Implement symlinks package

internal/symlinks/symlink_unix.go

@@ -0,0 +1,58 @@
+// Copyright (C) 2014 Jakob Borg and Contributors (see the CONTRIBUTORS file).
+//
+// This program is free software: you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by the Free
+// Software Foundation, either version 3 of the License, or (at your option)
+// any later version.
+//
+// This program is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+// more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program. If not, see <http://www.gnu.org/licenses/>.
+
+// +build !windows
+
+package symlinks
+
+import (
+	"os"
+
+	"github.com/syncthing/syncthing/internal/osutil"
+	"github.com/syncthing/syncthing/internal/protocol"
+)
+
+var (
+	Supported = true
+)
+
+func Read(path string) (string, uint32, error) {
+	var mode uint32
+	stat, err := os.Stat(path)
+	if err != nil {
+		mode = protocol.FlagSymlinkMissingTarget
+	} else if stat.IsDir() {
+		mode = protocol.FlagDirectory
+	}
+	path, err = os.Readlink(path)
+
+	return osutil.NormalizedFilename(path), mode, err
+}
+
+func IsSymlink(path string) (bool, error) {
+	lstat, err := os.Lstat(path)
+	if err != nil {
+		return false, err
+	}
+	return lstat.Mode()&os.ModeSymlink != 0, nil
+}
+
+func Create(source, target string, flags uint32) error {
+	return os.Symlink(osutil.NativeFilename(target), source)
+}
+
+func ChangeType(path string, flags uint32) error {
+	return nil
+}

