README
¶
errors
This package is a fork from github.com/pkg/errors package created by Dave Cheney. The original package has no longer accepting proposals for new functionality.
With the new errors on go 1.13, the way to using the errors on Go has some changes that can be applied into Dave Cheney library. We want to offer one way to migrate your code to new errors, but with the minimum refactor, for that we've created this package.
This package provide the same interface that the original library have, but using new go 1.13 errors, or in previous version golang.org/x/xerrors package.
How to start using friendsofgo/errors
If you previously was using the package github.com/pkg/errors, you only need
change your imports for github.com/friendsofgo/errors, with this simple change now you're capable to use
go 1.13 in your code, and use the new methods As and Is if you want.
Furthermore the method Wrap Wrapf become compatible with Unwrap` interface of new go 1.13 errors.
Adding context to an error
With the original package go 1.13 if you want add context, ergo wrap your error you need to create a new error and using the new verb `"%w" like that:
_, err := ioutil.ReadAll(r)
if err != nil {
return fmt.Errorf("read failed: %w", err)
}
Using our library you can do that forgetting to the new verb:
_, err := ioutil.ReadAll(r)
if err != nil {
return errors.Wrap(err, "read failed")
}
Retrieving the cause of an error
We want to keep the compatibility with the github.com/pkg/errors package, for that
our package provides a Cause method, but this method is not longer needed, because we can use the new methods Is or As
that provides the official package.
So previously if you needed to check an error cause, your error must be implemented the causer inteface:
type causer interface {
Cause() error
}
errors.Cause will recursively retrieve the topmost error which does not implement causer, which is assumed to be the original cause. For example:
switch err := errors.Cause(err).(type) {
case *MyError:
// handle specifically
default:
// unknown error
}
But now you can do:
var target *MyError
if errors.As(err, &target) {
// handle specifically
} else {
// unknown error
}
Or if you uses a sentinel error:
var ErrMyError = errors.New("my sentinel error")
if errors.Is(err, ErrMyError) {
// handle specifically
} else {
// unknown error
}
Disclaimer
This package was created to using with go 1.13 version however if you uses this package with a previous version, the methods
As, Is, Wrap and Wrapf will be using golang.org/x/xerrors package.
Contributing
Contributions are more than welcome, if you are interested please fork this repo and send your Pull Request.
Documentation
¶
Overview ¶
Original package created by Dave Cheney Copyright (c) 2015, Dave Cheney <dave@cheney.net>
Modifications of the original package by Friends of Go Copyright (c) 2019, Friends of Go <contact@friendsofgo.tech>
Package errors provides simple error handling primitives.
The traditional error handling idiom in Go is roughly akin to
if err != nil {
return err
}
which when applied recursively up the call stack results in error reports without context or debugging information. The errors package allows programmers to add context to the failure path in their code in a way that does not destroy the original value of the error.
Adding context to an error ¶
The errors.Wrap function returns a new error that adds context to the original error by recording a stack trace at the point Wrap is called, together with the supplied message. For example
_, err := ioutil.ReadAll(r)
if err != nil {
return errors.Wrap(err, "read failed")
}
If additional control is required, the errors.WithStack and errors.WithMessage functions destructure errors.Wrap into its component operations: annotating an error with a stack trace and with a message, respectively.
Retrieving the cause of an error ¶
Using errors.Wrap constructs a stack of errors, adding context to the preceding error. Depending on the nature of the error it may be necessary to reverse the operation of errors.Wrap to retrieve the original error for inspection. Any error value which implements this interface
type causer interface {
Cause() error
}
can be inspected by errors.Cause. errors.Cause will recursively retrieve the topmost error that does not implement causer, which is assumed to be the original cause. For example:
switch err := errors.Cause(err).(type) {
case *MyError:
// handle specifically
default:
// unknown error
}
Although the causer interface is not exported by this package, it is considered a part of its stable public interface.
With the new standard package error we have two new ways to figure what is the cause of our error:
var target *MyError
if errors.As(err, &target) {
// handle specifically
} else {
// unknown error
}
or even with sentinel errors:
var ErrMyError = errors.New("my sentinel error")
if errors.Is(err, ErrMyError) {
// handle specifically
} else {
// unknown error
}
Formatted printing of errors ¶
All error values returned from this package implement fmt.Formatter and can be formatted by the fmt package. The following verbs are supported:
%s print the error. If the error has a Cause it will be
printed recursively.
