Escape unsafe command failure diagnostics

AGENTS.md

@@ -9,7 +9,9 @@
 - Handle `preg_*` engine failures: when the result is used as data, test for
   `false` or `null` and throw a `\RuntimeException` including
   `preg_last_error_msg()`; boolean validation guards must compare strictly, such
-  as `=== 1`, so an engine failure can only ever fail closed.
+  as `=== 1`, so an engine failure can only ever fail closed. Diagnostic
+  escaping is the narrow exception: use a deterministic bytewise fallback rather
+  than throwing, so it cannot obscure the original exception.
 - Anchor validation patterns to the true end of input with the `D` modifier or
   `\z`; a bare `$` accepts a trailing newline.
 - Never embed raw control bytes in exception messages and other diagnostics;

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 * Drop support for PHP 7.2 and 7.3
 * Require `guzzlehttp/guzzle` ^8.0, `guzzlehttp/promises` ^3.0, and `guzzlehttp/psr7` ^3.0
+* Escape unsafe command names and previous messages in generated command exceptions
 * Reject native PHP serialization of `ServiceClient`
 * Require custom implementations and subclasses of public command APIs to match native method signatures
 * Require service client response transformers to return `ResultInterface` values

src/Exception/CommandException.php

@@ -8,6 +8,7 @@
 use GuzzleHttp\Exception\GuzzleException;
 use GuzzleHttp\Exception\ResponseException;
 use GuzzleHttp\Exception\TransferException;
+use GuzzleHttp\Psr7\DiagnosticValue;
 use Psr\Http\Client\NetworkExceptionInterface;
 use Psr\Http\Client\RequestExceptionInterface;
 use Psr\Http\Message\RequestInterface;
@@ -54,8 +55,7 @@ public static function fromPrevious(CommandInterface $command, \Exception $prev)
         }
 
         // Prepare the message.
-        $message = 'There was an error executing the '.$command->getName()
-            .' command: '.$prev->getMessage();
+        $message = \sprintf('There was an error executing the %s command: %s', DiagnosticValue::escape($command->getName()), DiagnosticValue::escape($prev->getMessage()));
 
         // Create the exception.
         return new $class($message, $command, $prev, $request, $response);

tests/Exception/CommandExceptionTest.php

@@ -52,6 +52,23 @@ public function testFactoryReturnsExceptionIfAlreadyCommandException(): void
         $this->assertSame($previous, $exception);
     }
 
+    public function testFactoryEscapesUnsafeCommandAndPreviousMessages(): void
+    {
+        $commandName = "command\xC2\x80";
+        $previousMessage = "failure\xFF";
+        $command = $this->createMock(CommandInterface::class);
+        $command->method('getName')->willReturn($commandName);
+        $previous = new \RuntimeException($previousMessage);
+
+        $exception = CommandException::fromPrevious($command, $previous);
+
+        $this->assertSame('There was an error executing the command\\x80 command: failure\\xFF', $exception->getMessage());
+        $this->assertSame($command, $exception->getCommand());
+        $this->assertSame($commandName, $command->getName());
+        $this->assertSame($previous, $exception->getPrevious());
+        $this->assertSame($previousMessage, $previous->getMessage());
+    }
+
     public function testFactoryReturnsClientExceptionFor400LevelStatusCode(): void
     {
         $command = $this->createMock(CommandInterface::class);