Store if an H2 connection was made

If a prior HTTPS connection returned a non-H2 connection, the pool assumes the next connection will also not be H2.

Related to #246.

src/Connection/UnlimitedConnectionPool.php

@@ -20,6 +20,9 @@ final class UnlimitedConnectionPool implements ConnectionPool
     /** @var Promise[][] */
     private $connections = [];
 
+    /** @var bool[] */
+    private $waitForPriorConnection = [];
+
     /** @var int */
     private $totalConnectionAttempts = 0;
 
@@ -76,15 +79,15 @@ public function getStream(Request $request, CancellationToken $cancellation): Pr
             }
 
             $authority = $host . ':' . $port;
-            $key = $scheme . '://' . $authority;
+            $uri = $scheme . '://' . $authority;
 
-            $connections = $this->connections[$key] ?? new \ArrayObject;
+            $connections = $this->connections[$uri] ?? new \ArrayObject;
 
             foreach ($connections as $connectionPromise) {
                 \assert($connectionPromise instanceof Promise);
 
                 try {
-                    if ($isHttps) {
+                    if ($isHttps && ($this->waitForPriorConnection[$uri] ?? true)) {
                         // Wait for first successful connection if using a secure connection (maybe we can use HTTP/2).
                         $connection = yield $connectionPromise;
                     } else {
@@ -117,23 +120,27 @@ public function getStream(Request $request, CancellationToken $cancellation): Pr
             $connectionPromise = $this->connectionFactory->create($request, $cancellation);
 
             $hash = \spl_object_hash($connectionPromise);
-            $this->connections[$key] = $this->connections[$key] ?? new \ArrayObject;
-            $this->connections[$key][$hash] = $connectionPromise;
+            $this->connections[$uri] = $this->connections[$uri] ?? new \ArrayObject;
+            $this->connections[$uri][$hash] = $connectionPromise;
 
             try {
                 $connection = yield $connectionPromise;
                 $this->openConnectionCount++;
 
                 \assert($connection instanceof Connection);
             } catch (\Throwable $exception) {
-                $this->dropConnection($key, $hash);
+                $this->dropConnection($uri, $hash);
 
                 throw $exception;
             }
 
-            $connection->onClose(function () use ($key, $hash): void {
+            if ($isHttps) {
+                $this->waitForPriorConnection[$uri] = \in_array('2', $connection->getProtocolVersions());
+            }
+
+            $connection->onClose(function () use ($uri, $hash): void {
                 $this->openConnectionCount--;
-                $this->dropConnection($key, $hash);
+                $this->dropConnection($uri, $hash);
             });
 
             $stream = yield $connection->getStream($request);
@@ -150,6 +157,7 @@ private function dropConnection(string $uri, string $connectionHash): void
 
         if (empty($this->connections[$uri])) {
             unset($this->connections[$uri]);
+            unset($this->waitForPriorConnection[$uri]);
         }
     }
 }