lib/model: Handle filename conflicts on Windows.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3810
LGTM: calmh

lib/osutil/name_conflict.go

@@ -0,0 +1,17 @@
+// Copyright (C) 2016 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+// +build !windows
+
+package osutil
+
+// CheckNameConflict returns true if every path component of name up to and
+// including filepath.Join(base, name) doesn't conflict with any existing
+// files or folders with different names. Base and name must both be clean and
+// name must be relative to base.
+func CheckNameConflict(base, name string) bool {
+	return true
+}

lib/osutil/name_conflict_windows.go

@@ -0,0 +1,48 @@
+// Copyright (C) 2016 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+// +build windows
+
+package osutil
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"syscall"
+)
+
+// CheckNameConflict returns true if every path component of name up to and
+// including filepath.Join(base, name) doesn't conflict with any existing
+// files or folders with different names. Base and name must both be clean and
+// name must be relative to base.
+func CheckNameConflict(base, name string) bool {
+	// Conflicts can be caused by different casing (e.g. foo and FOO) or
+	// by the use of short names (e.g. foo.barbaz and FOO~1.BAR).
+	path := base
+	parts := strings.Split(name, string(os.PathSeparator))
+	for _, part := range parts {
+		path = filepath.Join(path, part)
+		pathp, err := syscall.UTF16PtrFromString(path)
+		if err != nil {
+			return false
+		}
+		var data syscall.Win32finddata
+		handle, err := syscall.FindFirstFile(pathp, &data)
+		if err == syscall.ERROR_FILE_NOT_FOUND {
+			return true
+		}
+		if err != nil {
+			return false
+		}
+		syscall.FindClose(handle)
+		fileName := syscall.UTF16ToString(data.FileName[:])
+		if part != fileName {
+			return false
+		}
+	}
+	return true
+}

lib/osutil/name_conflict_windows_test.go

@@ -0,0 +1,108 @@
+// Copyright (C) 2016 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+// +build windows
+
+package osutil_test
+
+import (
+	"os"
+	"path"
+	"path/filepath"
+	"syscall"
+	"testing"
+	"unsafe"
+
+	"github.com/syncthing/syncthing/lib/osutil"
+)
+
+func TestCheckNameConflictCasing(t *testing.T) {
+	os.RemoveAll("testdata")
+	defer os.RemoveAll("testdata")
+	os.MkdirAll("testdata/Foo/BAR/baz", 0755)
+	// check if the file system is case-sensitive
+	if _, err := os.Lstat("testdata/foo"); err != nil {
+		t.Skip("pointless test")
+		return
+	}
+
+	cases := []struct {
+		name         string
+		conflictFree bool
+	}{
+		// Exists
+		{"Foo", true},
+		{"Foo/BAR", true},
+		{"Foo/BAR/baz", true},
+		// Doesn't exist
+		{"bar", true},
+		{"Foo/baz", true},
+		// Conflicts
+		{"foo", false},
+		{"foo/BAR", false},
+		{"Foo/bar", false},
+		{"Foo/BAR/BAZ", false},
+	}
+
+	for _, tc := range cases {
+		nativeName := filepath.FromSlash(tc.name)
+		if res := osutil.CheckNameConflict("testdata", nativeName); res != tc.conflictFree {
+			t.Errorf("CheckNameConflict(%q) = %v, should be %v", tc.name, res, tc.conflictFree)
+		}
+	}
+}
+
+func TestCheckNameConflictShortName(t *testing.T) {
+	os.RemoveAll("testdata")
+	defer os.RemoveAll("testdata")
+	os.MkdirAll("testdata/foobarbaz/qux", 0755)
+	ppath, err := syscall.UTF16PtrFromString("testdata/foobarbaz")
+	if err != nil {
+		t.Fatal("unexpected error", err)
+	}
+	// check if the file system supports short names
+	bufferSize, err := syscall.GetShortPathName(ppath, nil, 0)
+	if err != nil {
+		t.Skip("pointless test")
+		return
+	}
+
+	// get the short name
+	buffer := make([]uint16, bufferSize)
+	length, err := syscall.GetShortPathName(ppath,
+		(*uint16)(unsafe.Pointer(&buffer[0])), bufferSize)
+	if err != nil {
+		t.Fatal("unexpected error", err)
+	}
+	// on success length doesn't contain the terminating null character
+	if bufferSize != length+1 {
+		t.Fatal("length of short name changed")
+	}
+	shortName := filepath.Base(syscall.UTF16ToString(buffer))
+
+	cases := []struct {
+		name         string
+		conflictFree bool
+	}{
+		// Exists
+		{"foobarbaz", true},
+		{"foobarbaz/qux", true},
+		// Doesn't exist
+		{"foo", true},
+		{"foobarbaz/quux", true},
+		// Conflicts
+		{shortName, false},
+		{path.Join(shortName, "qux"), false},
+		{path.Join(shortName, "quux"), false},
+	}
+
+	for _, tc := range cases {
+		nativeName := filepath.FromSlash(tc.name)
+		if res := osutil.CheckNameConflict("testdata", nativeName); res != tc.conflictFree {
+			t.Errorf("CheckNameConflict(%q) = %v, should be %v", tc.name, res, tc.conflictFree)
+		}
+	}
+}