errors

package module
v0.11.1 Latest Latest
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 Go to latest Published: Nov 30, 2023 License: BSD-2-Clause Imports: 10 Imported by: 0

README

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Package errors provides simple error handling primitives.

go get github.com/pkg/errors

The traditional error handling idiom in Go is roughly akin to

if err != nil {
        return err
}

which 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. For example

_, err := ioutil.ReadAll(r)
if err != nil {
        return errors.Wrap(err, "read failed")
}

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 can be inspected by errors.Cause.

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
}

Read the package documentation for more information.

Roadmap

With the upcoming Go2 error proposals this package is moving into maintenance mode. The roadmap for a 1.0 release is as follows:

  • 0.9. Remove pre Go 1.9 and Go 1.10 support, address outstanding pull requests (if possible)
  • 1.0. Final release.

Contributing

Because of the Go2 errors changes, this package is not accepting proposals for new functionality. With that said, we welcome pull requests, bug fixes and issue reports.

Before sending a PR, please discuss your change by raising an issue.

License

BSD-2-Clause

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) 
package main

import (
	"fmt"

	"github.com/bynil/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/bynil/errors_test.fn
	//	/home/dfc/src/github.com/bynil/errors/example_test.go:47
	// github.com/bynil/errors_test.Example_stackTrace
	//	/home/dfc/src/github.com/bynil/errors/example_test.go:127
}

Output:

Index

Examples

Constants

View Source 
const (
	// TypeInternal is error type for when there is an internal system error. e.g. Database errors
	TypeInternal errType = iota
	// TypeValidation is error type for when there is a validation error. e.g. invalid email address
	TypeValidation
	// TypeInput is error type for when an input data type error. e.g. invalid JSON
	TypeInput
	// TypeDuplicate is error type for when there's duplicate content
	TypeDuplicate
	// TypeUnauthenticated is error type when trying to access an authenticated API without authentication
	TypeUnauthenticated
	// TypeNoPermission is error type for when there's an unauthorized access attempt
	TypeNoPermission
	// TypeEmpty is error type for when an expected non-empty resource, is empty
	TypeEmpty
	// TypeNotFound is error type for an expected resource is not found e.g. user ID not found
	TypeNotFound
	// TypeLimitExceeded is error type for attempting the same action more than allowed
	TypeLimitExceeded
	// TypeSubscriptionExpired is error type for when a user's 'paid' account has expired
	TypeSubscriptionExpired

	// DefaultMessage is the default user friendly message
	DefaultMessage = "unknown error occurred"
)

While adding a new Type, the respective helper functions should be added, also update the WriteHTTP method accordingly

Variables

This section is empty.

Functions

func As added in v0.9.0 

func As(err error, target interface{}) bool

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 

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 
package main

import (
	"fmt"

	"github.com/bynil/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/bynil/errors"
)

func main() {
	err := errors.Wrap(func() error {
		return func() error {
			return errors.New("hello world")
		}()
	}(), "failed")

	fmt.Printf("%v", err)

}

Output:

failed: hello world

func Duplicate added in v0.10.0 

func Duplicate(message string) error

Duplicate is a helper function to create a new error of type TypeDuplicate

func Duplicatef added in v0.10.0 

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

Duplicatef is a helper function to create a new error of type TypeDuplicate, with formatted message

func Empty added in v0.10.0 

func Empty(message string) error

Empty is a helper function to create a new error of type TypeEmpty

func Emptyf added in v0.10.0 

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

Emptyf is a helper function to create a new error of type TypeEmpty, with formatted message

func Errorf added in v0.3.0 

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) 
package main

import (
	"fmt"

	"github.com/bynil/errors"
)

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

	// Example output:
	// whoops: foo
	// github.com/bynil/errors_test.ExampleErrorf
	//         /home/dfc/src/github.com/bynil/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/bynil/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 GetAPIError added in v0.10.0 

func GetAPIError(err error) (code int, msg string)

GetAPIError tries to get the code and message from any error.

func GetLocalizeConfig added in v0.11.1 

func GetLocalizeConfig(err error) (lc *i18n.LocalizeConfig)

GetLocalizeConfig tries to get the localize config from error, may be nil.

func HasType added in v0.10.0 

func HasType(err error, et Typer) bool

HasType will check if the provided err type is available anywhere nested in the error

func Input added in v0.10.0 

func Input(message string) error

Input is a helper function to create a new error of type TypeInput

func Inputf added in v0.10.0 

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

Inputf is a helper function to create a new error of type TypeInput, with formatted message

func Internal added in v0.10.0 

func Internal(message string) error

Internal helper method for creating internal errors

func Internalf added in v0.10.0 

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

Internalf helper method for creating internal errors with formatted message

func Is added in v0.9.0 

func Is(err, target error) bool

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 Join added in v0.10.3 

func Join(errs ...error) error

func LimitExceeded added in v0.10.0 

func LimitExceeded(message string) error

LimitExceeded is a helper function to create a new error of type TypeLimitExceeded

func LimitExceededf added in v0.10.0 

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

LimitExceededf is a helper function to create a new error of type TypeLimitExceeded, with formatted message

