Bazel client, JNI, Windows: impl. CreateJunction

Implement a CreateJunction function in the Windows
JNI library. Also move a bit of code from
file_windows to the JNI library, where it is
(also) needed.

This implementation is an improved version of
`blaze_util::SymlinkDirectories` in
blaze_util_windows: this version handles Windows
paths as `name` and `target`, and performs more
validation (e.g. on the length of `target`), plus
has more comments explaining the logic. In a
subsequent change I'll start using this new
function in blaze_util_windows.

This method will also be helpful in tests: we will
no longer have to shell out to mklink.

See https://github.com/bazelbuild/bazel/issues/2107

--
Change-Id: I7e9b085fdc2ba47be83da5319bded02bd323e71b
Reviewed-on: https://cr.bazel.build/8892
PiperOrigin-RevId: 147585207
MOS_MIGRATED_REVID=147585207

8 files changed, 287 insertions, 15 deletions

diff --git a/src/main/cpp/util/file_windows.cc b/src/main/cpp/util/file_windows.cc
index 9d22444dc8..e2e12950eb 100644
--- a/src/main/cpp/util/file_windows.cc
+++ b/src/main/cpp/util/file_windows.cc
@@ -35,6 +35,7 @@ using std::pair;
 using std::string;
 using std::unique_ptr;
 using std::wstring;
+using windows_util::HasUncPrefix;
 
 // Returns the current working directory as a Windows path.
 // The result may have a UNC prefix.
@@ -101,12 +102,6 @@ static bool HasDriveSpecifierPrefix(const char_type* ch) {
   return CharTraits<char_type>::IsAlpha(ch[0]) && ch[1] == ':';
 }
 
-template <typename char_type>
-static bool HasUncPrefix(const char_type* path) {
-  return path[0] == '\\' && (path[1] == '\\' || path[1] == '?') &&
-         (path[2] == '.' || path[2] == '?') && path[3] == '\\';
-}
-
 static void AddUncPrefixMaybe(wstring* path) {
   if (path->size() >= MAX_PATH && !HasUncPrefix(path->c_str())) {
     *path = wstring(L"\\\\?\\") + *path;
diff --git a/src/main/native/windows_file_operations.cc b/src/main/native/windows_file_operations.cc
index b5780b2c86..0b02fb9238 100644
--- a/src/main/native/windows_file_operations.cc
+++ b/src/main/native/windows_file_operations.cc
@@ -15,13 +15,17 @@
 #include <windows.h>
 
 #include <memory>
+#include <sstream>
+#include <string>
 
 #include "src/main/native/windows_file_operations.h"
 #include "src/main/native/windows_util.h"
 
 namespace windows_util {
 
+using std::string;
 using std::unique_ptr;
+using std::wstring;
 
 int IsJunctionOrDirectorySymlink(const WCHAR* path) {
   DWORD attrs = ::GetFileAttributesW(path);
@@ -60,4 +64,121 @@ HANDLE OpenDirectory(const WCHAR* path, bool read_write) {
       /* hTemplateFile */ NULL);
 }
 
