Add the ability to limit address resolution by type

Allows restricting to A or AAAA only via the ClientConnectContext.

Relates to #35, but doesn't fully fix it. Further work needs to be done
to avoid IPv6 automatically when IPv6 support is not available.

lib/ClientConnectContext.php

@@ -2,12 +2,14 @@
 
 namespace Amp\Socket;
 
+use Amp\Dns\Record;
 use function Amp\Socket\Internal\normalizeBindToOption;
 
 final class ClientConnectContext {
     private $bindTo = null;
     private $connectTimeout = 10000;
     private $maxAttempts = 2;
+    private $typeRestriction = null;
 
     public function withBindTo(string $bindTo = null): self {
         $bindTo = normalizeBindToOption($bindTo);
@@ -52,6 +54,21 @@ public function getMaxAttempts(): int {
         return $this->maxAttempts;
     }
 
+    public function withDnsTypeRestriction(int $type = null): self {
+        if ($type !== null && $type !== Record::AAAA && $type !== Record::A) {
+            throw new \Error("Invalid resolver type restriction");
+        }
+
+        $clone = clone $this;
+        $clone->typeRestriction = $type;
+
+        return $clone;
+    }
+
+    public function getDnsTypeRestriction() {
+        return $this->typeRestriction;
+    }
+
     public function toStreamContextArray(): array {
         $options = [];
 

lib/functions.php

@@ -76,7 +76,7 @@ function connect(string $uri, ClientConnectContext $socketContext = null, Cancel
             $uris = [$uri];
         } else {
             // Host is not an IP address, so resolve the domain name.
-            $records = yield Dns\resolve($host);
+            $records = yield Dns\resolve($host, $socketContext->getDnsTypeRestriction());
             foreach ($records as $record) {
                 /** @var Dns\Record $record */
                 if ($record->getType() === Dns\Record::AAAA) {