Introductory Guide to Socket Network Programming with PHP_php Tips

What are TCP/IP and UDP?

TCP/IP (Transmission Control Protocol/Internet Protocol) is an industrial standard protocol set designed for wide area networks (WANs).
UDP (User Data Protocol, User Datagram Protocol) is a protocol corresponding to TCP. It is a member of the TCP/IP protocol suite.
​ ​ ​ Here is a diagram showing the relationship between these protocols.

The TCP/IP protocol suite includes the transport layer, network layer, and link layer. Now you know the relationship between TCP/IP and UDP.
Where is the Socket?
In Figure 1, we don’t see the shadow of Socket, so where is it? Let’s let pictures speak for themselves.

It turns out that the Socket is here.
What is Socket?
Socket is an intermediate software abstraction layer for communication between the application layer and the TCP/IP protocol family. It is a set of interfaces. In the design mode, Socket is actually a facade mode, which hides the complex TCP/IP protocol family behind the Socket interface. For users, a set of simple interfaces is all, allowing Socket to organize data to meet the specified requirements. protocol.
Can you use them?
Previous generations have done a lot for us, and communication between networks has become much simpler, but after all, there is still a lot of work to be done. When I heard about Socket programming before, I thought it was relatively advanced programming knowledge, but as long as we understand the working principle of Socket programming, the mystery will be lifted.
A scene in life. If you want to call a friend, dial the number first. After the friend hears the ringing tone, he picks up the phone. At this time, you and your friend are connected and you can talk. When the communication is over, hang up the phone to end the conversation. Scenes in life explain how this works. Maybe the TCP/IP protocol family was born in life, but this is not necessarily the case.

Overview of Socket Programming in PHP
php5.3 comes with a socket module, which enables php to have socket communication capabilities. For specific APIs, please refer to the official manual: http://php.net/manual/zh/function.socket-create.php. The specific implementation follows c Very similar, except that the underlying operations

such as memory allocation and network byte order conversion are missing

At the same time, the pcntl module of PHP and the posix module can realize basic process management, signal processing and other operating system level functions. There are two very key functions here, pcntl_fork() and posix_setsid(). Forking () a process means creating a copy of the running process. The copy is considered a child process, and the original process is considered the parent process. After fork() is run, it can be separated from the process and terminal control that started it, which also means that the parent process can exit freely. pcntl_fork() return value, -1 indicates execution failure, 0 indicates in the child process, and greater than 0 indicates in the parent process. setsit(), which first makes the new process the "leader" of a new session, and finally makes the process no longer control the terminal. This is also the most critical step in becoming a daemon process, which means that the process will not be forced to exit when the terminal is closed. This is a critical step for a resident process that cannot be interrupted. Perform the last fork(). This step is not necessary, but it is usually done. Its greatest significance is to prevent the control terminal from being obtained

What is a daemon? A daemon is usually thought of as a background task that does not control the terminal. It has three obvious characteristics:

1. Running in the background
2. Detach from the process that started it
3. No terminal control required

The most common implementation method: fork() -> setsid() -> fork(). The run_server() method in the code implements the daemon process.

Server side socket monitoring code

  <&#63;php 
   
  // 接受客户端请求，回复固定的响应内容 
  function server_listen_socket ($address, $port) 
  { 
    $buffer = "Msg from wangzhengyi server, so kubi..."; 
    $len = strlen($buffer); 
     
    // create, bind and listen to socket 
    $socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP); 
    if (! $socket) { 
      echo "failed to create socket:" . socket_strerror($socket) . "\n"; 
      exit(); 
    } 
     
    $bind_flag = socket_bind($socket, $address, $port); 
    if (! $bind_flag) { 
      echo "failed to bind socket:" . socket_strerror($bind_flag) . "\n"; 
      exit(); 
    } 
     
    $backlog = 20; 
    $listen_flag = socket_listen($socket, $backlog); 
    if (! $listen_flag) { 
      echo "failed to listen to socket:" . socket_strerror($listen_flag) . "\n"; 
      exit(); 
    } 
     
    echo "waiting for clients to connect\n"; 
     
    while (1) { 
      if (($accept_socket = socket_accept($socket)) == FALSE) { 
        continue; 
      } else { 
        socket_write($accept_socket, $buffer, $len); 
        socket_close($accept_socket); 
      } 
    } 
  } 
   
  function run_server () 
  { 
    $pid1 = pcntl_fork(); 
    if ($pid1 == 0) { 
      // first child process 
       
      // 守护进程的一般流程：fork()->setsid()->fork() 
      posix_setsid(); 
       
      if (($pid2 = pcntl_fork()) == 0) { 
        $address = "192.168.1.71"; 
        $port = "8767"; 
        server_listen_socket($address, $port); 
      } else { 
        // 防止获得控制终端 
        exit(); 
      } 
    } else { 
      // wait for first child process exit 
      pcntl_wait($status); 
    } 
  } 
   
  // server守护进程 
  run_server(); 

Operation effect
Start the server-side socket process and see if it is running in the background. The effect is as shown below:

Client access can be accessed through a browser or curl. Here, curl is used directly to access