From 9ed331ae3dc32bb1b175239dc1d2f65f6d997826 Mon Sep 17 00:00:00 2001
From: Niklas Keller <me@kelunik.com>
Date: Fri, 23 Jun 2017 17:48:03 +0200
Subject: [PATCH] Implement request sharing for concurrent requests to the same
 resource

---
 lib/BasicResolver.php    | 16 +++++++++++++++-
 test/IntegrationTest.php | 14 ++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/lib/BasicResolver.php b/lib/BasicResolver.php
index 346ede7..455a643 100644
--- a/lib/BasicResolver.php
+++ b/lib/BasicResolver.php
@@ -30,6 +30,9 @@ class BasicResolver implements Resolver {
     /** @var array */
     private $servers = [];
 
+    /** @var array */
+    private $pendingQueries = [];
+
     public function __construct(Cache $cache = null, ConfigLoader $configLoader = null) {
         $this->cache = $cache ?? new ArrayCache;
         $this->configLoader = $configLoader ?? \stripos(PHP_OS, "win") === 0
@@ -134,7 +137,11 @@ class BasicResolver implements Resolver {
 
     /** @inheritdoc */
     public function query(string $name, int $type): Promise {
-        return call(function () use ($name, $type) {
+        if (isset($this->pendingQueries[$type . " " . $name])) {
+            return $this->pendingQueries[$type . " " . $name];
+        }
+
+        $promise = call(function () use ($name, $type) {
             if (!$this->config) {
                 $this->config = yield $this->configLoader->loadConfig();
             }
@@ -209,6 +216,13 @@ class BasicResolver implements Resolver {
 
             throw new ResolutionException("No response from any nameserver after {$attempts} attempts");
         });
+
+        $this->pendingQueries[$type . " " . $name] = $promise;
+        $promise->onResolve(function () use ($name, $type) {
+            unset($this->pendingQueries[$type . " " . $name]);
+        });
+
+        return $promise;
     }
 
     /**
diff --git a/test/IntegrationTest.php b/test/IntegrationTest.php
index 6559f08..f329fc1 100644
--- a/test/IntegrationTest.php
+++ b/test/IntegrationTest.php
@@ -38,6 +38,20 @@ class IntegrationTest extends TestCase {
         });
     }
 
+    /**
+     * Test that two concurrent requests to the same resource share the same request and do not result in two requests
+     * being sent.
+     */
+    public function testRequestSharing() {
+        Loop::run(function () {
+            $promise1 = Dns\query("example.com", Record::A);
+            $promise2 = Dns\query("example.com", Record::A);
+
+            $this->assertSame($promise1, $promise2);
+            $this->assertSame(yield $promise1, yield $promise2);
+        });
+    }
+
     public function provideHostnames() {
         return [
             ["google.com"],