Golang golang-debug (snippet)

Go programming example 'golang-debug'

golang-debug

Golang beginners example: golang-debug

package main

import (
    "bytes"
    "fmt"
    "io/ioutil"
    "log"
    "path"
    "runtime"
    "runtime/debug"
    "runtime/trace"
)

var (
    dunno     = []byte("???")
    centerDot = []byte("·")
    dot       = []byte(".")
    slash     = []byte("/")
)

func source(lines [][]byte, n int) []byte {
    if n < 0 || n >= len(lines) {
        return dunno
    }
    return bytes.Trim(lines[n], " \t")
}

func function(pc uintptr) []byte {
    fn := runtime.FuncForPC(pc)
    if fn == nil {
        return dunno
    }
    name := []byte(fn.Name())
    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
}

func debugExample() []byte {
    buf := new(bytes.Buffer)
    var lines [][]byte
    var lastFile string
    for i := 0; ; i++ {
        pc, file, line, ok := runtime.Caller(i)
        if !ok {
            break
        }
        if file != lastFile {
            data, err := ioutil.ReadFile(file)
            if err != nil {
                continue
            }
            lines = bytes.Split(data, []byte{'\n'})
            lastFile = file
        }
        line--
        fn, _ := path.Split(file)
        fmt.Fprintf(buf, "%s:%s:%d: %s\n", fn, function(pc), line+1, source(lines, line))
    }
    return buf.Bytes()
}

func fn3() {
    fmt.Printf("%v\n", string(debugExample()))
}

func fn2() {
    fn3()
}

func fn() {
    log.Printf("log inside a function")
    debug.PrintStack()
    log.Printf("%v\n", string(debug.Stack()))
    fn2()
}

func main() {
    var b bytes.Buffer
    trace.Start(&b)
    log.SetFlags(log.Ltime | log.Lshortfile)

    log.Println("first log output")
    log.Printf("second log output\n")
    fn()
    log.Printf("tace: %v\n", b.String())
}

Useful links

• Learn Go: https://golangr.com
• Download Go: https://golang.org