hedzr/logg

A golang logging library with log/slog style APIs, with colorful console output.

Features

The abilities are:

• fast enough: performance is not our unique aim, and this one is enough quick.
• colorful console output by default.
• switch to logfmt or json format dynamically.
• interfaces and abilities similar with log/slog.
• adapted into log/slog to enable color logging, here some our verbs (such as Fatal, Panic) cannot work directly.
• cascade child logger and dump attrs of parent recursively (need enable LattrsR to avoid taking more cpu usages).
• very lite child loggers.
• user-defined levels, writer, and value stringer.
• privacy enough: harden filepath, shorten package name (by Lprivacypath and Lprivacypathregexp); and implement LogObjectMarshaller or LogArrayMarshaller to security sensitive fields.
• better multiline outputs.

Since v0.7.3, a locking version of printOut added. This would take more safeties to splitted writer (if your writer had implemented LevelSettable interface to compliant with logg/slog's log level).

Chanages

See also CHANGELOG.

Since v1.0.0, the streaming calls changed their behaviour: .WithXXX will make a new instance as a child logger and apply the settings; .SetXXX will take the effects on the place.

NOTE: v0.7.0 is pre-release version of v1.0.0.

Since v0.5.7, logg/slog enables privacy hardening flags by default now.

Motivation

As an opt-in copy of log/slog, we provide an out-of-box colored text outputting logger with more verbs.

And an auto-optimized Verb: Verbose(msg, args...) would print logging contents only if build tag verbose defined. The point is it will be optimized completely in a default build.

Guide

Basics

logg/slog provides package-level functions for logging, Info, Error, and so on They will be mapped to the builtin default logger.

Default() returns the default logger and SetDefult() replaces it.

The basic usages are:

import "github.com/hedzr/logg/slog"

msg := "A message"
args := []any{
    "attr1", 0,
    "attr2", false,
    "attr3", 3.13,
    "attr4", errors.New("simple"),
    // ,,,
    slog.Group("group1",
        "attr1", 0,
        "attr2", false,
        slog.NewAttr("attr3", "any styles what u prefer"),
        "attrn", // unpaired key can work here 
        slog.Group("more", "group", []byte("more subgroup here")),
    ),
    // ...
    slog.Int("id", 23123),
    slog.Group("properties",
        slog.Int("width", 4000),
        slog.Int("height", 3000),
        slog.String("format", "jpeg"),
    ),
}

slog.Print("")    // logging a clean newline without decorations
slog.Println("")  // logging a clean newline without decorations
slog.Println()    // logging a clean newline without decorations
slog.Print(msg, args...)
slog.Println(msg) // synosym of Print
slog.Fatal(msg, args...)
slog.Panic(msg, args...)
slog.Error(msg, args...)
slog.Warn(msg, args...)
slog.Info(msg, args...)
slog.Debug(msg, args...)
slog.Trace(msg, args...)

// only print the logging contents while built with `-tags verbose`
slog.Verbose(msg, args...) // 

// some verbs with more meanings
slog.OK("ok")
slog.OK("ok", args...)
slog.Success(msg, args...)
slog.Fail(msg, args...)

// Contextual logging
slog.InfoContext(context.TODO(), "info msg", args...)

// No-featured predicate here
slog.LogAttrs(context.TODO(), slog.Debug, "debug msg", args...)

The sub-loggers are also supported, see SubLogger.

Println

A Println(args ...any) has slight differences with other verbs like Print(msg string, args ...any). But you are using it with same form like others. That is, the first of the args passing to Println is indeed a msg string. Just a little benefit, you can pass nothing to Println. If you're doing with this way, a complete blank line prints by slog.Println(), no timestamp, no serverity, and no caller info.

slog.Info("1")
slog.Println() // this makes a real blank line, for colorful and logfmt formats
slog.Info("2")

In a large long logging outputs, one and more blank line(s) maybe help your focus.