internal/symlinks/symlink_windows.go

@@ -0,0 +1,203 @@
+// Copyright (C) 2014 Jakob Borg and Contributors (see the CONTRIBUTORS file).
+//
+// This program is free software: you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by the Free
+// Software Foundation, either version 3 of the License, or (at your option)
+// any later version.
+//
+// This program is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+// more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program. If not, see <http://www.gnu.org/licenses/>.
+
+// +build windows
+
+package symlinks
+
+import (
+	"os"
+	"path/filepath"
+
+	"github.com/syncthing/syncthing/internal/osutil"
+	"github.com/syncthing/syncthing/internal/protocol"
+
+	"syscall"
+	"unicode/utf16"
+	"unsafe"
+)
+
+const (
+	FSCTL_GET_REPARSE_POINT      = 0x900a8
+	FILE_FLAG_OPEN_REPARSE_POINT = 0x00200000
+	FILE_ATTRIBUTE_REPARSE_POINT = 0x400
+	IO_REPARSE_TAG_SYMLINK       = 0xA000000C
+	SYMBOLIC_LINK_FLAG_DIRECTORY = 0x1
+)
+
+var (
+	modkernel32            = syscall.NewLazyDLL("kernel32.dll")
+	procDeviceIoControl    = modkernel32.NewProc("DeviceIoControl")
+	procCreateSymbolicLink = modkernel32.NewProc("CreateSymbolicLinkW")
+
+	Supported = false
+)
+
+func init() {
+	// Needs administrator priviledges.
+	// Let's check that everything works.
+	// This could be done more officially:
+	// http://stackoverflow.com/questions/2094663/determine-if-windows-process-has-privilege-to-create-symbolic-link
+	// But I don't want to define 10 more structs just to look this up.
+	base := os.TempDir()
+	path := filepath.Join(base, "symlinktest")
+	defer os.Remove(path)
+
+	err := Create(path, base, protocol.FlagDirectory)
+	if err != nil {
+		return
+	}
+
+	isLink, err := IsSymlink(path)
+	if err != nil || !isLink {
+		return
+	}
+
+	target, flags, err := Read(path)
+	if err != nil || osutil.NativeFilename(target) != base || flags&protocol.FlagDirectory == 0 {
+		return
+	}
+	Supported = true
+}
+
+type reparseData struct {
+	reparseTag          uint32
+	reparseDataLength   uint16
+	reserved            uint16
+	substitueNameOffset uint16
+	substitueNameLength uint16
+	printNameOffset     uint16
+	printNameLength     uint16
+	flags               uint32
+	// substituteName - 264 widechars max = 528 bytes
+	// printName      - 260 widechars max = 520 bytes
+	//                                    = 1048 bytes total
+	buffer [1048]uint16
+}
+
+func (r *reparseData) PrintName() string {
+	// No clue why the offset and length is doubled...
+	offset := r.printNameOffset / 2
+	length := r.printNameLength / 2
+	return string(utf16.Decode(r.buffer[offset : offset+length]))
+}
+
+func (r *reparseData) SubstituteName() string {
+	// No clue why the offset and length is doubled...
+	offset := r.substitueNameOffset / 2
+	length := r.substitueNameLength / 2
+	return string(utf16.Decode(r.buffer[offset : offset+length]))
+}
+
+func Read(path string) (string, uint32, error) {
+	ptr, err := syscall.UTF16PtrFromString(path)
+	if err != nil {
+		return "", protocol.FlagSymlinkMissingTarget, err
+	}
+	handle, err := syscall.CreateFile(ptr, 0, syscall.FILE_SHARE_READ|syscall.FILE_SHARE_WRITE|syscall.FILE_SHARE_DELETE, nil, syscall.OPEN_EXISTING, syscall.FILE_FLAG_BACKUP_SEMANTICS|FILE_FLAG_OPEN_REPARSE_POINT, 0)
+	if err != nil || handle == syscall.InvalidHandle {
+		return "", protocol.FlagSymlinkMissingTarget, err
+	}
+	defer syscall.Close(handle)
+	var ret uint16
+	var data reparseData
+
+	r1, _, err := syscall.Syscall9(procDeviceIoControl.Addr(), 8, uintptr(handle), FSCTL_GET_REPARSE_POINT, 0, 0, uintptr(unsafe.Pointer(&data)), unsafe.Sizeof(data), uintptr(unsafe.Pointer(&ret)), 0, 0)
+	if r1 == 0 {
+		return "", protocol.FlagSymlinkMissingTarget, err
+	}
+
+	var flags uint32 = 0
+	attr, err := syscall.GetFileAttributes(ptr)
+	if err != nil {
+		flags = protocol.FlagSymlinkMissingTarget
+	} else if attr&syscall.FILE_ATTRIBUTE_DIRECTORY != 0 {
+		flags = protocol.FlagDirectory
+	}
+
+	return osutil.NormalizedFilename(data.PrintName()), flags, nil
+}
+
+func IsSymlink(path string) (bool, error) {
+	ptr, err := syscall.UTF16PtrFromString(path)
+	if err != nil {
+		return false, err
+	}
+
+	attr, err := syscall.GetFileAttributes(ptr)
+	if err != nil {
+		return false, err
+	}
+	return attr&FILE_ATTRIBUTE_REPARSE_POINT != 0, nil
+}
+
+func Create(source, target string, flags uint32) error {
+	srcp, err := syscall.UTF16PtrFromString(source)
+	if err != nil {
+		return err
+	}
+
+	trgp, err := syscall.UTF16PtrFromString(osutil.NativeFilename(target))
+	if err != nil {
+		return err
+	}
+
+	// Sadly for Windows we need to specify the type of the symlink,
+	// whether it's a directory symlink or a file symlink.
+	// If the flags doesn't reveal the target type, try to evaluate it
+	// ourselves, and worst case default to the symlink pointing to a file.
+	mode := 0
+	if flags&protocol.FlagSymlinkMissingTarget != 0 {
+		path := target
+		if !filepath.IsAbs(target) {
+			path = filepath.Join(filepath.Dir(source), target)
+		}
+
+		stat, err := os.Stat(path)
+		if err == nil && stat.IsDir() {
+			mode = SYMBOLIC_LINK_FLAG_DIRECTORY
+		}
+	} else if flags&protocol.FlagDirectory != 0 {
+		mode = SYMBOLIC_LINK_FLAG_DIRECTORY
+	}
+
+	r0, _, err := syscall.Syscall(procCreateSymbolicLink.Addr(), 3, uintptr(unsafe.Pointer(srcp)), uintptr(unsafe.Pointer(trgp)), uintptr(mode))
+	if r0 == 1 {
+		return nil
+	}
+	return err
+}
+
+func ChangeType(path string, flags uint32) error {
+	target, cflags, err := Read(path)
+	if err != nil {
+		return err
+	}
+	// If it's the same type, nothing to do.
+	if cflags&protocol.SymlinkTypeMask == flags&protocol.SymlinkTypeMask {
+		return nil
+	}
+
+	// If the actual type is unknown, but the new type is file, nothing to do
+	if cflags&protocol.FlagSymlinkMissingTarget != 0 && flags&protocol.FlagDirectory == 0 {
+		return nil
+	}
+	return osutil.InWritableDir(func(path string) error {
+		// It should be a symlink as well hence no need to change permissions on
+		// the file.
+		os.Remove(path)
+		return Create(path, target, flags)
+	}, path)
+}