errors

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

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

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

Retrieving the cause of an error

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

type causer interface {
        Cause() error
}

can be inspected by errorstack.Cause. errorstack.Cause will recursively retrieve the topmost error which does not implement causer, which is assumed to be the original cause. For example:

switch err := errorstack.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.

Formatted printing of errorstack

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() errorstack.StackTrace
}

Where errorstack.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 err, ok := err.(stackTracer); ok {
        for _, f := range err.StackTrace() {
                fmt.Printf("%+s:%d", f)
        }
}

stackTracer interface is not exported by this package, but is considered a part of stable public API.

See the documentation for Frame.Format for more details.

Index

• Variables
• func Cause(err error) error
• func Errorf(format string, args ...interface{}) error
• func New(message string) error
• func WithMessage(err error, message string) error
• func WithStack(err error) error
• func Wrap(err error, message string) error
• func Wrapf(err error, format string, args ...interface{}) error
• type Frame
  • func (f Frame) Format(s fmt.State, verb rune)
• type StackTrace
  • func (st StackTrace) Format(s fmt.State, verb rune)

Variables

var ErrorAddress = Errorf("The address is error")

var ErrorCodecNotReady = Errorf("The codec is not ready")

var ErrorDataIsDamage = Errorf("Data length is not match")

var ErrorDataNotEnough = Errorf("The length of the head data is not enough to be decoded")

var ErrorDataNotMatch = Errorf("Cannot match any packet format")

var ErrorDataNotReady = Errorf("Data length is not enough")

var ErrorDataSentIncomplete = Errorf("The data sent is incomplete")

var ErrorDataTooShort = Errorf("The length of the head data is too short")

var ErrorDecryptFunctionNotBind = Errorf("The packet is encrypted, but the decrypt function is not bind")

var ErrorPacketFormatNotReady = Errorf("The packet format is not ready")

var ErrorRemoteReqClose = Errorf("The remote host request close it")

var ErrorSessionIsNotExists = Errorf("The session is not exists")

var ErrorTypeNotSupported = Errorf("Type is not supported")

var ErrorUncompressFunctionNotBind = Errorf("The packet is compressed, but the uncompress function is not bind")

Functions

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 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 WithMessage

func WithMessage(err error, message string) error

WithMessage annotates err with a new message. If err is nil, WithMessage 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 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 call, and the format specifier. If err is nil, Wrapf returns nil.

Types

type Frame

type Frame uintptr

Frame represents a program counter inside a stack frame.

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

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.