# README
errors
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
func AlreadyExistsf(format string, args ...interface{}) error
AlreadyExistsf returns an error which satisfies IsAlreadyExists().
func Annotate
func Annotate(other error, message string) error
Annotate 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
func Annotatef(other error, format string, args ...interface{}) error
Annotatef 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
func BadRequestf(format string, args ...interface{}) error
BadRequestf returns an error which satisfies IsBadRequest().
func Cause
func Cause(err error) error
Cause 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
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
func Details(err error) string
Details 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
func ErrorStack(err error) string
ErrorStack 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
func Errorf(format string, args ...interface{}) error
Errorf 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
func Forbiddenf(format string, args ...interface{}) error
Forbiddenf returns an error which satistifes IsForbidden()
func IsAlreadyExists
func IsAlreadyExists(err error) bool
IsAlreadyExists reports whether the error was created with AlreadyExistsf() or NewAlreadyExists().
func IsBadRequest
func IsBadRequest(err error) bool
IsBadRequest reports whether err was created with BadRequestf() or NewBadRequest().
func IsForbidden
func IsForbidden(err error) bool
IsForbidden reports whether err was created with Forbiddenf() or NewForbidden().
func IsMethodNotAllowed
func IsMethodNotAllowed(err error) bool
IsMethodNotAllowed reports whether err was created with MethodNotAllowedf() or NewMethodNotAllowed().
func IsNotAssigned
func IsNotAssigned(err error) bool
IsNotAssigned reports whether err was created with NotAssignedf() or NewNotAssigned().
func IsNotFound
func IsNotFound(err error) bool
IsNotFound reports whether err was created with NotFoundf() or NewNotFound().
func IsNotImplemented
func IsNotImplemented(err error) bool
IsNotImplemented reports whether err was created with NotImplementedf() or NewNotImplemented().
func IsNotProvisioned
func IsNotProvisioned(err error) bool
IsNotProvisioned reports whether err was created with NotProvisionedf() or NewNotProvisioned().
func IsNotSupported
func IsNotSupported(err error) bool
IsNotSupported reports whether the error was created with NotSupportedf() or NewNotSupported().
func IsNotValid
func IsNotValid(err error) bool
IsNotValid reports whether the error was created with NotValidf() or NewNotValid().
func IsUnauthorized
func IsUnauthorized(err error) bool
IsUnauthorized reports whether err was created with Unauthorizedf() or NewUnauthorized().
func IsUserNotFound
func IsUserNotFound(err error) bool
IsUserNotFound reports whether err was created with UserNotFoundf() or NewUserNotFound().
func Mask
func Mask(other error) error
Mask hides the underlying error type, and records the location of the masking.
func Maskf
func Maskf(other error, format string, args ...interface{}) error
Mask 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
func MethodNotAllowedf(format string, args ...interface{}) error
MethodNotAllowedf returns an error which satisfies IsMethodNotAllowed().
func New
func New(message string) error
New 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
func NewAlreadyExists(err error, msg string) error
NewAlreadyExists returns an error which wraps err and satisfies IsAlreadyExists().
func NewBadRequest
func NewBadRequest(err error, msg string) error
NewBadRequest returns an error which wraps err that satisfies IsBadRequest().
func NewForbidden
func NewForbidden(err error, msg string) error
NewForbidden returns an error which wraps err that satisfies IsForbidden().
func NewMethodNotAllowed
func NewMethodNotAllowed(err error, msg string) error
NewMethodNotAllowed returns an error which wraps err that satisfies IsMethodNotAllowed().
func NewNotAssigned
func NewNotAssigned(err error, msg string) error
NewNotAssigned returns an error which wraps err that satisfies IsNotAssigned().
func NewNotFound
func NewNotFound(err error, msg string) error
NewNotFound returns an error which wraps err that satisfies IsNotFound().
func NewNotImplemented
func NewNotImplemented(err error, msg string) error
NewNotImplemented returns an error which wraps err and satisfies IsNotImplemented().
func NewNotProvisioned
func NewNotProvisioned(err error, msg string) error
NewNotProvisioned returns an error which wraps err that satisfies IsNotProvisioned().
func NewNotSupported
func NewNotSupported(err error, msg string) error
NewNotSupported returns an error which wraps err and satisfies IsNotSupported().
func NewNotValid
func NewNotValid(err error, msg string) error
NewNotValid returns an error which wraps err and satisfies IsNotValid().
func NewUnauthorized
func NewUnauthorized(err error, msg string) error
NewUnauthorized returns an error which wraps err and satisfies IsUnauthorized().
func NewUserNotFound
func NewUserNotFound(err error, msg string) error
NewUserNotFound returns an error which wraps err and satisfies IsUserNotFound().