%v see %s
%+v extended format. Each Frame of the error's StackTrace will
be printed in detail.
Retrieving the stack trace of an error or wrapper ¶
New, Errorf, Wrap, and Wrapf record a stack trace at the point they are invoked. This information can be retrieved with the following interface:
type stackTracer interface {
StackTrace() errors.StackTrace
}
The returned errors.StackTrace type is defined as
type StackTrace []Frame
The Frame type represents a call site in the stack trace. Frame supports the fmt.Formatter interface that can be used for printing information about the stack trace of this error. For example:
if err, ok := err.(stackTracer); ok {
for _, f := range err.StackTrace() {
fmt.Printf("%+s:%d\n", f, f)
}
}
Although the stackTracer interface is not exported by this package, it is considered a part of its stable public interface.
See the documentation for Frame.Format for more details.
Example (StackTrace) ¶
package main
import (
"fmt"
"github.com/friendsofgo/errors"
)
func fn() error {
e1 := errors.New("error")
e2 := errors.Wrap(e1, "inner")
e3 := errors.Wrap(e2, "middle")
return errors.Wrap(e3, "outer")
}
func main() {
type stackTracer interface {
StackTrace() errors.StackTrace
}
err, ok := errors.Cause(fn()).(stackTracer)
if !ok {
panic("oops, err does not implement stackTracer")
}
st := err.StackTrace()
fmt.Printf("%+v", st[0:2]) // top two frames
// Example output:
// github.com/friendsofgo/errors_test.fn
// /home/dfc/src/github.com/friendsofgo/errors/example_test.go:47
// github.com/friendsofgo/errors_test.Example_stackTrace
// /home/dfc/src/github.com/friendsofgo/errors/example_test.go:127
}
Output:
Index ¶
- func As(err error, target interface{}) bool
- func Cause(err error) error
- func Errorf(format string, args ...interface{}) error
- func Is(err error, target error) bool
- func New(message string) error
- func WithMessage(err error, message string) error
- func WithMessagef(err error, format string, args ...interface{}) error
- func WithStack(err error) error
- func Wrap(err error, message string) error
- func Wrapf(err error, format string, args ...interface{}) error
- type Frame
- type StackTrace
Examples ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func As ¶ added in v0.9.1
As finds the first error in err's chain that matches target, and if so, sets target to that error value and returns true.
The chain consists of err itself followed by the sequence of errors obtained by repeatedly calling Unwrap.
An error matches target if the error's concrete value is assignable to the value pointed to by target, or if the error has a method As(interface{}) bool such that As(target) returns true. In the latter case, the As method is responsible for setting target.
As will panic if target is not a non-nil pointer to either a type that implements error, or to any interface type. As returns false if err is nil.
func Cause ¶
Cause returns the underlying cause of the error, if possible. An error value has a cause if it implements the following interface:
type causer interface {
Cause() error
}
If the error does not implement Cause, the original error will be returned. If the error is nil, nil will be returned without further investigation.
Example ¶
package main
import (
"fmt"
"github.com/friendsofgo/errors"
)
func fn() error {
e1 := errors.New("error")
e2 := errors.Wrap(e1, "inner")
e3 := errors.Wrap(e2, "middle")
return errors.Wrap(e3, "outer")
}
func main() {
err := fn()
fmt.Println(err)
fmt.Println(errors.Cause(err))
}
Output: outer: middle: inner: error error
Example (Printf) ¶
package main
import (
"fmt"
"github.com/friendsofgo/errors"
)
func main() {
err := errors.Wrap(func() error {
return func() error {
return errors.Errorf("hello %s", fmt.Sprintf("world"))
}()
}(), "failed")
fmt.Printf("%v", err)
}
Output: failed: hello world
func Errorf ¶ added in v0.3.0
Errorf formats according to a format specifier and returns the string as a value that satisfies error. Errorf also records the stack trace at the point it was called.