+#pragma pack(push, 4)
+typedef struct _JunctionDescription {
+  typedef struct _Header {
+    DWORD ReparseTag;
+    WORD ReparseDataLength;
+    WORD Reserved;
+  } Header;
+
+  typedef struct _WriteDesc {
+    WORD SubstituteNameOffset;
+    WORD SubstituteNameLength;
+    WORD PrintNameOffset;
+    WORD PrintNameLength;
+  } WriteDesc;
+
+  Header header;
+  WriteDesc write;
+  WCHAR PathBuffer[ANYSIZE_ARRAY];
+} JunctionDescription;
+#pragma pack(pop)
+
+string CreateJunction(const wstring& junction_name,
+                      const wstring& junction_target) {
+  const wstring target = HasUncPrefix(junction_target.c_str())
+                             ? junction_target.substr(4)
+                             : junction_target;
+  // The entire JunctionDescription cannot be larger than
+  // MAXIMUM_REPARSE_DATA_BUFFER_SIZE bytes.
+  //
+  // The structure's layout is:
+  //   [JunctionDescription::Header]
+  //   [JunctionDescription::WriteDesc]
+  //   ---- start of JunctionDescription::PathBuffer ----
+  //   [4 WCHARs]             : "\??\" prefix
+  //   [target.size() WCHARs] : junction target name
+  //   [1 WCHAR]              : null-terminator
+  //   [target.size() WCHARs] : junction target displayed name
+  //   [1 WCHAR]              : null-terminator
+  // The sum of these must not exceed MAXIMUM_REPARSE_DATA_BUFFER_SIZE.
+  // We can rearrange this to get the limit for target.size().
+  static const size_t kMaxJunctionTargetLen =
+      ((MAXIMUM_REPARSE_DATA_BUFFER_SIZE - sizeof(JunctionDescription::Header) -
+        sizeof(JunctionDescription::WriteDesc) -
+        /* one "\??\" prefix */ sizeof(WCHAR) * 4 -
+        /* two null terminators */ sizeof(WCHAR) * 2) /
+       /* two copies of the string are stored */ 2) /
+      sizeof(WCHAR);
+  if (target.size() > kMaxJunctionTargetLen) {
+    std::stringstream error;
+    error << "junction target is too long (" << target.size()
+          << " characters, limit: " << kMaxJunctionTargetLen << ")";
+    return error.str();
+  }
+  const wstring name = HasUncPrefix(junction_name.c_str())
+                           ? junction_name
+                           : (wstring(L"\\\\?\\") + junction_name);
+
+  // Junctions are directories, so create one
+  if (!::CreateDirectoryW(name.c_str(), NULL)) {
+    return string("CreateDirectoryW failed");
+  }
+
+  AutoHandle handle(OpenDirectory(name.c_str(), true));
+  if (!handle.IsValid()) {
+    return string("OpenDirectory failed");
+  }
+
+  char reparse_buffer_bytes[MAXIMUM_REPARSE_DATA_BUFFER_SIZE];
+  JunctionDescription* reparse_buffer =
+      reinterpret_cast<JunctionDescription*>(reparse_buffer_bytes);
+  memset(reparse_buffer_bytes, 0, MAXIMUM_REPARSE_DATA_BUFFER_SIZE);
+
+  // "\??\" is meaningful to the kernel, it's a synomym for the "\DosDevices\"
+  // object path. (NOT to be confused with "\\?\" which is meaningful for the
+  // Win32 API.) We need to use this prefix to tell the kernel where the reparse
+  // point is pointing to.
+  memcpy(reparse_buffer->PathBuffer, L"\\??\\", 4 * sizeof(WCHAR));
+  memcpy(reparse_buffer->PathBuffer + 4, target.c_str(),
+         target.size() * sizeof(WCHAR));
+
+  // In addition to their target, junctions also have another string which is a
+  // user-visible name of where the junction points, as listed by "dir". This
+  // can be any string and won't affect the usability of the junction.
+  // MKLINK uses the target path without the "\??\" prefix as the display name,
+  // so let's do that here too. This is also in line with how UNIX behaves.
+  // Using a dummy or fake display name would be pure evil, it would make the
+  // output of `dir` look like:
+  //   2017-01-18  01:37 PM    <JUNCTION>     juncname [dummy string]
+  memcpy(reparse_buffer->PathBuffer + 4 + target.size() + 1, target.c_str(),
+         target.size() * sizeof(WCHAR));
+
+  reparse_buffer->write.SubstituteNameOffset = 0;
+  reparse_buffer->write.SubstituteNameLength =
+      (4 + target.size()) * sizeof(WCHAR);
+  reparse_buffer->write.PrintNameOffset =
+      reparse_buffer->write.SubstituteNameLength +
+      /* null-terminator */ sizeof(WCHAR);
+  reparse_buffer->write.PrintNameLength = target.size() * sizeof(WCHAR);
+
+  reparse_buffer->header.ReparseTag = IO_REPARSE_TAG_MOUNT_POINT;
+  reparse_buffer->header.ReparseDataLength =
+      sizeof(JunctionDescription::WriteDesc) +
+      reparse_buffer->write.SubstituteNameLength +
+      reparse_buffer->write.PrintNameLength +
+      /* 2 null-terminators */ (2 * sizeof(WCHAR));
+  reparse_buffer->header.Reserved = 0;
+
+  DWORD bytes_returned;
+  if (!::DeviceIoControl(handle, FSCTL_SET_REPARSE_POINT, reparse_buffer,
+                         reparse_buffer->header.ReparseDataLength +
+                             sizeof(JunctionDescription::Header),
+                         NULL, 0, &bytes_returned, NULL)) {
+    return string("DeviceIoControl(FSCTL_SET_REPARSE_POINT) failed");
+  }
+  return "";
+}
+
 }  // namespace windows_util
diff --git a/src/main/native/windows_file_operations.h b/src/main/native/windows_file_operations.h
index ded07b0a1f..9b2c76837a 100644
--- a/src/main/native/windows_file_operations.h
+++ b/src/main/native/windows_file_operations.h
@@ -17,10 +17,19 @@
 #include <windows.h>
 