Customizing Your Verbs

Like OK, Success and Fail, you could wrap logg/slogg package-level predicates/verbs for giving more features.

func Tip(msg string, args...any) {
  if myConditionSatisfied {
    slog.WithSkip(1).OK(msg, args...)
  }
}

WithSkip(n) tells log/slog to strip extra 1 level(s) from caller stack frames so the logged message can hook to the caller of Tip(), rather than Line 3 in Tip().

Also, using a custom level is a not-bad idea. See the Customizing the Level.

By creating and managing a sublogger, make your own logger might be dead simple:

func newMyLogger2() *mylogger2 {
    l := slog.New("mylogger").SetLevel(slog.InfoLevel)
    s := &mylogger2{
        l, // Provides basic Logger interface such as Info, Debug, etc.
    true, // enable Infof()
        l.WithSkip(1), // A sublogger created here. specially for Infof
    }
    return s
}

type mylogger2 struct {
    slog.Logger
    SprintfLikeLoggingIsEnabled bool
    sl                          slog.Logger
}

func (s *mylogger2) Close() { s.Logger.Close() }

func (s *mylogger2) Infof(msg string, args ...any) {
    if s.SprintfLikeLoggingIsEnabled {
        if len(args) > 0 {
            // msg = fmt.Sprintf(msg, args...)

            var data []byte
            data = fmt.Appendf(data, msg, args...)
            s.sl.Info(string(data))
        }
        s.sl.Info(msg)
    }
}

func TestSlogBasic4(t *testing.T) {
    l := newMyLogger2()
    l.Infof("what's wrong with %v", "him")
    l.Info("no matter")
    // l.Infof("what's wrong with %v, %v, %v, %v, %v, %v", m1AttrsAsAnySlice()...)
}

That is it.

Builtin Output Formats

logg/slog has tree builtin optput formats: logfmt, json and colorful mode.

The default output is colorful to fit for debug console. But you can switch to the other two easily:

slog.SetJSONMode()       // to get JSON format
slog.SetColorMode(false) // to get logfmt format
slog.SetColorMode()      // return to colorful mode

The above settings modify and apply effects to all loggers globally.

logg/slog has no way to modify formats for certain a logger or sub-logger. We do believe that's normal action to keep a uniform output format.

The outputs:

{"time":"14:53:10.907238+08:00","level":"debug","msg":"Debug message","source":{"function":"github.com/hedzr/logg/slog_test.TestSlogJSON","file":"./i_test.go","line":42}}

time="14:52:50.083343+08:00" level="debug" msg="Debug message" source.function="github.com/hedzr/logg/slog_test.TestSlogLogfmt" source.file="./i_test.go" source.line=68

and,

Set Level

The default is WarnLevel for a released app. If debugger detected the DebugLevel will be assumed.

Also the executable path will be tested for looking up if runing in test mode.

slog.SetLevel(slog.InfoLevel)
println(slog.Level)

Each sub-logger can hold its own level different with their parents or default logger.

To restore old level on Default logger, SaveLevelAndSet is available:

func TestSlogBasic2(t *testing.T) {
    defer slog.SaveLevelAndSet(slog.TraceLevel)()
    slog.Debug("Debug message") // should be enabled now
    slog.Info("Info message")   // should be enabled now
    slog.Warn("Warning message")
    slog.Error("Error message")
}

Sublogger

Creating a detached logger is possible. Different from default logger, the logger's methods are used to log your message.

logger := slog.New() // colorful logger
logger := slog.New().SetJSONMode() // json format logger
logger := slog.New().SetColorMode(false) // logfmt logger
logger := slog.New().Set("attr1", v1, "attr2", v2))

logger := slog.New("name")
logger := slog.New("name", slog.WithAttrs(args...))
logger := slog.New("name", slog.NewAttr("attr1", v1))
logger := slog.New("name", slog.Int("attr1", i1))
logger := slog.New("name", slog.Group("group1", slog.Int("attr1", i1)))
logger := slog.New("name", "attr1", v1, "attr2", v2).SetAttrs(args...)

