errors

README

errors

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

Index

• type Frame
  • func (f Frame) Format(s fmt.State, verb rune)
  • func (f Frame) MarshalText() ([]byte, error)
• type Stack
  • func Callers() *Stack
  • func (s *Stack) Format(st fmt.State, verb rune)
  • func (s *Stack) StackTrace() StackTrace
• type StackTrace
  • func (st StackTrace) Format(s fmt.State, verb rune)

Types

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 Stack

type Stack []uintptr

stack represents a stack of program counters.

func Callers

func Callers() *Stack

func (*Stack) Format

func (s *Stack) Format(st fmt.State, verb rune)

func (*Stack) StackTrace

func (s *Stack) StackTrace() StackTrace

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.