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Modern logger with pipelines for Swift.
.package(url: "https://github.com/ikhvorost/DLog.git", from: "1.0.1")


Language: Swift Platform: iOS 8+/macOS10.11 SPM compatible CI codecov swift doc coverage

DLog: Modern logger with pipelines for Swift

DLog supports emoji and colored text output, oslog, pipelines, filtering, scopes, intervals and more.

Getting started

By default DLog provides basic text console output:

// Import DLog package
import DLog

// Create the logger
let log = DLog()

// Log a message
log.log("Hello DLog!")


• 13:09:25.854 [00] [DLOG] [LOG] <DLog:12> Hello DLog!


  • - start sign (useful for filtering)
  • 13:12:41.437 - timestamp (HH:mm:ss.SSS)
  • [00] - global scope level (see Scope)
  • [DLOG] - category tag ('DLOG' by default)
  • [LOG] - log type tag
  • <DLog:7> - location (file:line)
  • Hello DLog! - message

Log levels


Log a message:

log.log("App start")


13:36:59.086 [00] [DLOG] [LOG] <DLog:7> App start


Log an information message and helpful data:

let uuid = UUID().uuidString
log.info("uuid: \(uuid)")


13:37:54.934 [00] [DLOG] [INFO] <DLog:8> uuid: 104B6491-B2A8-4043-A5C6-93CEB60864FA


Log the current function name and a message (if it is provided) to help in debugging problems during the development:

func startup() {



13:38:31.903 [00] [DLOG] [TRACE] <DLog:8> startup() Start
13:38:31.905 [00] [DLOG] [TRACE] <DLog:9> startup()


Log a debug message to help debug problems during the development:

let session = URLSession(configuration: .default)
session.dataTask(with: URL(string: "https://apple.com")!) { data, response, error in
	guard let http = response as? HTTPURLResponse else { return }

	let text = HTTPURLResponse.localizedString(forStatusCode: http.statusCode)
	log.debug("\(http.url!.absoluteString): \(http.statusCode) - \(text)")


13:39:41.662 [00] [DLOG] [DEBUG] <DLog:12> https://www.apple.com/: 200 - no error


Log a warning message that occurred during the execution of your code.

log.warning("No Internet connection.")


13:44:49.992 [00] [DLOG] [WARNING] <DLog:7> No Internet connection.


Log an error that occurred during the execution of your code.

let fromURL = URL(fileURLWithPath: "source.txt")
let toURL = URL(fileURLWithPath: "destination.txt")
do {
	try FileManager.default.moveItem(at: fromURL, to: toURL)
catch {


13:53:20.398 [00] [DLOG] [ERROR] <DLog:13> “source.txt” couldn’t be moved to “com.apple.dt.playground.stub.iOS_Simulator.DLog-AA29FA84-10A1-45D7-BAEC-FC5402BAFB0C” because either the former doesn’t exist, or the folder containing the latter doesn’t exist.


Sanity check and log a message (if it is provided) when a condition is false.

let user = "John"
let password = ""

log.assert(user.isEmpty == false, "User is empty")
log.assert(password.isEmpty == false)
log.assert(password.isEmpty == false, "Password is empty")


13:55:15.108 [00] [DLOG] [ASSERT] <DLog:11>
13:55:15.110 [00] [DLOG] [ASSERT] <DLog:12> Password is empty


Log a critical bug that occurred during the execution in your code.

guard let modelURL = Bundle.main.url(forResource: "DataModel", withExtension:"momd") else {
	log.fault("Error loading model from bundle")


13:56:46.895 [00] [DLOG] [FAULT] <DLog:8> Error loading model from bundle


scope provides a mechanism for grouping work that's done in your program, so that can see all log messages related to a defined scope of your code in a tree view:

log.scope("Loading") { scope in
	if let path = Bundle.main.path(forResource: "data", ofType: "json") {
		scope.info("File: \(path)")
		if let data = try? String(contentsOfFile: path) {
			scope.debug("Loaded \(data.count) bytes")

NOTE: To pin your messages to a needed scope you should use the provided parameter of the closure that is scope logger.


