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// Copyright 2012, Google Inc. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package tb
import (
"bytes"
"fmt"
"io/ioutil"
"runtime"
)
var (
dunno = []byte("???")
centerDot = []byte("·")
dot = []byte(".")
)
// This package exposes some handy traceback functionality buried in the runtime.
//
// It can also be used to provide context to errors reducing the temptation to
// panic carelessly, just to get stack information.
//
// The theory is that most errors that are created with the fmt.Errorf
// style are likely to be rare, but require more context to debug
// properly. The additional cost of computing a stack trace is
// therefore negligible.
type StackError interface {
Error() string
StackTrace() string
}
type stackError struct {
err error
stackTrace string
}
func (e stackError) Error() string {
return fmt.Sprintf("%v\n%v", e.err, e.stackTrace)
}
func (e stackError) StackTrace() string {
return e.stackTrace
}
func Errorf(msg string, args ...interface{}) error {
stack := ""
// See if any arg is already embedding a stack - no need to
// recompute something expensive and make the message unreadable.
for _, arg := range args {
if stackErr, ok := arg.(stackError); ok {
stack = stackErr.stackTrace
break
}
}
if stack == "" {
// magic 5 trims off just enough stack data to be clear
stack = string(Stack(5))
}
return stackError{fmt.Errorf(msg, args...), stack}
}
// Taken from runtime/debug.go
func Stack(calldepth int) []byte {
return stack(calldepth)
}
func stack(calldepth 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 := calldepth; ; i++ { // Caller we care about is the user, 2 frames up
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
}
line-- // in stack trace, lines are 1-indexed but our array is 0-indexed
fmt.Fprintf(buf, "\t%s: %s\n", function(pc), source(lines, line))
}
return buf.Bytes()
}
// source returns a space-trimmed slice of the n'th line.
func source(lines [][]byte, n int) []byte {
if n < 0 || n >= len(lines) {
return dunno
}
return bytes.Trim(lines[n], " \t")
}
// 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
if period := bytes.Index(name, dot); period >= 0 {
name = name[period+1:]
}
name = bytes.Replace(name, centerDot, dot, -1)
return name
}
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