Truncate oversized log records

src/AppConfig.php

@@ -16,6 +16,7 @@
 use craft\helpers\App;
 use craft\log\MonologTarget;
 use craft\queue\Queue as CraftQueue;
+use Monolog\Handler\FormattableHandlerInterface;
 use yii\caching\ArrayCache;
 use yii\redis\Cache as RedisCache;
 
@@ -161,9 +162,17 @@ private function getDefinitions(): array
         return [
             Temp::class => TmpFs::class,
             MonologTarget::class => function($container, $params, $config) {
-                return new MonologTarget([
+                $target = new MonologTarget([
                     'logContext' => false,
                 ] + $config);
+
+                foreach ($target->getLogger()->getHandlers() as $handler) {
+                    if ($handler instanceof FormattableHandlerInterface) {
+                        $handler->setFormatter(new TruncatingFormatter($handler->getFormatter()));
+                    }
+                }
+
+                return $target;
             },
 
             /**

src/TruncatingFormatter.php

@@ -0,0 +1,49 @@
+<?php
+
+namespace craft\cloud;
+
+use Monolog\Formatter\FormatterInterface;
+
+class TruncatingFormatter implements FormatterInterface
+{
+    /**
+     * Caps records at 240 KiB, leaving 10 KiB below Bref's 256000-byte FPM limit.
+     *
+     * @see https://github.com/brefphp/aws-lambda-layers/blob/main/src/php-fpm.conf Bref's FPM configuration
+     * @see https://www.php.net/manual/en/install.fpm.configuration.php#log-limit PHP's log_limit
+     * @see https://docs.aws.amazon.com/lambda/latest/dg/runtimes-logs-api.html#runtimes-logs-api-buffering Lambda Logs API buffering
+     * @see https://docs.aws.amazon.com/AmazonCloudWatchLogs/latest/APIReference/API_InputLogEvent.html CloudWatch InputLogEvent limits
+     */
+    private const MAX_BYTES = 240 * 1024;
+    private const SUFFIX = '... [truncated]';
+
+    public function __construct(private readonly FormatterInterface $formatter)
+    {
+    }
+
+    public function format($record)
+    {
+        return $this->truncate($this->formatter->format($record));
+    }
+
+    public function formatBatch(array $records)
+    {
+        return $this->truncate($this->formatter->formatBatch($records));
+    }
+
+    private function truncate(mixed $formatted): mixed
+    {
+        if (is_array($formatted)) {
+            return array_map($this->truncate(...), $formatted);
+        }
+
+        if (!is_string($formatted) || strlen($formatted) <= self::MAX_BYTES) {
+            return $formatted;
+        }
+
+        $lineEnding = preg_match('/\R\z/', $formatted, $matches) ? $matches[0] : '';
+        $bytes = self::MAX_BYTES - strlen(self::SUFFIX . $lineEnding);
+
+        return mb_strcut($formatted, 0, $bytes, 'UTF-8') . self::SUFFIX . $lineEnding;
+    }
+}

tests/unit/TruncatingFormatterTest.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace craft\cloud\tests\unit;
+
+use Codeception\Test\Unit;
+use craft\cloud\TruncatingFormatter;
+use Monolog\Formatter\FormatterInterface;
+
+class TruncatingFormatterTest extends Unit
+{
+    public function testCapsFormattedStrings(): void
+    {
+        $formatter = new class implements FormatterInterface {
+            public string $formatted = '';
+
+            public function format($record): string
+            {
+                return $this->formatted;
+            }
+
+            public function formatBatch(array $records): string
+            {
+                return $this->formatted;
+            }
+        };
+        $truncatingFormatter = new TruncatingFormatter($formatter);
+
+        $formatter->formatted = "short\r\n";
+        $this->assertSame($formatter->formatted, $truncatingFormatter->format(null));
+
+        $formatter->formatted = str_repeat('é', 240 * 1024) . "\r\n";
+        $formatted = $truncatingFormatter->format(null);
+
+        $this->assertLessThanOrEqual(240 * 1024, strlen($formatted));
+        $this->assertTrue(mb_check_encoding($formatted, 'UTF-8'));
+        $this->assertStringEndsWith("... [truncated]\r\n", $formatted);
+    }
+}