• 12:36:43.656 [01] [DLOG] ┌ [Loading]
• 12:36:43.657 [01] [DLOG] |	[INFO] <DLog:8> File: .../data.json
• 12:36:43.658 [01] [DLOG] |	[DEBUG] <DLog:10> Loaded 121 bytes
• 12:36:43.658 [01] [DLOG] └ [Loading] (0.028s)


  • [01] - a global level of the scope
  • [Loading] - a name of the scope
  • (0.028s) - a time duration of the scope

You can get duration value of a finished scope programatically:

var scope = log.scope("scope") { _ in


It's possible to enter and leave a scope asynchronously:

let scope = log.scope("Request")

let session = URLSession(configuration: .default)
session.dataTask(with: URL(string: "https://apple.com")!) { data, response, error in
	defer {

	guard let data = data, let http = response as? HTTPURLResponse else {

	scope.debug("\(http.url!.absoluteString) - HTTP \(http.statusCode)")
	scope.debug("Loaded: \(data.count) bytes")


• 12:42:58.844 [01] [DLOG] ┌ [Request]
• 12:43:00.262 [01] [DLOG] |	[DEBUG] <DLog:19> https://www.apple.com/ - HTTP 200
• 12:43:00.263 [01] [DLOG] |	[DEBUG] <DLog:20> Loaded: 72705 bytes
• 12:43:00.263 [01] [DLOG] └ [Request] (1.418s)

Scopes can be nested one into one and that implements a global stack of scopes:

log.scope("Loading") { scope1 in
	if let url = Bundle.main.url(forResource: "data", withExtension: "json") {
		scope1.info("File: \(url)")

		if let data = try? Data(contentsOf: url) {
			scope1.debug("Loaded \(data.count) bytes")

			log.scope("Parsing") { scope2 in
				if let items = try? JSONDecoder().decode([Item].self, from: data) {
					scope2.debug("Parsed \(items.count) items")


• 12:46:44.729 [01] [DLOG] ┌ [Loading]
• 12:46:44.730 [01] [DLOG] |	[INFO] <DLog:13> File: .../data.json
• 12:46:44.731 [01] [DLOG] |	[DEBUG] <DLog:16> Loaded 121 bytes
• 12:46:44.731 [02] [DLOG] |	┌ [Parsing]
• 12:46:44.739 [02] [DLOG] |	|	[DEBUG] <DLog:20> Parsed 3 items
• 12:46:44.739 [02] [DLOG] |	└ [Parsing] (0.008s)
• 12:46:44.756 [01] [DLOG] └ [Loading] (0.027s)

As you can see from the sample above the scopes have different scope nesting levels "Loading" - [01] and "Parsing" - [02] and it's useful for filtering.


interval measures performance of your code by a running time and logs a detailed message with accumulated statistics:

for _ in 0..<10 {
	log.interval("Sort") {
		var arr = (1...10000).map {_ in arc4random()}


• 12:14:09.740 [00] [DLOG] [INTERVAL] <DLog:7> Sort - count: 1, duration: 0.342s, total: 0.342s, min: 0.342s, max: 0.342s, avg: 0.342s
• 12:14:10.039 [00] [DLOG] [INTERVAL] <DLog:7> Sort - count: 2, duration: 0.290s, total: 0.632s, min: 0.290s, max: 0.342s, avg: 0.316s
• 12:14:10.302 [00] [DLOG] [INTERVAL] <DLog:7> Sort - count: 3, duration: 0.261s, total: 0.893s, min: 0.261s, max: 0.342s, avg: 0.298s
• 12:14:10.554 [00] [DLOG] [INTERVAL] <DLog:7> Sort - count: 4, duration: 0.250s, total: 1.144s, min: 0.250s, max: 0.342s, avg: 0.286s
• 12:14:10.805 [00] [DLOG] [INTERVAL] <DLog:7> Sort - count: 5, duration: 0.250s, total: 1.393s, min: 0.250s, max: 0.342s, avg: 0.279s
• 12:14:11.061 [00] [DLOG] [INTERVAL] <DLog:7> Sort - count: 6, duration: 0.255s, total: 1.648s, min: 0.250s, max: 0.342s, avg: 0.275s
• 12:14:11.315 [00] [DLOG] [INTERVAL] <DLog:7> Sort - count: 7, duration: 0.252s, total: 1.900s, min: 0.250s, max: 0.342s, avg: 0.271s
• 12:14:11.566 [00] [DLOG] [INTERVAL] <DLog:7> Sort - count: 8, duration: 0.249s, total: 2.149s, min: 0.249s, max: 0.342s, avg: 0.269s
• 12:14:11.816 [00] [DLOG] [INTERVAL] <DLog:7> Sort - count: 9, duration: 0.249s, total: 2.398s, min: 0.249s, max: 0.342s, avg: 0.266s
• 12:14:12.075 [00] [DLOG] [INTERVAL] <DLog:7> Sort - count: 10, duration: 0.257s, total: 2.655s, min: 0.249s, max: 0.342s, avg: 0.265s


