From d22556d04e89703da67d754e70253949a58d7b09 Mon Sep 17 00:00:00 2001
From: "T. R. Bernstein" <developer@tabshift.dev>
Date: Mon, 2 Mar 2026 18:53:17 +0100
Subject: [PATCH] Output metadata as JSON

Metadata shall be machine readable (see SwiftLog/Structured Logging) and
the previous metadata serialization erased the nesting structure.
The JSON output ensures that the metadata can be quickly analyzed by either a
copy and paste into a JSON editor or a small CLI pipeline.

See https://swiftpackageindex.com/apple/swift-log/1.10.1/documentation/logging/002-structuredlogging
for more information on metadata.
---
 .../Logger Metadata Extension.swift           | 41 +++++++++++++++++++
 Sources/Logging OSLog/Logging OSLog.swift     |  7 +---
 Tests/Logging OSLog Tests/Logging Test.swift  | 14 ++++++-
 3 files changed, 55 insertions(+), 7 deletions(-)
 create mode 100644 Sources/Logging OSLog/Logger Metadata Extension.swift

diff --git a/Sources/Logging OSLog/Logger Metadata Extension.swift b/Sources/Logging OSLog/Logger Metadata Extension.swift
new file mode 100644
index 0000000..5dd3304
--- /dev/null
+++ b/Sources/Logging OSLog/Logger Metadata Extension.swift	
@@ -0,0 +1,41 @@
+import Logging
+
+extension Logging.Logger.Metadata {
+	public func asJSON() -> String {
+		return Self.asJSON(self)
+	}
+
+	private static func asJSON(_ metadata: Logging.Logger.Metadata) -> String {
+		var outputParts: [String: String] = [:]
+		for (key, value) in metadata {
+			let jsonKey = Self.escapeForJSON(key)
+			outputParts[jsonKey] = Self.asJSON(value)
+		}
+		return "{" + outputParts.map { "\"\($0)\": \($1)" }.joined(separator: ", ") + "}"
+	}
+
+	private static func asJSON(_ metadata: [Logging.Logger.MetadataValue]) -> String {
+		var outputParts: [String] = []
+		for item in metadata {
+			outputParts.append(Self.asJSON(item))
+		}
+		return "[" + outputParts.joined(separator: ", ") + "]"
+	}
+
+	private static func asJSON(_ metadata: Logging.Logger.MetadataValue) -> String {
+		switch metadata {
+		case .dictionary(let subvalues):
+			return Self.asJSON(subvalues)
+		case .array(let subvalues):
+			return Self.asJSON(subvalues)
+		case .string(let subvalue):
+			return "\"" + Self.escapeForJSON(subvalue) + "\""
+		case .stringConvertible(let subvalue):
+			return "\"" + Self.escapeForJSON("\(subvalue)") + "\""
+		}
+	}
+
+	private static func escapeForJSON(_ data: String) -> String {
+		return data.replacingOccurrences(of: "\"", with: "\\\"")
+	}
+}
diff --git a/Sources/Logging OSLog/Logging OSLog.swift b/Sources/Logging OSLog/Logging OSLog.swift
index a8197d1..bfd965e 100644
--- a/Sources/Logging OSLog/Logging OSLog.swift	
+++ b/Sources/Logging OSLog/Logging OSLog.swift	
@@ -103,11 +103,6 @@ public struct LoggingOSLog: LogHandler {
 			guard let metadata = metadata else { continue }
 			metadataAggregator.merge(metadata) { return $1 }
 		}
-		return Self.joinedMetadata(metadataAggregator)
-	}
-
-	private static func joinedMetadata(_ metadata: Logging.Logger.Metadata, with separator: String = ", ") -> String? {
-		guard !metadata.isEmpty else { return nil }
-		return metadata.map { "\"\($0)\": \"\($1)\"" }.joined(separator: separator)
+		return metadataAggregator.asJSON()
 	}
 }
diff --git a/Tests/Logging OSLog Tests/Logging Test.swift b/Tests/Logging OSLog Tests/Logging Test.swift
index e475144..173fbc4 100644
--- a/Tests/Logging OSLog Tests/Logging Test.swift	
+++ b/Tests/Logging OSLog Tests/Logging Test.swift	
@@ -13,4 +13,16 @@ import LoggingOSLog
 @Test func canLogMessage() {
 	let logger = Logging.Logger(label: "de.astzweig.loggingoslog.Test")
 	logger.info("Test message")
-}
\ No newline at end of file
+}
+
+@Test func canLogMessageWithMetadata() {
+	let logger = Logging.Logger(label: "de.astzweig.loggingoslog.Test")
+	logger.info("Test message", metadata: [
+		"request.id": "20140801",
+		"request.dirname": "\"Impossible\"",
+		"request.authorization": [
+			"bearer": "empty"
+		],
+		"request.values": ["1", "rootID", ["key": "value"]]
+	])
+}