errors

README

基于 github.com/pkg/errors 包，增加对 error code 的支持，完全兼容 github.com/pkg/errors。

性能跟 github.com/pkg/errors 基本持平。

Documentation

Overview

Package errors is an errors package

Package errors provides simple errors handling primitives.

The traditional errors handling idiom in Go is roughly akin to

if err != nil {
        return err
}

which when applied recursively up the call stack results in errors 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 errors.

Adding context to an errors

The errors.Wrap function returns a new errors that adds context to the original errors 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 errors with a stack trace and with a message, respectively.

Retrieving the cause of an errors

Using errors.Wrap constructs a stack of errors, adding context to the preceding errors. Depending on the nature of the errors it may be necessary to reverse the operation of errors.Wrap to retrieve the original errors for inspection. Any errors value which implements this interface

type causer interface {
        Cause() errors
}

can be inspected by errors.Cause. errors.Cause will recursively retrieve the topmost errors 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 errors
}

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 errors values returned from this package implement fmt.Formatter and can be formatted by the fmt package. The following verbs are supported:

%s    print the errors. If the errors has a Cause it will be
      printed recursively.
%v    see %s
%+v   extended format. Each Frame of the errors's StackTrace will
      be printed in detail.

Retrieving the stack trace of an errors 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 errors. 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.

Index

• Variables
• func Cause(err error) error
• func Errorf(format string, args ...interface{}) error
• func FilterOut(err error, fns ...Matcher) error
• func IsCode(err error, code int) bool
• func MustRegister(coder Coder)
• func New(message string) error
• func Reduce(err error) error
• func Register(coder Coder)
• func WithCode(code int, format string, args ...interface{}) 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 WrapC(err error, code int, format string, args ...interface{}) error
• func Wrapf(err error, format string, args ...interface{}) error
• type Aggregate
  • func AggregateGoroutines(funcs ...func() error) Aggregate
  • func CreateAggregateFromMessageCountMap(m MessageCountMap) Aggregate
  • func Flatten(agg Aggregate) Aggregate
  • func NewAggregate(errlist []error) Aggregate
• type Coder
  • func ParseCoder(err error) Coder
• type Frame
  • func (f Frame) Format(s fmt.State, verb rune)
  • func (f Frame) MarshalText() ([]byte, error)
• type Matcher
• type MessageCountMap
• type StackTrace
  • func (st StackTrace) Format(s fmt.State, verb rune)

Variables

var ErrPreconditionViolated = errors.New("precondition is violated")

ErrPreconditionViolated is returned when the precondition is violated.

Functions

func Cause

func Cause(err error) error

Cause returns the underlying cause of the errors, if possible. An errors value has a cause if it implements the following interface:

type causer interface {
       Cause() errors
}

If the errors does not implement Cause, the original errors will be returned. If the errors is nil, nil will be returned without further investigation.

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 errors. Errorf also records the stack trace at the point it was called.

func FilterOut

func FilterOut(err error, fns ...Matcher) error

FilterOut removes all errors that match any of the matchers from the input error. If the input is a singular error, only that error is tested. If the input implements the Aggregate interface, the list of errors will be processed recursively.

This can be used, for example, to remove known-OK errors (such as io.EOF or os.PathNotFound) from a list of errors.

func IsCode

func IsCode(err error, code int) bool

IsCode reports whether any error in err's chain contains the given error code.

func MustRegister

func MustRegister(coder Coder)

MustRegister register a user define error code. It will panic when the same Code already exist.

func New

func New(message string) error

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

func Reduce

func Reduce(err error) error

Reduce will return err or, if err is an Aggregate and only has one item, the first item in the aggregate.

func Register

func Register(coder Coder)

Register registers a user define error code. It will overrid the exist code.

func WithCode

func WithCode(code int, format string, args ...interface{}) error

func WithMessage

func WithMessage(err error, message string) error

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

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.

func Wrap

func Wrap(err error, message string) error

Wrap returns an errors annotating err with a stack trace at the point Wrap is called, and the supplied message. If err is nil, Wrap returns nil.

func WrapC

func WrapC(err error, code int, format string, args ...interface{}) error

func Wrapf

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

Wrapf returns an errors annotating err with a stack trace at the point Wrapf is called, and the format specifier. If err is nil, Wrapf returns nil.

Types

type Aggregate

type Aggregate interface {
	error
	Errors() []error
	Is(error) bool
}

Aggregate represents an object that contains multiple errors, but does not necessarily have singular semantic meaning. The aggregate can be used with `errors.Is()` to check for the occurrence of a specific error type. Errors.As() is not supported, because the caller presumably cares about a specific error of potentially multiple that match the given type.

func AggregateGoroutines

func AggregateGoroutines(funcs ...func() error) Aggregate

AggregateGoroutines runs the provided functions in parallel, stuffing all non-nil errors into the returned Aggregate. Returns nil if all the functions complete successfully.

func CreateAggregateFromMessageCountMap

func CreateAggregateFromMessageCountMap(m MessageCountMap) Aggregate

CreateAggregateFromMessageCountMap converts MessageCountMap Aggregate.

func Flatten

func Flatten(agg Aggregate) Aggregate

Flatten takes an Aggregate, which may hold other Aggregates in arbitrary nesting, and flattens them all into a single Aggregate, recursively.

func NewAggregate

func NewAggregate(errlist []error) Aggregate

NewAggregate converts a slice of errors into an Aggregate interface, which is itself an implementation of the error interface. If the slice is empty, this returns nil. It will check if any of the element of input error list is nil, to avoid nil pointer panic when call Error().

type Coder

type Coder interface {
	// HTTPStatus that should be used for the associated error code.
	HTTPStatus() int

	// String returns the external (user) facing error text.
	String() string

	// Reference returns the detail documents for user.
	Reference() string

	// Code returns the code of the coder
	Code() int
}

Coder defines an interface for an error code detail information.

func ParseCoder

func ParseCoder(err error) Coder

ParseCoder parse any error into *withCode. nil error will return nil direct. None withStack error will be parsed as ErrUnknown.

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 Matcher

type Matcher func(error) bool

Matcher is used to match errors. Returns true if the error matches.

type MessageCountMap

type MessageCountMap map[string]int

MessageCountMap contains occurrence for each error message.

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.