add stack util for readability usage

README.md

@@ -65,4 +65,17 @@ pkg: kumoly.io/lib/klog
 cpu: AMD Ryzen 9 5900X 12-Core Processor            
 BenchmarkDefault-12        24697             47673 ns/op           21337 B/op        291 allocs/op
 BenchmarkSub1-12           22639             52841 ns/op           22103 B/op        351 allocs/op
+
+v0.0.5
+go test -bench . -run none --benchmem
+goos: linux
+goarch: amd64
+pkg: kumoly.io/lib/klog
+cpu: AMD Ryzen 9 5900X 12-Core Processor            
+BenchmarkDefault-12                25216             47204 ns/op           20953 B/op        291 allocs/op
+BenchmarkSub1-12                   22789             52306 ns/op           21719 B/op        351 allocs/op
+BenchmarkStackSTD-12              105280             11347 ns/op            3596 B/op         26 allocs/op
+BenchmarkStackSTDStr-12           234535              5109 ns/op            2755 B/op         27 allocs/op
+BenchmarkStackCust-12              14764             80228 ns/op          171553 B/op         60 allocs/op
+BenchmarkStackCustStr-12           15417             78187 ns/op          171262 B/op         61 allocs/op
 ```

log_test.go

@@ -3,6 +3,7 @@ package klog
 import (
 	"io"
 	"os"
+	"runtime"
 	"testing"
 )
 
@@ -182,3 +183,53 @@ func TestIntercept(t *testing.T) {
 	})
 	l.Info("original")
 }
+
+func BenchmarkStackSTD(b *testing.B) {
+	f := func() []byte {
+		buf := make([]byte, 1024)
+		for {
+			n := runtime.Stack(buf, false)
+			if n < len(buf) {
+				return buf[:n]
+			}
+			buf = make([]byte, 2*len(buf))
+		}
+	}
+	LEVEL = 15
+	l := Sub("StackSTD")
+	l.SetErrOutput(io.Discard)
+	l.SetOutput(io.Discard)
+	for i := 0; i < b.N; i++ {
+		l.Info(f())
+	}
+}
+
+func BenchmarkStackSTDStr(b *testing.B) {
+	LEVEL = 15
+	l := Sub("StackSTD")
+	l.SetErrOutput(io.Discard)
+	l.SetOutput(io.Discard)
+	for i := 0; i < b.N; i++ {
+		l.Info(stack())
+	}
+}
+
+func BenchmarkStackCust(b *testing.B) {
+	LEVEL = 15
+	l := Sub("StackCust")
+	l.SetErrOutput(io.Discard)
+	l.SetOutput(io.Discard)
+	for i := 0; i < b.N; i++ {
+		l.Info(Stack(3))
+	}
+}
+
+func BenchmarkStackCustStr(b *testing.B) {
+	LEVEL = 15
+	l := Sub("StackCust")
+	l.SetErrOutput(io.Discard)
+	l.SetOutput(io.Discard)
+	for i := 0; i < b.N; i++ {
+		l.Info(string(Stack(3)))
+	}
+}

util.go

@@ -1,7 +1,9 @@
 package klog
 
 import (
+	"bytes"
 	"fmt"
+	"io/ioutil"
 	"runtime"
 )
 
@@ -38,3 +40,71 @@ func getAllOffsprings(l *Logger) []*Logger {
 	}
 	return loggers
 }
+
+var (
+	dunno     = []byte("???")
+	centerDot = []byte("·")
+	dot       = []byte(".")
+	slash     = []byte("/")
+)
+
+// Stack returns a nicely formatted stack frame, skipping skip frames.
+func Stack(skip int) []byte {
+	buf := new(bytes.Buffer) // the returned data
+	// As we loop, we open files and read them. These variables record the currently
+	// loaded file.
+	var lines [][]byte
+	var lastFile string
+	for i := skip; ; i++ { // Skip the expected number of frames
+		pc, file, line, ok := runtime.Caller(i)
+		if !ok {
+			break
+		}
+		// Print this much at least.  If we can't find the source, it won't show.
+		fmt.Fprintf(buf, "%s:%d (0x%x)\n", file, line, pc)
+		if file != lastFile {
+			data, err := ioutil.ReadFile(file)
+			if err != nil {
+				continue
+			}
+			lines = bytes.Split(data, []byte{'\n'})
+			lastFile = file
+		}
+		fmt.Fprintf(buf, "\t%s: %s\n", function(pc), source(lines, line))
+	}
+	return buf.Bytes()
+}
+
+// function returns, if possible, the name of the function containing the PC.
+func function(pc uintptr) []byte {
+	fn := runtime.FuncForPC(pc)
+	if fn == nil {
+		return dunno
+	}
+	name := []byte(fn.Name())
+	// The name includes the path name to the package, which is unnecessary
+	// since the file name is already included.  Plus, it has center dots.
+	// That is, we see
+	//	runtime/debug.*T·ptrmethod
+	// and want
+	//	*T.ptrmethod
+	// Also the package path might contains dot (e.g. code.google.com/...),
+	// so first eliminate the path prefix
+	if lastSlash := bytes.LastIndex(name, slash); lastSlash >= 0 {
+		name = name[lastSlash+1:]
+	}
+	if period := bytes.Index(name, dot); period >= 0 {
+		name = name[period+1:]
+	}
+	name = bytes.Replace(name, centerDot, dot, -1)
+	return name
+}
+
+// source returns a space-trimmed slice of the n'th line.
+func source(lines [][]byte, n int) []byte {
+	n-- // in stack trace, lines are 1-indexed but our array is 0-indexed
+	if n < 0 || n >= len(lines) {
+		return dunno
+	}
+	return bytes.TrimSpace(lines[n])
+}