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 
package main

import (
	"fmt"

	"github.com/bynil/errors"
)

func main() {
	err := errors.New("whoops")
	fmt.Println(err)

}

Output:

whoops
Example (Printf) 
package main

import (
	"fmt"

	"github.com/bynil/errors"
)

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

	// Example output:
	// whoops
	// github.com/bynil/errors_test.ExampleNew_printf
	//         /home/dfc/src/github.com/bynil/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/bynil/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 NewI18n added in v0.11.0 

func NewI18n(eType Typer, lc *i18n.LocalizeConfig) error

func NoPermission added in v0.11.0 

func NoPermission(message string) error

NoPermission is a helper function to create a new error of type TypeNoPermission

func NoPermissionf added in v0.11.0 

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

NoPermissionf is a helper function to create a new error of type TypeNoPermission, with formatted message

func NotFound added in v0.10.0 

func NotFound(message string) error

NotFound is a helper function to create a new error of type TypeNotFound

func NotFoundf added in v0.10.0 

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

NotFoundf is a helper function to create a new error of type TypeNotFound, with formatted message

func SetDefaultType added in v0.10.0 

func SetDefaultType(e errType)

SetDefaultType will set the default error type, which is used in the 'New' function

func SubscriptionExpired added in v0.10.0 

func SubscriptionExpired(message string) error

SubscriptionExpired is a helper function to create a new error of type TypeSubscriptionExpired

func SubscriptionExpiredf added in v0.10.0 

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

SubscriptionExpiredf is a helper function to create a new error of type TypeSubscriptionExpired, with formatted message

func Unauthenticated added in v0.10.0 

func Unauthenticated(message string) error

Unauthenticated is a helper function to create a new error of type TypeUnauthenticated

func Unauthenticatedf added in v0.10.0 

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

Unauthenticatedf is a helper function to create a new error of type TypeUnauthenticated, with formatted message

func Unwrap added in v0.9.0 

func Unwrap(err error) error

Unwrap returns the result of calling the Unwrap method on err, if err's type contains an Unwrap method returning error. Otherwise, Unwrap returns nil.

func Validation added in v0.10.0 

func Validation(message string) error

Validation is a helper function to create a new error of type TypeValidation

func Validationf added in v0.10.0 

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

Validationf is a helper function to create a new error of type TypeValidation, with formatted message

func WithMessage added in v0.8.0 

func WithMessage(err error, message string) error

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

Example 
package main

import (
	"fmt"

	"github.com/bynil/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 

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 added in v0.8.0 

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 
package main

import (
	"fmt"

	"github.com/bynil/errors"
)

func main() {
	cause := errors.New("whoops")
	err := errors.WithStack(cause)
	fmt.Println(err)

}

Output:

whoops
Example (Printf) 
package main

import (
	"fmt"

	"github.com/bynil/errors"
)

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

	// Example Output:
	// whoops
	// github.com/bynil/errors_test.ExampleWithStack_printf
	//         /home/fabstu/go/src/github.com/bynil/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/bynil/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/bynil/errors_test.ExampleWithStack_printf
	//         /home/fabstu/go/src/github.com/bynil/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/bynil/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 

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 
package main

import (
	"fmt"

	"github.com/bynil/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/bynil/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/bynil/errors_test.fn
	//         /home/dfc/src/github.com/bynil/errors/example_test.go:47
	// github.com/bynil/errors_test.ExampleCause_printf
	//         /home/dfc/src/github.com/bynil/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/bynil/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/bynil/errors_test.fn
	// 	  /home/dfc/src/github.com/bynil/errors/example_test.go:48: inner
	// github.com/bynil/errors_test.fn
	//        /home/dfc/src/github.com/bynil/errors/example_test.go:49: middle
	// github.com/bynil/errors_test.fn
	//      /home/dfc/src/github.com/bynil/errors/example_test.go:50: outer
}

Output:

func WrapType added in v0.10.0 

func WrapType(err error, eType Typer, message string) error

func WrapTypef added in v0.10.0 

func WrapTypef(err error, eType Typer, format string, args ...interface{}) error

func Wrapf added in v0.2.0 

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 
package main

import (
	"fmt"

	"github.com/bynil/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 APIError added in v0.10.0 

type APIError interface {
	APIError() (statusCode int, msg string)
}

APIError returns an HTTP status code and an API-safe error message.

type CustomType added in v0.10.1 

type CustomType struct {
	Detail     string
	StatusCode int
}

func NewCustomType added in v0.10.1 

func NewCustomType(detail string, statusCode int) CustomType

func (CustomType) HTTPStatusCode added in v0.10.1 

func (c CustomType) HTTPStatusCode() int

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 

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 added in v0.9.0 

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 I18ner added in v0.11.0 

type I18ner interface {
	LocalizeConfig() (lc *i18n.LocalizeConfig)
}

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.

type Typer added in v0.10.0 

type Typer interface {
	HTTPStatusCode() int
}

Source Files

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