lgr

README

lgr - simple logger with some extras

install

go get github.com/go-pkgz/lgr

usage

    l := lgr.New(lgr.Msec, lgr.Debug, lgr.CallerFile, lgr.CallerFunc) // allow debug and caller info, timestamp with milliseconds
    l.Logf("INFO some important message, %v", err)
    l.Logf("DEBUG some less important message, %v", err)

output looks like this:

2018/01/07 13:02:34.000 INFO  {svc/handler.go:101 h.MyFunc1} some important message, can't open file myfile.xyz
2018/01/07 13:02:34.015 DEBUG {svc/handler.go:155 h.MyFunc2} some less important message, file is too small`

Without lgr.Caller* it will drop {caller} part

details

interfaces and default loggers

• lgr package provides a single interface lgr.L with a single method Logf(format string, args ...interface{}). Function wrapper lgr.Func allows to make lgr.L from a function directly.
• Default logger functionality can be used without lgr.New (see "global logger")
• Two predefined loggers available: lgr.NoOp (do-nothing logger) and lgr.Std (passing directly to stdlib log)

options

lgr.New call accepts functional options:

• lgr.Debug - turn debug mode on to allow messages with "DEBUG" level (filtered otherwise)
• lgr.Out(io.Writer) - sets the output writer, default os.Stdout
• lgr.Err(io.Writer) - sets the error writer, default os.Stderr
• lgr.CallerFile - adds the caller file info
• lgr.CallerFunc - adds the caller function info
• lgr.CallerPkg - adds the caller package
• lgr.LevelBraces - wraps levels with "[" and "]"
• lgr.Msec - adds milliseconds to timestamp
• lgr.Format - sets custom template, overwrite all other formatting modifiers.

example: l := lgr.New(lgr.Debug, lgr.Msec)

formatting templates:

Several predefined templates provided and can be passed directly to lgr.Format, i.e. lgr.Format(lgr.WithMsec)

	Short      = `{{.DT.Format "2006/01/02 15:04:05"}} {{.Level}} {{.Message}}`
	WithMsec   = `{{.DT.Format "2006/01/02 15:04:05.000"}} {{.Level}} {{.Message}}`
	WithPkg    = `{{.DT.Format "2006/01/02 15:04:05.000"}} {{.Level}} ({{.CallerPkg}}) {{.Message}}`
	ShortDebug = `{{.DT.Format "2006/01/02 15:04:05.000"}} {{.Level}} ({{.CallerFile}}:{{.CallerLine}}) {{.Message}}`
	FuncDebug  = `{{.DT.Format "2006/01/02 15:04:05.000"}} {{.Level}} ({{.CallerFunc}}) {{.Message}}`
	FullDebug  = `{{.DT.Format "2006/01/02 15:04:05.000"}} {{.Level}} ({{.CallerFile}}:{{.CallerLine}} {{.CallerFunc}}) {{.Message}}`

User can make a custom template and pass it directly to lgr.Format. For example:

    lgr.Format(`{{.Level}} - {{.DT.Format "2006-01-02T15:04:05Z07:00"}} - {{.CallerPkg}} - {{.Message}}`)

Note: formatter (predefined or custom) adds measurable overhead - the cost will depend on the version of Go, but is between 30 and 50% in recent tests with 1.12. You can validate this in your environment via benchmarks: go test -bench=. -run=Bench

levels

lgr.Logf recognizes prefixes like "INFO" or "[INFO]" as levels. The full list of supported levels - "TRACE", "DEBUG", "INFO", "WARN", "ERROR", "PANIC" and "FATAL"

• TRACE will be filtered unless lgr.Trace option defined
• DEBUG will be filtered unless lgr.Debug or lgr.Trace options defined
• INFO and WARN don't have any special behavior attached
• ERROR sends messages to both out and err writers
• FATAL and send messages to both out and err writers and exit(1)
• PANIC does the same as FATAL but in addition sends dump of callers and runtime info to err.

adaptors

lgr logger can be converted to io.Writer or *log.Logger

• lgr.ToWriter(l lgr.L, level string) io.Writer - makes io.Writer forwarding write ops to underlying lgr.L
• lgr.ToStdLogger(l lgr.L, level string) *log.Logger - makes standard logger on top of lgr.L

level parameter is optional, if defined (non-empty) will enforce the level.

global logger

Users should avoid global logger and pass the concrete logger as a dependency. However, in some cases a global logger may be needed, for example migration from stdlib log to lgr. For such cases log "github.com/go-pkgz/lgr" can be imported instead of log package.

