Merge pull request #93 from clue-labs/config

Add Config::loadSystemConfigBlocking() to load default system config

Author: jsor

README.md

@@ -28,8 +28,12 @@ names, baby!
 
 ```php
 $loop = React\EventLoop\Factory::create();
+
+$config = React\Dns\Config\Config::loadSystemConfigBlocking();
+$server = $config->nameservers ? reset($config->nameservers) : '8.8.8.8';
+
 $factory = new React\Dns\Resolver\Factory();
-$dns = $factory->create('8.8.8.8', $loop);
+$dns = $factory->create($server, $loop);
 
 $dns->resolve('igor.io')->then(function ($ip) {
     echo "Host: $ip\n";
@@ -40,6 +44,14 @@ $loop->run();
 
 See also the [first example](examples).
 
+The `Config` class can be used to load the system default config. This is an
+operation that may access the filesystem and block. Ideally, this method should
+thus be executed only once before the loop starts and not repeatedly while it is
+running.
+Note that this class may return an *empty* configuration if the system config
+can not be loaded. As such, you'll likely want to apply a default nameserver
+as above if none can be found.
+
 > Note that the factory loads the hosts file from the filesystem once when
   creating the resolver instance.
   Ideally, this method should thus be executed only once before the loop starts
@@ -61,8 +73,12 @@ You can cache results by configuring the resolver to use a `CachedExecutor`:
 
 ```php
 $loop = React\EventLoop\Factory::create();
+
+$config = React\Dns\Config\Config::loadSystemConfigBlocking();
+$server = $config->nameservers ? reset($config->nameservers) : '8.8.8.8';
+
 $factory = new React\Dns\Resolver\Factory();
-$dns = $factory->createCached('8.8.8.8', $loop);
+$dns = $factory->createCached($server, $loop);
 
 $dns->resolve('igor.io')->then(function ($ip) {
     echo "Host: $ip\n";

examples/01-one.php

@@ -1,13 +1,17 @@
 <?php
 
+use React\Dns\Config\Config;
 use React\Dns\Resolver\Factory;
 
 require __DIR__ . '/../vendor/autoload.php';
 
 $loop = React\EventLoop\Factory::create();
 
+$config = Config::loadSystemConfigBlocking();
+$server = $config->nameservers ? reset($config->nameservers) : '8.8.8.8';
+
 $factory = new Factory();
-$resolver = $factory->create('8.8.8.8', $loop);
+$resolver = $factory->create($server, $loop);
 
 $name = isset($argv[1]) ? $argv[1] : 'www.google.com';
 

examples/02-concurrent.php

@@ -1,13 +1,17 @@
 <?php
 
+use React\Dns\Config\Config;
 use React\Dns\Resolver\Factory;
 
 require __DIR__ . '/../vendor/autoload.php';
 
 $loop = React\EventLoop\Factory::create();
 
+$config = Config::loadSystemConfigBlocking();
+$server = $config->nameservers ? reset($config->nameservers) : '8.8.8.8';
+
 $factory = new Factory();
-$resolver = $factory->create('8.8.8.8', $loop);
+$resolver = $factory->create($server, $loop);
 
 $names = array_slice($argv, 1);
 if (!$names) {

examples/03-cached.php

@@ -1,13 +1,17 @@
 <?php
 
+use React\Dns\Config\Config;
 use React\Dns\Resolver\Factory;
 
 require __DIR__ . '/../vendor/autoload.php';
 
 $loop = React\EventLoop\Factory::create();
 
+$config = Config::loadSystemConfigBlocking();
+$server = $config->nameservers ? reset($config->nameservers) : '8.8.8.8';
+
 $factory = new Factory();
-$resolver = $factory->createCached('8.8.8.8', $loop);
+$resolver = $factory->createCached($server, $loop);
 
 $name = isset($argv[1]) ? $argv[1] : 'www.google.com';
 

src/Config/Config.php

@@ -4,5 +4,28 @@
 
 class Config
 {
+    /**
+     * Loads the system DNS configuration
+     *
+     * Note that this method may block while loading its internal files and/or
+     * commands and should thus be used with care! While this should be
+     * relatively fast for most systems, it remains unknown if this may block
+     * under certain circumstances. In particular, this method should only be
+     * executed before the loop starts, not while it is running.
+     *
+     * Note that this method will try to access its files and/or commands and
+     * try to parse its output. Currently, this is only a placeholder that does
+     * not actually parse any nameserver entries.
+     *
+     * Note that the previous section implies that this may return an empty
+     * `Config` object if no valid nameserver entries can be found.
+     *
+     * @return self
+     */
+    public static function loadSystemConfigBlocking()
+    {
+        return new self();
+    }
+
     public $nameservers = array();
 }