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. 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
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 ¶
Constants ¶
This section is empty.
Variables ¶
var UnhandledErrCount int64
UnhandledErrCount keepds track of error counts formatting or displaying error value when the error return has no place to go
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 ConsolidateErrors ¶
ConsolidateErrors merges a slice of errors to a single MultiErr error
func Errorf ¶
Errorf formats according to a format specifier and returns the string as a value that satisfies error.
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
type StackTrace ¶
type StackTrace []Frame
StackTrace is stack of Frames from innermost (newest) to outermost (oldest).
Source Files