errors

package module
v2.0.1 Latest Latest
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 Go to latest Published: Feb 2, 2023 License: BSD-2-Clause Imports: 9 Imported by: 18

README

Errors with stack info

Version Support Go
v1 >= 1.13
v2 >= 1.20

New Features

v2
  1. Join
  2. Is
  3. UnWrap
  4. ErrorfWithSkip
v1
  1. SetSkipCallers: set global depth to skip callers
  2. WrapWithSkip:
  3. WrapfWithSkip:
Set global depth to skip callers
import "github.com/Laisky/errors/v2"

errors.SetSkipCallers(3)  // default to 3

Documentation

Overview

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.

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) 
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/Laisky/errors_test.fn
//	/home/dfc/src/github.com/Laisky/errors/v2example_test.go:47
// github.com/Laisky/errors_test.Example_stackTrace
//	/home/dfc/src/github.com/Laisky/errors/v2example_test.go:127

Output:

Index

Examples

Constants

This section is empty.

Variables

This section is empty.

Functions

func As 

func As(err error, target any) bool

As finds the first error in err's tree that matches target, and if one is found, sets target to that error value and returns true. Otherwise, it returns false.

The tree consists of err itself, followed by the errors obtained by repeatedly calling Unwrap. When err wraps multiple errors, As examines err followed by a depth-first traversal of its children.

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.

An error type might provide an As method so it can be treated as if it were a different error type.

As panics if target is not a non-nil pointer to either a type that implements error, or to any interface type.

func Cause 

func Cause(err error) error

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 
err := fn()
fmt.Println(err)
fmt.Println(errors.Cause(err))

Output:

outer: middle: inner: error
error
Example (Printf) 
err := errors.Wrap(func() error {
	return func() error {
		return errors.New("hello world")
	}()
}(), "failed")

fmt.Printf("%v", err)

Output:

failed: hello world

func Errorf 

func Errorf(format string, args ...interface{}) error

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) 
err := errors.Errorf("whoops: %s", "foo")
fmt.Printf("%+v", err)

// Example output:
// whoops: foo
// github.com/Laisky/errors_test.ExampleErrorf
//         /home/dfc/src/github.com/Laisky/errors/v2example_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/Laisky/errors/v2_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 ErrorfWithStack added in v2.0.1 

func ErrorfWithStack(skip int, format string, args ...interface{}) error

ErrorfWithStack same as Errorf, but you can skip arbitrary stacks

func GetSkipCallers 

func GetSkipCallers() int

GetSkipCallers get depth of skip callers

func Is 

func Is(err, target error) bool

Is reports whether any error in err's tree matches target.

The tree consists of err itself, followed by the errors obtained by repeatedly calling Unwrap. When err wraps multiple errors, Is examines err followed by a depth-first traversal of its children.

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.

An error type might provide an Is method so it can be treated as equivalent to an existing error. For example, if MyError defines 

func (m MyError) Is(target error) bool { return target == fs.ErrExist }

then Is(MyError{}, fs.ErrExist) returns true. See syscall.Errno.Is for an example in the standard library. An Is method should only shallowly compare err and the target and not call Unwrap on either.

func Join 

func Join(err ...error) error

Join returns an error that wraps the given errors. Any nil error values are discarded. Join returns nil if errs contains no non-nil values. The error formats as the concatenation of the strings obtained by calling the Error method of each element of errs, with a newline between each string.

func New 

func New(message string) error

New returns an error with the supplied message. New also records the stack trace at the point it was called.

Example 
err := errors.New("whoops")
fmt.Println(err)

Output:

whoops
Example (Printf) 
err := errors.New("whoops")
fmt.Printf("%+v", err)

// Example output:
// whoops
// github.com/Laisky/errors_test.ExampleNew_printf
//         /home/dfc/src/github.com/Laisky/errors/v2example_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/Laisky/errors/v2_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 SetSkipCallers 

func SetSkipCallers(skip int)

SetSkipCallers set depth of skip callers

func Unwrap added in v2.0.1 

func Unwrap(err error)

func WithMessage 

func WithMessage(err error, message string) error

WithMessage annotates err with a new message. If err is nil, WithMessage returns nil.

Example 
cause := errors.New("whoops")
err := errors.WithMessage(cause, "oh noes")
fmt.Println(err)

Output:

oh noes: whoops

func WithMessagef 

func WithMessagef(err error, format string, args ...interface{}) error

WithMessagef annotates err with the format specifier. If err is nil, WithMessagef returns nil.

func WithStack 

func WithStack(err error) error

WithStack annotates err with a stack trace at the point WithStack was called. If err is nil, WithStack returns nil.

Example 
cause := errors.New("whoops")
err := errors.WithStack(cause)
fmt.Println(err)

Output:

whoops
Example (Printf) 
cause := errors.New("whoops")
err := errors.WithStack(cause)
fmt.Printf("%+v", err)

// Example Output:
// whoops
// github.com/Laisky/errors_test.ExampleWithStack_printf
//         /home/fabstu/go/src/github.com/Laisky/errors/v2example_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/Laisky/errors/v2_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/Laisky/errors_test.ExampleWithStack_printf
//         /home/fabstu/go/src/github.com/Laisky/errors/v2example_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/Laisky/errors/v2_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 WithStackWithSkip 

func WithStackWithSkip(skip int, err error) error

WithStackWithSkip like WithStackm but you can skip arbitrary stacks

func Wrap 

func Wrap(err error, message string) error

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 
cause := errors.New("whoops")
err := errors.Wrap(cause, "oh noes")
fmt.Println(err)

Output:

oh noes: whoops
Example (Extended) 
err := fn()
fmt.Printf("%+v\n", err)

// Example output:
// error
// github.com/Laisky/errors_test.fn
//         /home/dfc/src/github.com/Laisky/errors/v2example_test.go:47
// github.com/Laisky/errors_test.ExampleCause_printf
//         /home/dfc/src/github.com/Laisky/errors/v2example_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/Laisky/errors/v2_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/Laisky/errors_test.fn
// 	  /home/dfc/src/github.com/Laisky/errors/v2example_test.go:48: inner
// github.com/Laisky/errors_test.fn
//        /home/dfc/src/github.com/Laisky/errors/v2example_test.go:49: middle
// github.com/Laisky/errors_test.fn
//      /home/dfc/src/github.com/Laisky/errors/v2example_test.go:50: outer

Output:

func WrapWithSkip 

func WrapWithSkip(skip int, err error, message string) error

WrapWithSkip same as Wrap, but you can skip arbitrary stacks

func Wrapf 

func Wrapf(err error, format string, args ...interface{}) error

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 
cause := errors.New("whoops")
err := errors.Wrapf(cause, "oh noes #%d", 2)
fmt.Println(err)

Output:

oh noes #2: whoops

func WrapfWithSkip 

func WrapfWithSkip(skip int, err error, format string, args ...interface{}) error

WrapfWithSkip same as Wrapf, but you can skip arbitrary stacks

Types

type Frame 

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 

func (f Frame) Format(s fmt.State, verb rune)

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 

func (f Frame) MarshalText() ([]byte, error)

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 

type StackTrace []Frame

StackTrace is stack of Frames from innermost (newest) to outermost (oldest).

func (StackTrace) Format 

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

View all Source files

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