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brainfinance/StackdriverLogging 3.1.0
Swift (apple/swift-log) LogHandler for logging JSON to GCP Stackdriver
⭐️ 20
🕓 1 year ago
.package(url: "https://github.com/brainfinance/StackdriverLogging.git", from: "3.1.0")


A SwiftLog LogHandler that logs GCP Stackdriver formatted JSON.

For more information on Stackdriver structured logging, see: https://cloud.google.com/logging/docs/structured-logging and LogEntry


This Stackdriver LogHandler depends on SwiftNIO which is used to create and save your new log entries in a non-blocking fashion.

How to install

Swift Package Manager

.package(url: "https://github.com/Brainfinance/StackdriverLogging.git", from:"3.0.0")

In your target's dependencies add "StackdriverLogging" e.g. like this:

.target(name: "App", dependencies: ["StackdriverLogging"]),


A factory is used to instantiate StackdriverLogHandler instances. Before bootstrapping your swift-log LoggingSystem, you must first call the StackdriverLogHandler.Factory.prepare(_:_:) function with your logging destination. The Logging destination can be either the standard output or a file of your choice. You are also responsible for gracefully shutting down the NIO dependencies used internally by the StackdriverLogHandler.Factory by calling its shutdown function, preferably in a defer statement right after preparing the factory.

try StackdriverLogHandler.Factory.prepare(for: .stdout)
defer {
    try! StackdriverLogHandler.Factory.syncShutdownGracefully()
let logLevel = Logger.Level.info
LoggingSystem.bootstrap { label -> LogHandler in
    var logger = StackdriverLogHandler.Factory.make()
    logger.logLevel = logLevel
    return logger

Vapor 4

Here's a bootstrapping example for a standard Vapor 4 application.

import App
import Vapor

var env = try Environment.detect()
try StackdriverLogHandler.Factory.prepare(for: .stdout)
defer {
    try! StackdriverLogHandler.Factory.syncShutdownGracefully()
try LoggingSystem.bootstrap(from: &env) { (logLevel) -> (String) -> LogHandler in
    return { label -> LogHandler in
        var logger = StackdriverLogHandler.Factory.make()
        logger.logLevel = logLevel
        return logger
let app = Application(env)
defer { app.shutdown() }
try configure(app)
try app.run()

Logging JSON values using Logger.MetadataValue

To log metadata values as JSON, simply log all JSON values other than String as a Logger.MetadataValue.stringConvertible and, instead of the usual conversion of your value to a String in the log entry, it will keep the original JSON type of your values whenever possible.

For example:

var logger = Logger(label: "Stackdriver")
logger[metadataKey: "jsonpayload-example-object"] = [
    "json-null": .stringConvertible(NSNull()),
    "json-bool": .stringConvertible(true),
    "json-integer": .stringConvertible(1),
    "json-float": .stringConvertible(1.5),
    "json-string": .string("Example"),
    "stackdriver-timestamp": .stringConvertible(Date()),
    "json-array-of-numbers": [.stringConvertible(1), .stringConvertible(5.8)],
    "json-object": [
        "key": "value"

Will log the non pretty-printed representation of:


Logging from a managed platform

If your app is running inside a managed environment such as Google Cloud Run or a container based Compute Engine, logging to stdout should get you up and running automatically.

Stackdriver logging agent + fluentd config

If you prefer logging to a file, you can use a file destination StackdriverLogHandler.Destination.file in combination with the Stackdriver logging agent https://cloud.google.com/logging/docs/agent/installation and a matching json format google-fluentd config (/etc/google-fluentd/config.d/example.conf) to automatically send your JSON logs to Stackdriver for you.

Here's an example google-fluentd conf file that monitors a json based logfile and send new log entries to Stackdriver:

    @type tail
    # Format 'JSON' indicates the log is structured (JSON).
    format json
    # The path of the log file.
    path /var/log/example.log
    # The path of the position file that records where in the log file
    # we have processed already. This is useful when the agent
    # restarts.
    pos_file /var/lib/google-fluentd/pos/example-log.pos
    read_from_head true
    # The log tag for this log input.
    tag exampletag


Stars: 20
Last commit: 2 days ago
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Release Notes

1 year ago

Add support for the new swift-log metadata provider.

Thanks for the contribution @Sherlouk

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