errors

package module
v1.1.4 Latest Latest
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 Go to latest Published: Dec 2, 2020 License: BSD-2-Clause Imports: 9 Imported by: 9

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.

Contributing

We welcome pull requests, bug fixes and issue reports. With that said, the bar for adding new symbols to this package is intentionally set high.

Before proposing a change, 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 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.Annotate function returns a new error that adds context to the original error by recording a stack trace at the point Annotate is called, and the supplied message. For example 

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

If additional control is required the errors.AddStack and errors.WithMessage functions destructure errors.Annotate into its component operations of annotating an error with a stack trace and an a message, respectively.

Retrieving the cause of an error

Using errors.Annotate 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.Annotate 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 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
}

causer interface is not exported by this package, but is considered a part of stable public API. errors.Unwrap is also available: this will retrieve the next error in the chain.

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, Annotate, and Annotatef record a stack trace at the point they are invoked. This information can be retrieved with the StackTracer interface that returns a StackTrace. Where errors.StackTrace 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 stacked := errors.GetStackTracer(err); stacked != nil {
        for _, f := range stacked.StackTrace() {
                fmt.Printf("%+s:%d", f)
        }
}

See the documentation for Frame.Format for more details.

errors.Find can be used to search for an error in the error chain.

Example (StackTrace) 
package main

import (
	"fmt"

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

Output:

Index

Examples

Constants

This section is empty.

Variables

View Source 
var RedactLogEnabled atomic.Bool

RedactLogEnabled defines whether the arguments of Error need to be redacted.

Functions

func AddStack added in v0.9.0 

func AddStack(err error) error

AddStack is similar to WithStack. However, it will first check with HasStack to see if a stack trace already exists in the causer chain before creating another one.

func AlreadyExistsf added in v0.11.0 

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

AlreadyExistsf represents an error with already exists message.

func Annotate added in v0.9.0 

func Annotate(err error, message string) error

Annotate adds a message and ensures there is a stack trace.

func Annotatef added in v0.9.0 

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

Annotatef adds a message and ensures there is a stack trace.

func BadRequestf added in v0.9.0 

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

BadRequestf represents an error with bad request message.

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/pkg/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/pkg/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 ErrorEqual added in v1.1.2 

func ErrorEqual(err1, err2 error) bool

ErrorEqual returns a boolean indicating whether err1 is equal to err2.

func ErrorNotEqual added in v1.1.2 

func ErrorNotEqual(err1, err2 error) bool

ErrorNotEqual returns a boolean indicating whether err1 isn't equal to err2.

func ErrorStack added in v0.9.0 

func ErrorStack(err error) string

ErrorStack will format a stack trace if it is available, otherwise it will be Error() If the error is nil, the empty string is returned Note that this just calls fmt.Sprintf("%+v", err)

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/pkg/errors"
)

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

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

func Errors(err error) []error

Errors uses the ErrorGroup interface to return a slice of errors. If the ErrorGroup interface is not implemented it returns an array containing just the given error.

func Find added in v0.9.0 

func Find(origErr error, test func(error) bool) error

Find an error in the chain that matches a test function. returns nil if no error is found.

func HasStack added in v0.9.0 

func HasStack(err error) bool

HasStack tells whether a StackTracer exists in the error chain

func IsAlreadyExists added in v0.11.0 

func IsAlreadyExists(err error) bool

IsAlreadyExists reports whether err was already exists error.

func IsNotFound added in v0.11.0 

func IsNotFound(err error) bool

IsNotFound reports whether err was not found error.

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/pkg/errors"
)

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

}

Output:

whoops
Example (Printf) 
package main

import (
	"fmt"

	"github.com/pkg/errors"
)

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

	// Example output:
	// whoops
	// github.com/pkg/errors_test.ExampleNew_printf
	//         /home/dfc/src/github.com/pkg/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/pkg/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 NewNoStackError added in v0.11.2 

func NewNoStackError(msg string) error

NewNoStackError creates error without error stack later duplicate trace will no longer generate Stack too.

func NotFoundf added in v0.9.0 

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

NotFoundf represents an error with not found message.

func NotSupportedf added in v0.9.0 

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

NotSupportedf represents an error with not supported message.

