125 lines
3.1 KiB
Go
125 lines
3.1 KiB
Go
// Copyright 2012, Google Inc. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package tb
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import (
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"bytes"
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"fmt"
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"io/ioutil"
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"runtime"
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)
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var (
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dunno = []byte("???")
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centerDot = []byte("·")
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dot = []byte(".")
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)
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// This package exposes some handy traceback functionality buried in the runtime.
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//
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// It can also be used to provide context to errors reducing the temptation to
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// panic carelessly, just to get stack information.
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//
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// The theory is that most errors that are created with the fmt.Errorf
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// style are likely to be rare, but require more context to debug
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// properly. The additional cost of computing a stack trace is
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// therefore negligible.
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type StackError interface {
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Error() string
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StackTrace() string
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}
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type stackError struct {
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err error
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stackTrace string
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}
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func (e stackError) Error() string {
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return fmt.Sprintf("%v\n%v", e.err, e.stackTrace)
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}
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func (e stackError) StackTrace() string {
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return e.stackTrace
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}
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func Errorf(msg string, args ...interface{}) error {
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stack := ""
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// See if any arg is already embedding a stack - no need to
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// recompute something expensive and make the message unreadable.
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for _, arg := range args {
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if stackErr, ok := arg.(stackError); ok {
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stack = stackErr.stackTrace
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break
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}
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}
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if stack == "" {
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// magic 5 trims off just enough stack data to be clear
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stack = string(Stack(5))
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}
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return stackError{fmt.Errorf(msg, args...), stack}
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}
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// Taken from runtime/debug.go
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func Stack(calldepth int) []byte {
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return stack(calldepth)
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}
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func stack(calldepth int) []byte {
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buf := new(bytes.Buffer) // the returned data
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// As we loop, we open files and read them. These variables record the currently
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// loaded file.
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var lines [][]byte
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var lastFile string
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for i := calldepth; ; i++ { // Caller we care about is the user, 2 frames up
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pc, file, line, ok := runtime.Caller(i)
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if !ok {
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break
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}
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// Print this much at least. If we can't find the source, it won't show.
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fmt.Fprintf(buf, "%s:%d (0x%x)\n", file, line, pc)
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if file != lastFile {
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data, err := ioutil.ReadFile(file)
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if err != nil {
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continue
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}
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lines = bytes.Split(data, []byte{'\n'})
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lastFile = file
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}
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line-- // in stack trace, lines are 1-indexed but our array is 0-indexed
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fmt.Fprintf(buf, "\t%s: %s\n", function(pc), source(lines, line))
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}
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return buf.Bytes()
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}
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// source returns a space-trimmed slice of the n'th line.
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func source(lines [][]byte, n int) []byte {
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if n < 0 || n >= len(lines) {
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return dunno
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}
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return bytes.Trim(lines[n], " \t")
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}
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// function returns, if possible, the name of the function containing the PC.
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func function(pc uintptr) []byte {
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fn := runtime.FuncForPC(pc)
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if fn == nil {
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return dunno
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}
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name := []byte(fn.Name())
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// The name includes the path name to the package, which is unnecessary
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// since the file name is already included. Plus, it has center dots.
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// That is, we see
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// runtime/debug.*T·ptrmethod
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// and want
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// *T.ptrmethod
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if period := bytes.Index(name, dot); period >= 0 {
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name = name[period+1:]
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}
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name = bytes.Replace(name, centerDot, dot, -1)
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return name
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}
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