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()

zorion79/lgr