func NotValidf added in v0.11.0 

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

NotValidf represents an error with not valid message.

func RedactErrorArg added in v1.1.2 

func RedactErrorArg(args []interface{}, position []int)

RedactErrorArg redacts the args by position if RedactLogEnabled is enabled.

func SuspendStack added in v0.11.3 

func SuspendStack(err error) error

SuspendStack suspends stack generate for error.

func Trace added in v0.9.0 

func Trace(err error) error

Trace just calls AddStack.

func Unwrap added in v0.9.0 

func Unwrap(err error) error

Unwrap uses causer to return the next error in the chain or nil. This goes one-level deeper, whereas Cause goes as far as possible

func WalkDeep added in v0.9.0 

func WalkDeep(err error, visitor func(err error) bool) bool

WalkDeep does a depth-first traversal of all errors. Any ErrorGroup is traversed (after going deep). The visitor function can return true to end the traversal early In that case, WalkDeep will return true, otherwise false.

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/pkg/errors"
)

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

}

Output:

oh noes: whoops

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.

For most use cases this is deprecated and AddStack should be used (which will ensure just one stack trace). However, one may want to use this in some situations, for example to create a 2nd trace across a goroutine.

Example 
package main

import (
	"fmt"

	"github.com/pkg/errors"
)

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

}

Output:

whoops
Example (Printf) 
package main

import (
	"fmt"

	"github.com/pkg/errors"
)

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

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

For most use cases this is deprecated in favor of Annotate. Annotate avoids creating duplicate stack traces.

Example 
package main

import (
	"fmt"

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

Output:

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 call, and the format specifier. If err is nil, Wrapf returns nil.

For most use cases this is deprecated in favor of Annotatef. Annotatef avoids creating duplicate stack traces.

Example 
package main

import (
	"fmt"

	"github.com/pkg/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 ErrCode added in v1.1.2 

type ErrCode int

ErrCode represents a specific error type in a error class. Same error code can be used in different error classes.

type ErrCodeText added in v1.1.2 

type ErrCodeText string

ErrCodeText is a textual error code that represents a specific error type in a error class.

type Error added in v1.1.2 

type Error struct {
	// contains filtered or unexported fields
}

Error is the 'prototype' of a type of errors. Use DefineError to make a *Error: var ErrUnavailable = errors.Normalize("Region %d is unavailable", errors.RFCCodeText("Unavailable"))

"throw" it at runtime: 

func Somewhat() error {
    ...
    if err != nil {
        // generate a stackful error use the message template at defining,
        // also see FastGen(it's stackless), GenWithStack(it uses custom message template).
        return ErrUnavailable.GenWithStackByArgs(region.ID)
    }
}

testing whether an error belongs to a prototype: 

if ErrUnavailable.Equal(err) {
    // handle this error.
}

func Normalize added in v1.1.2 

func Normalize(message string, opts ...NormalizeOption) *Error

Normalize creates a new Error object.

func (*Error) Cause added in v1.1.2 

func (e *Error) Cause() error

func (*Error) Code added in v1.1.2 

func (e *Error) Code() ErrCode

Code returns the numeric code of this error. ID() will return textual error if there it is, when you just want to get the purely numeric error (e.g., for mysql protocol transmission.), this would be useful.

func (*Error) Equal added in v1.1.2 

func (e *Error) Equal(err error) bool

Equal checks if err is equal to e.

func (*Error) Error added in v1.1.2 

func (e *Error) Error() string

Error implements error interface.

func (*Error) FastGen added in v1.1.2 

func (e *Error) FastGen(format string, args ...interface{}) error

FastGen generates a new *Error with the same class and code, and a new formatted message. This will not call runtime.Caller to get file and line.

func (*Error) FastGenByArgs added in v1.1.2 

func (e *Error) FastGenByArgs(args ...interface{}) error

FastGen generates a new *Error with the same class and code, and a new arguments. This will not call runtime.Caller to get file and line.

func (*Error) FastGenWithCause added in v1.1.2 

func (e *Error) FastGenWithCause(args ...interface{}) error

func (*Error) GenWithStack added in v1.1.2 

func (e *Error) GenWithStack(format string, args ...interface{}) error

GenWithStack generates a new *Error with the same class and code, and a new formatted message.

