Simple PHP Redis Sentinel master request

simple_redis_sentinel.php

<?php

/*
 * Parse RESP (REdis Serialization Protocol)
 */
function read_resp($fp = null) {
  // File descripter to the Redis server connection
  // (static to limit recursion stack size)
  static $conn = null;
  if (!$conn) $conn = $fp;

  // The max size of a Redis string data type is 512MB
  $type = fgets($conn, 524290);
  if ($type === FALSE) {
    error_log('RESP unexpected stream error reading type');
    return false;
  }

  // First byte of type string identifies data type
  switch (substr($type, 0, 1)) {
    // Array
    case '*':
      // Remainder of type string is array item count
      $count = (int) substr($type, 1);
      // -1 sized array is a way of representing nil object
      if ($count === -1) {
        return null;
      }
      $a = array();
      for ($i = 0; $i < $count; $i++) {
        // Recurse to read array value
        $a[] = read_resp();
      }
      return $a;
    // Simple String
    case '+':
      // Remainder of type string is the string itself
      return substr($type, 1);
    // Error
    case '-':
      // Remainder of type string is an error message
      error_log(substr($type, 1));
      return false;
    // Integer
    case ':':
      // Remainder of type string is an integer
      return (int) substr($type, 1);
    // Bulk String
    case '$':
      // Remainder of type string is string length
      $count = (int) substr($type, 1);
      // -1 sized string is a way of representing nil object
      if ($count === -1) {
        return null;
      }
      $s = fread($conn, $count);
      if ($s === FALSE) {
        error_log("RESP unable to read bulk string of size $count");
        return false;
      }
      // consume the final \r\n
      if (fread($conn, 2) === FALSE) {
        error_log('RESP termination of bulk string missing');
        return false;
      }
      return $s;
  }
}

// Attempt connection to local Sentinel using very short timeout
$fp = @stream_socket_client('tcp://localhost:26379', $errno, $errstr, 0.1);
if (!$fp) {
  error_log("RESP $errstr ($errno)");
  header((isset($_SERVER['SERVER_PROTOCOL']) ? $_SERVER['SERVER_PROTOCOL'] : 'HTTP/1.0') . ' 503 Service Unavailable');
  exit;
}

// Set the name of the monitored Redis instance
$redis_name = 'CHANGEME';

// Send a get-master-addr-by-name request to the sentinel
fwrite($fp, "*3\r\n\$8\r\nSENTINEL\r\n\$23\r\nget-master-addr-by-name\r\n\$" . strlen($redis_name) . "\r\n" . $redis_name . "\r\n");

// Parse the serialized RESP response
$r = read_resp($fp);
fclose($fp);

// Response should be (hostname, port) array
if (!is_array($r) || count($r) !== 2) {
  header((isset($_SERVER['SERVER_PROTOCOL']) ? $_SERVER['SERVER_PROTOCOL'] : 'HTTP/1.0') . ' 503 Service Unavailable');
  error_log('RESP unexpected response to get-master-addr-by-name');
  exit;
}

// HOST TO PASS TO REDIS CLIENT IS $r[0]
// PORT TO PASS TO REDIS CLIENT IS $r[1]

// DEBUG
var_dump($r);