Sublogger should derive from Default() or a detached logger.

logger := slog.New(args...).SetLevel(slog.InfoLevel)

// .New() makes a child logger,
sl1 := logger.New().SetLevel(slog.TraceLevel)
sl2 := Default().New() // keep the parent's level
// .WithXXX() makes a child logger
sl3 := logger.WithLevel(slog.TraceLevel)

By default, parent shares his features (level and other settings) to children, so sl2 get InfoLevel same with logger.

If LattrsR is set, the parent's attributes will be inherited to. For performance reason, it's unset by default.

logger := slog.New("parent-logger").Set("attr", "parent").SetLevel(slog.InfoLevel)
sl := logger.New("child-logger")

slog.AddFlags(slog.LattrsR)
sl.Info("info", "attr1", 1)
slog.RemoveFlags(slog.LattrsR)
sl.Info("info", "attr1", 1)

The outputs looks like:

13:35:31.524263+08:00 child-logger [INF] info                                                    attr=parent attr1=1 /Volumes/VolHack/work/godev/cmdr.v2/libs.logg/slog/i_test.go:454 slog_test.TestSlogAttrsR
13:35:31.524276+08:00 child-logger [INF] info                                                    attr1=1 /Volumes/VolHack/work/godev/cmdr.v2/libs.logg/slog/i_test.go:456 slog_test.TestSlogAttrsR

A logger or a sublogger could be identify by a unique name. Passing a string as first parameter to New(...), it's assumed the logger name.

And attributes and WithOpts can follow the logger name. New(...) parses all of them and process them. For examples:

    l := slog.New("standalone-logger-for-app",
        slog.NewAttr("attr1", 2),
        slog.NewAttrs("attr2", 3, "attr3", 4.1),
        "attr4", true, "attr3", "string",
        slog.WithLevel(slog.AlwaysLevel),
    )
    defer l.Close()

    sub1 := l.New("sub1").Set("logger", "sub1")
    sub2 := l.New("sub2").Set("logger", "sub2").SetLevel(slog.InfoLevel)

    sub1.Debug("hi debug", "AA", 1.23456789)

Making children loggers is possible.

Logging with Attributes

The attributes can be prepared or passed in several forms.

Plain form

    logger.Info("info message",
        "attr1", 0,
        "attr2", false,
        "attr3", 3.13,
    ) // plain key and value pairs

NewAttr and NewGroupedAttr

logger.Info("info message",
        "attr1", 0,
        "attr4", errors.New("simple"),
        "attr3", 3.13,
        slog.NewAttr("attr3", "any styles what u prefer"),
        slog.NewGroupedAttrEasy("group1", "attr1", 13, "attr2", false),
    ) // use NewAttr, NewGroupedAttrs

Int, Float, String, Any, ..., Group

logg/slog supports strong typed attributes:

logger.Info("image uploaded",
        slog.Int("id", 23123),
        slog.Group("properties",
            slog.Int("width", 4000),
            slog.Int("height", 3000),
            slog.String("format", "jpeg"),
        ),
    ) // use Int, Float, String, Any, ..., and Group

These interfaces are very similar with standard log/slog.

Mixes all above forms

The above forms can be mixed in any order together.

logger.Info("image uploaded",
        "attr1", 0,
        "attr2", false,
        "attr3", 3.13,
        "attr4", errors.New("simple"),
        // ,,,
        slog.Group("group1", 
            "attr1", 0,
            "attr2", false,
            slog.NewAttr("attr3", "any styles what u prefer"),
            slog.Group("more", "group", []byte("more sub-attrs")),
            "attrN", // unpaired key can work here
        ),
        // ...
        slog.Int("id", 23123),
        slog.Group("properties",
            slog.Int("width", 4000),
            slog.Int("height", 3000),
            slog.String("format", "jpeg"),
        ),
    )

Work with common Attributes

While creating a sublogger, you could specify some common attributes. They are no more effects for performance reason by default. log.Info and others printers will check out and print all of parents' common attributes while LattrsR is set.

