README.md

The below file is REALLY OLD!

Instead, check out the library I put together at https://github.com/navarr/Sockets

SocketServer.class.php

<?php
	/*!	@class		SocketServer
		@author		Navarr Barnier
		@abstract 	A Framework for creating a multi-client server using the PHP language.
	 */
	class SocketServer
	{
		/*!	@var		config
			@abstract	Array - an array of configuration information used by the server.
		 */
		protected $config;

		/*!	@var		hooks
			@abstract	Array - a dictionary of hooks and the callbacks attached to them.
		 */
		protected $hooks;

		/*!	@var		master_socket
			@abstract	resource - The master socket used by the server.
		 */
		protected $master_socket;
		
		/*!	@var		max_clients
			@abstract	unsigned int - The maximum number of clients allowed to connect.
		 */
		public $max_clients = 10;

		/*!	@var		max_read
			@abstract	unsigned int - The maximum number of bytes to read from a socket at a single time.
		 */
		public $max_read = 1024;

		/*!	@var		clients
			@abstract	Array - an array of connected clients.
		 */
		public $clients;

		/*!	@function	__construct
			@abstract	Creates the socket and starts listening to it.
			@param		string	- IP Address to bind to, NULL for default.
			@param		int	- Port to bind to
			@result		void
		 */
		public function __construct($bind_ip,$port)
		{
			set_time_limit(0);
			$this->hooks = array();

			$this->config["ip"] = $bind_ip;
			$this->config["port"] = $port;

			$this->master_socket = socket_create(AF_INET, SOCK_STREAM, 0);
			socket_bind($this->master_socket,$this->config["ip"],$this->config["port"]) or die("Issue Binding");
			socket_getsockname($this->master_socket,$bind_ip,$port);
			socket_listen($this->master_socket);
			SocketServer::debug("Listenting for connections on {$bind_ip}:{$port}");
		}

		/*!	@function	hook
			@abstract	Adds a function to be called whenever a certain action happens.  Can be extended in your implementation.
			@param		string	- Command
			@param		callback- Function to Call.
			@see		unhook
			@see		trigger_hooks
			@result		void
		 */
		public function hook($command,$function)
		{
			$command = strtoupper($command);
			if(!isset($this->hooks[$command])) { $this->hooks[$command] = array(); }
			$k = array_search($function,$this->hooks[$command]);
			if($k === FALSE)
			{
				$this->hooks[$command][] = $function;
			}
		}

		/*!	@function	unhook
			@abstract	Deletes a function from the call list for a certain action.  Can be extended in your implementation.
			@param		string	- Command
			@param		callback- Function to Delete from Call List
			@see		hook
			@see		trigger_hooks
			@result		void
		 */
		public function unhook($command = NULL,$function)
		{
			$command = strtoupper($command);
			if($command !== NULL)
			{
				$k = array_search($function,$this->hooks[$command]);
				if($k !== FALSE)
				{
					unset($this->hooks[$command][$k]);
				}
			} else {
				$k = array_search($this->user_funcs,$function);
				if($k !== FALSE)
				{
					unset($this->user_funcs[$k]);
				}
			}
		}

		/*!	@function	loop_once
			@abstract	Runs the class's actions once.
			@discussion	Should only be used if you want to run additional checks during server operation.  Otherwise, use infinite_loop()
			@param		void
			@see		infinite_loop
			@result 	bool	- True
		*/
		public function loop_once()
		{
			// Setup Clients Listen Socket For Reading
			$read[0] = $this->master_socket;
			for($i = 0; $i < $this->max_clients; $i++)
			{
				if(isset($this->clients[$i]))
				{
					$read[$i + 1] = $this->clients[$i]->socket;
				}
			}

			// Set up a blocking call to socket_select
			if(socket_select($read,$write = NULL, $except = NULL, $tv_sec = 5) < 1)
			{
			//	SocketServer::debug("Problem blocking socket_select?");
				return true;
			}

			// Handle new Connections
			if(in_array($this->master_socket, $read))
			{
				for($i = 0; $i < $this->max_clients; $i++)
				{
					if(empty($this->clients[$i]))
					{
						$temp_sock = $this->master_socket;
						$this->clients[$i] = new SocketServerClient($this->master_socket,$i);
						$this->trigger_hooks("CONNECT",$this->clients[$i],"");
						break;
					}
					elseif($i == ($this->max_clients-1))
					{
						SocketServer::debug("Too many clients... :( ");
					}
				}

			}

			// Handle Input
			for($i = 0; $i < $this->max_clients; $i++) // for each client
			{
				if(isset($this->clients[$i]))
				{
					if(in_array($this->clients[$i]->socket, $read))
					{
						$input = socket_read($this->clients[$i]->socket, $this->max_read);
						if($input == null)
						{
							$this->disconnect($i);
						}
						else
						{
							SocketServer::debug("{$i}@{$this->clients[$i]->ip} --> {$input}");
							$this->trigger_hooks("INPUT",$this->clients[$i],$input);
						}
					}
				}
			}
			return true;
		}

