Separate metadata by a unicode arrow in log

Use a single unicode right arrow instead of the two char ASCII right
arrow to separate the metadata from the actual log message. This is just
a preference decision and has no functional background.

Sources/Logging OSLog/Docs.docc/index.md

@@ -66,6 +66,13 @@ func init() {
 		"main": Logger(label: "com.example.yourapp.Main"),
 		"mail": Logger(label: "com.example.yourapp.Mail System"),
 	]
+
+	// And using loggers
+	logger["main"]!.debug("Starting build",
+		metadata: [
+			"input.output_directory": "\(output)",
+			"input.data": "\(data ?? "-")"
+	])
 }
 ```
 
@@ -78,6 +85,14 @@ library maps a reverse domain style label to the subsystem and category
 parameters of the unified logging system. See
 ``/LoggingOSLog/LoggingOSLog/init(label:)`` for more information.
 
+Metadata is appended as JSON to the logged message after a simple unicode right
+arrow ("→").
+
+### What this library does not supply
+This library does not implement any of the interpolation privacy features of
+the unified logging system, i.e. there is no way to redact or align a meta
+information, like the `Logging` API would allow.
+
 [subsystem]: https://developer.apple.com/documentation/os/generating-log-messages-from-your-code#:~:text=The%20subsystem%20string,for%20each%20subsystem%20string.
 [category]: https://developer.apple.com/documentation/os/generating-log-messages-from-your-code#:~:text=The%20category%20string,for%20these%20strings.
 

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: "\\\"")
+	}
+}

Sources/Logging OSLog/Logging OSLog.swift

@@ -78,11 +78,11 @@ public struct LoggingOSLog: LogHandler {
 		function: String,
 		line: UInt
 	) {
-		let metadataCSV = Self.joinMetadata(self.metadata, self.metadataProvider?.get(), metadata)
+		let metadataCSV = Self.joinedMetadata(self.metadata, self.metadataProvider?.get(), metadata)
 		let messageParts = [message.description, metadataCSV]
 
-		let message = messageParts.compactMap { $0 }.joined(separator: " -> ")
+		let message = messageParts.compactMap { $0 }.joined(separator: " → ")
-		self.oslogger.log(level: OSLogType.from(loggerLevel: level), "\(message)")
+		self.oslogger.log(level: OSLogType.from(loggerLevel: level), "\(message, privacy: .public)")
 	}
 
 	/**
@@ -97,17 +97,12 @@ public struct LoggingOSLog: LogHandler {
 		}
 	}
 	
-	private static func joinMetadata(_ metadataList: Logging.Logger.Metadata?...) -> String? {
+	private static func joinedMetadata(_ metadataList: Logging.Logger.Metadata?...) -> String? {
 		var metadataAggregator: Logging.Logger.Metadata = [:]
 		for metadata in metadataList {
 			guard let metadata = metadata else { continue }
 			metadataAggregator.merge(metadata) { return $1 }
 		}
-		return Self.joinMetadata(metadataAggregator)
+		return metadataAggregator.asJSON()
-	}
-
-	private static func joinMetadata(_ metadata: Logging.Logger.Metadata, with separator: String = ", ") -> String? {
-		guard !metadata.isEmpty else { return nil }
-		return metadata.map { "\($0) = \($1)" }.joined(separator: separator)
 	}
 }

Tests/Logging OSLog Tests/Logging Test.swift

@@ -14,3 +14,15 @@ import LoggingOSLog
 	let logger = Logging.Logger(label: "de.astzweig.loggingoslog.Test")
 	logger.info("Test message")
 }
+
+@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"]]
+	])
+}