Both of the following forms are valid:

// available forms
logger := slog.New("logger-name")
logger := slog.New("logger-name", slog.WithAttrs(args...))
logger := slog.New("logger-name", slog.NewAttr("attr1", v1))
logger := slog.New("logger-name", slog.Int("attr1", i1))
logger := slog.New("logger-name", slog.Group("group1", slog.Int("attr1", i1)))
logger := slog.New("logger-name", "attr1", v1, "attr2", v2).WithAttrs(args...)

// the attributes will be printed out if LattrsR set,
slog.AddFlags(slog.LattrsR)
logger.Info("message", "type", "int") // Out: ,,, A message    attr1=v1 attr2=v2 ... type=int

Grouping attributes

See above of above.

Logging contextual attrs

Same to standard log/slog, logg/slog has LogAttrs() to log attributes contextually.

    logger := slog.New().SetAttrs(slog.String("app-version", "v0.0.1-beta"))
    ctx := context.Background()
    logger.InfoContext(ctx, "info msg", "attr1", 111333,
        slog.Group("memory",
            slog.Int("current", 50),
            slog.Int("min", 20),
            slog.Int("max", 80)),
        slog.Int("cpu", 10),
    )

Extracting attrs from context

Sometimes the attributes can be extracted from context.Context.

func TestSlogWithContext(t *testing.T) {
    logger := slog.New().SetAttrs(slog.String("app-version", "v0.0.1-beta"))
    ctx := context.WithValue(context.Background(), "ctx", "oh,oh,oh")
    logger.SetContextKeys("ctx").
      InfoContext(ctx, "info msg",
        "attr1", 111333,
        slog.Group("memory",
            slog.Int("current", 50),
            slog.Int("min", 20),
            slog.Int("max", 80)),
        slog.Int("cpu", 10),
    )
}

The result:

As you seen, the value in context was been extracted and printed out.

Set Writer

logg/slog uses a dualWriter to serialize the logging contents.

A dualWriter sends contents to stdout or stderr in accord to the requesting logging level. For example, a Info(...) calling will be dispatched to stdout and a Warn, Error, Panic, or Fatal to stderr.

Not only for those, the dualWriter allows you stack many writers as its Normal or Error output devices. That means, a console os.Stdout and a file writer can be bundled into Normal at once. How to do it? It's simple:

logger := New("tty+file").AddWriter(slog.NewFileWriter("/tmp/app-stdout.log"))

Using WithWriter to replace the stocked version, which is stdout+stderr by default.

AddWriter(w)/RemoveWriter/ResetWriter can append/remove/reset the stdout device.

AddErrorWriter(w)/RemoveErrorWriter/ResetErrorWriter can append/remove/reset to the stderr device.

Of course, ResetWriters works so we can always back to default state.

A standard io.Writer is needed when using AddWriter/WithWriter:

// Simple file
tf, _ := os.CreateTempFile("", "stdout.log")
logger.AddWriter(tf)

Your writer can implement LevelSettable to handling the requesting logging level.

package mywriter
import (
 "logz" "github.com/hedzr/logg/slog"
)
type myWriter struct {
 level logz.Level
}
func (s *myWriter) SetLevel(level logz.Level) { s.level = level } // logz.LevelSettable
func (s *myWriter) Write(data []byte) (n int, err error) {
 switch(s.level) {
 case logz.DebugLevel:
 // ...
 }
 return
}

In this scene, logg/slog will call Write following SetLevel. It's safe in many cases, but you can take more safety for it by using locked mechanism: go build tags -tags=logglock will enable a special version with wrapping the two calls in a sync.Mutex. See the source code in entry_lock.go.

