// is already closed. This method is on File so that we can incorporate
// a nil test.
func (f *File) incref(op string) (err error) {
	if f == nil {
		return ErrInvalid
	}
	if !f.fdmu.Incref() {
		err = ErrClosed
		if op != "" {
			err = &PathError{Op: op, Path: f.name, Err: err}
		}
	}
	return err
}

// decref removes a reference to the file. If this is the last

		return fmt.Errorf("error string %q does not contain expected string %q", nestedErr, want)
	}

	if !isShutdown && !errors.Is(nestedErr, ErrClosed) {
		return fmt.Errorf("errors.Is(%v, errClosed) returns false, want true", nestedErr)
	}

	switch err := nestedErr.(type) {
	case *OpError:
		if err := err.isValid(); err != nil {
			return err
		}
		nestedErr = err.Err

	// Deprecated: No longer used.
	ErrClosed = &http.ProtocolError{ErrorString: "connection closed by user"}

	// Deprecated: No longer used.
	ErrPipeline = &http.ProtocolError{ErrorString: "pipeline error"}
)

// This is an API usage error - the local side is closed.
// ErrPersistEOF (above) reports that the remote side is closed.
var errClosed = errors.New("i/o operation on closed connection")

package network

import (
	"errors"
	"net"
	"net/http"
)

func IsUnexpectedListenerError(err error) bool {
	if err == nil {
		return false
	}
	if errors.Is(err, net.ErrClosed) {
		return false
	}
	if errors.Is(err, http.ErrServerClosed) {
		return false
	}
	return true

	ErrClosed     = errClosed()     // "file already closed"
)

func errInvalid() error    { return oserror.ErrInvalid }
func errPermission() error { return oserror.ErrPermission }
func errExist() error      { return oserror.ErrExist }
func errNotExist() error   { return oserror.ErrNotExist }
func errClosed() error     { return oserror.ErrClosed }

// w's underlying writer.
func (w *Writer) Close() error {
	if w.err != nil {
		if w.err == errClosed {
			return nil
		}
		return w.err
	}
	// Make any future calls to Write return errClosed.
	w.err = errClosed
	// Write the savedCode if valid.
	if w.savedCode != invalidCode {
		if err := w.write(w, w.savedCode); err != nil {
			return err
		}

	}
	if err := f.Close(); err != nil {
		t.Fatal(err)
	}
	_, err = f.Stat()
	if err == nil {
		t.Error("Stat succeeded on closed File")
	} else if !errors.Is(err, os.ErrClosed) {
		t.Errorf("error from Stat on closed file did not match ErrClosed: %q, type %T", err, err)
	}

import "errors"

var (
	ErrInvalid    = errors.New("invalid argument")
	ErrPermission = errors.New("permission denied")
	ErrExist      = errors.New("file already exists")
	ErrNotExist   = errors.New("file does not exist")
	ErrClosed     = errors.New("file already closed")

	ErrPermission = fs.ErrPermission // "permission denied"
	ErrExist      = fs.ErrExist      // "file already exists"
	ErrNotExist   = fs.ErrNotExist   // "file does not exist"
	ErrClosed     = fs.ErrClosed     // "file already closed"

	ErrNoDeadline       = errNoDeadline()       // "file type does not support deadline"
	ErrDeadlineExceeded = errDeadlineExceeded() // "i/o timeout"
)

	{&fs.PathError{Err: fs.ErrNotExist}, false, true},
	{&fs.PathError{Err: fs.ErrClosed}, false, false},
	{&os.LinkError{Err: fs.ErrInvalid}, false, false},
	{&os.LinkError{Err: fs.ErrPermission}, false, false},
	{&os.LinkError{Err: fs.ErrExist}, true, false},
	{&os.LinkError{Err: fs.ErrNotExist}, false, true},
	{&os.LinkError{Err: fs.ErrClosed}, false, false},
	{&os.SyscallError{Err: fs.ErrNotExist}, false, true},