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package errors
import (
"bufio"
"bytes"
"fmt"
"os"
"runtime"
"strings"
)
// A StackFrame contains all necessary information about to generate a line
// in a callstack.
type StackFrame struct {
// The path to the file containing this ProgramCounter
File string
// The LineNumber in that file
LineNumber int
// The Name of the function that contains this ProgramCounter
Name string
// The Package that contains this function
Package string
// The underlying ProgramCounter
ProgramCounter uintptr
}
// NewStackFrame popoulates a stack frame object from the program counter.
func NewStackFrame(pc uintptr) (frame StackFrame) {
frame = StackFrame{ProgramCounter: pc}
if frame.Func() == nil {
return
}
frame.Package, frame.Name = packageAndName(frame.Func())
// pc -1 because the program counters we use are usually return addresses,
// and we want to show the line that corresponds to the function call
frame.File, frame.LineNumber = frame.Func().FileLine(pc - 1)
return
}
// Func returns the function that contained this frame.
func (frame *StackFrame) Func() *runtime.Func {
if frame.ProgramCounter == 0 {
return nil
}
return runtime.FuncForPC(frame.ProgramCounter)
}
// String returns the stackframe formatted in the same way as go does
// in runtime/debug.Stack()
func (frame *StackFrame) String() string {
str := fmt.Sprintf("%s:%d (0x%x)\n", frame.File, frame.LineNumber, frame.ProgramCounter)
source, err := frame.SourceLine()
if err != nil {
return str
}
return str + fmt.Sprintf("\t%s: %s\n", frame.Name, source)
}
// SourceLine gets the line of code (from File and Line) of the original source if possible.
func (frame *StackFrame) SourceLine() (string, error) {
if frame.LineNumber <= 0 {
return "???", nil
}
file, err := os.Open(frame.File)
if err != nil {
return "", New(err)
}
defer file.Close()
scanner := bufio.NewScanner(file)
currentLine := 1
for scanner.Scan() {
if currentLine == frame.LineNumber {
return string(bytes.Trim(scanner.Bytes(), " \t")), nil
}
currentLine++
}
if err := scanner.Err(); err != nil {
return "", New(err)
}
return "???", nil
}
func packageAndName(fn *runtime.Func) (string, string) {
name := fn.Name()
pkg := ""
// 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
// Since the package path might contains dots (e.g. code.google.com/...),
// we first remove the path prefix if there is one.
if lastslash := strings.LastIndex(name, "/"); lastslash >= 0 {
pkg += name[:lastslash] + "/"
name = name[lastslash+1:]
}
if period := strings.Index(name, "."); period >= 0 {
pkg += name[:period]
name = name[period+1:]
}
name = strings.Replace(name, "·", ".", -1)
return pkg, name
}
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