Leveled Writers

Also we provides sub-feature to allow you specify special writer for a special logging level:

func TestAddLevelWriter1(t *testing.T) {
    logger := New().AddLevelWriter(InfoLevel, &decorated{os.Stdout})
    logger.Info("info msg")
    logger.Debug(getMessage(0))
}

type decorated struct {
    *os.File
}

func (s *decorated) Write(p []byte) (n int, err error) {
    if s.File != nil {
        if ni, e := s.File.WriteString("[decorated] "); e != nil {
            err = errors.Join(err, e)
        } else {
            n += ni
        }
        if ni, e := s.File.Write(p); e != nil {
            err = errors.Join(err, e)
        } else {
            n += ni
        }
    }
    return
}

The result is similar with:

[decorated] 10:57:22.986797+08:00 [INF] info msg                              ./new_test.go:170 slog.TestAddLevelWriter1
10:57:22.987031+08:00 [DBG] Test logging, but use a somewhat realistic message length. (#0)  ./new_test.go:171 slog.TestAddLevelWriter1

Close()

In most cases, Logger's Close() has no more attentions to you.

But adding defer close codes is a best practice, like this:

package main

import "github.com/hedzr/logg/slog"

func main() {
  logger := slog.New("tty+file").AddWriter(slog.NewFileWriter("/tmp/app-stdout.log"))
  defer logger.Close()
  
  logger.Info("info msg")
}

The file writer will get a chance to shutdown itself gracefully.

Set Handler

Customizing the Level

In logg/slog, using your own logging level is enough simple:

const (
    NoticeLevel = slog.Level(17) // A custom level must have a value greater than slog.MaxLevel
    HintLevel   = slog.Level(-8) // Or use a negative number
    SwellLevel  = slog.Level(12) // Sometimes, you may use the value equal with slog.MaxLevel
)

func TestSlogCustomizedLevel(t *testing.T) {
    checkerr(t, slog.RegisterLevel(NoticeLevel, "NOTICE",
        slog.RegWithShortTags([6]string{"", "N", "NT", "NTC", "NOTC", "NOTIC"}),
        slog.RegWithColor(color.FgWhite, color.BgUnderline),
        slog.RegWithTreatedAsLevel(slog.InfoLevel),
    ))

    checkerr(t, slog.RegisterLevel(HintLevel, "Hint",
        slog.RegWithShortTags([6]string{"", "H", "HT", "HNT", "HINT", "HINT "}),
        slog.RegWithColor(color.NoColor, color.BgInverse),
        slog.RegWithTreatedAsLevel(slog.InfoLevel),
    ))

    checkerr(t, slog.RegisterLevel(SwellLevel, "SWELL",
        slog.RegWithShortTags([6]string{"", "S", "SW", "SWL", "SWEL", "SWEEL"}),
        slog.RegWithColor(color.FgRed, color.BgBoldOrBright),
        slog.RegWithTreatedAsLevel(slog.ErrorLevel),
        slog.RegWithPrintToErrorDevice(),
    ))

    logger := slog.New()

    logger.Debug("Debug message")
    logger.Info("Info message")
    logger.Warn("Warning message")
    logger.Error("Error message")

    slog.SetLevelOutputWidth(5)

    ctx := context.Background()
    logger.LogAttrs(ctx, NoticeLevel, "Notice message")
    logger.LogAttrs(ctx, HintLevel, "Hint message")
    logger.LogAttrs(ctx, SwellLevel, "Swell level")
}

func checkerr(t *testing.T, err error) {
    if err != nil {
        t.Error(err)
    }
}

Its outputs looks like

The ansi color representations relyes on your terminal settings.

SetLevelOutputWidth(n) lets you can control the level serverity's display width (from 1 to 5). At customizing you should pass a array ([6]string) for each levels. For example, HintLevel can be displayed as "HINT" when output width is 4, or as "H" when width is 1. You could change it globally at any time. Just like the snapshot above, it was changed to 5 at last time, so HintLevel has width 5.

Customizing the Colors

Dislike logg/slog's console colors of each levels? No matter, setup with yours:

import color "github.com/hedzr/is/term/color"

slog.SetLevelColors(slog.PanicLevel, color.FgWhite, color.NoColor)

These are standard ANSI escaped sequences, any of SGR fore-, background colors. A special NoColor is -1.

const NoColor = color.Color(-1)

hedzr/is provides a color Translator to format your html-like string to ansi colored text for terminal outputting. For more information see hedzr/is doc.

