// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package poll supports non-blocking I/O on file descriptors with polling.
// This supports I/O operations that block only a goroutine, not a thread.
// This is used by the net and os packages.
// It uses a poller built into the runtime, with support from the
// runtime scheduler.
package poll

import (
	"errors"
)

// errNetClosing is the type of the variable ErrNetClosing.
// This is used to implement the net.Error interface.
type errNetClosing struct{}

// Error returns the error message for ErrNetClosing.
// Keep this string consistent because of issue #4373:
// since historically programs have not been able to detect
// this error, they look for the string.
func (e errNetClosing) Error() string { return "use of closed network connection" }

func (e errNetClosing) Timeout() bool   { return false }
func (e errNetClosing) Temporary() bool { return false }

// ErrNetClosing is returned when a network descriptor is used after
// it has been closed.
var ErrNetClosing = errNetClosing{}

// ErrFileClosing is returned when a file descriptor is used after it
// has been closed.
var ErrFileClosing = errors.New("use of closed file")

// ErrNoDeadline is returned when a request is made to set a deadline
// on a file type that does not use the poller.
var ErrNoDeadline = errors.New("file type does not support deadline")

// Return the appropriate closing error based on isFile.
func errClosing(isFile bool) error {
	if isFile {
		return ErrFileClosing
	}
	return ErrNetClosing
}

// ErrDeadlineExceeded is returned for an expired deadline.
// This is exported by the os package as os.ErrDeadlineExceeded.
var ErrDeadlineExceeded error = &DeadlineExceededError{}

// DeadlineExceededError is returned for an expired deadline.
type DeadlineExceededError struct{}

// Implement the net.Error interface.
// The string is "i/o timeout" because that is what was returned
// by earlier Go versions. Changing it may break programs that
// match on error strings.
func (e *DeadlineExceededError) Error() string   { return "i/o timeout" }
func (e *DeadlineExceededError) Timeout() bool   { return true }
func (e *DeadlineExceededError) Temporary() bool { return true }

// ErrNotPollable is returned when the file or socket is not suitable
// for event notification.
var ErrNotPollable = errors.New("not pollable")

// consume removes data from a slice of byte slices, for writev.
func consume(v *[][]byte, n int64) {
	for len(*v) > 0 {
		ln0 := int64(len((*v)[0]))
		if ln0 > n {
			(*v)[0] = (*v)[0][n:]
			return
		}
		n -= ln0
		(*v)[0] = nil
		*v = (*v)[1:]
	}
}

// TestHookDidWritev is a hook for testing writev.
var TestHookDidWritev = func(wrote int) {}

// String is an internal string definition for methods/functions
// that is not intended for use outside the standard libraries.
//
// Other packages in std that import internal/poll and have some
// exported APIs (now we've got some in net.rawConn) which are only used
// internally and are not intended to be used outside the standard libraries,
// Therefore, we make those APIs use internal types like poll.FD or poll.String
// in their function signatures to disable the usability of these APIs from
// external codebase.
type String string