// The error built-in interface type is the conventional interface for
// representing an error condition, with the nil value representing no error.
type error interface {
    Error() string
}

package errors

// New returns an error that formats as the given text.
// Each call to New returns a distinct error value even if the text is identical.
func New(text string) error {
    return &errorString{text}
}

// errorString is a trivial implementation of error.
type errorString struct {
    s string
}

func (e *errorString) Error() string {
    return e.s
}

// ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer.
var ErrTooLarge = errors.New("bytes.Buffer: too large")
var errNegativeRead = errors.New("bytes.Buffer: reader returned negative count from Read")

func New(text string) error {
    return &errorString{text}
}

if err == ErrSomething {
    ...
}

// An Error represents a network error.
type Error interface {
    error
    Timeout() bool // Is the error a timeout?

    // Deprecated: Temporary errors are not well-defined.
    // Most "temporary" errors are timeouts, and the few exceptions are surprising.
    // Do not use this method.
    Temporary() bool
}

type timeout interface {
    Timeout() bool
}

func (e *OpError) Timeout() bool {
    if ne, ok := e.Err.(*os.SyscallError); ok {
        t, ok := ne.Err.(timeout)
        return ok && t.Timeout()
    }
    t, ok := e.Err.(timeout)
    return ok && t.Timeout()
}

type temporary interface {
    Temporary() bool
}

func (e *OpError) Temporary() bool {
    // Treat ECONNRESET and ECONNABORTED as temporary errors when
    // they come from calling accept. See issue 6163.
    if e.Op == "accept" && isConnError(e.Err) {
        return true
    }

    if ne, ok := e.Err.(*os.SyscallError); ok {
        t, ok := ne.Err.(temporary)
        return ok && t.Temporary()
    }
    t, ok := e.Err.(temporary)
    return ok && t.Temporary()
}

if ne, ok := err.(net.Error); ok && ne.Temporary() {
    if tempDelay == 0 {
        tempDelay = 5 * time.Millisecond
    } else {
        tempDelay *= 2
    }
    if max := 1 * time.Second; tempDelay > max {
        tempDelay = max
    }
    srv.logf("http: Accept error: %v; retrying in %v", err, tempDelay)
    time.Sleep(tempDelay)
    continue
}

func (s *Scanner) Scan() bool {
    if s.done {
        return false
    }
    s.scanCalled = true
    // Loop until we have a token.
    for {
        // See if we can get a token with what we already have.
        // If we've run out of data but have an error, give the split function
        // a chance to recover any remaining, possibly empty token.
        if s.end > s.start || s.err != nil {
            advance, token, err := s.split(s.buf[s.start:s.end], s.err != nil)
            if err != nil {
                if err == ErrFinalToken {
                    s.token = token
                    s.done = true
                    return true
                }
                s.setErr(err)
                return false
            }
            if !s.advance(advance) {
                return false
            }
            s.token = token
            if token != nil {
                if s.err == nil || advance > 0 {
                    s.empties = 0
                } else {
                    // Returning tokens not advancing input at EOF.
                    s.empties++
                    if s.empties > maxConsecutiveEmptyReads {
                        panic("bufio.Scan: too many empty tokens without progressing")
                    }
                }
                return true
            }
        }
        // We cannot generate a token with what we are holding.
        // If we've already hit EOF or an I/O error, we are done.
        if s.err != nil {
            // Shut it down.
            s.start = 0
            s.end = 0
            return false
        }
        // Must read more data.
        // First, shift data to beginning of buffer if there's lots of empty space
        // or space is needed.
        if s.start > 0 && (s.end == len(s.buf) || s.start > len(s.buf)/2) {
            copy(s.buf, s.buf[s.start:s.end])
            s.end -= s.start
            s.start = 0
        }
        // Is the buffer full? If so, resize.
        if s.end == len(s.buf) {
            // Guarantee no overflow in the multiplication below.
            const maxInt = int(^uint(0) >> 1)
            if len(s.buf) >= s.maxTokenSize || len(s.buf) > maxInt/2 {
                s.setErr(ErrTooLong)
                return false
            }
            newSize := len(s.buf) * 2
            if newSize == 0 {
                newSize = startBufSize
            }
            if newSize > s.maxTokenSize {
                newSize = s.maxTokenSize
            }
            newBuf := make([]byte, newSize)
            copy(newBuf, s.buf[s.start:s.end])
            s.buf = newBuf
            s.end -= s.start
            s.start = 0
        }
        // Finally we can read some input. Make sure we don't get stuck with
        // a misbehaving Reader. Officially we don't need to do this, but let's
        // be extra careful: Scanner is for safe, simple jobs.
        for loop := 0; ; {
            n, err := s.r.Read(s.buf[s.end:len(s.buf)])
            if n < 0 || len(s.buf)-s.end < n {
                s.setErr(ErrBadReadCount)
                break
            }
            s.end += n
            if err != nil {
                s.setErr(err)
                break
            }
            if n > 0 {
                s.empties = 0
                break
            }
            loop++
            if loop > maxConsecutiveEmptyReads {
                s.setErr(io.ErrNoProgress)
                break
            }
        }
    }
}

