133 lines
2.5 KiB
Go
133 lines
2.5 KiB
Go
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/* SPDX-License-Identifier: GPL-2.0
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*
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* Copyright (C) 2017-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
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*/
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package rwcancel
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import (
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"errors"
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"golang.org/x/sys/unix"
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"os"
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"runtime"
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"syscall"
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)
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type RWCancel struct {
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fd int
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closingReader *os.File
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closingWriter *os.File
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}
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type fdSet struct {
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fdset unix.FdSet
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}
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func (fdset *fdSet) set(i int) {
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bits := 32 << (^uint(0) >> 63)
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fdset.fdset.Bits[i/bits] |= 1 << uint(i%bits)
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}
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func (fdset *fdSet) check(i int) bool {
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bits := 32 << (^uint(0) >> 63)
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return (fdset.fdset.Bits[i/bits] & (1 << uint(i%bits))) != 0
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}
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func max(a, b int) int {
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if a > b {
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return a
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}
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return b
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}
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func NewRWCancel(fd int) (*RWCancel, error) {
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err := unix.SetNonblock(fd, true)
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if err != nil {
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return nil, err
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}
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rwcancel := RWCancel{fd: fd}
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rwcancel.closingReader, rwcancel.closingWriter, err = os.Pipe()
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if err != nil {
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return nil, err
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}
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runtime.SetFinalizer(&rwcancel, func(rw *RWCancel) {
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rw.Cancel()
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})
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return &rwcancel, nil
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}
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/* https://golang.org/src/crypto/rand/eagain.go */
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func ErrorIsEAGAIN(err error) bool {
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if pe, ok := err.(*os.PathError); ok {
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if errno, ok := pe.Err.(syscall.Errno); ok && errno == syscall.EAGAIN {
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return true
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}
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}
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if errno, ok := err.(syscall.Errno); ok && errno == syscall.EAGAIN {
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return true
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}
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return false
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}
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func (rw *RWCancel) ReadyRead() bool {
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closeFd := int(rw.closingReader.Fd())
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fdset := fdSet{}
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fdset.set(rw.fd)
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fdset.set(closeFd)
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_, err := unix.Select(max(rw.fd, closeFd)+1, &fdset.fdset, nil, nil, nil)
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if err != nil {
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return false
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}
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if fdset.check(closeFd) {
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return false
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}
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return fdset.check(rw.fd)
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}
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func (rw *RWCancel) ReadyWrite() bool {
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closeFd := int(rw.closingReader.Fd())
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fdset := fdSet{}
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fdset.set(rw.fd)
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fdset.set(closeFd)
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_, err := unix.Select(max(rw.fd, closeFd)+1, nil, &fdset.fdset, nil, nil)
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if err != nil {
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return false
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}
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if fdset.check(closeFd) {
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return false
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}
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return fdset.check(rw.fd)
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}
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func (rw *RWCancel) Read(p []byte) (n int, err error) {
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for {
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n, err := unix.Read(rw.fd, p)
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if err == nil || !ErrorIsEAGAIN(err) {
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return n, err
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}
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if !rw.ReadyRead() {
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return 0, errors.New("fd closed")
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}
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}
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}
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func (rw *RWCancel) Write(p []byte) (n int, err error) {
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for {
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n, err := unix.Write(rw.fd, p)
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if err == nil || !ErrorIsEAGAIN(err) {
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return n, err
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}
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if !rw.ReadyWrite() {
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return 0, errors.New("fd closed")
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}
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}
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}
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func (rw *RWCancel) Cancel() (err error) {
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_, err = rw.closingWriter.Write([]byte{0})
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return
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}
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