  • Sort - a name of the interval
  • count - a number of calls
  • duration - the current time duration
  • total - a total time duration
  • min - the shortest time duration
  • max - the longest time duration
  • avg - an average time duration

You can get all metrics values of the interval programatically:

let interval = log.interval("signpost") {


To measure asynchronous tasks you can use begin and end methods:

let interval = log.interval("Video")

let asset = AVURLAsset(url: url)
asset.loadValuesAsynchronously(forKeys: ["duration"]) {
	let status = asset.statusOfValue(forKey: "duration", error: nil)
	if status == .loaded {
		log.info("Duration: \(asset.duration.value)")


00:42:25.885 [00] [DLOG] [INFO] <Package.playground:16> Duration: 155000
00:42:25.888 [00] [DLOG] [INTERVAL] <Package.playground:9> Video - count: 1, duration: 0.390s, total: 0.390s, min: 0.390s, max: 0.390s, avg: 0.390s


You can define category name to differentiate unique areas and parts of your app and DLog uses this value to categorize and filter related log messages. For example, you might define separate strings for your app’s user interface, data model, and networking code.

let log = DLog()
let tableLog = log["TABLE"]
let netLog = log["NET"]

netLog.debug("Successfully fetched recordings.")
tableLog.debug("Updating with network response.")


16:21:10.777 [00] [DLOG] [DEBUG] <DLog:9> Refresh
16:21:10.779 [00] [NET] [DEBUG] <DLog:10> Successfully fetched recordings.
16:21:10.779 [00] [TABLE] [DEBUG] <DLog:11> Updating with network response.



Text is a source output that generates text representation of log messages. It doesn't deliver text to any target outputs (stdout, file etc.) and usually other outputs use it.

It supports thee styles:

  • .plain - universal plain text
  • .emoji - text with type icons for info, debug etc. (useful fo<img style="max-width:100%;" src="https://raw.github.com/ikhvorost/DLog/master/nsole)
  • .colored - colored text with ANSI escape codes (useful for Terminal and files)
let outputs = [
	"Plain" : Text(style: .plain),
	"Emoji" : Text(style: .emoji),
	"Colored" : Text(style: .colored),

for (name, output) in outputs {
	let log = DLog(output)



16:25:38.303 [00] [DLOG] [INFO] <DLog:16> info
16:25:38.305 [00] [DLOG] [LOG] <DLog:17> log
16:25:38.311 [00] [DLOG] [FAULT] <DLog:18> fatal

16:25:38.312 [00] [DLOG] ✅ [INFO] <DLog:16> info
16:25:38.312 [00] [DLOG] 💬 [LOG] <DLog:17> log
16:25:38.312 [00] [DLOG] 🆘 [FAULT] <DLog:18> fatal

16:25:38.312 [00] DLOG  INFO  <DLog:16> info
16:25:38.318 [00] DLOG  LOG  <DLog:17> log
16:25:38.318 [00] DLOG  FAULT  <DLog:18> fatal

Colored text in Terminal:

DLog: Colored log in Terminal

You can also use shortcuts .textPlain, .textEmoji and .textColored to create the output:

let logEmoji = DLog(.textEmoji)


Standard is a target output that can output text messages to POSIX streams:

  • stdout - Standard Output
  • stderr - Standard Error
// Prints to stdout
let logOut = DLog(Standard())

// Prints to stderr
let logErr = DLog(Standard(stream: Darwin.stderr))

You can also use shortcuts .stdout and .stderr to create the output for the logger:

let log = DLog(.stderr)
log.info("It's error stream")

By default <img style="max-width:100%;" src="https://raw.github.com/ikhvorost/DLog/master/ uses Text(style: .plain) output as a source to write text to the streams but you can set other:

let output = Standard(source: .textEmoji)
let log = DLog(output)



17:59:55.516 [00] [DLOG] ✅ [INFO] <DLog:7> Emoji


File is a target output that writes text messages to a file by a provided path:

let file = File(path: "/users/user/dlog.txt")
let log = DLog(file)

log.info("It's a file")

By default File output clears content of a opened file but if you want to append data to the existed file you should set append parameter to true:

let file = File(path: "/users/user/dlog.txt", append: true)

You can also use .file shortcut to create the output:

let log = DLog(.file("dlog.txt"))

File output uses Text(style: .plain) as a source by default but you can change it:

let file = File(path: "/users/user/dlog.txt", source: .textColored)
let log = DLog(file)

log.scope("File") { scope in
	scope.info("It's a file")

File "dlog.txt":

DLog: Colored text in a file.


