SwiftyLogger

A simple and flexible logging library written in Swift

Getting started

Swift Package Manager

You can add SwiftyLogger to your project by adding it as a dependency in your Package.swift file:

// swift-tools-version:5.8
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "MyProject",
    products: [
        .library(name: "MyProject", targets: ["MyProject"])
    ],
    dependencies: [
         .package(url: "https://github.com/mtynior/SwiftyLogger.git", .upToNextMajor(from: "1.0.0")),
    ],
    targets: [
        .target(name: "MyProject", dependencies: ["SwiftyLogger"]),
        .testTarget(name: "MyProjectTests", dependencies: ["MyProject"])
    ]
)

Xcode

Open your project in Xcode, then:

Click File -> Add Packages,
In the search bar type: https://github.com/mtynior/SwiftyLogger.git and press Enter,
Once Xcode finds the library, set Dependency rule to Up to next major version,
Click Add Package,
Select the desired Target (If you have multiple targets, you can add the dependency manually from Xcode)
Confirm selection by clicking on Add Package.

TL;DR

SwiftyLogger allows you to quickly start logging:

import SwiftyLogger

// 1. Create logger
let logger = Logger()
    .addConsole()
    .addFile()
    
// 2. Log messages
logger.logDebug("Debug message")
logger.logVerbose("Verbose message")
logger.logInfo("Info message")
logger.logWarning("Warning message")
logger.logError("Error message")
logger.logFatal("Fatal message")

Available log functions

logDebug(message: "Debug log")
logDebug(message: "Debug log", file: "Main.swift")
logDebug(message: "Debug log", file: "Main.swift", function: "show()")
logDebug(message: "Debug log", file: "Main.swift", function: "show()", line: 21)
logDebug(message: "Debug log", file: "Main.swift", function: "show()", line: 21, timestamp: Date())
logDebug(message: "Debug log", file: "Main.swift", function: "show()", line: 21, timestamp: Date(), threadName: "Main")

logVerbose(message: "Debug log")
logVerbose(message: "Debug log", file: "Main.swift")
logVerbose(message: "Debug log", file: "Main.swift", function: "show()")
logVerbose(message: "Debug log", file: "Main.swift", function: "show()", line: 21)
logVerbose(message: "Debug log", file: "Main.swift", function: "show()", line: 21, timestamp: Date())
logVerbose(message: "Debug log", file: "Main.swift", function: "show()", line: 21, timestamp: Date(), threadName: "Main")

logInfo(message: "Debug log")
logInfo(message: "Debug log", file: "Main.swift")
logInfo(message: "Debug log", file: "Main.swift", function: "show()")
logInfo(message: "Debug log", file: "Main.swift", function: "show()", line: 21)
logInfo(message: "Debug log", file: "Main.swift", function: "show()", line: 21, timestamp: Date())
logInfo(message: "Debug log", file: "Main.swift", function: "show()", line: 21, timestamp: Date(), threadName: "Main")

logWarning(message: "Debug log")
logWarning(message: "Debug log", file: "Main.swift")
logWarning(message: "Debug log", file: "Main.swift", function: "show()")
logWarning(message: "Debug log", file: "Main.swift", function: "show()", line: 21)
logWarning(message: "Debug log", file: "Main.swift", function: "show()", line: 21, timestamp: Date())
logWarning(message: "Debug log", file: "Main.swift", function: "show()", line: 21, timestamp: Date(), threadName: "Main")

logError(message: "Debug log")
logError(message: "Debug log", file: "Main.swift")
logError(message: "Debug log", file: "Main.swift", function: "show()")
logError(message: "Debug log", file: "Main.swift", function: "show()", line: 21)
logError(message: "Debug log", file: "Main.swift", function: "show()", line: 21, timestamp: Date())
logError(message: "Debug log", file: "Main.swift", function: "show()", line: 21, timestamp: Date(), threadName: "Main")

logFatal(message: "Debug log")
logFatal(message: "Debug log", file: "Main.swift")
logFatal(message: "Debug log", file: "Main.swift", function: "show()")
logFatal(message: "Debug log", file: "Main.swift", function: "show()", line: 21)
logFatal(message: "Debug log", file: "Main.swift", function: "show()", line: 21, timestamp: Date())
logFatal(message: "Debug log", file: "Main.swift", function: "show()", line: 21, timestamp: Date(), threadName: "Main")

Console Logger

Default Console Logger uses print function to display log messages:

let logger = Logger()
    .addConsole()

