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error.go
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error.go
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//Copyright 2020 Google LLC
//
//Licensed under the Apache License, Version 2.0 (the "License");
//you may not use this file except in compliance with the License.
//You may obtain a copy of the License at
//
//https://www.apache.org/licenses/LICENSE-2.0
//
//Unless required by applicable law or agreed to in writing, software
//distributed under the License is distributed on an "AS IS" BASIS,
//WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//See the License for the specific language governing permissions and
//limitations under the License.
// Package zerrors provides error wrapping functionality.
package zerrors
import (
"bytes"
"errors"
"fmt"
"io"
"path"
"runtime"
"strconv"
"sync"
"github.com/JavierZunzunegui/zerrors/internal"
)
func init() {
internal.SetBasic(func(err error) string {
return err.(*wrapError).basic()
})
internal.SetDetail(func(err error) string {
return err.(*wrapError).detail()
})
}
var bufPool = sync.Pool{
New: func() interface{} { return new(bytes.Buffer) },
}
// wrapError is a linked list of errors, providing the wrapping functionality.
type wrapError struct {
value error
next *wrapError
pc [1]uintptr
}
// Error uses the 'basic' function to serialise the error.
// By default it is, and under custom options it is expected to be, the shorter and more efficient form of wrapError
// serialisation.
// By default this is in the form "{err1}: {err2}: ... : {errN}" without any frame information.
func (w *wrapError) Error() string {
return internal.Basic(w)
}
// basic provides a default format to how wrapped errors will be serialised under %s, %v, %q format or with the Error
// method :
// "{err1}: {err2}: ... : {errN}"
func (w *wrapError) basic() string {
if w.next == nil && w.pc[0] == 0 {
// Taking a shortcut.
return w.value.Error()
}
return w.basicViaBuf()
}
func (w *wrapError) basicViaBuf() string {
buf := bufPool.Get().(*bytes.Buffer)
buf.WriteString(w.value.Error())
for current := w.next; current != nil; current = current.next {
buf.WriteString(": ")
buf.WriteString(current.value.Error())
}
s := buf.String()
buf.Reset()
bufPool.Put(buf)
return s
}
// Detail is an alternative error encoding to err.Error(), equivalent to the %+v format form.
// It can be called on any error but for non-zerror errors is encodes it in the standard %+v fmt form.
// For zerror errors, it uses the 'detail' function to serialise and it and is expected to (and by default, is) more
// detailed and expensive than err.Error() and contains frame information.
// By default this is in the form:
// "{err1} ({file}:{line}): {err2} ({file}:{line}): ... : {errN} ({file}:{line})".
func Detail(err error) string {
if _, ok := err.(*wrapError); ok {
return internal.Detail(err)
}
return fmt.Sprintf("%+v", err)
}
// detail provides a default format to how wrapped errors will be serialised under %+v format or with the Detail
// function:
// "{err1} ({file}:{line}): {err2} ({file}:{line}): ... : {errN} ({file}:{line})"
func (w *wrapError) detail() string {
if !internal.GetFrameCapture() {
return w.basic()
}
if w.next == nil && w.pc[0] == 0 {
// Taking a shortcut.
return w.value.Error()
}
return w.detailViaBuf()
}
func (w *wrapError) detailViaBuf() string {
buf := bufPool.Get().(*bytes.Buffer)
buf.WriteString(w.value.Error())
if w.pc[0] != 0 {
w.frameToBuffer(buf)
}
for current := w.next; current != nil; current = current.next {
buf.WriteString(": ")
buf.WriteString(current.value.Error())
if current.pc[0] != 0 {
current.frameToBuffer(buf)
}
}
s := buf.String()
buf.Reset()
bufPool.Put(buf)
return s
}
func (w *wrapError) frameToBuffer(buf *bytes.Buffer) {
if w.pc[0] == 0 {
return
}
frame, _ := runtime.CallersFrames(w.pc[:]).Next()
buf.WriteString(" (")
buf.WriteString(path.Base(frame.File))
buf.WriteString(":")
// alternative to buf.WriteString(strconv.Itoa(frame.Line)), without allocating.
b := buf.Bytes()
l := len(b)
buf.Write(strconv.AppendInt(b, int64(frame.Line), 10)[l:])
buf.WriteString(")")
}
// Unwrap is required by the current error wrapping functionality in pkg/errors.
// It returns either a non-nil WrapError or nil.
func (w *wrapError) Unwrap() error {
if w.next == nil {
return nil
}
return w.next
}
// Is is the custom method required by pkg/errors.Is.
func (w *wrapError) Is(err error) bool {
return errors.Is(w.value, err)
}
// As is the custom method required by pkg/errors.As.
func (w *wrapError) As(i interface{}) bool {
return errors.As(w.value, i)
}
func (w *wrapError) deepCopy() *wrapError {
if w == nil {
return nil
}
return &wrapError{value: w.value, next: w.next.deepCopy(), pc: w.pc}
}
// Format supports the fmt Printf (and variants) for wrapError.
