slog

README

slog

Package slog defines a logger interface and provides a default implementation of a subsystem-aware leveled logger implementing the same interface.

Installation and Updating

$ go get -u github.com/fistchain/slog

License

Package slog is licensed under the copyfree ISC License.

Documentation

Overview

Package slog defines an interface and default implementation for subsystem logging.

Log level verbosity may be modified at runtime for each individual subsystem logger.

The default implementation in this package must be created by the Backend type. Backends can write to any io.Writer, including multi-writers created by io.MultiWriter. Multi-writers allow log output to be written to many writers, including standard output and log files.

Optional logging behavior can be specified by using the LOGFLAGS environment variable and overridden per-Backend by using the WithFlags call option. Multiple LOGFLAGS options can be specified, separated by commas. The following options are recognized:

longfile: Include the full filepath and line number in all log messages

shortfile: Include the filename and line number in all log messages.
Overrides longfile.

Index

• Constants
• type Backend
  • func NewBackend(w io.Writer, opts ...BackendOption) *Backend
  • func (b *Backend) Logger(subsystemTag string) Logger
• type BackendOption
  • func WithFlags(flags uint32) BackendOption
• type Level
  • func LevelFromString(s string) (l Level, ok bool)
  • func (l Level) String() string
• type Logger

Constants

const (
	// Llongfile modifies the logger output to include full path and line number
	// of the logging callsite, e.g. /a/b/c/main.go:123.
	Llongfile uint32 = 1 << iota

	// Lshortfile modifies the logger output to include filename and line number
	// of the logging callsite, e.g. main.go:123.  Overrides Llongfile.
	Lshortfile
)

Flags to modify Backend's behavior.

Types

type Backend

type Backend struct {
	// contains filtered or unexported fields
}

Backend is a logging backend. Subsystems created from the backend write to the backend's Writer. Backend provides atomic writes to the Writer from all subsystems.

func NewBackend

func NewBackend(w io.Writer, opts ...BackendOption) *Backend

NewBackend creates a logger backend from a Writer.

func (*Backend) Logger

func (b *Backend) Logger(subsystemTag string) Logger

Logger returns a new logger for a particular subsystem that writes to the Backend b. A tag describes the subsystem and is included in all log messages. The logger uses the info verbosity level by default.

type BackendOption

type BackendOption func(b *Backend)

BackendOption is a function used to modify the behavior of a Backend.

func WithFlags

func WithFlags(flags uint32) BackendOption

WithFlags configures a Backend to use the specified flags rather than using the package's defaults as determined through the LOGFLAGS environment variable.

type Level

type Level uint32

Level is the level at which a logger is configured. All messages sent to a level which is below the current level are filtered.

const (
	LevelTrace Level = iota
	LevelDebug
	LevelInfo
	LevelWarn
	LevelError
	LevelCritical
	LevelOff
)

Level constants.

func LevelFromString

func LevelFromString(s string) (l Level, ok bool)

LevelFromString returns a level based on the input string s. If the input can't be interpreted as a valid log level, the info level and false is returned.

func (Level) String

func (l Level) String() string

String returns the tag of the logger used in log messages, or "OFF" if the level will not produce any log output.

type Logger

type Logger interface {
	// Tracef formats message according to format specifier and writes to
	// to log with LevelTrace.
	Tracef(format string, params ...interface{})

	// Debugf formats message according to format specifier and writes to
	// log with LevelDebug.
	Debugf(format string, params ...interface{})

	// Infof formats message according to format specifier and writes to
	// log with LevelInfo.
	Infof(format string, params ...interface{})

	// Warnf formats message according to format specifier and writes to
	// to log with LevelWarn.
	Warnf(format string, params ...interface{})

	// Errorf formats message according to format specifier and writes to
	// to log with LevelError.
	Errorf(format string, params ...interface{})

	// Criticalf formats message according to format specifier and writes to
	// log with LevelCritical.
	Criticalf(format string, params ...interface{})

	// Trace formats message using the default formats for its operands
	// and writes to log with LevelTrace.
	Trace(v ...interface{})

	// Debug formats message using the default formats for its operands
	// and writes to log with LevelDebug.
	Debug(v ...interface{})

	// Info formats message using the default formats for its operands
	// and writes to log with LevelInfo.
	Info(v ...interface{})

	// Warn formats message using the default formats for its operands
	// and writes to log with LevelWarn.
	Warn(v ...interface{})

	// Error formats message using the default formats for its operands
	// and writes to log with LevelError.
	Error(v ...interface{})

	// Critical formats message using the default formats for its operands
	// and writes to log with LevelCritical.
	Critical(v ...interface{})

	// Level returns the current logging level.
	Level() Level

	// SetLevel changes the logging level to the passed level.
	SetLevel(level Level)
}

Logger is an interface which describes a level-based logger. A default implementation of Logger is implemented by this package and can be created by calling (*Backend).Logger.

var Disabled Logger

Disabled is a Logger that will never output anything.