Windows: implement readSymbolicLink
In this PR:
- Implement ReadSymlinkOrJunction in the JNI
library, and expose it to Java code. This method
can resolve symlinks and junctions.
- Override readSymbolicLink in WindowsFileSystem
and use the new native method
- Add unit tests to exercise junction resolution.
Manual testing shows the code works for symlinks
too, however we cannot reliably create them in
tests because that requires unprivileged symlink
creation support (i.e. for the test to run as
Admin, or for the OS having enabled it)
Fixes https://github.com/bazelbuild/bazel/issues/7907
Closes #7929.
PiperOrigin-RevId: 241899544
diff --git a/src/main/java/com/google/devtools/build/lib/windows/WindowsFileSystem.java b/src/main/java/com/google/devtools/build/lib/windows/WindowsFileSystem.java
index d39173a..ee457b7 100644
--- a/src/main/java/com/google/devtools/build/lib/windows/WindowsFileSystem.java
+++ b/src/main/java/com/google/devtools/build/lib/windows/WindowsFileSystem.java
@@ -90,6 +90,12 @@
}
@Override
+ protected PathFragment readSymbolicLink(Path path) throws IOException {
+ java.nio.file.Path nioPath = getNioPath(path);
+ return PathFragment.create(WindowsFileOperations.readSymlinkOrJunction(nioPath.toString()));
+ }
+
+ @Override
public boolean supportsSymbolicLinksNatively(Path path) {
return false;
}
diff --git a/src/main/java/com/google/devtools/build/lib/windows/jni/WindowsFileOperations.java b/src/main/java/com/google/devtools/build/lib/windows/jni/WindowsFileOperations.java
index c8243e4..8208618 100644
--- a/src/main/java/com/google/devtools/build/lib/windows/jni/WindowsFileOperations.java
+++ b/src/main/java/com/google/devtools/build/lib/windows/jni/WindowsFileOperations.java
@@ -44,33 +44,44 @@
private static final int MAX_PATH = 260;
- // Keep IS_JUNCTION_* values in sync with src/main/native/windows/file.cc.
+ // Keep IS_JUNCTION_* values in sync with src/main/native/windows/file.h.
private static final int IS_JUNCTION_YES = 0;
private static final int IS_JUNCTION_NO = 1;
- private static final int IS_JUNCTION_ERROR = 2;
+ // IS_JUNCTION_ERROR = 2;
- // Keep CREATE_JUNCTION_* values in sync with src/main/native/windows/file.cc.
+ // Keep CREATE_JUNCTION_* values in sync with src/main/native/windows/file.h.
private static final int CREATE_JUNCTION_SUCCESS = 0;
- private static final int CREATE_JUNCTION_ERROR = 1;
+ // CREATE_JUNCTION_ERROR = 1;
private static final int CREATE_JUNCTION_TARGET_NAME_TOO_LONG = 2;
private static final int CREATE_JUNCTION_ALREADY_EXISTS_WITH_DIFFERENT_TARGET = 3;
private static final int CREATE_JUNCTION_ALREADY_EXISTS_BUT_NOT_A_JUNCTION = 4;
private static final int CREATE_JUNCTION_ACCESS_DENIED = 5;
private static final int CREATE_JUNCTION_DISAPPEARED = 6;
- // Keep DELETE_PATH_* values in sync with src/main/native/windows/file.cc.
+ // Keep DELETE_PATH_* values in sync with src/main/native/windows/file.h.
private static final int DELETE_PATH_SUCCESS = 0;
- private static final int DELETE_PATH_ERROR = 1;
+ // DELETE_PATH_ERROR = 1;
private static final int DELETE_PATH_DOES_NOT_EXIST = 2;
private static final int DELETE_PATH_DIRECTORY_NOT_EMPTY = 3;
private static final int DELETE_PATH_ACCESS_DENIED = 4;
+ // Keep READ_SYMLINK_OR_JUNCTION_* values in sync with src/main/native/windows/file.h.
