// Copyright 2016 The Bazel 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 com.google.devtools.build.lib.windows;
import java.io.IOException;
/** File operations on Windows. */
public class WindowsFileOperations {
// A note about UNC paths and path prefixes on Windows. The prefixes can be:
// - "\\?\", meaning it's a UNC path that is passed to user mode unicode WinAPI functions
// (e.g. CreateFileW) or a return value of theirs (e.g. GetLongPathNameW); this is the
// prefix we'll most often see
// - "\??\", meaning it's Device Object path; it's mostly only used by kernel/driver functions
// but we may come across it when resolving junction targets, as the target's path is
// specified with this prefix, see usages of DeviceIoControl with FSCTL_GET_REPARSE_POINT
// - "\\.\", meaning it's a Device Object path again; both "\??\" and "\\.\" are shorthands
// for the "\DosDevices\" Object Directory, so "\\.\C:" and "\??\C:" and "\DosDevices\C:"
// and "C:\" all mean the same thing, but functions like CreateFileW don't understand the
// fully qualified device path, only the shorthand versions; the difference between "\\.\"
// is "\??\" is not entirely clear (one is not available while Windows is booting, but
// that only concerns device drivers) but we most likely won't come across them anyway
// Some of this is documented here:
// - https://msdn.microsoft.com/en-us/library/windows/hardware/ff557762(v=vs.85).aspx
// - https://msdn.microsoft.com/en-us/library/windows/hardware/ff565384(v=vs.85).aspx
// - http://stackoverflow.com/questions/23041983
// - http://stackoverflow.com/questions/14482421
private WindowsFileOperations() {
// Prevent construction
}
private static final int MAX_PATH = 260;
// Keep IS_JUNCTION_* values in sync with src/main/native/windows_file_operations.cc.
private static final int IS_JUNCTION_YES = 0;
private static final int IS_JUNCTION_NO = 1;
private static final int IS_JUNCTION_ERROR = 2;
static native int nativeIsJunction(String path, String[] error);
static native boolean nativeGetLongPath(String path, String[] result, String[] error);
static native boolean nativeCreateJunction(String name, String target, String[] error);
/** Determines whether `path` is a junction point or directory symlink. */
public static boolean isJunction(String path) throws IOException {
WindowsJniLoader.loadJni();
String[] error = new String[] {null};
switch (nativeIsJunction(asLongPath(path), error)) {
case IS_JUNCTION_YES:
return true;
case IS_JUNCTION_NO:
return false;
default:
throw new IOException(error[0]);
}
}
/**
* Returns the long path associated with the input `path`.
*
* <p>This method resolves all 8dot3 style components of the path and returns the long format. For
* example, if the input is "C:/progra~1/micros~1" the result may be "C:\Program Files\Microsoft
* Visual Studio 14.0". The returned path is Windows-style in that it uses backslashes, even if
* the input uses forward slashes.
*
* <p>May return an UNC path if `path` or its resolution is sufficiently long.
*
* @throws IOException if the `path` is not found or some other I/O error occurs
*/
public static String getLongPath(String path) throws IOException {
WindowsJniLoader.loadJni();
String[] result = new String[] {null};
String[] error = new String[] {null};
if (nativeGetLongPath(asLongPath(path), result, error)) {
return result[0];
} else {
throw new IOException(error[0]);
}
}
/**
* Returns a Windows-style path suitable to pass to unicode WinAPI functions.
*
* <p>Returns an UNC path if `path` is at least `MAX_PATH` long. If it's shorter or is already an
* UNC path, then this method returns `path` itself.
*/
static String asLongPath(String path) {
return path.length() >= MAX_PATH && !path.startsWith("\\\\?\\")
? ("\\\\?\\" + path.replace('/', '\\'))
: path;
}
/**
* Creates a junction at `name`, pointing to `target`.
*
* <p>Both `name` and `target` may be Unix-style Windows paths (i.e. use forward slashes), and
* they don't need to have a UNC prefix, not even if they are longer than `MAX_PATH`. The
* underlying logic will take care of adding the prefixes if necessary.
*
* @throws IOException if some error occurs
*/
public static void createJunction(String name, String target) throws IOException {
WindowsJniLoader.loadJni();
String[] error = new String[] {null};
if (!nativeCreateJunction(name.replace('/', '\\'), target.replace('/', '\\'), error)) {
throw new IOException(
String.format("Cannot create junction (name=%s, target=%s): %s", name, target, error[0]));
}
}
}