Adapt into log/slog

If you are using unified log/slog interfaces, put logg/slog into it:

import "log/slog"
import logslog "github.com/hedzr/logg/slog"

func TestSlogUsedForLogSlog(t *testing.T) {
    l := slog.New("standalone-logger-for-app",
        slog.NewAttr("attr1", 2),
        slog.NewAttrs("attr2", 3, "attr3", 4.1),
        "attr4", true, "attr3", "string",
        slog.WithLevel(slog.AlwaysLevel),
    )
    defer l.Close()

    sub1 := l.New("sub1").With("logger", "sub1")
    sub2 := l.New("sub2").With("logger", "sub2").WithLevel(slog.InfoLevel)

    // create a log/slog logger HERE
    logger := logslog.New(slog.NewSlogHandler(l, nil))

    t.Logf("logger: %v", logger)
    t.Logf("l: %v", l)

    // and logging with log/slog
    logger.Debug("hi debug", "AA", 1.23456789)
    logger.Info(
        "incoming request",
        logslog.String("method", "GET"),
        logslog.String("path", "/api/user"),
        logslog.Int("status", 200),
    )

    // now using our logg/slog interface
    sub1.Debug("hi debug", "AA", 1.23456789)
    sub2.Debug("hi debug", "AA", 1.23456789)
    sub2.Info("hi info", "AA", 1.23456789)
}

The result:

Our testing keeps logg/slog native outputs as the last three lines.

In this case, some features of our logg/slog cannot be used via log/slog APIs but it's still colorful.

Customizing ValueStringer

logg/slog allows you handle stringerize value with customizing ValueStringer. So you can pass yours.

Here is a sample to pretty print the values in attributes:

import "github.com/alecthomas/repr"

func NewSpewPrinter() *prettyPrinter { //nolint:revive // just a test
    return &prettyPrinter{
        repr.New(os.Stdout, repr.Indent("  ")),
    }
}

type prettyPrinter struct {
    *repr.Printer
}

func (p *prettyPrinter) SetWriter(w io.Writer) {
    p.Printer = repr.New(w, repr.Indent("  "))
}

func (p *prettyPrinter) WriteValue(value any) {
    // p.reprValue(map[reflect.Value]bool{}, reflect.ValueOf(value), "", true, false)
    p.Print(value)
}

func TestSlogCustomValueStringer(t *testing.T) {
    // slog.SetLevel(slog.InfoLevel)
    slog.AddFlags(slog.Lprivacypathregexp | slog.Lprivacypath)

    defer slog.SaveFlagsAnd(func() { //nolint:revive // ok
        slog.AddFlags(slog.Lprettyprint)
    })()

    printer := NewSpewPrinter()

    for _, logger := range []slog.Logger{
        slog.New(" spew ").WithValueStringer(printer),
        slog.New("normal"),
    } {
        logger.Println()
        logger.LogAttrs(
            context.Background(),
            slog.InfoLevel,
            "image uploaded",
            slog.Int("id", 23123),
            slog.Group("properties",
                slog.Int("width", 4000),
                slog.Int("height", 3000),
                slog.String("format", "jpeg"),
                slog.Any("Map", map[int][]float64{3: {3.14, 2.72}, 5: {0.717, 1.732}}),
            ),
        )
    }
}

The outputs are:

To integrete go-spew is similar and simple.

Hide the sensitive fields

Your struct can implement LogObjectMashaller or LogArrayMashaller so that the sensitive fields can be harden.

type users []*user

func (uu users) MarshalLogArray(enc *slog.PrintCtx) (err error) {
    for i := range uu {
        if i > 0 {
            enc.WriteRune(',')
        }
        if e := uu[i].MarshalLogObject(enc); e != nil {
            err = errors.Join(err, e)
        }
    }
    return
}

type user struct {
    Name      string    `json:"name"`
    Email     string    `json:"email"`
    CreatedAt time.Time `json:"created_at"`
}

func (u *user) MarshalLogObject(enc *slog.PrintCtx) (err error) {
    enc.AddString("name", u.Name)
    enc.AddRune(',')
    enc.AddString("email", u.Email)
    enc.AddRune(',')
    enc.AddInt64("createdAt", u.CreatedAt.UnixNano())
    return
}

*slog.PrintCtx is our value encoder.