 #include <memory>
+#include <string>
 
 namespace windows_util {
 
+using std::string;
 using std::unique_ptr;
+using std::wstring;
+
+template <typename char_type>
+bool HasUncPrefix(const char_type* path) {
+  return path[0] == '\\' && (path[1] == '\\' || path[1] == '?') &&
+         (path[2] == '.' || path[2] == '?') && path[3] == '\\';
+}
 
 // Keep in sync with j.c.g.devtools.build.lib.windows.WindowsFileOperations
 enum {
@@ -61,6 +70,15 @@ bool GetLongPath(const WCHAR* path, unique_ptr<WCHAR[]>* result);
 // otherwise only for reading.
 HANDLE OpenDirectory(const WCHAR* path, bool read_write);
 
+// Creates a junction at `name`, pointing to `target`.
+// Returns the empty string upon success, or a human-readable error message upon
+// failure.
+// Neither `junction_name` nor `junction_target` needs to have a "\\?\" prefix,
+// not even if they are longer than MAX_PATH, though it's okay if they do. This
+// function will add the right prefixes as necessary.
+string CreateJunction(const wstring& junction_name,
+                      const wstring& junction_target);
+
 }  // namespace windows_util
 
 #endif  // BAZEL_SRC_MAIN_NATIVE_WINDOWS_FILE_OPERATIONS_H_
diff --git a/src/test/cpp/util/BUILD b/src/test/cpp/util/BUILD
index c8b2f57caf..3e696ce828 100644
--- a/src/test/cpp/util/BUILD
+++ b/src/test/cpp/util/BUILD
@@ -82,20 +82,34 @@ cc_library(
         "//src:windows_msvc": ["windows_test_util.cc"],
         "//conditions:default": [],
     }),
-    deps = ["//third_party:gtest"],
+    hdrs = select({
+        "//src:windows": ["windows_test_util.h"],
+        "//src:windows_msvc": ["windows_test_util.h"],
+        "//conditions:default": [],
+    }),
+    visibility = [
+        "//src/test/cpp:__subpackages__",
+        "//src/test/native:__subpackages__",
+    ],
 )
 
 cc_test(
     name = "windows_test_util_test",
     size = "small",
     srcs = select({
-        "//src:windows": ["windows_test_util.cc"],
-        "//src:windows_msvc": ["windows_test_util.cc"],
+        "//src:windows": ["windows_test_util_test.cc"],
+        "//src:windows_msvc": ["windows_test_util_test.cc"],
         "//conditions:default": ["dummy_test.cc"],
     }),
     deps = select({
-        "//src:windows": ["//third_party:gtest"],
-        "//src:windows_msvc": ["//third_party:gtest"],
+        "//src:windows": [
+            ":windows_test_util",
+            "//third_party:gtest",
+        ],
+        "//src:windows_msvc": [
+            ":windows_test_util",
+            "//third_party:gtest",
+        ],
         "//conditions:default": [],
     }),
 )
diff --git a/src/test/cpp/util/windows_test_util.cc b/src/test/cpp/util/windows_test_util.cc
index dfea7b05bb..47bdc31bbf 100644
--- a/src/test/cpp/util/windows_test_util.cc
+++ b/src/test/cpp/util/windows_test_util.cc
@@ -34,6 +34,9 @@ wstring GetTestTmpDirW() {
   ::GetEnvironmentVariableW(L"TEST_TMPDIR", buf.get(), size);
   wstring result(buf.get());
   std::replace(result.begin(), result.end(), '/', '\\');
+  if (result.back() == '\\') {
+    result.pop_back();
+  }
   return result;
 }
 
