Fix LspFraming permanently poisoning the stream on stray non-LSP output

src/Transport/JsonRpc/LspFraming.php

@@ -62,7 +62,13 @@ private static function extractOneMessage(string $buffer): ?array
 
         $contentLength = self::parseContentLength($headers);
         if (null === $contentLength) {
-            throw new \InvalidArgumentException('Missing or invalid Content-Length header');
+            // resync: skip stray non-LSP output (e.g. browser crash spew) up to the next frame
+            $resyncPos = strpos($buffer, 'Content-Length:', 1);
+            if (false === $resyncPos) {
+                return null;
+            }
+
+            return self::extractOneMessage(substr($buffer, $resyncPos));
         }
 
         if (strlen($buffer) < $contentStart + $contentLength) {

tests/Unit/Transport/JsonRpc/LspFramingTest.php

@@ -0,0 +1,78 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * This file is part of the community-maintained Playwright PHP project.
+ * It is not affiliated with or endorsed by Microsoft.
+ *
+ * (c) 2025-Present - Playwright PHP - https://github.com/playwright-php
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Playwright\Tests\Unit\Transport\JsonRpc;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use Playwright\Transport\JsonRpc\LspFraming;
+
+#[CoversClass(LspFraming::class)]
+final class LspFramingTest extends TestCase
+{
+    public function testDecodesASingleWellFormedMessage(): void
+    {
+        $decoded = LspFraming::decode(LspFraming::encode('{"ok":1}'));
+
+        $this->assertSame(['{"ok":1}'], $decoded['messages']);
+        $this->assertSame('', $decoded['remainingBuffer']);
+    }
+
+    public function testDecodesMultipleConsecutiveMessages(): void
+    {
+        $buffer = LspFraming::encode('{"ok":1}').LspFraming::encode('{"ok":2}');
+
+        $decoded = LspFraming::decode($buffer);
+
+        $this->assertSame(['{"ok":1}', '{"ok":2}'], $decoded['messages']);
+    }
+
+    public function testBuffersAnIncompleteMessageInsteadOfFailing(): void
+    {
+        $partial = substr(LspFraming::encode('{"ok":1}'), 0, -3);
+
+        $decoded = LspFraming::decode($partial);
+
+        $this->assertSame([], $decoded['messages']);
+        $this->assertSame($partial, $decoded['remainingBuffer']);
+    }
+
+    public function testResyncsPastStrayNonLspOutputInsteadOfThrowing(): void
+    {
+        $frame1 = LspFraming::encode('{"ok":1}');
+        $frame2 = LspFraming::encode('{"ok":2}');
+        $polluted = "crash spew\nstack line\n".$frame1.'garbage'.$frame2;
+
+        $decoded = LspFraming::decode($polluted);
+
+        $this->assertSame(['{"ok":1}', '{"ok":2}'], $decoded['messages']);
+    }
+
+    public function testBuffersPureGarbageWithNoContentLengthMarkerAtAll(): void
+    {
+        $decoded = LspFraming::decode("this is not a frame at all\r\n\r\n");
+
+        $this->assertSame([], $decoded['messages']);
+    }
+
+    public function testMalformedContentLengthValueIsSkippedRatherThanThrown(): void
+    {
+        $frame = LspFraming::encode('{"ok":1}');
+        $polluted = "Content-Length: not-a-number\r\n\r\n".$frame;
+
+        $decoded = LspFraming::decode($polluted);
+
+        $this->assertSame(['{"ok":1}'], $decoded['messages']);
+    }
+}