Logging¶
Vapor's logging API is built on top of SwiftLog. This means Vapor is compatible with all of SwiftLog's backend implementations.
Logger¶
Instances of Logger are used for outputting log messages. Vapor provides a few easy ways to get access to a logger.
Request¶
Each incoming Request has a unique logger that you should use for any logs specific to that request.
app.get("hello") { req -> String in
req.logger.info("Hello, logs!")
return "Hello, world!"
}
The request logger includes a unique UUID identifying the incoming request to make tracking logs easier.
[ INFO ] Hello, logs! [request-id: C637065A-8CB0-4502-91DC-9B8615C5D315] (App/routes.swift:10)
Info
Logger metadata will only be shown in debug log level or lower.
Application¶
For log messages during app boot and configuration, use Application's logger.
app.logger.info("Setting up migrations...")
app.migrations.use(...)
Custom Logger¶
In situations where you don't have access to Application or Request, you can initialize a new Logger.
let logger = Logger(label: "dev.logger.my")
logger.info(...)
While custom loggers will still output to your configured logging backend, they will not have important metadata attached like request UUID. Use the request or application specific loggers wherever possible.
Level¶
SwiftLog supports several different logging levels.
| name | description |
|---|---|
| trace | Appropriate for messages that contain information normally of use only when tracing the execution of a program. |
| debug | Appropriate for messages that contain information normally of use only when debugging a program. |
| info | Appropriate for informational messages. |
| notice | Appropriate for conditions that are not error conditions, but that may require special handling. |
| warning | Appropriate for messages that are not error conditions, but more severe than notice. |
| error | Appropriate for error conditions. |
| critical | Appropriate for critical error conditions that usually require immediate attention. |
When a critical message is logged, the logging backend is free to perform more heavy-weight operations to capture system state (such as capturing stack traces) to facilitate debugging.
By default, Vapor will use info level logging. When run with the production environment, notice will be used to improve performance.
Changing Log Level¶
Regardless of environment mode, you can override the logging level to increase or decrease the amount of logs produced.
The first method is to pass the optional --log flag when booting your application.
swift run App serve --log debug
The second method is to set the LOG_LEVEL environment variable.
export LOG_LEVEL=debug
swift run App serve
Both of these can be done in Xcode by editing the App scheme.
Configuration¶
SwiftLog is configured by bootstrapping the LoggingSystem once per process. Vapor projects typically do this in entrypoint.swift.
var env = try Environment.detect()
try LoggingSystem.bootstrap(from: &env)
bootstrap(from:) is a helper method provided by Vapor that will configure the default log handler based on command-line arguments and environment variables. The default log handler supports outputting messages to the terminal with ANSI color support.
Custom Handler¶
You can override Vapor's default log handler and register your own.
import Logging
LoggingSystem.bootstrap { label in
StreamLogHandler.standardOutput(label: label)
}
All of SwiftLog's supported backends will work with Vapor. However, changing the log level with command-line arguments and environment variables is only compatible with Vapor's default log handler.