diff --git a/src/test/cpp/util/windows_test_util.h b/src/test/cpp/util/windows_test_util.h
index 2ec5844e41..ababc3e685 100644
--- a/src/test/cpp/util/windows_test_util.h
+++ b/src/test/cpp/util/windows_test_util.h
@@ -21,7 +21,8 @@ namespace blaze_util {
 using std::wstring;
 
 // Returns $TEST_TMPDIR as a wstring.
-// The result will have backslashes as directory separators (but no UNC prefix).
+// The result will have backslashes as directory separators, but no UNC prefix.
+// The result will also not have a trailing backslash.
 wstring GetTestTmpDirW();
 
 // Deletes all files and directories under `path`.
diff --git a/src/test/native/BUILD b/src/test/native/BUILD
index bd3f90d40b..be04c76466 100644
--- a/src/test/native/BUILD
+++ b/src/test/native/BUILD
@@ -9,19 +9,28 @@ filegroup(
 )
 
 cc_test(
-    name = "windows_util_test",
+    name = "windows_jni_test",
+    size = "small",
     srcs = select({
-        "//src:windows": ["windows_util_test.cc"],
-        "//src:windows_msvc": ["windows_util_test.cc"],
+        "//src:windows": [
+            "windows_util_test.cc",
+            "windows_file_operations_test.cc",
+        ],
+        "//src:windows_msvc": [
+            "windows_util_test.cc",
+            "windows_file_operations_test.cc",
+        ],
         "//conditions:default": ["dummy_test.cc"],
     }),
     deps = select({
         "//src:windows": [
             "//src/main/native:windows_jni_lib",
+            "//src/test/cpp/util:windows_test_util",
             "//third_party:gtest",
         ],
         "//src:windows_msvc": [
             "//src/main/native:windows_jni_lib",
+            "//src/test/cpp/util:windows_test_util",
             "//third_party:gtest",
         ],
         "//conditions:default": [],
diff --git a/src/test/native/windows_file_operations_test.cc b/src/test/native/windows_file_operations_test.cc
new file mode 100644
index 0000000000..f3258a9a86
--- /dev/null
+++ b/src/test/native/windows_file_operations_test.cc
@@ -0,0 +1,111 @@
+// Copyright 2017 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.
+#include <stdlib.h>
+#include <string.h>
+#include <windows.h>
+
+#include <memory>  // unique_ptr
+#include <sstream>
+#include <string>
+
+#include "gtest/gtest.h"
+#include "src/main/native/windows_file_operations.h"
+#include "src/test/cpp/util/windows_test_util.h"
+
+#if !defined(COMPILER_MSVC) && !defined(__CYGWIN__)
+#error("This test should only be run on Windows")
+#endif  // !defined(COMPILER_MSVC) && !defined(__CYGWIN__)
+
+namespace windows_util {
+
+using blaze_util::DeleteAllUnder;
+using blaze_util::GetTestTmpDirW;
+using std::string;
+using std::unique_ptr;
+using std::wstring;
+
+static const wstring kUncPrefix = wstring(L"\\\\?\\");
+
+class WindowsFileOperationsTest : public ::testing::Test {
+ public:
+  void TearDown() override { DeleteAllUnder(GetTestTmpDirW()); }
+};
+
+TEST_F(WindowsFileOperationsTest, TestCreateJunction) {