Example (Extended) ¶
package main
import (
"fmt"
"github.com/friendsofgo/errors"
)
func main() {
err := errors.Errorf("whoops: %s", "foo")
fmt.Printf("%+v", err)
// Example output:
// whoops: foo
// github.com/friendsofgo/errors_test.ExampleErrorf
// /home/dfc/src/github.com/friendsofgo/errors/example_test.go:101
// testing.runExample
// /home/dfc/go/src/testing/example.go:114
// testing.RunExamples
// /home/dfc/go/src/testing/example.go:38
// testing.(*M).Run
// /home/dfc/go/src/testing/testing.go:744
// main.main
// /github.com/friendsofgo/errors/_test/_testmain.go:102
// runtime.main
// /home/dfc/go/src/runtime/proc.go:183
// runtime.goexit
// /home/dfc/go/src/runtime/asm_amd64.s:2059
}
Output:
func Is ¶ added in v0.9.1
Is reports whether any error in err's chain matches target.
The chain consists of err itself followed by the sequence of errors obtained by repeatedly calling Unwrap.
An error is considered to match a target if it is equal to that target or if it implements a method Is(error) bool such that Is(target) returns true.
func New ¶
New returns an error with the supplied message. New also records the stack trace at the point it was called.
Example ¶
package main
import (
"fmt"
"github.com/friendsofgo/errors"
)
func main() {
err := errors.New("whoops")
fmt.Println(err)
}
Output: whoops
Example (Printf) ¶
package main
import (
"fmt"
"github.com/friendsofgo/errors"
)
func main() {
err := errors.New("whoops")
fmt.Printf("%+v", err)
// Example output:
// whoops
// github.com/friendsofgo/errors_test.ExampleNew_printf
// /home/dfc/src/github.com/friendsofgo/errors/example_test.go:17
// testing.runExample
// /home/dfc/go/src/testing/example.go:114
// testing.RunExamples
// /home/dfc/go/src/testing/example.go:38
// testing.(*M).Run
// /home/dfc/go/src/testing/testing.go:744
// main.main
// /github.com/friendsofgo/errors/_test/_testmain.go:106
// runtime.main
// /home/dfc/go/src/runtime/proc.go:183
// runtime.goexit
// /home/dfc/go/src/runtime/asm_amd64.s:2059
}
Output:
func WithMessage ¶ added in v0.8.0
WithMessage annotates err with a new message. If err is nil, WithMessage returns nil.
Example ¶
package main
import (
"fmt"
"github.com/friendsofgo/errors"
)
func main() {
cause := errors.New("whoops")
err := errors.WithMessage(cause, "oh noes")
fmt.Println(err)
}
Output: oh noes: whoops
func WithMessagef ¶ added in v0.8.1
WithMessagef annotates err with the format specifier. If err is nil, WithMessagef returns nil.
func WithStack ¶ added in v0.8.0
WithStack annotates err with a stack trace at the point WithStack was called. If err is nil, WithStack returns nil.
Example ¶
package main
import (
"fmt"
"github.com/friendsofgo/errors"
)
func main() {
cause := errors.New("whoops")
err := errors.WithStack(cause)
fmt.Println(err)
}
Output: whoops
Example (Printf) ¶
package main
import (
"fmt"
"github.com/friendsofgo/errors"
)
func main() {
cause := errors.New("whoops")
err := errors.WithStack(cause)
fmt.Printf("%+v", err)
// Example Output:
// whoops
// github.com/friendsofgo/errors_test.ExampleWithStack_printf
// /home/fabstu/go/src/github.com/friendsofgo/errors/example_test.go:55
// testing.runExample
// /usr/lib/go/src/testing/example.go:114
// testing.RunExamples
// /usr/lib/go/src/testing/example.go:38
// testing.(*M).Run
// /usr/lib/go/src/testing/testing.go:744
// main.main
// github.com/friendsofgo/errors/_test/_testmain.go:106
// runtime.main
// /usr/lib/go/src/runtime/proc.go:183
// runtime.goexit
// /usr/lib/go/src/runtime/asm_amd64.s:2086
// github.com/friendsofgo/errors_test.ExampleWithStack_printf
// /home/fabstu/go/src/github.com/friendsofgo/errors/example_test.go:56
// testing.runExample
// /usr/lib/go/src/testing/example.go:114
// testing.RunExamples
// /usr/lib/go/src/testing/example.go:38
// testing.(*M).Run
// /usr/lib/go/src/testing/testing.go:744
// main.main
// github.com/friendsofgo/errors/_test/_testmain.go:106
// runtime.main
// /usr/lib/go/src/runtime/proc.go:183
// runtime.goexit
// /usr/lib/go/src/runtime/asm_amd64.s:2086
}
Output:
func Wrap ¶
Wrap returns an error annotating err with a stack trace at the point Wrap is called, and the supplied message. If err is nil, Wrap returns nil.
