Cache last parsed host

Artax re-parses the same host multiple times, because it's parsed in Artax, then parsed in HttpSocketPool, then parsed in BasicSocketPool. All calls happen synchronously, so it makes sense to cache exactly the last parsed host. Other similar uses might benefit, too.

I'm not sure about benefits for non-benchmarks, but it brings significant benefits in benchmark situations.

src/Uri.php

@@ -6,6 +6,11 @@
  * Provides URI parsing and can resolve URIs.
  */
 final class Uri {
+    private static $lastHost;
+    private static $lastHostNormalized;
+    private static $lastHostIpV4;
+    private static $lastHostIpV6;
+
     private $defaultPortMap = [
         "http" => 80,
         "https" => 443,
@@ -45,23 +50,33 @@ public function __construct(string $uri) {
         // "schemes are case-insensitive"
         $this->scheme = \strtolower($this->scheme);
 
-        // http://www.apps.ietf.org/rfc/rfc3986.html#sec-3.2.2
-        // "Although host is case-insensitive, producers and normalizers should use lowercase for
-        // registered names and hexadecimal addresses for the sake of uniformity"
-        if ($inAddr = @\inet_pton(\trim($this->host, "[]"))) {
-            $this->host = \strtolower($this->host);
-
-            if (isset($inAddr[4])) {
-                $this->isIpV6 = true;
-            } else {
-                $this->isIpV4 = true;
-            }
-        } elseif ($this->host) {
-            try {
-                $this->host = normalizeDnsName($this->host);
-            } catch (InvalidDnsNameException $e) {
-                throw new InvalidUriException("Invalid URI: Invalid host: {$this->host}", 0, $e);
+        if ($this->host === self::$lastHost) {
+            $this->host = self::$lastHostNormalized;
+            $this->isIpV4 = self::$lastHostIpV4;
+            $this->isIpV6 = self::$lastHostIpV6;
+        } else {
+            // http://www.apps.ietf.org/rfc/rfc3986.html#sec-3.2.2
+            // "Although host is case-insensitive, producers and normalizers should use lowercase for
+            // registered names and hexadecimal addresses for the sake of uniformity"
+            if ($inAddr = @\inet_pton(\trim($this->host, "[]"))) {
+                $this->host = \strtolower($this->host);
+
+                if (isset($inAddr[4])) {
+                    $this->isIpV6 = true;
+                } else {
+                    $this->isIpV4 = true;
+                }
+            } elseif ($this->host) {
+                try {
+                    $this->host = normalizeDnsName($this->host);
+                } catch (InvalidDnsNameException $e) {
+                    throw new InvalidUriException("Invalid URI: Invalid host: {$this->host}", 0, $e);
+                }
             }
+
+            self::$lastHostNormalized = $this->host;
+            self::$lastHostIpV4 = $this->isIpV4;
+            self::$lastHostIpV6 = $this->isIpV6;
         }
 
         if ($this->port === 0) {