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 +85,9 @@ 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

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

@@ -78,10 +78,10 @@ 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, 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)
-	}
-
-	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)
+		return metadataAggregator.asJSON()
 	}
 }

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")
-}
+}
+
+@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"]]
+	])
+}