1 files changed, 58 insertions, 0 deletions
diff --git a/lib/public/Log/functions.php b/lib/public/Log/functions.php
new file mode 100644
index 00000000000..75e07deab34
--- /dev/null
+++ b/lib/public/Log/functions.php
@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2022 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCP\Log;
+
+use OC;
+use OCP\AppFramework\QueryException;
+use Psr\Log\LoggerInterface;
+use Psr\Log\NullLogger;
+use function class_exists;
+
+/**
+ * Get a PSR logger
+ *
+ * Whenever possible, inject a logger into your classes instead of relying on
+ * this helper function.
+ *
+ * @warning the returned logger implementation is not guaranteed to be the same
+ *          between two function calls. During early stages of the process you
+ *          might in fact get a noop implementation when Nextcloud isn't ready
+ *          to log. Therefore you MUST NOT cache the result of this function but
+ *          fetch a new logger for every log line you want to write.
+ *
+ * @param string|null $appId optional parameter to acquire the app-specific logger
+ *
+ * @return LoggerInterface
+ * @since 24.0.0
+ */
+function logger(?string $appId = null): LoggerInterface {
+	/** @psalm-suppress TypeDoesNotContainNull false-positive, it may contain null if we are logging from initialization */
+	if (!class_exists(OC::class) || OC::$server === null) {
+		// If someone calls this log before Nextcloud is initialized, there is
+		// no logging available. In that case we return a noop implementation
+		// TODO: evaluate whether logging to error_log could be an alternative
+		return new NullLogger();
+	}
+
+	if ($appId !== null) {
+		try {
+			$appContainer = OC::$server->getRegisteredAppContainer($appId);
+			return $appContainer->get(LoggerInterface::class);
+		} catch (QueryException $e) {
+			// Ignore and return the server logger below
+		}
+	}
+
+	try {
+		return OC::$server->get(LoggerInterface::class);
+	} catch (QueryException $e) {
+		return new NullLogger();
+	}
+}