Swift Package Index

Swift (apple/swift-log) LogHandler for logging JSON to GCP Stackdriver

  • The latest stable release is 3.0.0. Released 2 months ago.
  • The last commit to master was about 2 months ago.

Swift Version Compatibility

  • 3.0.0 and master
Full build results

Platform Compatibility

  • 3.0.0 and master
Full build results


A SwiftLog LogHandler that logs GCP Stackdriver formatted JSON to a file.

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 which would be whats expected under a gcp Cloud Run environment 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:


Stackdriver logging agent + fluentd config

You should preferably run the agent using the standard output destination StackdriverLogHandler.Destination.stdout which will get you up and running automatically under certain gcp environments such as Cloud Run.

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