+  wstring tmp(kUncPrefix + GetTestTmpDirW());
+  wstring target(tmp + L"\\junc_target");
+  EXPECT_TRUE(::CreateDirectoryW(target.c_str(), NULL));
+  wstring file1(target + L"\\foo");
+  EXPECT_TRUE(blaze_util::CreateDummyFile(file1));
+
+  EXPECT_EQ(IS_JUNCTION_NO, IsJunctionOrDirectorySymlink(target.c_str()));
+  EXPECT_NE(INVALID_FILE_ATTRIBUTES, ::GetFileAttributesW(file1.c_str()));
+
+  wstring name(tmp + L"\\junc_name");
+
+  // Create junctions from all combinations of UNC-prefixed or non-prefixed name
+  // and target paths.
+  ASSERT_EQ("", CreateJunction(name + L"1", target));
+  ASSERT_EQ("", CreateJunction(name + L"2", target.substr(4)));
+  ASSERT_EQ("", CreateJunction(name.substr(4) + L"3", target));
+  ASSERT_EQ("", CreateJunction(name.substr(4) + L"4", target.substr(4)));
+
+  // Assert creation of the junctions.
+  ASSERT_EQ(IS_JUNCTION_YES,
+            IsJunctionOrDirectorySymlink((name + L"1").c_str()));
+  ASSERT_EQ(IS_JUNCTION_YES,
+            IsJunctionOrDirectorySymlink((name + L"2").c_str()));
+  ASSERT_EQ(IS_JUNCTION_YES,
+            IsJunctionOrDirectorySymlink((name + L"3").c_str()));
+  ASSERT_EQ(IS_JUNCTION_YES,
+            IsJunctionOrDirectorySymlink((name + L"4").c_str()));
+
+  // Assert that the file is visible under all junctions.
+  ASSERT_NE(INVALID_FILE_ATTRIBUTES,
+            ::GetFileAttributesW((name + L"1\\foo").c_str()));
+  ASSERT_NE(INVALID_FILE_ATTRIBUTES,
+            ::GetFileAttributesW((name + L"2\\foo").c_str()));
+  ASSERT_NE(INVALID_FILE_ATTRIBUTES,
+            ::GetFileAttributesW((name + L"3\\foo").c_str()));
+  ASSERT_NE(INVALID_FILE_ATTRIBUTES,
+            ::GetFileAttributesW((name + L"4\\foo").c_str()));
+
+  // Assert that no other file exists under the junctions.
+  wstring file2(target + L"\\bar");
+  ASSERT_EQ(INVALID_FILE_ATTRIBUTES, ::GetFileAttributesW(file2.c_str()));
+  ASSERT_EQ(INVALID_FILE_ATTRIBUTES,
+            ::GetFileAttributesW((name + L"1\\bar").c_str()));
+  ASSERT_EQ(INVALID_FILE_ATTRIBUTES,
+            ::GetFileAttributesW((name + L"2\\bar").c_str()));
+  ASSERT_EQ(INVALID_FILE_ATTRIBUTES,
+            ::GetFileAttributesW((name + L"3\\bar").c_str()));
+  ASSERT_EQ(INVALID_FILE_ATTRIBUTES,
+            ::GetFileAttributesW((name + L"4\\bar").c_str()));
+
+  // Create a new file.
+  EXPECT_TRUE(blaze_util::CreateDummyFile(file2));
+  EXPECT_NE(INVALID_FILE_ATTRIBUTES, ::GetFileAttributesW(file2.c_str()));
+
+  // Assert that the newly created file appears under all junctions.
+  ASSERT_NE(INVALID_FILE_ATTRIBUTES,
+            ::GetFileAttributesW((name + L"1\\bar").c_str()));
+  ASSERT_NE(INVALID_FILE_ATTRIBUTES,
+            ::GetFileAttributesW((name + L"2\\bar").c_str()));
+  ASSERT_NE(INVALID_FILE_ATTRIBUTES,
+            ::GetFileAttributesW((name + L"3\\bar").c_str()));
+  ASSERT_NE(INVALID_FILE_ATTRIBUTES,
+            ::GetFileAttributesW((name + L"4\\bar").c_str()));
+}
+
+}  // namespace windows_util