+ private static final int READ_SYMLINK_OR_JUNCTION_SUCCESS = 0;
+ // READ_SYMLINK_OR_JUNCTION_ERROR = 1;
+ private static final int READ_SYMLINK_OR_JUNCTION_ACCESS_DENIED = 2;
+ private static final int READ_SYMLINK_OR_JUNCTION_DOES_NOT_EXIST = 3;
+ private static final int READ_SYMLINK_OR_JUNCTION_NOT_A_LINK = 4;
+ private static final int READ_SYMLINK_OR_JUNCTION_UNKNOWN_LINK_TYPE = 5;
+
private static native int nativeIsJunction(String path, String[] error);
private static native boolean nativeGetLongPath(String path, String[] result, String[] error);
private static native int nativeCreateJunction(String name, String target, String[] error);
+ private static native int nativeReadSymlinkOrJunction(
+ String name, String[] result, String[] error);
+
private static native int nativeDeletePath(String path, String[] error);
/** Determines whether `path` is a junction point or directory symlink. */
@@ -83,6 +94,7 @@
case IS_JUNCTION_NO:
return false;
default:
+ // This is IS_JUNCTION_ERROR. The JNI code puts a custom message in 'error[0]'.
throw new IOException(error[0]);
}
}
@@ -140,36 +152,63 @@
public static void createJunction(String name, String target) throws IOException {
WindowsJniLoader.loadJni();
String[] error = new String[] {null};
- int result = nativeCreateJunction(name.replace('/', '\\'), target.replace('/', '\\'), error);
- if (result != CREATE_JUNCTION_SUCCESS) {
- switch (result) {
- case CREATE_JUNCTION_TARGET_NAME_TOO_LONG:
- error[0] = "target name is too long";
- break;
- case CREATE_JUNCTION_ALREADY_EXISTS_WITH_DIFFERENT_TARGET:
- error[0] = "junction already exists with different target";
- break;
- case CREATE_JUNCTION_ALREADY_EXISTS_BUT_NOT_A_JUNCTION:
- error[0] = "a file or directory already exists at the junction's path";
- break;
- case CREATE_JUNCTION_ACCESS_DENIED:
- error[0] = "access is denied";
- break;
- case CREATE_JUNCTION_DISAPPEARED:
- error[0] = "the junction's path got modified unexpectedly";
- break;
- default:
- break;
- }
- throw new IOException(
- String.format("Cannot create junction (name=%s, target=%s): %s", name, target, error[0]));
+ switch (nativeCreateJunction(asLongPath(name), asLongPath(target), error)) {
+ case CREATE_JUNCTION_SUCCESS:
+ return;
+ case CREATE_JUNCTION_TARGET_NAME_TOO_LONG:
+ error[0] = "target name is too long";
+ break;
+ case CREATE_JUNCTION_ALREADY_EXISTS_WITH_DIFFERENT_TARGET:
+ error[0] = "junction already exists with different target";
+ break;
+ case CREATE_JUNCTION_ALREADY_EXISTS_BUT_NOT_A_JUNCTION:
+ error[0] = "a file or directory already exists at the junction's path";
+ break;
+ case CREATE_JUNCTION_ACCESS_DENIED:
+ error[0] = "access is denied";
+ break;
+ case CREATE_JUNCTION_DISAPPEARED:
+ error[0] = "the junction's path got modified unexpectedly";
+ break;
+ default:
+ // This is CREATE_JUNCTION_ERROR (1). The JNI code puts a custom message in 'error[0]'.