func NotAssignedf
func NotAssignedf(format string, args ...interface{}) error
NotAssignedf returns an error which satisfies IsNotAssigned().
func NotFoundf
func NotFoundf(format string, args ...interface{}) error
NotFoundf returns an error which satisfies IsNotFound().
func NotImplementedf
func NotImplementedf(format string, args ...interface{}) error
NotImplementedf returns an error which satisfies IsNotImplemented().
func NotProvisionedf
func NotProvisionedf(format string, args ...interface{}) error
NotProvisionedf returns an error which satisfies IsNotProvisioned().
func NotSupportedf
func NotSupportedf(format string, args ...interface{}) error
NotSupportedf returns an error which satisfies IsNotSupported().
func NotValidf
func NotValidf(format string, args ...interface{}) error
NotValidf returns an error which satisfies IsNotValid().
func Trace
func Trace(other error) error
Trace adds the location of the Trace call to the stack. The Cause of the resulting error is the same as the error parameter. If the other error is nil, the result will be nil.
For example:
if err := SomeFunc(); err != nil {
return errors.Trace(err)
}
func Unauthorizedf
func Unauthorizedf(format string, args ...interface{}) error
Unauthorizedf returns an error which satisfies IsUnauthorized().
func UserNotFoundf
func UserNotFoundf(format string, args ...interface{}) error
UserNotFoundf returns an error which satisfies IsUserNotFound().
func Wrap
func Wrap(other, newDescriptive error) error
Wrap changes the Cause of the error. The location of the Wrap call is also stored in the error stack.
For example:
if err := SomeFunc(); err != nil {
newErr := &packageError{"more context", private_value}
return errors.Wrap(err, newErr)
}
func Wrapf
func Wrapf(other, newDescriptive error, format string, args ...interface{}) error
Wrapf changes the Cause of the error, and adds an annotation. The location of the Wrap call is also stored in the error stack.
For example:
if err := SomeFunc(); err != nil {
return errors.Wrapf(err, simpleErrorType, "invalid value %q", value)
}
type Err
type Err struct {
// contains filtered or unexported fields
}
Err holds a description of an error along with information about where the error was created.
It may be embedded in custom error types to add extra information that this errors package can understand.
func NewErr
func NewErr(format string, args ...interface{}) Err
NewErr is used to return an Err for the purpose of embedding in other structures. The location is not specified, and needs to be set with a call to SetLocation.
For example:
type FooError struct {
errors.Err
code int
}
func NewFooError(code int) error {
err := &FooError{errors.NewErr("foo"), code}
err.SetLocation(1)
return err
}
func NewErrWithCause
func NewErrWithCause(other error, format string, args ...interface{}) Err
NewErrWithCause is used to return an Err with cause by other error for the purpose of embedding in other structures. The location is not specified, and needs to be set with a call to SetLocation.
For example:
type FooError struct {
errors.Err
code int
}
func (e *FooError) Annotate(format string, args ...interface{}) error {
err := &FooError{errors.NewErrWithCause(e.Err, format, args...), e.code}
err.SetLocation(1)
return err
})
func (*Err) Cause
func (e *Err) Cause() error
The Cause of an error is the most recent error in the error stack that meets one of these criteria: the original error that was raised; the new error that was passed into the Wrap function; the most recently masked error; or nil if the error itself is considered the Cause. Normally this method is not invoked directly, but instead through the Cause stand alone function.
func (*Err) Error
func (e *Err) Error() string
Error implements error.Error.
func (*Err) Format
func (e *Err) Format(s fmt.State, verb rune)
Format implements fmt.Formatter When printing errors with %+v it also prints the stack trace. %#v unsurprisingly will print the real underlying type.
func (*Err) Location
func (e *Err) Location() (filename string, line int)
Location is the file and line of where the error was most recently created or annotated.
func (*Err) Message
func (e *Err) Message() string
Message returns the message stored with the most recent location. This is the empty string if the most recent call was Trace, or the message stored with Annotate or Mask.
func (*Err) SetLocation
func (e *Err) SetLocation(callDepth int)
SetLocation records the source location of the error at callDepth stack frames above the call.
func (*Err) StackTrace
func (e *Err) StackTrace() []string
StackTrace returns one string for each location recorded in the stack of errors. The first value is the originating error, with a line for each other annotation or tracing of the error.
func (*Err) Underlying
func (e *Err) Underlying() error
Underlying returns the previous error in the error stack, if any. A client
should not ever really call this method. It is used to build the error
stack and should not be introspected by client calls. Or more
specifically, clients should not depend on anything but the Cause of an
error.
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