Global logger provides lgr.Printf, lgr.Print and lgr.Fatalf functions. User can customize the logger by calling lgr.Setup(options ...). The instance of this logger can be retrieved with lgr.Default()

Documentation

Index

• Constants
• Variables
• func CallerFile(l *Logger)
• func CallerFunc(l *Logger)
• func CallerPkg(l *Logger)
• func Debug(l *Logger)
• func Fatalf(format string, args ...interface{})
• func LevelBraces(l *Logger)
• func Msec(l *Logger)
• func Print(line string)
• func Printf(format string, args ...interface{})
• func Setup(opts ...Option)
• func ToStdLogger(l L, level string) *log.Logger
• func Trace(l *Logger)
• type Func
  • func (f Func) Logf(format string, args ...interface{})
• type L
  • func Default() L
• type Logger
  • func New(options ...Option) *Logger
  • func (l *Logger) Logf(format string, args ...interface{})
• type Option
  • func CallerDepth(n int) Option
  • func Err(w io.Writer) Option
  • func Format(f string) Option
  • func Out(w io.Writer) Option
• type Writer
  • func ToWriter(l L, level string) *Writer
  • func (w *Writer) Write(p []byte) (n int, err error)

Constants

const (
	Short      = `{{.DT.Format "2006/01/02 15:04:05"}} {{.Level}} {{.Message}}`
	WithMsec   = `{{.DT.Format "2006/01/02 15:04:05.000"}} {{.Level}} {{.Message}}`
	WithPkg    = `{{.DT.Format "2006/01/02 15:04:05.000"}} {{.Level}} ({{.CallerPkg}}) {{.Message}}`
	ShortDebug = `{{.DT.Format "2006/01/02 15:04:05.000"}} {{.Level}} ({{.CallerFile}}:{{.CallerLine}}) {{.Message}}`
	FuncDebug  = `{{.DT.Format "2006/01/02 15:04:05.000"}} {{.Level}} ({{.CallerFunc}}) {{.Message}}`
	FullDebug  = `{{.DT.Format "2006/01/02 15:04:05.000"}} {{.Level}} ({{.CallerFile}}:{{.CallerLine}} {{.CallerFunc}}) {{.Message}}`
)

Variables

var NoOp = Func(func(format string, args ...interface{}) {})

NoOp logger

var Std = Func(func(format string, args ...interface{}) { stdlog.Printf(format, args...) })

Std logger sends to std default logger directly

Functions

func CallerFile

func CallerFile(l *Logger)

CallerFile adds caller info with file, and line number. Ignored if Format option used.

func CallerFunc

func CallerFunc(l *Logger)

CallerFunc adds caller info with function name. Ignored if Format option used.

func CallerPkg

func CallerPkg(l *Logger)

CallerPkg adds caller's package name. Ignored if Format option used.

func Debug

func Debug(l *Logger)

Debug turn on dbg mode

func Fatalf

func Fatalf(format string, args ...interface{})

Fatalf simplifies replacement of std logger

func LevelBraces

func LevelBraces(l *Logger)

LevelBraces surrounds level with [], i.e. [INFO]. Ignored if Format option used.

func Msec

func Msec(l *Logger)

Msec adds .msec to timestamp. Ignored if Format option used.

func Print

func Print(line string)

Print simplifies replacement of std logger

func Printf

func Printf(format string, args ...interface{})

Printf simplifies replacement of std logger

func Setup

func Setup(opts ...Option)

Setup default logger with options

func ToStdLogger

func ToStdLogger(l L, level string) *log.Logger

func Trace

func Trace(l *Logger)

Trace turn on trace + dbg mode

Types

type Func

type Func func(format string, args ...interface{})

Func type is an adapter to allow the use of ordinary functions as Logger.

func (Func) Logf

func (f Func) Logf(format string, args ...interface{})

Logf calls f(format, args...)

type L

type L interface {
	Logf(format string, args ...interface{})
}

L defines minimal interface used to log things

func Default

func Default() L

Default returns pre-constructed def logger (debug off, callers disabled)

type Logger

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

Logger provided simple logger with basic support of levels. Thread safe

func New

func New(options ...Option) *Logger

New makes new leveled logger. By default writes to stdout/stderr. default format: 2018/01/07 13:02:34.123 DEBUG some message 123

func (*Logger) Logf

func (l *Logger) Logf(format string, args ...interface{})

Logf implements L interface to output with printf style. DEBUG and TRACE filtered out by dbg and trace flags. ERROR and FATAL also send the same line to err writer. FATAL and PANIC adds runtime stack and os.exit(1), like panic.

type Option

type Option func(l *Logger)

Option func type

func CallerDepth

func CallerDepth(n int) Option

CallerDepth sets number of stack frame skipped for caller reporting, 0 by default

func Err

func Err(w io.Writer) Option

Err sets error writer, stderr by default

func Format

func Format(f string) Option

Format sets output layout, overwrites all options for individual parts, i.e. Caller*, Msec and LevelBraces

func Out

func Out(w io.Writer) Option

Out sets out writer, stdout by default

type Writer

type Writer struct {
	L
	// contains filtered or unexported fields
}

Writer holds lgr.L and wraps with io.Writer interface

func ToWriter

func ToWriter(l L, level string) *Writer

ToWriter makes io.Writer for given lgr.L with optional level

func (*Writer) Write

func (w *Writer) Write(p []byte) (n int, err error)

Write to lgr.L