redirfd_unix.go

// +build !windows

/*
Copyright 2015 The Kubernetes Authors All rights reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package redirfd

import (
	"fmt"
	"os"
	"syscall"
)

type RedirectMode int

const (
	Read           RedirectMode = iota // open file for reading
	Write                              // open file for writing, truncating if it exists
	Update                             // open file for read & write
	Append                             // open file for append, create if it does not exist
	AppendExisting                     // open file for append, do not create if it does not already exist
	WriteNew                           // open file for writing, creating it, failing if it already exists
)

// see https://github.com/skarnet/execline/blob/master/src/execline/redirfd.c
func (mode RedirectMode) Redirect(nonblock, changemode bool, fd FileDescriptor, name string) (*os.File, error) {
	flags := 0
	what := -1

	switch mode {
	case Read:
		what = syscall.O_RDONLY
		flags &= ^(syscall.O_APPEND | syscall.O_CREAT | syscall.O_TRUNC | syscall.O_EXCL)
	case Write:
		what = syscall.O_WRONLY
		flags |= syscall.O_CREAT | syscall.O_TRUNC
		flags &= ^(syscall.O_APPEND | syscall.O_EXCL)
	case Update:
		what = syscall.O_RDWR
		flags &= ^(syscall.O_APPEND | syscall.O_CREAT | syscall.O_TRUNC | syscall.O_EXCL)
	case Append:
		what = syscall.O_WRONLY
		flags |= syscall.O_CREAT | syscall.O_APPEND
		flags &= ^(syscall.O_TRUNC | syscall.O_EXCL)
	case AppendExisting:
		what = syscall.O_WRONLY
		flags |= syscall.O_APPEND
		flags &= ^(syscall.O_CREAT | syscall.O_TRUNC | syscall.O_EXCL)
	case WriteNew:
		what = syscall.O_WRONLY
		flags |= syscall.O_CREAT | syscall.O_EXCL
		flags &= ^(syscall.O_APPEND | syscall.O_TRUNC)
	default:
		return nil, fmt.Errorf("unexpected mode %d", mode)
	}
	if nonblock {
		flags |= syscall.O_NONBLOCK
	}
	flags |= what

	fd2, e := open(name, flags, 0666)
	if (what == syscall.O_WRONLY) && (e == syscall.ENXIO) {
		// Opens file in read-only, non-blocking mode. Returns a valid fd number if it succeeds, or -1 (and sets errno) if it fails.
		fdr, e2 := open(name, syscall.O_RDONLY|syscall.O_NONBLOCK, 0)
		if e2 != nil {
			return nil, &os.PathError{Op: "open_read", Path: name, Err: e2}
		}
		fd2, e = open(name, flags, 0666)
		fd_close(fdr)
	}
	if e != nil {
		return nil, &os.PathError{Op: "open", Path: name, Err: e}
	}
	if e = fd_move(fd, fd2); e != nil {
		return nil, &os.PathError{Op: "fd_move", Path: name, Err: e}
	}
	if changemode {
		if nonblock {
			e = ndelay_off(fd)
		} else {
			e = ndelay_on(fd)
		}
		if e != nil {
			return nil, &os.PathError{Op: "ndelay", Path: name, Err: e}
		}
	}
	return os.NewFile(uintptr(fd2), name), nil
}

// proxy to return a FileDescriptor
func open(path string, openmode int, perm uint32) (FileDescriptor, error) {
	fdint, err := syscall.Open(path, openmode, perm)
	return FileDescriptor(fdint), err
}

// see https://github.com/skarnet/skalibs/blob/master/src/libstddjb/fd_move.c
func fd_move(to, from FileDescriptor) (err error) {
	if to == from {
		return
	}
	for {
		_, _, e1 := syscall.RawSyscall(syscall.SYS_DUP2, uintptr(from), uintptr(to), 0)
		if e1 != syscall.EINTR {
			if e1 != 0 {
				err = e1
			}
			break
		}
	}
	if err != nil {
		err = fd_close(from)
	}
	return
	/*
	   do
	     r = dup2(from, to) ;
	   while ((r == -1) && (errno == EINTR)) ;
	   return (r == -1) ? -1 : fd_close(from) ;
	*/
}

// see https://github.com/skarnet/skalibs/blob/master/src/libstddjb/fd_close.c
func fd_close(fd FileDescriptor) (err error) {
	i := 0
	var e error
	for {
		if e = syscall.Close(int(fd)); e != nil {
			return nil
		}
		i++
		if e != syscall.EINTR {
			break
		}
	}
	if e == syscall.EBADF && i > 1 {
		return nil
	}
	return e
}

/*
int fd_close (int fd)
{
  register unsigned int i = 0 ;
doit:
  if (!close(fd)) return 0 ;
  i++ ;
  if (errno == EINTR) goto doit ;
  return ((errno == EBADF) && (i > 1)) ? 0 : -1 ;
}
*/

// see https://github.com/skarnet/skalibs/blob/master/src/libstddjb/ndelay_on.c
func ndelay_on(fd FileDescriptor) error {
	// 32-bit will likely break because it needs SYS_FCNTL64
	got, _, e := syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), uintptr(syscall.F_GETFL), 0)
	if e != 0 {
		return e
	}
	_, _, e = syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), uintptr(syscall.F_SETFL), uintptr(got|syscall.O_NONBLOCK))
	if e != 0 {
		return e
	}
	return nil
}

/*
int ndelay_on (int fd)
{
  register int got = fcntl(fd, F_GETFL) ;
  return (got == -1) ? -1 : fcntl(fd, F_SETFL, got | O_NONBLOCK) ;
}
*/

// see https://github.com/skarnet/skalibs/blob/master/src/libstddjb/ndelay_off.c
func ndelay_off(fd FileDescriptor) error {
	// 32-bit will likely break because it needs SYS_FCNTL64
	got, _, e := syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), uintptr(syscall.F_GETFL), 0)
	if e != 0 {
		return e
	}
	_, _, e = syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), uintptr(syscall.F_SETFL), uintptr(int(got) & ^syscall.O_NONBLOCK))
	if e != 0 {
		return e
	}
	return nil
}

/*
int ndelay_off (int fd)
{
  register int got = fcntl(fd, F_GETFL) ;
  return (got == -1) ? -1 : fcntl(fd, F_SETFL, got & ^O_NONBLOCK) ;
}
*/