Add liveliness check to Connection interface

src/Connection/Connection.php

@@ -29,7 +29,13 @@ public function getProtocolVersions(): array;
     /**
      * @return bool True if a stream is still available, false if the connection is completely busy.
      */
-    public function isBusy(): bool;
+    public function hasStreamAvailable(): bool;
+
+    /**
+     * @return Promise<bool> True if the connection is safe to use for a new request, false if a new connection should
+     *                       be opened.
+     */
+    public function checkLiveliness(): Promise;
 
     public function close(): Promise;
 

src/Connection/DefaultConnectionPool.php

@@ -100,23 +100,16 @@ public function getStream(Request $request, CancellationToken $cancellation): Pr
 
                 \assert($connection instanceof Connection);
 
-                if ($connection->isBusy()) {
+                if ($connection->hasStreamAvailable()) {
                     continue; // Connection is currently used to full capacity.
                 }
 
                 if (!\array_intersect($request->getProtocolVersions(), $connection->getProtocolVersions())) {
                     continue; // Connection does not support any of the requested protocol versions.
                 }
 
-                if ($connection instanceof Http2Connection && $connection->isIdle() && !(yield $connection->ping())) {
-                    continue; // Connection closed while idle.
-                }
-
-                if ($connection instanceof Http1Connection
-                    && $connection->getRemainingTime() < $this->timeoutGracePeriod
-                    && !$request->isIdempotent()
-                ) {
-                    continue; // Connection is at high-risk of closing before the request can be sent.
+                if (!yield $connection->checkLiveliness()) {
+                    continue;
                 }
 
                 return $connection->getStream($request);
@@ -194,7 +187,7 @@ private function createConnection(
         }
 
         if (!$isHttps) {
-            return new Http1Connection($socket);
+            return new Http1Connection($socket, $this->timeoutGracePeriod);
         }
 
         try {
@@ -253,7 +246,7 @@ private function createConnection(
             );
         }
 
-        return new Http1Connection($socket);
+        return new Http1Connection($socket, $this->timeoutGracePeriod);
     }
 
     private function dropConnection(string $uri, string $connectionHash): void

src/Connection/Http1Connection.php

@@ -61,17 +61,21 @@ final class Http1Connection implements Connection
     /** @var callable[]|null */
     private $onClose = [];
 
+    /** @var int */
+    private $timeoutGracePeriod;
+
     /** @var int */
     private $estimatedClose;
 
-    public function __construct(Socket $socket)
+    public function __construct(Socket $socket, int $timeoutGracePeriod)
     {
         $this->socket = $socket;
 
         if ($this->socket->isClosed()) {
             $this->onClose = null;
         }
 
+        $this->timeoutGracePeriod = $timeoutGracePeriod;
         $this->estimatedClose = (int) ((\microtime(true) + self::MAX_KEEP_ALIVE_TIMEOUT) * 1000);
     }
 
@@ -80,9 +84,14 @@ public function __destruct()
         $this->close();
     }
 
-    public function isBusy(): bool
+    public function hasStreamAvailable(): bool
+    {
+        return !$this->busy && !$this->socket->isClosed();
+    }
+
+    public function checkLiveliness(): Promise
     {
-        return $this->busy || $this->socket->isClosed();
+        return new Success($this->getRemainingTime() > $this->timeoutGracePeriod);
     }
 
     public function onClose(callable $onClose): void
@@ -343,7 +352,7 @@ private function readResponse(
     /**
      * @return int Approximate number of milliseconds remaining until the connection is closed.
      */
-    public function getRemainingTime(): int
+    private function getRemainingTime(): int
     {
         return (int) \max(0, $this->estimatedClose - \microtime(true) * 1000);
     }

src/Connection/Http2Connection.php

@@ -228,7 +228,7 @@ public function getStream(Request $request): Stream
     /**
      * @return Promise<bool> Fulfilled with true if a pong is received within the timeout, false if none is received.
      */
-    public function ping(): Promise
+    private function ping(): Promise
     {
         if ($this->onClose === null) {
             return new Success(false);
@@ -248,14 +248,23 @@ public function ping(): Promise
         return $this->pongDeferred->promise();
     }
 
-    public function isIdle(): bool
+    private function isIdle(): bool
     {
         return empty($this->streams) && $this->onClose !== null;
     }
 
-    public function isBusy(): bool
+    public function hasStreamAvailable(): bool
     {
-        return $this->remainingStreams <= 0 || $this->onClose === null;
+        return $this->remainingStreams > 0 && $this->onClose !== null;
+    }
+
+    public function checkLiveliness(): Promise
+    {
+        if (!$this->isIdle()) {
+            return new Success(true);
+        }
+
+        return $this->ping();
     }
 
     public function onClose(callable $onClose): void
@@ -1489,6 +1498,10 @@ private function shutdown(?int $lastId = null, ?\Throwable $reason = null): Prom
                 $this->pongDeferred->resolve(false);
             }
 
+            if ($this->pongWatcher !== null) {
+                Loop::cancel($this->pongWatcher);
+            }
+
             if ($this->onClose !== null) {
                 $onClose = $this->onClose;
                 $this->onClose = null;
@@ -1498,10 +1511,6 @@ private function shutdown(?int $lastId = null, ?\Throwable $reason = null): Prom
                 }
             }
 
-            if ($this->pongWatcher !== null) {
-                Loop::cancel($this->pongWatcher);
-            }
-
             yield $promise;
 
             $this->socket->close();