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