+ break;
}
+ throw new IOException(
+ String.format("Cannot create junction (name=%s, target=%s): %s", name, target, error[0]));
+ }
+
+ public static String readSymlinkOrJunction(String name) throws IOException {
+ WindowsJniLoader.loadJni();
+ String[] target = new String[] {null};
+ String[] error = new String[] {null};
+ switch (nativeReadSymlinkOrJunction(asLongPath(name), target, error)) {
+ case READ_SYMLINK_OR_JUNCTION_SUCCESS:
+ return removeUncPrefixAndUseSlashes(target[0]);
+ case READ_SYMLINK_OR_JUNCTION_ACCESS_DENIED:
+ error[0] = "access is denied";
+ break;
+ case READ_SYMLINK_OR_JUNCTION_DOES_NOT_EXIST:
+ error[0] = "path does not exist";
+ break;
+ case READ_SYMLINK_OR_JUNCTION_NOT_A_LINK:
+ error[0] = "path is not a link";
+ break;
+ case READ_SYMLINK_OR_JUNCTION_UNKNOWN_LINK_TYPE:
+ error[0] = "unknown link type";
+ break;
+ default:
+ // This is READ_SYMLINK_OR_JUNCTION_ERROR (1). The JNI code puts a custom message in
+ // 'error[0]'.
+ break;
+ }
+ throw new IOException(String.format("Cannot read link (name=%s): %s", name, error[0]));
}
public static boolean deletePath(String path) throws IOException {
WindowsJniLoader.loadJni();
String[] error = new String[] {null};
- int result = nativeDeletePath(asLongPath(path.replace('/', '\\')), error);
+ int result = nativeDeletePath(asLongPath(path), error);
switch (result) {
case DELETE_PATH_SUCCESS:
return true;
@@ -180,6 +219,7 @@
case DELETE_PATH_ACCESS_DENIED:
throw new java.nio.file.AccessDeniedException(path);
default:
+ // This is DELETE_PATH_ERROR (1). The JNI code puts a custom message in 'error[0]'.
throw new IOException(String.format("Cannot delete path '%s': %s", path, error[0]));
}
}
diff --git a/src/main/native/windows/file-jni.cc b/src/main/native/windows/file-jni.cc
index 09934ec..3befe0f 100644
--- a/src/main/native/windows/file-jni.cc
+++ b/src/main/native/windows/file-jni.cc
@@ -94,7 +94,30 @@
wname + L", " + wtarget, error),
env, error_msg_holder);
}
- return result;
+ return static_cast<jint>(result);
+}
+
+extern "C" JNIEXPORT jint JNICALL
+Java_com_google_devtools_build_lib_windows_jni_WindowsFileOperations_nativeReadSymlinkOrJunction(
+ JNIEnv* env, jclass clazz, jstring name, jobjectArray target_holder,
+ jobjectArray error_msg_holder) {
+ std::wstring wname(bazel::windows::GetJavaWstring(env, name));
+ std::wstring target, error;
+ int result = bazel::windows::ReadSymlinkOrJunction(wname, &target, &error);
+ if (result == bazel::windows::ReadSymlinkOrJunctionResult::kSuccess) {
+ env->SetObjectArrayElement(
+ target_holder, 0,
+ env->NewString(reinterpret_cast<const jchar*>(target.c_str()),
+ target.size()));
+ } else {
+ if (!error.empty() && CanReportError(env, error_msg_holder)) {
+ ReportLastError(bazel::windows::MakeErrorMessage(
+ WSTR(__FILE__), __LINE__,
+ L"nativeReadSymlinkOrJunction", wname, error),
+ env, error_msg_holder);
+ }
+ }
+ return static_cast<jint>(result);
}
extern "C" JNIEXPORT jint JNICALL
diff --git a/src/main/native/windows/file.cc b/src/main/native/windows/file.cc
index 091f527..e7cf81a 100644
--- a/src/main/native/windows/file.cc
+++ b/src/main/native/windows/file.cc
@@ -161,7 +161,7 @@
WSTR(__FILE__), __LINE__, L"CreateJunction", junction_name,
L"expected an absolute Windows path for junction_name");
}
- CreateJunctionResult::kError;
+ return CreateJunctionResult::kError;
}
if (!IsAbsoluteNormalizedWindowsPath(junction_target)) {
if (error) {
@@ -169,7 +169,7 @@
WSTR(__FILE__), __LINE__, L"CreateJunction", junction_target,
