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Explore Logging in Swift

New Swift logging APIs

Logs are:

  • archived on device
  • low perf overhead

Creating Logs

import os

let logger = Logger(subsystem: "com.foo", category: "bar")
logger.log("This is my log")
logger.log("This is my log with data: \(someData)")

Pass data into logs using string interpolation - like print

log isn't like print though...

  • logs aren't always converted to String (slow) - only when displayed
  • format is based on the type of logged data

Data types supoorted in logs: - Numeric (Int/Double) - Objc-C (description) - CustomStringConvertible

Nonnumeric values are redacted by default

Retrieving Logs

# fruta.logarchive is the "output" file name
$log collect --device --start '2020-06-22 0:41:00' --output fruta.logarchive

Open logs in Console.app

Log Levels

Debug

  • only during debugging
  • not persisted
  • fastest - compiler optimizes away unless streaming logs

Info

  • helpful, but not required for troubleshooting
  • persisted for a short time

Notice (Default)

  • required for troubleshooting
  • persisted up to storage limit

Error

  • error during execution
  • persisted up to storage limit

Fault

  • bug
  • persisted up to storage limit
  • slowest (but still fast)

Formating Log Data

  • Optional formatting parameters!
  • Pass with data (like shown in privacy section above).
  • No additional runtime cost

Privacy

Privacy modifiers can be applied to logged data:

  • .public - shows info
  • .private(mask: .hash)

Example of hiding PII in logs

logger.log("Ordered smoothie \(smoothieName, privacy: .public)")

Version Support

  • New APIs on new OS versions
  • backward support for string interpolation via overloads