errors

package
v0.0.0-...-772bc38 Latest Latest
Warning

This package is not in the latest version of its module.

 Go to latest Published: May 8, 2023 License: MulanPSL-2.0 Imports: 13 Imported by: 0

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.

Index

Constants

This section is empty.

Variables

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

ErrPreconditionViolated is returned when the precondition is violated

Functions

func As 

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.

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.

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 Is 

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 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 error 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 register a user define error code. It will overrid the exist code.

func Unwrap 

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 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 error 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 error 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 {
	// HTTP status that should be used for the associated error code.
	HTTPStatus() int

	// 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 Empty 

type Empty struct{}

Empty is public since it is used by some internal API objects for conversions between external string arrays and internal sets, and conversion logic requires public types today.

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.

type String 

type String map[string]Empty

String is a set of strings, implemented via map[string]struct{} for minimal memory consumption.

func NewString 

func NewString(items ...string) String

NewString creates a String from a list of values.

func StringKeySet 

func StringKeySet(theMap interface{}) String

StringKeySet creates a String from a keys of a map[string](? extends interface{}). If the value passed in is not actually a map, this will panic.

func (String) Delete 

func (s String) Delete(items ...string) String

Delete removes all items from the set.

func (String) Difference 

func (s String) Difference(s2 String) String

Difference returns a set of objects that are not in s2 For example: s = {a1, a2, a3} s2 = {a1, a2, a4, a5} s.Difference(s2) = {a3} s2.Difference(s) = {a4, a5}

func (String) Equal 

func (s String) Equal(s2 String) bool

Equal returns true if and only if s is equal (as a set) to s2. Two sets are equal if their membership is identical. (In practice, this means same elements, order doesn't matter)

func (String) Has 

func (s String) Has(item string) bool

Has returns true if and only if item is contained in the set.

func (String) HasAll 

func (s String) HasAll(items ...string) bool

HasAll returns true if and only if all items are contained in the set.

func (String) HasAny 

func (s String) HasAny(items ...string) bool

HasAny returns true if any items are contained in the set.

func (String) Insert 

func (s String) Insert(items ...string) String

Insert adds items to the set.

func (String) Intersection 

func (s String) Intersection(s2 String) String

Intersection returns a new set which includes the item in BOTH s and s2 For example: s = {a1, a2} s2 = {a2, a3} s.Intersection(s2) = {a2}

func (String) IsSuperset 

func (s String) IsSuperset(s2 String) bool

IsSuperset returns true if and only if s is a superset of s2.

func (String) Len 

func (s String) Len() int

Len returns the size of the set.

func (String) List 

func (s String) List() []string

List returns the contents as a sorted string slice.

func (String) PopAny 

func (s String) PopAny() (string, bool)

PopAny returns a single element from the set.

func (String) Union 

func (s String) Union(s2 String) String

Union returns a new set which includes items in either s or s2. For example: s = {a1, a2} s2 = {a3, a4} s.Union(s2) = {a1, a2, a3, a4} s2.Union(s) = {a1, a2, a3, a4}

func (String) UnsortedList 

func (s String) UnsortedList() []string

UnsortedList returns the slice with contents in random order.

Source Files

View all Source files

Jump to

Keyboard shortcuts

? : This menu
/ : Search site
f or F : Jump to
y or Y : Canonical URL
go.dev uses cookies from Google to deliver and enhance the quality of its services and to analyze traffic. Learn more.