		/*!	@function	disconnect
			@abstract	Disconnects a client from the server.
			@param		int	- Index of the client to disconnect.
			@param		string	- Message to send to the hooks
			@result		void
		*/
		public function disconnect($client_index,$message = "")
		{
			$i = $client_index;
			SocketServer::debug("Client {$i} from {$this->clients[$i]->ip} Disconnecting");
			$this->trigger_hooks("DISCONNECT",$this->clients[$i],$message);
			$this->clients[$i]->destroy();
			unset($this->clients[$i]);			
		}

		/*!	@function	trigger_hooks
			@abstract	Triggers Hooks for a certain command.
			@param		string	- Command who's hooks you want to trigger.
			@param		object	- The client who activated this command.
			@param		string	- The input from the client, or a message to be sent to the hooks.
			@result		void
		*/
		public function trigger_hooks($command,&$client,$input)
		{
			if(isset($this->hooks[$command]))
			{
				foreach($this->hooks[$command] as $function)
				{
					SocketServer::debug("Triggering Hook '{$function}' for '{$command}'");
					$continue = call_user_func($function,&$this,&$client,$input);
					if($continue === FALSE) { break; }
				}
			}
		}

		/*!	@function	infinite_loop
			@abstract	Runs the server code until the server is shut down.
			@see		loop_once
			@param		void
			@result		void
		*/
		public function infinite_loop()
		{
			$test = true;
			do
			{
				$test = $this->loop_once();
			}
			while($test);
		}

		/*!	@function	debug
			@static
			@abstract	Outputs Text directly.
			@discussion	Yeah, should probably make a way to turn this off.
			@param		string	- Text to Output
			@result		void
		*/
		public static function debug($text)
		{
			echo("{$text}\r\n");
		}

		/*!	@function	socket_write_smart
			@static
			@abstract	Writes data to the socket, including the length of the data, and ends it with a CRLF unless specified.
			@discussion	It is perfectly valid for socket_write_smart to return zero which means no bytes have been written. Be sure to use the === operator to check for FALSE in case of an error. 
			@param		resource- Socket Instance
			@param		string	- Data to write to the socket.
			@param		string	- Data to end the line with.  Specify a "" if you don't want a line end sent.
			@result		mixed	- Returns the number of bytes successfully written to the socket or FALSE on failure. The error code can be retrieved with socket_last_error(). This code may be passed to socket_strerror() to get a textual explanation of the error.
		*/
		public static function socket_write_smart(&$sock,$string,$crlf = "\r\n")
		{
			SocketServer::debug("<-- {$string}");
			if($crlf) { $string = "{$string}{$crlf}"; }
			return socket_write($sock,$string,strlen($string));
		}

		/*!	@function	__get
			@abstract	Magic Method used for allowing the reading of protected variables.
			@discussion	You never need to use this method, simply calling $server->variable works because of this method's existence.
			@param		string	- Variable to retrieve
			@result		mixed	- Returns the reference to the variable called.
		*/
		function &__get($name)
		{
			return $this->{$name};
		}
	}

	/*!	@class		SocketServerClient
		@author		Navarr Barnier
		@abstract	A Client Instance for use with SocketServer
	 */
	class SocketServerClient
	{
		/*!	@var		socket
			@abstract	resource - The client's socket resource, for sending and receiving data with.
		 */
		protected $socket;

		/*!	@var		ip
			@abstract	string - The client's IP address, as seen by the server.
		 */
		protected $ip;

		/*!	@var		hostname
			@abstract	string - The client's hostname, as seen by the server.
			@discussion	This variable is only set after calling lookup_hostname, as hostname lookups can take up a decent amount of time.
			@see		lookup_hostname
		 */
		protected $hostname;

		/*!	@var		server_clients_index
			@abstract	int - The index of this client in the SocketServer's client array.
		 */
		protected $server_clients_index;

		/*!	@function	__construct
			@param		resource- The resource of the socket the client is connecting by, generally the master socket.
			@param		int	- The Index in the Server's client array.
			@result		void
		 */
		public function __construct(&$socket,$i)
		{
			$this->server_clients_index = $i;
			$this->socket = socket_accept($socket) or die("Failed to Accept");
			SocketServer::debug("New Client Connected");
			socket_getpeername($this->socket,$ip);
			$this->ip = $ip;
		}
		
		/*!	@function	lookup_hostname
			@abstract	Searches for the user's hostname and stores the result to hostname.
			@see		hostname
			@param		void
			@result		string	- The hostname on success or the IP address on failure.
		 */
		public function lookup_hostname()
		{
			$this->hostname = gethostbyaddr($this->ip);
			return $this->hostname;
		}

		/*!	@function	destroy
			@abstract	Closes the socket.  Thats pretty much it.
			@param		void
			@result		void
		 */
		public function destroy()
		{
			socket_close($this->socket);
		}

		function &__get($name)
		{
			return $this->{$name};
		}
		
		function __isset($name)
		{
			return isset($this->{$name});
		}
	}

@nalkat I would say it's still multi-user, but of course a process (and a processor) can only do one thing at a time. That is just how it is. Forking would help here.

You should check out https://reactphp.org/ for non-blocking IO. It is likely closer to what you want.

It has the same problem, however it has features to work around it

Checkout my example, in plain php (no oop) demonstration how socket_select() can handle multiple connections without block
https://gist.github.com/RomanStone/8ec2472d2c90440ea1c11cda2581d058