Getting Started ⋅ Parsing Line-Delimited Messages
Previously, we successfully completed the basic chat server. In this section we’ll parse the input stream into lines.
Our previous code for reading from the client and passing messages to other clients looked like that:
You can find the code for this tutorial on GitHub.
while (null !== $chunk = yield $socket->read()) {
$this->broadcast($remoteAddr . " says: " . trim($chunk) . PHP_EOL);
}
Using coroutines, it’s quite simple to extend this to parse the stream into separate lines.
$buffer = "";
while (null !== $chunk = yield $socket->read()) {
$buffer .= $chunk;
while (($pos = strpos($buffer, "\n")) !== false) {
$this->broadcast($remoteAddr . " says: " . substr($buffer, 0, $pos) . PHP_EOL);
$buffer = substr($buffer, $pos + 1);
}
}
We create a $buffer variable to store the current buffer content. If we can’t find a newline character in the $buffer, we just continue reading. If we find one, we broadcast the message to all clients as before and remove the message we just broadcasted from the buffer. We use a while loop here, as a client also send multiple messages in a single packet.
Parsing Commands
This section is about parsing, but just parsing newlines is boring, right? Let’s add some commands to our server. Commands are special messages that will be treated differently by the server and their result will not be broadcasted to all clients.
All commands in our server will start with a /, so let’s parse them. We will modify our above code to separate message handling from parsing the stream into lines.
$buffer = "";
while (null !== $chunk = yield $socket->read()) {
$buffer .= $chunk;
while (($pos = strpos($buffer, "\n")) !== false) {
$this->handleMessage($socket, substr($buffer, 0, $pos));
$buffer = substr($buffer, $pos + 1);
}
}
function handleMessage(ServerSocket $socket, string $message) {
if ($message === "") {
// ignore all empty messages
return;
}
if ($message[0] === "/") {
// message is a command
$message = substr($message, 1); // remove slash
$args = explode(" ", $message); // parse message into parts separated by space
$name = strtolower(array_shift($args)); // the first arg is our command name
switch ($name) {
case "time":
$socket->write(date("l jS \of F Y h:i:s A") . PHP_EOL);
break;
case "up":
$socket->write(strtoupper(implode(" ", $args)) . PHP_EOL);
break;
case "down":
$socket->write(strtolower(implode(" ", $args)) . PHP_EOL);
break;
default:
$socket->write("Unknown command: {$name}" . PHP_EOL);
break;
}
return;
}
$this->broadcast($socket->getRemoteAddress() . " says: " . $message . PHP_EOL);
}
We have three commands now: time, up and down. time reports the current server time to the client, while up and down change the rest of the message to upper / lower case and return the result to the client.
As you can see, adding commands is pretty easy now. Let’s add another one to allow the client to exit (you can do that via Ctrl + C in nc anyway).
case "exit":
$socket->end("Bye." . PHP_EOL);
break;
$socket->end() sends a final message before closing the socket.
Adding Usernames
As we already have commands now, why not add a command that let’s a client choose its username? Currently we just used the socket address as a username. Let’s add a new nick command.
case "nick":
$nick = implode(" ", $args);
if (!preg_match("(^[a-z0-9-.]{3,15}$)i", $nick)) {
$error = "Username must only contain letters, digits and " .
"its length must be between 3 and 15 characters.";
$socket->write($error . PHP_EOL);
return;
}
$remoteAddr = $socket->getRemoteAddress();
$oldnick = $this->usernames[$remoteAddr] ?? $remoteAddr;
$this->usernames[$remoteAddr] = $nick;
$this->broadcast($oldnick . " is now " . $nick . PHP_EOL);
break;
We also need to change our broadcast calls now to use the username, and also need to unset the username when the client disconnects.
$remoteAddr = $socket->getRemoteAddress();
$user = $this->usernames[$remoteAddr] ?? $remoteAddr;
$this->broadcast($user . " says: " . $message . PHP_EOL);
Adding Authentication
Adding authentication is a task left to you, we’ll just give some hints. You could for example create a register command that accepts a name and password and save that somewhere using password_hash. You could then extend nick with the same mechanism and require the right password using password_verify otherwise disallow changing to that name.
In the next step we will use Redis for Pub/Sub to broadcast messages over multiple instances.