// 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 }

// Unwrap provides compatibility for Go 1.13 error chains.
func (w *withStack) Unwrap() 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 called, 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,
    }
}

// WithMessagef annotates err with the format specifier.
// If err is nil, WithMessagef returns nil.
func WithMessagef(err error, format string, args ...interface{}) error {
    if err == nil {
        return nil
    }
    return &withMessage{
        cause: err,
        msg:   fmt.Sprintf(format, args...),
    }
}

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 }

// Unwrap provides compatibility for Go 1.13 error chains.
func (w *withMessage) Unwrap() 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
}

// Is reports whether any error in err's chain matches target.
//
// The chain consists of err itself followed by the sequence of errors obtained by
// repeatedly calling Unwrap.
//
// An error is considered to match a target if it is equal to that target or if
// it implements a method Is(error) bool such that Is(target) returns true.
//
// An error type might provide an Is method so it can be treated as equivalent
// to an existing error. For example, if MyError defines
//
//    func (m MyError) Is(target error) bool { return target == fs.ErrExist }
//
// then Is(MyError{}, fs.ErrExist) returns true. See syscall.Errno.Is for
// an example in the standard library. An Is method should only shallowly
// compare err and the target and not call Unwrap on either.
func Is(err, target error) bool {
    if target == nil {
        return err == target
    }

    isComparable := reflectlite.TypeOf(target).Comparable()
    for {
        if isComparable && err == target {
            return true
        }
        if x, ok := err.(interface{ Is(error) bool }); ok && x.Is(target) {
            return true
        }
        // TODO: consider supporting target.Is(err). This would allow
        // user-definable predicates, but also may allow for coping with sloppy
        // APIs, thereby making it easier to get away with them.
        if err = Unwrap(err); err == nil {
            return false
        }
    }
}

// As finds the first error in err's chain that matches target, and if one is found, sets
// target to that error value and returns true. Otherwise, it returns false.
//
// The chain consists of err itself followed by the sequence of errors obtained by
// repeatedly calling Unwrap.
//
// An error matches target if the error's concrete value is assignable to the value
// pointed to by target, or if the error has a method As(interface{}) bool such that
// As(target) returns true. In the latter case, the As method is responsible for
// setting target.
//
// An error type might provide an As method so it can be treated as if it were a
// different error type.
//
// As panics if target is not a non-nil pointer to either a type that implements
// error, or to any interface type.
func As(err error, target any) bool {
    if target == nil {
        panic("errors: target cannot be nil")
    }
    val := reflectlite.ValueOf(target)
    typ := val.Type()
    if typ.Kind() != reflectlite.Ptr || val.IsNil() {
        panic("errors: target must be a non-nil pointer")
    }
    targetType := typ.Elem()
    if targetType.Kind() != reflectlite.Interface && !targetType.Implements(errorType) {
        panic("errors: *target must be interface or implement error")
    }
    for err != nil {
        if reflectlite.TypeOf(err).AssignableTo(targetType) {
            val.Elem().Set(reflectlite.ValueOf(err))
            return true
        }
        if x, ok := err.(interface{ As(any) bool }); ok && x.As(target) {
            return true
        }
        err = Unwrap(err)
    }
    return false
}

// Unwrap provides compatibility for Go 1.13 error chains.
func (w *withStack) Unwrap() error { return w.error }

// Is reports whether any error in err's chain matches target.
//
// The chain consists of err itself followed by the sequence of errors obtained by
// repeatedly calling Unwrap.
//
// An error is considered to match a target if it is equal to that target or if
// it implements a method Is(error) bool such that Is(target) returns true.
func Is(err, target error) bool { return stderrors.Is(err, target) }

// As finds the first error in err's chain that matches target, and if so, sets
// target to that error value and returns true.
//
// The chain consists of err itself followed by the sequence of errors obtained by
// repeatedly calling Unwrap.
//
// An error matches target if the error's concrete value is assignable to the value
// pointed to by target, or if the error has a method As(interface{}) bool such that
// As(target) returns true. In the latter case, the As method is responsible for
// setting target.
//
// As will panic if target is not a non-nil pointer to either a type that implements
// error, or to any interface type. As returns false if err is nil.
func As(err error, target interface{}) bool { return stderrors.As(err, target) }

// Unwrap returns the result of calling the Unwrap method on err, if err's
// type contains an Unwrap method returning error.
// Otherwise, Unwrap returns nil.
func Unwrap(err error) error {
    return stderrors.Unwrap(err)
}