OSLog is a target output that writes messages to the Unified Logging System (https://developer.apple.com/documentation/<img style="max-width:100%;" src="https://raw.github.com/ikhvorost/DLog/master/) that captures telemetry from your app for debugging and performance analysis and then you can use various tools to retrieve log information such as: Console and Instruments apps, command line tool log etc.

To create OSLog you can use subsystem strings that identify major functional areas of your app, and you specify them in revers<img style="max-width:100%;" src="https://raw.github.com/ikhvorost/DLog/master/tion—for example, com.your_company.your_subsystem_name. OSLog uses com.dlog.logger subsystem by default:

let output1 = OSLog() // subsystem = "com.dlog.logger"
let output2 = OSLog(subsystem: "com.company.app") // subsystem = "com.company.app"

You can also use .oslog shortcut to create the output:

let log1 = DLog(.oslog)
let log2 = <img style="max-width:100%;" src="https://raw.github.com/ikhvorost/DLog/master/g("com.company.app"))

All DLog's methods map to the system logger ones with appropriate log levels e.g.:

let log = DLog(.oslog)

log.assert(false, "assert")

Console.app with log levels:

DLog: Logs in Console.app

DLog's scopes map to the system logger activities:

let log = DLog(.oslog)

log.scope("Loading") { scope1 in
	log.scope("Parsing") { scope2 in
		scope2.debug("Parsed 1000 items")

Console.app with activities:

DLog: Activities in Console.app

DLog's intervals map to the system logger signposts:

let log = DLog(.oslog)

for _ in 0..<10 {
	log.interval("Sorting") {
		let delay = [0.1, 0.2, 0.3].randomElement()!
		Thread.sleep(forTimeInterval: delay)

Instruments.app with signposts:

DLog: Signposts in Instruments.app


Net is a target output that sends log message<img style="max-width:100%;" src="https://raw.github.com/ikhvorost/DLog/master/onsole` service that can be run from a command line on your machine. The service is provided as executable inside DLog package and to start it you should run sh NetConsole.command (or just click on NetConsole.command file) inside the package's folder and then the service starts listening for incoming messages:

$ sh NetConsole.command # or 'xcrun --sdk macosx swift run'
> [39/39] Linking NetConsole
> NetConsole for DLog v.1.0

Then the output connects and sends your log messages to NetConsole:

let log = DLog(Net())

log.scope("Main") { scope1 in
	log.scope("Subtask") { scope2 in
		scope2.error("Token is invalid")
	scope1.info("Close connection")

iOS 14: Don't forget to make next changes in your Info.plist to support Bonjour:

<string>Looking for local tcp Bonjour  service</string>


DLog: NetConsole

By default Net uses Text(style: .colored) output as a source but you can set other:

let log = DLog(Net(source: .textEmoji))

And you can also use .net shortcut to create the output for the logger.

let log = DLog(.net)

To connect to a specific instance of the service in your network you should provide an unique name to both NetConsole and Net output ("DLog" name is used by default).

To run the NetConsole with a specific name run next command:

sh NetConsole.command -n "MyLogger" # or 'xcrun --sdk macosx swift run NetConsole -n "MyLogger"'

In swift code you should set the same name:

let log = DLog(.net("MyLogger"))

More params of NetConsole you can look at help:

sh NetConsole.command --help  # or 'xcrun --sdk macosx swift run NetConsole --help'
OVERVIEW: NetConsole for DLog v.1.0

USAGE: net-console [--name <name>] [--auto-clear] [--debug]

  -n, --name <name>       The name by which the service is identified to the network. The name must be unique and by default it equals
                          "DLog". If you pass the empty string (""), the system automatically advertises your service using the computer
                          name as the service name.
  -a, --auto-clear        Clear a terminal on new connection.
  -d, --debug             Enable debug messages.
  -h, --help              Show help information.