File Logger

By default, the File Logger saves log messages in application.log file located in Caches folder:

let logger = Logger()
    .addFile()

The name of the file can be changed:

let logger = Logger()
    .addFile(fileName: "myLogs.log")

Also the location of the file can be changed:

let url = URL(path: "/path/to/file.log")!

let logger = Logger()
    .addFile(fileURL: url)

Rotating File Logger

The Rotating File Logger saves log messages into log file. When the size of the log file exceeds the maximum size, then the logs are transferred to archive file. By default, the Rotating File Logger saves log messages in application.log file located in Caches folder. The archive logs are stored in application.log file:

let logger = Logger()
    .addRotatingFile()

By default the maximum log file size is set to 5MB, but can be changed with maximumFileSizeInBytes:

let logger = Logger()
    .addRotatingFile(maximumFileSizeInBytes: 1_048_576)

The name of both files can be changed:

let logger = Logger()
    .addFile(fileName: "myLogs.log", archiveFileName: "myArchiveLogs.log")

Also the location of both files can be changed:

let logFileUrl = URL(path: "/path/to/file.log")!
let archiveFileUrl = URL(path: "/path/to/archive.log")!

let logger = Logger()
    .addFile(fileURL: url, archiveLogFileURL: archiveFileUrl)

Subsystem and category

You can define loggers dedicated to specific area of you application. You can distinguish those areas using optional subsystem and category properties:

let logger = Logger(subsystem: "Settings", category: "General")
    .addConsole()
    .addFile()

Minimal log level

By default the minimum log level is set to LogLevel.debug.

If you want to change minimum log level globally, for all logger targets, then set the minimumLogLevel on LoggerConfiguration:

let configuration = LoggerConfiguration(minimumLogLevel: .warning)

let logger = Logger(configuration: configuration)
    .addConsole()
    .addFile()

You can also set the minimum log level for the specific logger destination:

let logger = Logger(configuration: LoggerConfiguration(minimumLogLevel: .warning))
    .addConsole() // logs warnings and above
    .addFile(loggerConfiguration: LoggerConfiguration(minimumLogLevel: .error)) // logs errors and above

If the minimum log level for specific logger destination is defined, then he global minimumLogLevel is ignored:

let logger = Logger(configuration: LoggerConfiguration(minimumLogLevel: .warning))
    .addConsole() // logs warnings and above
    .addFile(loggerConfiguration: LoggerConfiguration(minimumLogLevel: .debug)) // logs debug and above

Custom Destination

You can define your own destination. Every destination must conformance to the LoggingDestination protocol:

final class MyLogger: LoggingDestination {
    var configuration: LoggerConfiguration
    var queue: DispatchQueue
    
    init(configuration: LoggerConfiguration) {
        self.configuration = configuration
        self.queue = DispatchQueue(label: UUID().uuidString)
    }
    
    public func log(message: LogMessage, context: LoggingContext) {
        let formattedMessage = configuration.messageFormatter.format(message: message, context: context)
        print(formattedMessage, separator: "", terminator: "\n")
    }
}

Once the custom destination is defined, you can add it to Logger with addDestination(_:) method:

let logger = Logger()
    .addDestination(MyLogger(configuration: LoggerConfiguration.default))

Or you can extend the LoggerConfigurable protocol and make fluent API:

public extension LoggerConfigurable {
    func addMyLogger(configuration: LoggerConfiguration? = nil) -> Self {
        let actualConfiguration = configuration ?? self.configuration
        self.addDestination(MyLogger(configuration: actualConfiguration))
        return self
    }
}

Now, you can use your custom logger like this:

let logger = Logger()
    .addMyLogger()

Message formatter

By default, the Logger has formatter that produces following output:

[2023-09-01T17:01:31.921Z][Debug][Subsystem][Category] Hello world

If you want to change the format of the log message you can create your own formatter. The only requirement for custom formatter is conformance of the LogMessageFormatter protocol:

final class MyFormatter: LogMessageFormatter {
    func format(message: LogMessage, context: LoggingContext) -> String {          
        return "<\(logMessage.logLevel)> " + logMessage.message
    }
}

One the formatter is defined you can use it by adjusting logger's configuration:

var configuration = LoggerConfiguration.default
configuration.messageFormatter = MyFormatter()

let logger = Logger(configuration: configuration)
    .addConsole()

Now, Logger will produce following output:

<Debug> Hello world

License

SwiftyLogger is released under the MIT license. See LICENSE for details.

mtynior / SwiftyLogger