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[bytom/vapor.git] / vendor / github.com / pkg / errors / errors.go

// Package errors provides simple error handling primitives.
//
// 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 by recording a stack trace at the point Wrap is called,
// and the supplied message. For example
//
//     _, err := ioutil.ReadAll(r)
//     if err != nil {
//             return errors.Wrap(err, "read failed")
//     }
//
// If additional control is required the errors.WithStack and errors.WithMessage
// functions destructure errors.Wrap into its component operations of annotating
// an error with a stack trace and an a message, respectively.
//
// 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 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
//     }
//
// causer interface is not exported by this package, but is considered a part
// of stable public API.
//
// Formatted printing of errors
//
// All error values returned from this package implement fmt.Formatter and can
// be formatted by the fmt package. The following verbs are supported
//
//     %s    print the error. If the error has a Cause it will be
//           printed recursively
//     %v    see %s
//     %+v   extended format. Each Frame of the error's StackTrace will
//           be printed in detail.
//
// Retrieving the stack trace of an error or wrapper
//
// New, Errorf, Wrap, and Wrapf record a stack trace at the point they are
// invoked. This information can be retrieved with the following interface.
//
//     type stackTracer interface {
//             StackTrace() errors.StackTrace
//     }
//
// Where errors.StackTrace is defined as
//
//     type StackTrace []Frame
//
// The Frame type represents a call site in the stack trace. Frame supports
// the fmt.Formatter interface that can be used for printing information about
// the stack trace of this error. For example:
//
//     if err, ok := err.(stackTracer); ok {
//             for _, f := range err.StackTrace() {
//                     fmt.Printf("%+s:%d", f)
//             }
//     }
//
// stackTracer interface is not exported by this package, but is considered a part
// of stable public API.
//
// See the documentation for Frame.Format for more details.
package errors

import (
        "fmt"
        "io"
)

// New returns an error with the supplied message.
// New also records the stack trace at the point it was called.
func New(message string) error {
        return &fundamental{
                msg:   message,
                stack: callers(),
        }
}

// Errorf formats according to a format specifier and returns the string
// as a value that satisfies error.
// Errorf also records the stack trace at the point it was called.
func Errorf(format string, args ...interface{}) error {
        return &fundamental{
                msg:   fmt.Sprintf(format, args...),
                stack: callers(),
        }
}

// fundamental is an error that has a message and a stack, but no caller.
type fundamental struct {
        msg string
        *stack
}

func (f *fundamental) Error() string { return f.msg }

func (f *fundamental) Format(s fmt.State, verb rune) {
        switch verb {
        case 'v':
                if s.Flag('+') {
                        io.WriteString(s, f.msg)
                        f.stack.Format(s, verb)
                        return
                }
                fallthrough
        case 's':
                io.WriteString(s, f.msg)
        case 'q':
                fmt.Fprintf(s, "%q", f.msg)
        }
}

// WithStack annotates err with a stack trace at the point WithStack was called.
// If err is nil, WithStack returns nil.
func WithStack(err error) error {
        if err == nil {
                return nil
        }
        return &withStack{
                err,
                callers(),
        }
}

type withStack struct {
        error
        *stack
}

func (w *withStack) Cause() error { return w.error }

func (w *withStack) Format(s fmt.State, verb rune) {
        switch verb {
        case 'v':
                if s.Flag('+') {
                        fmt.Fprintf(s, "%+v", w.Cause())
                        w.stack.Format(s, verb)
                        return
                }
                fallthrough
        case 's':
                io.WriteString(s, w.Error())
        case 'q':
                fmt.Fprintf(s, "%q", w.Error())
        }
}

// Wrap returns an error annotating err with a stack trace
// at the point Wrap is called, and the supplied message.
// If err is nil, Wrap returns nil.
func Wrap(err error, message string) error {
        if err == nil {
                return nil
        }
        err = &withMessage{
                cause: err,
                msg:   message,
        }
        return &withStack{
                err,
                callers(),
        }
}

// Wrapf returns an error annotating err with a stack trace
// at the point Wrapf is call, and the format specifier.
// If err is nil, Wrapf returns nil.
func Wrapf(err error, format string, args ...interface{}) error {
        if err == nil {
                return nil
        }
        err = &withMessage{
                cause: err,
                msg:   fmt.Sprintf(format, args...),
        }
        return &withStack{
                err,
                callers(),
        }
}

// WithMessage annotates err with a new message.
// If err is nil, WithMessage returns nil.
func WithMessage(err error, message string) error {
        if err == nil {
                return nil
        }
        return &withMessage{
                cause: err,
                msg:   message,
        }
}

type withMessage struct {
        cause error
        msg   string
}

func (w *withMessage) Error() string { return w.msg + ": " + w.cause.Error() }
func (w *withMessage) Cause() error  { return w.cause }

func (w *withMessage) Format(s fmt.State, verb rune) {
        switch verb {
        case 'v':
                if s.Flag('+') {
                        fmt.Fprintf(s, "%+v\n", w.Cause())
                        io.WriteString(s, w.msg)
                        return
                }
                fallthrough
        case 's', 'q':
                io.WriteString(s, w.Error())
        }
}

// 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.
func Cause(err error) error {
        type causer interface {
                Cause() error
        }

        for err != nil {
                cause, ok := err.(causer)
                if !ok {
                        break
                }
                err = cause.Cause()
        }
        return err
}