// The 'basic' encoder (that of .Error()) is used in all encodings except for %+v, which uses the 'detail' one.
func (w *wrapError) Format(s fmt.State, verb rune) {
switch verb {
case 'v':
if s.Flag('+') {
_, _ = io.WriteString(s, internal.Detail(w))
return
}
_, _ = io.WriteString(s, w.Error())
case 's':
_, _ = io.WriteString(s, w.Error())
case 'q':
_, _ = fmt.Fprintf(s, "%q", w.Error())
}
}
// New produces a wrapError from a non-wrapError.
// If frame capture is enabled, it will get one at the caller of New.
// If err is a wrapError it returns itself, with no frame changes. This should be avoided.
func New(err error) error {
if err == nil {
return err
}
if _, ok := err.(*wrapError); ok {
// Anti-pattern.
return err
}
wErr := wrapError{value: err}
if internal.GetFrameCapture() {
_ = runtime.Callers(2, wErr.pc[:])
}
return &wErr
}
// Wrap produces a wrapError using any error type.
// The first argument is the error being wrapped, the second is the error being added to it.
// If the first error is nil, Wrap does nothing and returns nil.
// If the second error is nil, it returns the first error. This should be avoided.
// Otherwise it returns a wrapError.
// If frame capture is enabled, it will get one at the caller of Wrap.
func Wrap(inErr, outErr error) error {
if inErr == nil {
return nil
}
if outErr == nil {
// Anti-pattern.
return inErr
}
wInErr, ok := inErr.(*wrapError)
if !ok {
wInErr = &wrapError{value: inErr}
}
if wOutErr, ok := outErr.(*wrapError); ok {
// Anti-pattern.
wErr := wOutErr.deepCopy()
current := wErr
for ; current.next != nil; current = current.next {
}
current.next = wInErr
return wErr
}
wErr := wrapError{
value: outErr,
next: wInErr,
}
if internal.GetFrameCapture() {
_ = runtime.Callers(2, wErr.pc[:])
}
return &wErr
}
// errorString is a trivial implementation of error, identical to errors.errorString.
// It is implemented separately as a performance optimisation, as it saves one allocation.
type errorString struct {
s string
}
func (e *errorString) Error() string {
return e.s
}
// SNew produces a wrapError with a simple string error.
// If frame capture is enabled, it will get one at the caller of SNew.
func SNew(s string) error {
// a performance optimisation, makes wrapError and errorString in a single allocation.
alloc := struct {
sErr errorString
wErr wrapError
}{}
alloc.sErr = errorString{s}
alloc.wErr = wrapError{
value: &alloc.sErr,
}
if internal.GetFrameCapture() {
_ = runtime.Callers(2, alloc.wErr.pc[:])
}
return &alloc.wErr
}
// SWrap produces a wrapError using a simple string error.
// The first argument is the error being wrapped, the second is the string error being added to it.
// If the first error is nil, Wrap does nothing and returns nil.
// Otherwise it returns a wrapError.
// If frame capture is enabled, it will get one at the caller of SWrap.
func SWrap(inErr error, s string) error {
if inErr == nil {
return nil
}
wInErr, ok := inErr.(*wrapError)
if !ok {
wInErr = &wrapError{value: inErr}
}
// a performance optimisation, makes wrapError and errorString in a single allocation.
alloc := struct {
sErr errorString
wErr wrapError
}{}
alloc.sErr = errorString{s}
alloc.wErr = wrapError{
value: &alloc.sErr,
next: wInErr,
}
if internal.GetFrameCapture() {
_ = runtime.Callers(2, alloc.wErr.pc[:])
}
return &alloc.wErr
}
// Value returns the error contained at this particular node in the error chain.
// For non-wrapError errors, it returns itself.
// The return value is never a wrapError, and is only nil if the input is also nil.
func Value(err error) error {
if wErr, ok := err.(*wrapError); ok {
return wErr.value
}
return err
}
// Frame returns the frame contained at this particular node in the error chain.
// For non-wrapError errors or wrapError errors without a frame, it returns an empty frame and false.
// Otherwise it returns the populated frame and true.
func Frame(err error) (runtime.Frame, bool) {
wErr, ok := err.(*wrapError)
if !ok || wErr.pc[0] == 0 {
return runtime.Frame{}, false
}
frame, _ := runtime.CallersFrames(wErr.pc[:]).Next()
return frame, true
}