I writing a Command and then reading back from a server via sockets in PHP. We have 20 servers that all run a Node JS script which can receive these commands and execute them. The Node JS script will return "ok" which PHP reads back to confirm the command has gone through.

The Node JS script listens on port 9000 and is set to allow half open.

Most of the time this works fine, but when a high volume of commands are sent we get errors back occasionally that say this:

Contents: Message received back from socket was 'Unexpected token {'
Transport endpoint is not connected

The transport endpoint message suggests to me that it has not connected successfully.

I am no expert in sockets so I don't know whether the implementation I have used is "correct". It does work most of the time but I am aware that there are functions like socket_bind and socket_listen that may work better, though I am not sure what they do.

Here is the PHP code that we are using. Any suggestions would be most appreciated.

public function sendDaemonCommand($address, $template_id, $params = array()) {

    $hostname = $this->getHostnameFromPrivateIP($address);
    $port = 9000;
    $command = array('template_id' => $template_id, 'params' => $params);
    $command = json_encode($command);

    // Create a TCP Stream socket
    if (($sock = socket_create(AF_INET, SOCK_STREAM, SOL_TCP)) === false) {
        $this->mailError("Command Failed - " . $hostname, "Failed to create socket on " . $address . "\n\n" . socket_strerror(socket_last_error()) . "\n\nCommand:\n\n" . $command . "\n" . $this->functionTraceback());
        return false;
    }

    // Connect to socket
    if (socket_connect($sock, $address, $port) === false) {
        $this->mailError("Command Failed - " . $hostname, "Failed to connect to socket on " . $address . "\n\n" . socket_strerror(socket_last_error($sock)) . "\n\nCommand:\n\n" . $command. "\n" . $this->functionTraceback());
        socket_close($sock);
        return false;
    }

    // Write command to socket
    $_command = $command;
    $length = strlen($_command);

    while (true) {
        $sent = socket_write($sock, $_command, $length);

        if ($sent === false) {
            $this->mailError("Command Failed - " . $hostname, "Failed to write command to socket on " . $address . "\n\n" . socket_strerror(socket_last_error($sock)) . "\n\nCommand:\n\n" . $command. "\n" . $this->functionTraceback());
            socket_shutdown($sock, 2);
            socket_close($sock);
            return false;
        }

        if ($sent mailError("Command Failed - " . $hostname, "Message received back from socket was '" . $out . "' on " . $address . "\n\n" . socket_strerror(socket_last_error($sock)) . "\n\nCommand:\n\n" . $command. "\n" . $this->functionTraceback());
            socket_close($sock);
            return false;
        }
    }
    else {
        $this->mailError("Command Failed - " . $hostname, "Failed to read from socket on " . $address . "\n\n" . socket_strerror(socket_last_error($sock)) . "\n\nCommand:\n\n" . $command. "\n" . $this->functionTraceback());
        socket_shutdown($sock, 0);
        socket_close($sock);
        return false;
    }

    socket_close($sock);
    return $out;
}

For a simple socket client such as this, I much prefer fsockopen() - it drastically reduces the complication of the client code and does not require the sockets extension, which is not available everywhere. The main disadvantage to this is that you lose the string error messages, but these are rarely that useful anyway - you still get an error string from creating the socket, and if read/write operations fail it's because the socket has become disconnected.

I'm also not sure how useful "allow half open" is in this context - I think it is likely to create more problems than it solves. The calls to socket_shutdown() are not doing anything useful here (and may be the source of your problems) - you would only use this if you are operating on a socket that will not be closed and may be operated on at a later point in time by some other code. Since you create a new socket and destroy it in the same routine, this is not the case.

Here is your code rewritten to use fsockopen() - as you can see, it is somewhat shorter and simpler. I have also modified it slightly so that it always returns a bool - your code returns either bool FALSE or string ok, and since there are only these two options it makes more sense for the function to always return a bool.

public function sendDaemonCommand($address, $template_id, $params = array()) {

    // Prepare data
    $hostname = $this->getHostnameFromPrivateIP($address);
    $port = 9000;
    $command = array('template_id' => $template_id, 'params' => $params);
    $_command = $command = json_encode($command);
    $length = strlen($_command);

    // Connect to socket
    if (!$sock = fsockopen($address, $port, $errNo, $errStr)) {
        $this->mailError("Command Failed - " . $hostname, "Failed to connect to socket on " . $address . "\n\n" . $errStr . "\n\nCommand:\n\n" . $command. "\n" . $this->functionTraceback());
        return false;
    }

    // Write command to socket
    while (true) {

        // Try and write data to socket
        $sent = fwrite($sock, $_command, $length);

        // If it failed, error out
        if ($sent === false) {
            $this->mailError("Command Failed - " . $hostname, "Failed to write command to socket on " . $address . "\n\nCommand:\n\n" . $command. "\n" . $this->functionTraceback());
            fclose($sock);
            return false;
        }

        // If there is data left to send, try again
        if ($sent mailError("Command Failed - " . $hostname, "Failed to read from socket on " . $address . "\n\nCommand:\n\n" . $command. "\n" . $this->functionTraceback());
        return false;
    } else if (($out = trim($out)) !== "ok") {
        $this->mailError("Command Failed - " . $hostname, "Message received back from socket was '" . $out . "' on " . $address . "\n\nCommand:\n\n" . $command. "\n" . $this->functionTraceback());
        return false;
    } else {
        return true;
    }

}