Example ¶
package main
import (
"fmt"
"github.com/friendsofgo/errors"
)
func main() {
cause := errors.New("whoops")
err := errors.Wrap(cause, "oh noes")
fmt.Println(err)
}
Output: oh noes: whoops
Example (Extended) ¶
package main
import (
"fmt"
"github.com/friendsofgo/errors"
)
func fn() error {
e1 := errors.New("error")
e2 := errors.Wrap(e1, "inner")
e3 := errors.Wrap(e2, "middle")
return errors.Wrap(e3, "outer")
}
func main() {
err := fn()
fmt.Printf("%+v\n", err)
// Example output:
// error
// github.com/friendsofgo/errors_test.fn
// /home/dfc/src/github.com/friendsofgo/errors/example_test.go:47
// github.com/friendsofgo/errors_test.ExampleCause_printf
// /home/dfc/src/github.com/friendsofgo/errors/example_test.go:63
// testing.runExample
// /home/dfc/go/src/testing/example.go:114
// testing.RunExamples
// /home/dfc/go/src/testing/example.go:38
// testing.(*M).Run
// /home/dfc/go/src/testing/testing.go:744
// main.main
// /github.com/friendsofgo/errors/_test/_testmain.go:104
// runtime.main
// /home/dfc/go/src/runtime/proc.go:183
// runtime.goexit
// /home/dfc/go/src/runtime/asm_amd64.s:2059
// github.com/friendsofgo/errors_test.fn
// /home/dfc/src/github.com/friendsofgo/errors/example_test.go:48: inner
// github.com/friendsofgo/errors_test.fn
// /home/dfc/src/github.com/friendsofgo/errors/example_test.go:49: middle
// github.com/friendsofgo/errors_test.fn
// /home/dfc/src/github.com/friendsofgo/errors/example_test.go:50: outer
}
Output:
func Wrapf ¶ added in v0.2.0
Wrapf returns an error annotating err with a stack trace at the point Wrapf is called, and the format specifier. If err is nil, Wrapf returns nil.
Example ¶
package main
import (
"fmt"
"github.com/friendsofgo/errors"
)
func main() {
cause := errors.New("whoops")
err := errors.Wrapf(cause, "oh noes #%d", 2)
fmt.Println(err)
}
Output: oh noes #2: whoops
Types ¶
type Frame ¶ added in v0.6.0
type Frame uintptr
Frame represents a program counter inside a stack frame. For historical reasons if Frame is interpreted as a uintptr its value represents the program counter + 1.
func (Frame) Format ¶ added in v0.6.0
Format formats the frame according to the fmt.Formatter interface.
%s source file %d source line %n function name %v equivalent to %s:%d
Format accepts flags that alter the printing of some verbs, as follows:
%+s function name and path of source file relative to the compile time
GOPATH separated by \n\t (<funcname>\n\t<path>)
%+v equivalent to %+s:%d
func (Frame) MarshalText ¶ added in v0.9.1
MarshalText formats a stacktrace Frame as a text string. The output is the same as that of fmt.Sprintf("%+v", f), but without newlines or tabs.
type StackTrace ¶ added in v0.7.0
type StackTrace []Frame
StackTrace is stack of Frames from innermost (newest) to outermost (oldest).
func (StackTrace) Format ¶ added in v0.7.0
func (st StackTrace) Format(s fmt.State, verb rune)
Format formats the stack of Frames according to the fmt.Formatter interface.
%s lists source files for each Frame in the stack %v lists the source file and line number for each Frame in the stack
Format accepts flags that alter the printing of some verbs, as follows:
%+v Prints filename, function, and line number for each Frame in the stack.
Source Files