StackdriverLogging

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

Dependencies

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"]),

Bootstrapping

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"
    ]
]
logger.info("test")

Will log the non pretty-printed representation of:

{  
   "sourceLocation":{  
      "function":"boot(_:)",
      "file":"\/Sources\/App\/boot.swift",
      "line":25
   },
   "jsonpayload-example-object":{  
      "json-bool":true,
      "json-float":1.5,
      "json-string":"Example",
      "json-object":{  
         "key":"value"
      },
      "json-null":null,
      "json-integer":1,
      "json-array-of-numbers":[  
         1,
         5.8
      ],
      "stackdriver-timestamp":"2019-07-15T21:21:02.451Z"
   },
   "message":"test",
   "severity":"INFO"
}

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.