Windows uses hard-coded defaults for localhost instead of hosts file

Author: clue

src/Config/HostsFile.php

@@ -12,7 +12,9 @@
  *
  * Most notably, this file usually contains an entry to map "localhost" to the
  * local IP. Windows is a notable exception here, as Windows does not actually
- * include "localhost" in this file by default.
+ * include "localhost" in this file by default. To compensate for this, this
+ * class may explicitly be wrapped in another HostsFile instance which
+ * hard-codes these entries for Windows (see also Factory).
  *
  * This class mostly exists to abstract the parsing/extraction process so this
  * can be replaced with a faster alternative in the future.

src/Resolver/Factory.php

@@ -48,13 +48,24 @@ public function createCached($nameserver, LoopInterface $loop, CacheInterface $c
     private function decorateHostsFileExecutor(ExecutorInterface $executor)
     {
         try {
-            $hosts = HostsFile::loadFromPathBlocking();
+            $executor = new HostsFileExecutor(
+                HostsFile::loadFromPathBlocking(),
+                $executor
+            );
         } catch (\RuntimeException $e) {
             // ignore this file if it can not be loaded
-            return $executor;
         }
 
-        return new HostsFileExecutor($hosts, $executor);
+        // Windows does not store localhost in hosts file by default but handles this internally
+        // To compensate for this, we explicitly use hard-coded defaults for localhost
+        if (DIRECTORY_SEPARATOR === '\\') {
+            $executor = new HostsFileExecutor(
+                new HostsFile("127.0.0.1 localhost"),
+                $executor
+            );
+        }
+
+        return $executor;
     }
 
     protected function createExecutor(LoopInterface $loop)

tests/FunctionalResolverTest.php

@@ -19,10 +19,6 @@ public function setUp()
 
     public function testResolveLocalhostResolves()
     {
-        if (DIRECTORY_SEPARATOR === '\\') {
-            $this->markTestSkipped('Not supported on Windows');
-        }
-
         $promise = $this->resolver->resolve('localhost');
         $promise->then($this->expectCallableOnce(), $this->expectCallableNever());
 

tests/Resolver/FactoryTest.php

@@ -97,7 +97,8 @@ private function getResolverPrivateExecutor($resolver)
     {
         $executor = $this->getResolverPrivateMemberValue($resolver, 'executor');
 
-        if ($executor instanceof HostsFileExecutor) {
+        // extract underlying executor that may be wrapped in multiple layers of hosts file executors
+        while ($executor instanceof HostsFileExecutor) {
             $reflector = new \ReflectionProperty('React\Dns\Query\HostsFileExecutor', 'fallback');
             $reflector->setAccessible(true);