Programming language: Swift
License: MIT License
Tags: Logging    
Latest version: v0.5.0

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Swift5.4+ release CocoaPods CI codecov license

platforms SwiftPM|CMake|Bazel|Carthage

Puppy is a flexible logging library written in Swift ๐Ÿถ

It supports multiple transports(console, file, syslog, and oslog) as loggers. It not only works alone, but also as a backend for apple/swift-log.

Furthermore, it has file log rotation feature and you can also customize the log format as you like. And it supports cross-platform(Darwin, Linux, and Windows).


  • Written in Swift.
  • Supports cross-platform(Darwin, Linux, and Windows).
  • Supports console, file, syslog, and oslog as loggers.
  • Supports automatic log rotation about file logger.
  • Also Works as a backend for apple/swift-log.


Basic Usage

Logging to mutliple transports(e.g. console and file). It is recommended that the first argument of each logger be a unique reverse-order FQDN since it is also used internally for a DispatchQueue's label.

import Puppy

let console = ConsoleLogger("com.example.yourapp.console")
let fileURL = URL(fileURLWithPath: "./foo.log").absoluteURL
let file = FileLogger("com.example.yourapp.file",
                      fileURL: fileURL,
                      filePermission: "600")  // Default permission is "640". 

let log = Puppy()
// Set the logging level.
log.add(console, withLevel: .warning)
log.add(file, withLevel: .warning)

log.debug("DEBUG message")  // Will NOT be logged.
log.error("ERROR message")  // Will be logged.

Use with apple/swift-log

Logging to mutliple transports(e.g. console and syslog) as a backend for apple/swift-log.

import Puppy
import Logging

let console = ConsoleLogger("com.example.yourapp.console")
let syslog = SystemLogger("com.example.yourapp.syslog")

let puppy = Puppy.default

LoggingSystem.bootstrap {
    var handler = PuppyLogHandler(label: $0, puppy: puppy)
    // Set the logging level.
    handler.logLevel = .trace
    return handler

let log = Logger(label: "com.example.yourapp.swiftlog")

log.trace("TRACE message")  // Will be logged.
log.debug("DEBUG message")  // Will be logged.

Use file log rotation

Logging to file and use log rotation feature.

import Puppy

class ViewController: UIViewController {
    let delegate = SampleFileRotationDelegate()
    override func viewDidLoad() {
        let fileRotation = try! FileRotationLogger("com.example.yourapp.filerotation",
                                                   fileURL: "./logs/foo.log")
        fileRotation.suffixExtension = .date_uuid   // Default option is `.numbering`.
        fileRotation.maxFileSize = 10 * 1024 * 1024
        fileRotation.maxArchivedFilesCount = 5
        fileRotation.delegate = delegate
        let log = Puppy()
        log.info("INFO message")
        log.warning("WARNING message")

class SampleFileRotationDelegate: FileRotationLoggerDeletate {
    func fileRotationLogger(_ fileRotationLogger: FileRotationLogger,
                            didArchiveFileURL: URL, toFileURL: URL) {
        print("didArchiveFileURL: \(didArchiveFileURL), toFileURL: \(toFileURL)")
    func fileRotationLogger(_ fileRotationLogger: FileRotationLogger,
                            didRemoveArchivedFileURL: URL) {
        print("didRemoveArchivedFileURL: \(didRemoveArchivedFileURL)")

Customize the log format

Customize the log format using Formattable protocol. Logging to oslog for example.

import Puppy

class ViewController: UIViewController {
    override func viewDidLoad() {
        let oslog = OSLogger("com.yourapp.oslog")
        oslog.format = LogFormatter()
        let log = Puppy()
        log.info("INFO message")
        log.warning("WARNING message")

class LogFormatter: LogFormattable {
    func formatMessage(_ level: LogLevel, message: String, tag: String, function: String,
                       file: String, line: UInt, swiftLogInfo: [String : String],
                       label: String, date: Date, threadID: UInt64) -> String {
        let date = dateFormatter(date)
        let file = shortFileName(file)
        return "\(date) \(threadID) [\(level.emoji) \(level)] \(file)#L.\(line) \(function) \(message)"

Create a custom logger

You can create your own custom logger. All you have to do is inherit BaseLogger class and override log(_:string:) method.

import Puppy

class CustomLogger: BaseLogger {
    override func log(_ level: LogLevel, string: String) {
        // Implements the logging feature here.


Puppy is available under the MIT license. See the LICENSE file for details.

*Note that all licence references and agreements mentioned in the Puppy README section above are relevant to that project's source code only.