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{}) 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 BadRequestf(format string, args ...interface{}) error

BadRequestf returns an error which satisfies IsBadRequest().

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 Forbiddenf(format string, args ...interface{}) error

Forbiddenf returns an error which satistifes IsForbidden()

func IsAlreadyExists(err error) bool

IsAlreadyExists reports whether the error was created with AlreadyExistsf() or NewAlreadyExists().

func IsBadRequest(err error) bool

IsBadRequest reports whether err was created with BadRequestf() or NewBadRequest().

func IsForbidden(err error) bool

IsForbidden reports whether err was created with Forbiddenf() or NewForbidden().

func IsMethodNotAllowed(err error) bool

IsMethodNotAllowed reports whether err was created with MethodNotAllowedf() or NewMethodNotAllowed().

func IsNotAssigned(err error) bool

IsNotAssigned reports whether err was created with NotAssignedf() or NewNotAssigned().

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 IsNotProvisioned(err error) bool

IsNotProvisioned reports whether err was created with NotProvisionedf() or NewNotProvisioned().

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 IsUserNotFound(err error) bool

IsUserNotFound reports whether err was created with UserNotFoundf() or NewUserNotFound().

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 MethodNotAllowedf(format string, args ...interface{}) error

MethodNotAllowedf returns an error which satisfies IsMethodNotAllowed().

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(err error, msg string) error

NewAlreadyExists returns an error which wraps err and satisfies IsAlreadyExists().

func NewBadRequest(err error, msg string) error

NewBadRequest returns an error which wraps err that satisfies IsBadRequest().

func NewForbidden(err error, msg string) error

NewForbidden returns an error which wraps err that satisfies IsForbidden().

func NewMethodNotAllowed(err error, msg string) error

NewMethodNotAllowed returns an error which wraps err that satisfies IsMethodNotAllowed().

func NewNotAssigned(err error, msg string) error

NewNotAssigned returns an error which wraps err that satisfies IsNotAssigned().

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 NewNotProvisioned(err error, msg string) error

NewNotProvisioned returns an error which wraps err that satisfies IsNotProvisioned().

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 NewUserNotFound(err error, msg string) error

NewUserNotFound returns an error which wraps err and satisfies IsUserNotFound().

func NotAssignedf(format string, args ...interface{}) error

NotAssignedf returns an error which satisfies IsNotAssigned().

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 NotProvisionedf(format string, args ...interface{}) error

NotProvisionedf returns an error which satisfies IsNotProvisioned().

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 UserNotFoundf(format string, args ...interface{}) error

UserNotFoundf returns an error which satisfies IsUserNotFound().

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 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 (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) 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 (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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