; Q =0.9 Accept-encoding: gzip, deflate Accept-language: zh-cn,zh; Q = 0.9 Connection: keep aliveCopy the code

The response message

HTTP / 1.1 200 the content-type: text/HTML. charset=UTF-8 Content-Length: 3 Date: Thu, 22 Apr 2021 06:15:51 GMT Keep-Alive: timeout=60 Proxy-Connection: keep-alive aaaCopy the code

“Aaa” is the response data returned by the server.

4 Socket Encapsulates Http request implementation

After understanding the basic network architecture model, three-way handshake, four-way wave, and HTTP packets, the blogger uses socket to encapsulate the request to actually prove the HTTP packet structure as shown in the figure above.

try {
    StringBuffer requestMessage = new StringBuffer(); // Request message
    requestMessage.append("GET/HTTP / 1.0 \ r \ n"); / / request
	// Omit the request header
    requestMessage.append("\r\n");
    // omit the text

    // The kernel completes the three-way handshake when establishing a connection through the socket
    Socket socket = new Socket();
    SocketAddress socketAddress = new InetSocketAddress("www.baidu.com".80); // ip + port
    socket.connect(socketAddress); // Establish a connection

    BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
    bufferedWriter.write(requestMessage.toString());
    bufferedWriter.flush();

    InputStream inputStream = socket.getInputStream();
    BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
    String line;
    while((line = bufferedReader.readLine()) ! =null) {
        System.out.print(line + "\n");
    }
    inputStream.close();
} catch (IOException e) {
    e.printStackTrace();
}
Copy the code

Program running result