import "github.com/juju/errors"
The juju/errors provides an easy way to annotate errors without losing the
orginal 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{}) error
AlreadyExistsf returns an error which satisfies IsAlreadyExists().
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(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 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(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) 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(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(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 IsAlreadyExists(err error) bool
IsAlreadyExists reports whether the error was created with
AlreadyExistsf() or NewAlreadyExists().
func IsNotFound(err error) bool
IsNotFound reports whether err was created with NotFoundf() or
NewNotFound().
func IsNotImplemented(err error) bool
IsNotImplemented reports whether err was created with
NotImplementedf() or NewNotImplemented().
func IsNotSupported(err error) bool
IsNotSupported reports whether the error was created with
NotSupportedf() or NewNotSupported().
func IsNotValid(err error) bool
IsNotValid reports whether the error was created with NotValidf() or
NewNotValid().
func IsUnauthorized(err error) bool
IsUnauthorized reports whether err was created with Unauthorizedf() or
NewUnauthorized().
func Mask(other error) error
Mask hides the underlying error type, and records the location of the masking.
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 New(message string) error
New is a drop in replacement for the standard libary errors module that records
the location that the error is created.
For example:
return errors.New("validation failed")
func NewAlreadyExists(err error, msg string) error
NewAlreadyExists returns an error which wraps err and satisfies
IsAlreadyExists().
func NewNotFound(err error, msg string) error
NewNotFound returns an error which wraps err that satisfies
IsNotFound().
func NewNotImplemented(err error, msg string) error
NewNotImplemented returns an error which wraps err and satisfies
IsNotImplemented().
func NewNotSupported(err error, msg string) error
NewNotSupported returns an error which wraps err and satisfies
IsNotSupported().
func NewNotValid(err error, msg string) error
NewNotValid returns an error which wraps err and satisfies IsNotValid().
func NewUnauthorized(err error, msg string) error
NewUnauthorized returns an error which wraps err and satisfies
IsUnauthorized().
func NotFoundf(format string, args ...interface{}) error
NotFoundf returns an error which satisfies IsNotFound().
func NotImplementedf(format string, args ...interface{}) error
NotImplementedf returns an error which satisfies IsNotImplemented().
func NotSupportedf(format string, args ...interface{}) error
NotSupportedf returns an error which satisfies IsNotSupported().
func NotValidf(format string, args ...interface{}) error
NotValidf returns an error which satisfies IsNotValid().
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(format string, args ...interface{}) error
Unauthorizedf returns an error which satisfies IsUnauthorized().
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(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 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(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 (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 (e *Err) Error() string
Error implements error.Error.
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 (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 (e *Err) SetLocation(callDepth int)
SetLocation records the source location of the error at callDepth stack
frames above the call.
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 (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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