L"expected an absolute Windows path for junction_target");
}
- CreateJunctionResult::kError;
+ return CreateJunctionResult::kError;
}
const WCHAR* target = HasUncPrefix(junction_target.c_str())
@@ -420,6 +420,82 @@
return CreateJunctionResult::kSuccess;
}
+int ReadSymlinkOrJunction(const wstring& path, wstring* result,
+ wstring* error) {
+ if (!IsAbsoluteNormalizedWindowsPath(path)) {
+ if (error) {
+ *error = MakeErrorMessage(
+ WSTR(__FILE__), __LINE__, L"ReadSymlinkOrJunction", path,
+ L"expected an absolute Windows path for 'path'");
+ }
+ return ReadSymlinkOrJunctionResult::kError;
+ }
+
+ AutoHandle handle(CreateFileW(
+ AddUncPrefixMaybe(path).c_str(), 0,
+ FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
+ OPEN_EXISTING, FILE_FLAG_OPEN_REPARSE_POINT | FILE_FLAG_BACKUP_SEMANTICS,
+ NULL));
+ if (!handle.IsValid()) {
+ DWORD err = GetLastError();
+ if (err == ERROR_SHARING_VIOLATION) {
+ // The path is held open by another process.
+ return ReadSymlinkOrJunctionResult::kAccessDenied;
+ } else if (err == ERROR_FILE_NOT_FOUND || err == ERROR_PATH_NOT_FOUND) {
+ // Path or a parent directory does not exist.
+ return ReadSymlinkOrJunctionResult::kDoesNotExist;
+ }
+
+ // The path seems to exist yet we cannot open it for metadata-reading.
+ // Report as much information as we have, then give up.
+ if (error) {
+ *error =
+ MakeErrorMessage(WSTR(__FILE__), __LINE__, L"CreateFileW", path, err);
+ }
+ return ReadSymlinkOrJunctionResult::kError;
+ }
+
+ uint8_t raw_buf[MAXIMUM_REPARSE_DATA_BUFFER_SIZE];
+ PREPARSE_DATA_BUFFER buf = reinterpret_cast<PREPARSE_DATA_BUFFER>(raw_buf);
+ DWORD bytes_returned;
+ if (!::DeviceIoControl(handle, FSCTL_GET_REPARSE_POINT, NULL, 0, buf,
+ MAXIMUM_REPARSE_DATA_BUFFER_SIZE, &bytes_returned,
+ NULL)) {
+ DWORD err = GetLastError();
+ if (err == ERROR_NOT_A_REPARSE_POINT) {
+ return ReadSymlinkOrJunctionResult::kNotALink;
+ }
+
+ // Some unknown error occurred.
+ if (error) {
+ *error = MakeErrorMessage(WSTR(__FILE__), __LINE__, L"DeviceIoControl",
+ path, err);
+ }
+ return ReadSymlinkOrJunctionResult::kError;
+ }
+
+ switch (buf->ReparseTag) {
+ case IO_REPARSE_TAG_SYMLINK: {
+ wchar_t* p =
+ (wchar_t*)(((uint8_t*)buf->SymbolicLinkReparseBuffer.PathBuffer) +
+ buf->SymbolicLinkReparseBuffer.SubstituteNameOffset);
+ *result = wstring(p, buf->SymbolicLinkReparseBuffer.SubstituteNameLength /
+ sizeof(WCHAR));
+ return ReadSymlinkOrJunctionResult::kSuccess;
+ }
+ case IO_REPARSE_TAG_MOUNT_POINT: {
+ wchar_t* p =
+ (wchar_t*)(((uint8_t*)buf->MountPointReparseBuffer.PathBuffer) +
+ buf->MountPointReparseBuffer.SubstituteNameOffset);
+ *result = wstring(
+ p, buf->MountPointReparseBuffer.SubstituteNameLength / sizeof(WCHAR));
+ return ReadSymlinkOrJunctionResult::kSuccess;
+ }
+ default:
+ return ReadSymlinkOrJunctionResult::kUnknownLinkType;
+ }
+}
+
struct DirectoryStatus {
enum {
kDoesNotExist = 0,
diff --git a/src/main/native/windows/file.h b/src/main/native/windows/file.h
index 84cbde3..87d5f0a 100644
--- a/src/main/native/windows/file.h
+++ b/src/main/native/windows/file.h
@@ -65,6 +65,7 @@
};
};
+// Keep in sync with j.c.g.devtools.build.lib.windows.WindowsFileOperations
struct CreateJunctionResult {
enum {
kSuccess = 0,
@@ -77,6 +78,18 @@
};
};
+// Keep in sync with j.c.g.devtools.build.lib.windows.WindowsFileOperations
+struct ReadSymlinkOrJunctionResult {
+ enum {
+ kSuccess = 0,
+ kError = 1,
+ kAccessDenied = 2,
+ kDoesNotExist = 3,
+ kNotALink = 4,
+ kUnknownLinkType = 5,
+ };
+};
+
// Determines whether `path` is a junction (or directory symlink).
