// Package stack implements utilities to capture, manipulate, and format call
// stacks. It provides a simpler API than package runtime.
//
// The implementation takes care of the minutia and special cases of
// interpreting the program counter (pc) values returned by runtime.Callers.
//
// Package stack's types implement fmt.Formatter, which provides a simple and
// flexible way to declaratively configure formatting when used with logging
// or error tracking packages.
package stack
import (
"bytes"
"errors"
"fmt"
"io"
"runtime"
"strconv"
"strings"
)
// Call records a single function invocation from a goroutine stack.
type Call struct {
fn *runtime.Func
pc uintptr
}
// Caller returns a Call from the stack of the current goroutine. The argument
// skip is the number of stack frames to ascend, with 0 identifying the
// calling function.
func Caller(skip int) Call {
var pcs [2]uintptr
n := runtime.Callers(skip+1, pcs[:])
var c Call
if n < 2 {
return c
}
c.pc = pcs[1]
if runtime.FuncForPC(pcs[0]) != sigpanic {
c.pc--
}
c.fn = runtime.FuncForPC(c.pc)
return c
}
// String implements fmt.Stinger. It is equivalent to fmt.Sprintf("%v", c).
func (c Call) String() string {
return fmt.Sprint(c)
}
// MarshalText implements encoding.TextMarshaler. It formats the Call the same
// as fmt.Sprintf("%v", c).
func (c Call) MarshalText() ([]byte, error) {
if c.fn == nil {
return nil, ErrNoFunc
}
buf := bytes.Buffer{}
fmt.Fprint(&buf, c)
return buf.Bytes(), nil
}
// ErrNoFunc means that the Call has a nil *runtime.Func. The most likely
// cause is a Call with the zero value.
var ErrNoFunc = errors.New("no call stack information")
// Format implements fmt.Formatter with support for the following verbs.
//
// %s source file
// %d line number
// %n function name
// %v equivalent to %s:%d
//
// It accepts the '+' and '#' flags for most of the verbs as follows.
//
// %+s path of source file relative to the compile time GOPATH
// %#s full path of source file
// %+n import path qualified function name
// %+v equivalent to %+s:%d
// %#v equivalent to %#s:%d
func (c Call) Format(s fmt.State, verb rune) {
if c.fn == nil {
fmt.Fprintf(s, "%%!%c(NOFUNC)", verb)
return
}
switch verb {
case 's', 'v':
file, line := c.fn.FileLine(c.pc)
switch {
case s.Flag('#'):
// done
case s.Flag('+'):
file = file[pkgIndex(file, c.fn.Name()):]
default:
const sep = "/"
if i := strings.LastIndex(file, sep); i != -1 {
file = file[i+len(sep):]
}
}
io.WriteString(s, file)
if verb == 'v' {
buf := [7]byte{':'}
s.Write(strconv.AppendInt(buf[:1], int64(line), 10))
}
case 'd':
_, line := c.fn.FileLine(c.pc)
buf := [6]byte{}
s.Write(strconv.AppendInt(buf[:0], int64(line), 10))
case 'n':
name := c.fn.Name()
if !s.Flag('+') {
const pathSep = "/"
if i := strings.LastIndex(name, pathSep); i != -1 {
name = name[i+len(pathSep):]
}
const pkgSep = "."
if i := strings.Index(name, pkgSep); i != -1 {
name = name[i+len(pkgSep):]
}
}
io.WriteString(s, name)
}
}
// PC returns the program counter for this call frame; multiple frames may
// have the same PC value.
func (c Call) PC() uintptr {
return c.pc
}
// name returns the import path qualified name of the function containing the
// call.
func (c Call) name() string {
if c.fn == nil {
return "???"
}
return c.fn.Name()
}
func (c Call) file() string {
if c.fn == nil {
return "???"
}
file, _ := c.fn.FileLine(c.pc)
return file
}
func (c Call) line() int {
if c.fn == nil {
return 0
}
_, line := c.fn.FileLine(c.pc)
return line
}
// CallStack records a sequence of function invocations from a goroutine
// stack.
type CallStack []Call
// String implements fmt.Stinger. It is equivalent to fmt.Sprintf("%v", cs).
func (cs CallStack) String() string {
return fmt.Sprint(cs)
}
var (
openBracketBytes = []byte("[")
closeBracketBytes = []byte("]")
spaceBytes = []byte(" ")
)
// MarshalText implements encoding.TextMarshaler. It formats the CallStack the
// same as fmt.Sprintf("%v", cs).