func (*Error) GenWithStackByArgs added in v1.1.2 

func (e *Error) GenWithStackByArgs(args ...interface{}) error

GenWithStackByArgs generates a new *Error with the same class and code, and new arguments.

func (*Error) GenWithStackByCause added in v1.1.2 

func (e *Error) GenWithStackByCause(args ...interface{}) error

func (*Error) GetMsg added in v1.1.2 

func (e *Error) GetMsg() string

func (*Error) ID added in v1.1.2 

func (e *Error) ID() ErrorID

ID returns the ID of this error.

func (*Error) Location added in v1.1.2 

func (e *Error) Location() (file string, line int)

Location returns the location where the error is created, implements juju/errors locationer interface.

func (*Error) MarshalJSON added in v1.1.2 

func (e *Error) MarshalJSON() ([]byte, error)

MarshalJSON implements json.Marshaler interface. aware that this function cannot save a 'registered' status, since we cannot access the registry when unmarshaling, and the original global registry would be removed here. This function is reserved for compatibility.

func (*Error) MessageTemplate added in v1.1.2 

func (e *Error) MessageTemplate() string

MessageTemplate returns the error message template of this error.

func (*Error) NotEqual added in v1.1.2 

func (e *Error) NotEqual(err error) bool

NotEqual checks if err is not equal to e.

func (*Error) RFCCode added in v1.1.2 

func (e *Error) RFCCode() RFCErrorCode

Code returns ErrorCode, by the RFC:

The error code is a 3-tuple of abbreviated component name, error class and error code, joined by a colon like {Component}:{ErrorClass}:{InnerErrorCode}.

func (*Error) UnmarshalJSON added in v1.1.2 

func (e *Error) UnmarshalJSON(data []byte) error

UnmarshalJSON implements json.Unmarshaler interface. aware that this function cannot create a 'registered' error, since we cannot access the registry in this context, and the original global registry is removed. This function is reserved for compatibility.

func (*Error) Wrap added in v1.1.2 

func (e *Error) Wrap(err error) *Error

type ErrorGroup added in v0.9.0 

type ErrorGroup interface {
	Errors() []error
}

ErrorGroup is an interface for multiple errors that are not a chain. This happens for example when executing multiple operations in parallel.

type ErrorID added in v1.1.2 

type ErrorID string

type Frame added in v0.6.0 

type Frame uintptr

Frame represents a program counter inside a stack frame.

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

type NormalizeOption added in v1.1.2 

type NormalizeOption func(*Error)

func MySQLErrorCode added in v1.1.2 

func MySQLErrorCode(code int) NormalizeOption

MySQLErrorCode returns a NormalizeOption to set error code.

func RFCCodeText added in v1.1.2 

func RFCCodeText(codeText string) NormalizeOption

RFCCodeText returns a NormalizeOption to set RFC error code.

func RedactArgs added in v1.1.2 

func RedactArgs(pos []int) NormalizeOption

type RFCErrorCode added in v1.1.2 

type RFCErrorCode string

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 StackTraceAware added in v0.9.0 

type StackTraceAware interface {
	HasStack() bool
}

StackTraceAware is an optimization to avoid repetitive traversals of an error chain. HasStack checks for this marker first. Annotate/Wrap and Annotatef/Wrapf will produce this marker.

type StackTracer added in v0.9.0 

type StackTracer interface {
	StackTrace() StackTrace
}

StackTracer retrieves the StackTrace Generally you would want to use the GetStackTracer function to do that.

func GetStackTracer added in v0.9.0 

func GetStackTracer(origErr error) StackTracer

GetStackTracer will return the first StackTracer in the causer chain. This function is used by AddStack to avoid creating redundant stack traces.

You can also use the StackTracer interface on the returned error to get the stack trace.

func NewStack added in v0.9.0 

func NewStack(skip int) StackTracer

NewStack is for library implementers that want to generate a stack trace. Normally you should insted use AddStack to get an error with a stack trace.

The result of this function can be turned into a stack trace by calling .StackTrace()

This function takes an argument for the number of stack frames to skip. This avoids putting stack generation function calls like this one in the stack trace. A value of 0 will give you the line that called NewStack(0) A library author wrapping this in their own function will want to use a value of at least 1.

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