//
// `path` should be an absolute, normalized, Windows-style path, with "\\?\"
@@ -124,6 +137,12 @@
int CreateJunction(const wstring& junction_name, const wstring& junction_target,
wstring* error);
+// Reads the symlink or junction into 'result'.
+// Returns a value from 'ReadSymlinkOrJunctionResult'.
+// When the method returns 'ReadSymlinkOrJunctionResult::kError' and 'error' is
+// non-null then 'error' receives an error message.
+int ReadSymlinkOrJunction(const wstring& path, wstring* result, wstring* error);
+
// Deletes the file, junction, or empty directory at `path`.
// Returns DELETE_PATH_SUCCESS if it successfully deleted the path, otherwise
// returns one of the other DELETE_PATH_* constants (e.g. when the directory is
diff --git a/src/test/java/com/google/devtools/build/lib/windows/WindowsFileSystemTest.java b/src/test/java/com/google/devtools/build/lib/windows/WindowsFileSystemTest.java
index e547074..b0c9454 100644
--- a/src/test/java/com/google/devtools/build/lib/windows/WindowsFileSystemTest.java
+++ b/src/test/java/com/google/devtools/build/lib/windows/WindowsFileSystemTest.java
@@ -331,4 +331,42 @@
assertThat(p.isFile()).isTrue();
}
}
+
+ @Test
+ public void testReadJunction() throws Exception {
+ testUtil.scratchFile("dir\\hello.txt", "hello");
+ testUtil.createJunctions(ImmutableMap.of("junc", "dir"));
+
+ Path dirPath = testUtil.createVfsPath(fs, "dir");
+ Path juncPath = testUtil.createVfsPath(fs, "junc");
+
+ assertThat(dirPath.isDirectory()).isTrue();
+ assertThat(juncPath.isDirectory()).isTrue();
+
+ assertThat(dirPath.isSymbolicLink()).isFalse();
+ assertThat(juncPath.isSymbolicLink()).isTrue();
+
+ try {
+ testUtil.createVfsPath(fs, "does-not-exist").readSymbolicLink();
+ fail("expected exception");
+ } catch (IOException expected) {
+ assertThat(expected).hasMessageThat().matches(".*path does not exist");
+ }
+
+ try {
+ testUtil.createVfsPath(fs, "dir\\hello.txt").readSymbolicLink();
+ fail("expected exception");
+ } catch (IOException expected) {
+ assertThat(expected).hasMessageThat().matches(".*path is not a link");
+ }
+
+ try {
+ dirPath.readSymbolicLink();
+ fail("expected exception");
+ } catch (IOException expected) {
+ assertThat(expected).hasMessageThat().matches(".*path is not a link");
+ }
+
+ assertThat(juncPath.readSymbolicLink()).isEqualTo(dirPath.asFragment());
+ }
}
