import "github.com/juju/errors"
The juju/errors provides an easy way to annotate errors without losing the original error context.
The exported New and Errorf functions are designed to replace the
errors.New and fmt.Errorf functions respectively. The same underlying
error is there, but the package also records the location at which the error
was created.
A primary use case for this library is to add extra context any time an error is returned from a function.
if err := SomeFunc(); err != nil {
return err
}
This instead becomes:
if err := SomeFunc(); err != nil {
return errors.Trace(err)
}
which just records the file and line number of the Trace call, or
if err := SomeFunc(); err != nil {
return errors.Annotate(err, "more context")
}
which also adds an annotation to the error.
When you want to check to see if an error is of a particular type, a helper
function is normally exported by the package that returned the error, like the
os package does. The underlying cause of the error is available using the
Cause function.
os.IsNotExist(errors.Cause(err))
The result of the Error() call on an annotated error is the annotations joined
with colons, then the result of the Error() method for the underlying error
that was the cause.
err := errors.Errorf("original")
err = errors.Annotatef(err, "context")
err = errors.Annotatef(err, "more context")
err.Error() -> "more context: context: original"
Obviously recording the file, line and functions is not very useful if you cannot get them back out again.
errors.ErrorStack(err)
will return something like:
first error
github.com/juju/errors/annotation_test.go:193:
github.com/juju/errors/annotation_test.go:194: annotation
github.com/juju/errors/annotation_test.go:195:
github.com/juju/errors/annotation_test.go:196: more context
github.com/juju/errors/annotation_test.go:197:
The first error was generated by an external system, so there was no location associated. The second, fourth, and last lines were generated with Trace calls, and the other two through Annotate.
Sometimes when responding to an error you want to return a more specific error for the situation.
if err := FindField(field); err != nil {
return errors.Wrap(err, errors.NotFoundf(field))
}
This returns an error where the complete error stack is still available, and
errors.Cause() will return the NotFound error.
func AlreadyExistsf(format string, args ...interface{}) errorAlreadyExistsf returns an error which satisfies IsAlreadyExists().
func Annotate(other error, message string) errorAnnotate is used to add extra context to an existing error. The location of the Annotate call is recorded with the annotations. The file, line and function are also recorded.
For example:
if err := SomeFunc(); err != nil {
return errors.Annotate(err, "failed to frombulate")
}
func Annotatef(other error, format string, args ...interface{}) errorAnnotatef is used to add extra context to an existing error. The location of the Annotate call is recorded with the annotations. The file, line and function are also recorded.
For example:
if err := SomeFunc(); err != nil {
return errors.Annotatef(err, "failed to frombulate the %s", arg)
}
func BadRequestf(format string, args ...interface{}) errorBadRequestf returns an error which satisfies IsBadRequest().
func Cause(err error) errorCause returns the cause of the given error. This will be either the original error, or the result of a Wrap or Mask call.
Cause is the usual way to diagnose errors that may have been wrapped by the other errors functions.
func DeferredAnnotatef(err *error, format string, args ...interface{})DeferredAnnotatef annotates the given error (when it is not nil) with the given format string and arguments (like fmt.Sprintf). If *err is nil, DeferredAnnotatef does nothing. This method is used in a defer statement in order to annotate any resulting error with the same message.
For example:
defer DeferredAnnotatef(&err, "failed to frombulate the %s", arg)
func Details(err error) stringDetails returns information about the stack of errors wrapped by err, in the format:
[{filename:99: error one} {otherfile:55: cause of error one}]
This is a terse alternative to ErrorStack as it returns a single line.
func ErrorStack(err error) stringErrorStack returns a string representation of the annotated error. If the error passed as the parameter is not an annotated error, the result is simply the result of the Error() method on that error.
If the error is an annotated error, a multi-line string is returned where each line represents one entry in the annotation stack. The full filename from the call stack is used in the output.
first error
github.com/juju/errors/annotation_test.go:193:
github.com/juju/errors/annotation_test.go:194: annotation
github.com/juju/errors/annotation_test.go:195:
github.com/juju/errors/annotation_test.go:196: more context
github.com/juju/errors/annotation_test.go:197:
func Errorf(format string, args ...interface{}) errorErrorf creates a new annotated error and records the location that the error is created. This should be a drop in replacement for fmt.Errorf.
For example:
return errors.Errorf("validation failed: %s", message)
func Forbiddenf(format string, args ...interface{}) errorForbiddenf returns an error which satistifes IsForbidden()
func IsAlreadyExists(err error) boolIsAlreadyExists reports whether the error was created with AlreadyExistsf() or NewAlreadyExists().
func IsBadRequest(err error) boolIsBadRequest reports whether err was created with BadRequestf() or NewBadRequest().
func IsForbidden(err error) boolIsForbidden reports whether err was created with Forbiddenf() or NewForbidden().
func IsMethodNotAllowed(err error) boolIsMethodNotAllowed reports whether err was created with MethodNotAllowedf() or NewMethodNotAllowed().
func IsNotAssigned(err error) boolIsNotAssigned reports whether err was created with NotAssignedf() or NewNotAssigned().
func IsNotFound(err error) boolIsNotFound reports whether err was created with NotFoundf() or NewNotFound().
func IsNotImplemented(err error) boolIsNotImplemented reports whether err was created with NotImplementedf() or NewNotImplemented().
func IsNotProvisioned(err error) boolIsNotProvisioned reports whether err was created with NotProvisionedf() or NewNotProvisioned().
func IsNotSupported(err error) boolIsNotSupported reports whether the error was created with NotSupportedf() or NewNotSupported().
func IsNotValid(err error) boolIsNotValid reports whether the error was created with NotValidf() or NewNotValid().
func IsUnauthorized(err error) boolIsUnauthorized reports whether err was created with Unauthorizedf() or NewUnauthorized().
func IsUserNotFound(err error) boolIsUserNotFound reports whether err was created with UserNotFoundf() or NewUserNotFound().
func Mask(other error) errorMask hides the underlying error type, and records the location of the masking.
func Maskf(other error, format string, args ...interface{}) errorMask masks the given error with the given format string and arguments (like fmt.Sprintf), returning a new error that maintains the error stack, but hides the underlying error type. The error string still contains the full annotations. If you want to hide the annotations, call Wrap.
func MethodNotAllowedf(format string, args ...interface{}) errorMethodNotAllowedf returns an error which satisfies IsMethodNotAllowed().
func New(message string) errorNew is a drop in replacement for the standard library errors module that records the location that the error is created.
For example:
return errors.New("validation failed")
func NewAlreadyExists(err error, msg string) errorNewAlreadyExists returns an error which wraps err and satisfies IsAlreadyExists().
func NewBadRequest(err error, msg string) errorNewBadRequest returns an error which wraps err that satisfies IsBadRequest().
func NewForbidden(err error, msg string) errorNewForbidden returns an error which wraps err that satisfies IsForbidden().
func NewMethodNotAllowed(err error, msg string) errorNewMethodNotAllowed returns an error which wraps err that satisfies IsMethodNotAllowed().
func NewNotAssigned(err error, msg string) errorNewNotAssigned returns an error which wraps err that satisfies IsNotAssigned().
func NewNotFound(err error, msg string) errorNewNotFound returns an error which wraps err that satisfies IsNotFound().
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