Harden filepath, shorten package name

The caller information could leak the user's name, disk volumes, directory structure and others sensitive contents.

Harden filepath

For this test case:

func TestLogOneTwoThree(t *testing.T) {
    l := slogg.New().WithLevel(slogg.InfoLevel)
    l.Info("info msg", "Aa", 1, "Bbb", "a string", "Cc", 3.732, "D", 2.71828+5.3571i)
}

It may print out:

20:20:01.697577+08:00 [INF] info msg                             Aa=1 Bbb=a string Cc=3.732 D=(2.71828+5.3571i) /Volumes/VolHack/work/go.work/libs.log/bench/logg_test.go:17 bench.TestLogOneTwoThree

Now we enable privacy flags, a builtin regexp rule (/Volumes/.*/(.*) -> ~$1) will take effects:

20:22:33.688847+08:00 [INF] info msg                             Aa=1 Bbb=a string Cc=3.732 D=(2.71828+5.3571i) ~work/go.work/libs.log/bench/logg_test.go:17 bench.TestLogOneTwoThree

The codes looks like:

func init() {
    slog.AddFlags(slog.Lprivacypathregexp | slog.Lprivacypath)
}

The builtin rules includes truncate homdir to ~, disable absolute pathname, and using relative path, and so on.

You may make calls to AddKnownPathMapping(path,repl) and AddKnownPathRegexpMapping(expr, repl) to setup them.

Shorten package name

In outputs, package name in caller information has form github.com/user/repo/offset.object.function, By enabling Lcallerpackagename, github.com will be shortened to GH. The other well-known code-hosting providers are converted too:

• "github.com" -> "GH"
• "gitlab.com" -> "GL"
• "gitee.com" -> "GT"
• "bitbucker.com" -> "BB"

func init() {
    slog.AddFlags(slog.Lcallerpackagename)
}

If Lcallerpackagename is not present (this is default behavior), the package name will be truncated simply.

AddCodeHostingProviders(provide, repl) API can add more rules for shortening.

More Rules

You can always append yours with AddKnownPathMapping(pathname, repl string) and AddKnownPathRegexpMapping(pathnameRegexpExpr, repl string).

If Lprivacypathregexp and Lprivacypath is not present (this is default behavior), we try to truncate the pathname as possible as we can.

And, AddCodeHostingProviders(provider, repl string) do similar things and need Lcallerpackagename is enabled.

Other Helpers

Here are two saver so that you can write codes easiler:

// Save global Level and set to new, and restore original
defer slog.SaveLevelAndSet(slog.WarnLevel)

// Save global Flags and modify it for local logic, and restore it after going back to up level
defer slog.SaveFlagsAnd(func() {
    slog.AddFlags(slog.LattrsR) // add, remove, or set flags
})()

Others

What meaning the Multiline print?

In colorful print mode, one logging output starts with timestamp and serverity, and ends with attributes and caller info. So the message is put at center of one line with limited width.

A very long message will be wrapped to next line(s), right?

Thinking about another case, a logging line has title and details, what form output is better.

func TestLogLongLine(t *testing.T) {
    l := New()
    l.Info("/ERROR/ Started at "+time.Now().String()+", this is a multi-line test\nVersion: 2.0.1\nPackage: hedzr/hilog", "Aa", 1, "Bbb", "a string", "Cc", 3.732, "D", 2.71828+5.3571i)
}

It prints:

As you seen, a message will be splitted to first line (as a title) and rest lines (as a details text). So you can avoid write a long message. Instead, you write a title with some details to describe a logging line better clearly. By the way, its json or logfmt format is still a message field with key name "msg".

LICENSE

Apache 2.0