README
¶
errors 
Package errors implements functions for manipulating 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")
}
In addition, errors.Wrap records the file and line where it was called, allowing the programmer to retrieve the path to the original error.
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 recurse 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
}
Would you like to know more? Read the blog post.
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
MIT
Documentation
¶
Overview ¶
Package errors implements functions for manipulating 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")
}
In addition, errors.Wrap records the file and line where it was called, allowing the programmer to retrieve the path to the original error.
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 nor 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
}
Index ¶
Examples ¶
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.
Example ¶
package main
import (
"fmt"
"github.com/pkg/errors"
)
func fn() error {
e1 := errors.New("error")
e2 := errors.Wrap(e1, "inner")
e3 := errors.Wrap(e2, "middle")
return errors.Wrap(e3, "outer")
}
func main() {
err := fn()
fmt.Println(err)
fmt.Println(errors.Cause(err))
}
Output: outer: middle: inner: error error
func Errorf ¶ added in v0.3.0
Errorf formats according to a format specifier and returns the string as a value that satisfies error.
Example ¶
package main
import (
"os"
"github.com/pkg/errors"
)
func main() {
err := errors.Errorf("whoops: %s", "foo")
errors.Fprint(os.Stdout, err)
}
Output: github.com/pkg/errors/example_test.go:67: whoops: foo
func Fprint ¶
Fprint prints the error to the supplied writer. The format of the output is the same as Print. If err is nil, nothing is printed.
Example ¶
package main
import (
"os"
"github.com/pkg/errors"
)
func fn() error {
e1 := errors.New("error")
e2 := errors.Wrap(e1, "inner")
e3 := errors.Wrap(e2, "middle")
return errors.Wrap(e3, "outer")
}
func main() {
err := fn()
errors.Fprint(os.Stdout, err)
}
Output: github.com/pkg/errors/example_test.go:36: outer github.com/pkg/errors/example_test.go:35: middle github.com/pkg/errors/example_test.go:34: inner github.com/pkg/errors/example_test.go:33: error
func New ¶
New returns an error that formats as the given text.
Example ¶
package main
import (
"fmt"
"github.com/pkg/errors"
)
func main() {
err := errors.New("whoops")
fmt.Println(err)
}
Output: whoops
Example (Fprint) ¶
package main
import (
"os"
"github.com/pkg/errors"
)
func main() {
err := errors.New("whoops")
errors.Fprint(os.Stdout, err)
}
Output: github.com/pkg/errors/example_test.go:18: whoops
func Print ¶
func Print(err error)
Print prints the error to Stderr. If the error implements the Causer interface described in Cause Print will recurse into the error's cause. If the error implements the inteface:
type Location interface {
Location() (file string, line int)
}
Print will also print the file and line of the error.
func Wrap ¶
Wrap returns an error annotating the cause with message. If cause is nil, Wrap returns nil.
Example ¶
package main
import (
"fmt"
"github.com/pkg/errors"
)
func main() {
cause := errors.New("whoops")
err := errors.Wrap(cause, "oh noes")
fmt.Println(err)
}
Output: oh noes: whoops
func Wrapf ¶ added in v0.2.0
Wrapf returns an error annotating the cause with the format specifier. If cause is nil, Wrapf returns nil.
Example ¶
package main
import (
"fmt"
"github.com/pkg/errors"
)
func main() {
cause := errors.New("whoops")
err := errors.Wrapf(cause, "oh noes #%d", 2)
fmt.Println(err)
}
Output: oh noes #2: whoops
Types ¶
This section is empty.
Source Files