As described above File, Net and Standard outputs have source parameter in their initializers to set a source output that is very useful if we want to change an output by default:

let std = Standard(stream: .out, source: .textEmoji)
let log = DLog(std)

Actually any output has source property:

let std = Standard()
std.source = .textEmoji
let log = DLog(std)

So that it's possible to make a linked list of outputs:

// Text
let text: LogOutput = .textEmoji

// Standard
let std = Standard()
std.source = text

// File
let file = File(path: "dlog.txt")
file.source = std

let log = DLog(file)

Where text is a source for std and std is a source for file: text --> std --> file, and now each text message will be sent to both std and file outputs consecutive.

Lets rewrite this shorter:

let log = DLog(.textEmoji => .stdout => .file("dlog.txt"))

Where => is pipeline operator which defines a combined output from two outputs where the first one is a source and second is a target. So from example above emoji text messages will be written twice: first to standard output and then to the file.

You can combine any needed outputs together and create a final chained output from multiple outputs and your messages will be forwarded to all of them one by one:

// All log messages will be written:
// 1) as plain text to stdout
// 2) as colored text (with escape codes) to the file

let log = DLog(.textPlain => .stdout => .textColored => .file(path))


Filter or .filter represents a pipe output that can filter log messages by next available fields: time, category, type, fileName, funcName, line, text and scope. You can inject it to your pipeline where you need to log specific data only.


  1. Log messages to stardard output with 'NET' category only
let log = DLog(.textPlain => .filter { $0.category == "NET" } => .stdout)
let netLog = log["NET"]



22:44:56.386 [00] [NET] [INFO] <DLog:8> info
  1. Log debug messages only
let log = DLog(.textPlain => .filter { $0.type == .debug } => .stdout)



22:47:07.865 [00] [DLOG] [DEBUG] <DLog:8> debug
  1. Log messages that contain "hello" string only
let log = DLog(.textPlain => .filter { $0.text.contains("hello") } => .stdout)

log.log("hello world")


22:48:30.399 [00] [DLOG] [LOG] <DLog:7> hello world
  1. Log messages which are related to a specific scope:
let filter = Filter { item in
	let name = "Load"
	if let scope = item as? LogScope {
		return scope.text == name
	return item.scope?.text == name

let log = DLog(.textPlain => filter => .stdout)

log.scope("Load") { scope1 in

	log.scope("Parse") { scope2 in



22:58:16.401 [01] [DLOG] ┌ [Load]
22:58:16.402 [01] [DLOG] |	[DEBUG] <DLog:16> debug
22:58:16.413 [01] [DLOG] |	[ERROR] <DLog:21> error
22:58:16.414 [01] [DLOG] └ [Load] (0.012s)


It is the shared disabled logger constant that logging any messages and it's very useful when you want to turn off the logger for some build configuration, preference, condition etc.

// Logging is enabled for `Debug` build configuration only

	let log = DLog(.textPlain => .file(path))
	let log = DLog.disabled

When you disable the logger all your code continue running inside scopes and intervals except of log messages:

let log = DLog.disabled

log.scope("scope") { scope in

	print("scope code")
log.interval("signpost") {

	print("signpost code")


scope code
signpost code


XCode project

  1. Select Xcode > File > Swift Packages > Add Package Dependency...
  2. Add package repository: https://github.com/ikhvorost/DLog.git
  3. Import the package in your source files: import DLog

Swift Package

Add DLog package dependency to your Package.swift file:

let package = Package(
	dependencies: [
    	.package(url: "https://github.com/ikhvorost/DLog.git", from: "1.0.0")
	targets: [
		.target(name: "YourPackage",
			dependencies: [
				.product(name: "DLog", package: "DLog")


DLog is available under the MIT license. See the LICENSE file for more info.


Stars: 2
Last commit: 1 week ago

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iOS Software Engineer @ Perry Street Software
Perry Street Software is Jack’d and SCRUFF. We are two of the world’s largest gay, bi, trans and queer social dating apps on iOS and Android. Our brands reach more than 20 million members worldwide so members can connect, meet and express themselves on a platform that prioritizes privacy and security. We invest heavily into SwiftUI and using Swift Packages to modularize the codebase.

Release Notes

9 weeks ago

Removed ArgumentParser dependency.

Swiftpack is being maintained by Petr Pavlik | @ptrpavlik | @swiftpackco | API