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.
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.
Licence
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.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 errors.Wrap(err, "read failed")
}
If additional control is required the errors.WithStack and errors.WithMessage functions destructure errors.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 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 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.
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
}
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 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 ¶
- 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
- type StackTrace
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func Cause ¶
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 ¶
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 ¶
New returns an error with the supplied message. New also records the stack trace at the point it was called.
func WithMessage ¶
WithMessage annotates err with a new message. If err is nil, WithMessage returns nil.
func WithStack ¶
WithStack annotates err with a stack trace at the point WithStack was called. If err is nil, WithStack returns nil.
func Wrap ¶
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.
Types ¶
type Frame ¶
type Frame uintptr
Frame represents a program counter inside a stack frame.
func (Frame) Format ¶
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 path of source file relative to the compile time GOPATH %+v equivalent to %+s:%d
Source Files