func (cs CallStack) MarshalText() ([]byte, error) {
buf := bytes.Buffer{}
buf.Write(openBracketBytes)
for i, pc := range cs {
if pc.fn == nil {
return nil, ErrNoFunc
}
if i > 0 {
buf.Write(spaceBytes)
}
fmt.Fprint(&buf, pc)
}
buf.Write(closeBracketBytes)
return buf.Bytes(), nil
}
// Format implements fmt.Formatter by printing the CallStack as square brackets
// ([, ]) surrounding a space separated list of Calls each formatted with the
// supplied verb and options.
func (cs CallStack) Format(s fmt.State, verb rune) {
s.Write(openBracketBytes)
for i, pc := range cs {
if i > 0 {
s.Write(spaceBytes)
}
pc.Format(s, verb)
}
s.Write(closeBracketBytes)
}
// findSigpanic intentionally executes faulting code to generate a stack trace
// containing an entry for runtime.sigpanic.
func findSigpanic() *runtime.Func {
var fn *runtime.Func
var p *int
func() int {
defer func() {
if p := recover(); p != nil {
var pcs [512]uintptr
n := runtime.Callers(2, pcs[:])
for _, pc := range pcs[:n] {
f := runtime.FuncForPC(pc)
if f.Name() == "runtime.sigpanic" {
fn = f
break
}
}
}
}()
// intentional nil pointer dereference to trigger sigpanic
return *p
}()
return fn
}
var sigpanic = findSigpanic()
// Trace returns a CallStack for the current goroutine with element 0
// identifying the calling function.
func Trace() CallStack {
var pcs [512]uintptr
n := runtime.Callers(2, pcs[:])
cs := make([]Call, n)
for i, pc := range pcs[:n] {
pcFix := pc
if i > 0 && cs[i-1].fn != sigpanic {
pcFix--
}
cs[i] = Call{
fn: runtime.FuncForPC(pcFix),
pc: pcFix,
}
}
return cs
}
// TrimBelow returns a slice of the CallStack with all entries below c
// removed.
func (cs CallStack) TrimBelow(c Call) CallStack {
for len(cs) > 0 && cs[0].pc != c.pc {
cs = cs[1:]
}
return cs
}
// TrimAbove returns a slice of the CallStack with all entries above c
// removed.
func (cs CallStack) TrimAbove(c Call) CallStack {
for len(cs) > 0 && cs[len(cs)-1].pc != c.pc {
cs = cs[:len(cs)-1]
}
return cs
}
// pkgIndex returns the index that results in file[index:] being the path of
// file relative to the compile time GOPATH, and file[:index] being the
// $GOPATH/src/ portion of file. funcName must be the name of a function in
// file as returned by runtime.Func.Name.
func pkgIndex(file, funcName string) int {
// As of Go 1.6.2 there is no direct way to know the compile time GOPATH
// at runtime, but we can infer the number of path segments in the GOPATH.
// We note that runtime.Func.Name() returns the function name qualified by
// the import path, which does not include the GOPATH. Thus we can trim
// segments from the beginning of the file path until the number of path
// separators remaining is one more than the number of path separators in
// the function name. For example, given:
//
// GOPATH /home/user
// file /home/user/src/pkg/sub/file.go
// fn.Name() pkg/sub.Type.Method
//
// We want to produce:
//
// file[:idx] == /home/user/src/
// file[idx:] == pkg/sub/file.go
//
// From this we can easily see that fn.Name() has one less path separator
// than our desired result for file[idx:]. We count separators from the
// end of the file path until it finds two more than in the function name
// and then move one character forward to preserve the initial path
// segment without a leading separator.
const sep = "/"
i := len(file)
for n := strings.Count(funcName, sep) + 2; n > 0; n-- {
i = strings.LastIndex(file[:i], sep)
if i == -1 {
i = -len(sep)
break
}
}
// get back to 0 or trim the leading separator
return i + len(sep)
}
var runtimePath string
func init() {
var pcs [1]uintptr
runtime.Callers(0, pcs[:])
fn := runtime.FuncForPC(pcs[0])
file, _ := fn.FileLine(pcs[0])
idx := pkgIndex(file, fn.Name())
runtimePath = file[:idx]
if runtime.GOOS == "windows" {
runtimePath = strings.ToLower(runtimePath)
}
}
func inGoroot(c Call) bool {
file := c.file()
if len(file) == 0 || file[0] == '?' {
return true
}
if runtime.GOOS == "windows" {
file = strings.ToLower(file)
}
return strings.HasPrefix(file, runtimePath) || strings.HasSuffix(file, "/_testmain.go")
}
// TrimRuntime returns a slice of the CallStack with the topmost entries from
// the go runtime removed. It considers any calls originating from unknown
// files, files under GOROOT, or _testmain.go as part of the runtime.
func (cs CallStack) TrimRuntime() CallStack {
for len(cs) > 0 && inGoroot(cs[len(cs)-1]) {
cs = cs[:len(cs)-1]
}
return cs
}
