Enable long path on Windows

File APIs on Windows can now handle files and directories identified by
long paths (greater than 260 characters). For directory, the limit is
248.

Some restrictions from Windows:
1. The size limit for long path is 32,767 characters.
2. Each component separated by backslashes should not be more than 255
characters.

Reference: https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file#maximum-path-length-limitation.

Note that `Directory.current` does not work with long path.

Bug: dart-lang/sdk#42416
Change-Id: Ia1b4608d393fb36f1d843858c6f076f3c825dc83
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/152736
Reviewed-by: Alexander Aprelev <[email protected]>
Commit-Queue: Zichang Guo <[email protected]>

Author: zichangg

CHANGELOG.md

@@ -130,9 +130,14 @@ applications (issue [flutter/flutter#63038][]).
 *   [Abstract Unix Domain Socket][] is supported on Linux/Android now. Using an
     `InternetAddress` with `address` starting with '@' and type being
     `InternetAddressType.Unix` will create an abstract Unix Domain Socket.
+*   On Windows, file APIs can now handle files and directories identified by
+    long paths (greater than 260 characters). It complies with all restrictions
+    from [Long Path on Windows][]. Note that `Directory.current` does not work
+    with long path.
 
 [#42006]: https://github.com/dart-lang/sdk/issues/42006
 [Abstract Unix Domain Socket]: http://man7.org/linux/man-pages/man7/unix.7.html
+[Long Path on Windows]: https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file#maximum-path-length-limitation
 
 #### `dart:html`
 

runtime/bin/builtin_impl_sources.gni

@@ -45,6 +45,7 @@ builtin_impl_sources = [
   "file_macos.cc",
   "file_support.cc",
   "file_win.cc",
+  "file_win.h",
   "io_buffer.cc",
   "io_buffer.h",
   "isolate_data.cc",

runtime/bin/directory_win.cc

@@ -13,6 +13,7 @@
 #include "bin/crypto.h"
 #include "bin/dartutils.h"
 #include "bin/file.h"
+#include "bin/file_win.h"
 #include "bin/namespace.h"
 #include "bin/utils.h"
 #include "bin/utils_win.h"
@@ -21,8 +22,6 @@
 
 #undef DeleteFile
 
-#define MAX_LONG_PATH 32767
-
 namespace dart {
 namespace bin {
 
@@ -278,41 +277,47 @@ static bool DeleteEntry(LPWIN32_FIND_DATAW find_file_data, PathBuffer* path) {
 }
 
 static bool DeleteRecursively(PathBuffer* path) {
-  DWORD attributes = GetFileAttributesW(path->AsStringW());
+  PathBuffer prefixed_path;
+  if (!prefixed_path.Add(PrefixLongDirectoryPath(path->AsScopedString()))) {
+    return false;
+  }
+
+  DWORD attributes = GetFileAttributesW(prefixed_path.AsStringW());
   if (attributes == INVALID_FILE_ATTRIBUTES) {
     return false;
   }
   // If the directory is a junction, it's pointing to some other place in the
   // filesystem that we do not want to recurse into.
   if ((attributes & FILE_ATTRIBUTE_REPARSE_POINT) != 0) {
     // Just delete the junction itself.
-    return RemoveDirectoryW(path->AsStringW()) != 0;
+    return RemoveDirectoryW(prefixed_path.AsStringW()) != 0;
   }
   // If it's a file, remove it directly.
   if ((attributes & FILE_ATTRIBUTE_DIRECTORY) == 0) {
-    return DeleteFile(L"", path);
+    return DeleteFile(L"", &prefixed_path);
   }
 
-  if (!path->AddW(L"\\*")) {
+  if (!prefixed_path.AddW(L"\\*")) {
     return false;
   }
 
   WIN32_FIND_DATAW find_file_data;
-  HANDLE find_handle = FindFirstFileW(path->AsStringW(), &find_file_data);
+  HANDLE find_handle =
+      FindFirstFileW(prefixed_path.AsStringW(), &find_file_data);
 
   if (find_handle == INVALID_HANDLE_VALUE) {
     return false;
   }
 
   // Adjust the path by removing the '*' used for the search.
-  int path_length = path->length() - 1;
-  path->Reset(path_length);
+  int path_length = prefixed_path.length() - 1;
+  prefixed_path.Reset(path_length);
 
   do {
-    if (!DeleteEntry(&find_file_data, path)) {
+    if (!DeleteEntry(&find_file_data, &prefixed_path)) {
       break;
     }
-    path->Reset(path_length);  // DeleteEntry adds to the path.
+    prefixed_path.Reset(path_length);  // DeleteEntry adds to the path.
   } while (FindNextFileW(find_handle, &find_file_data) != 0);
 
   DWORD last_error = GetLastError();
@@ -324,8 +329,9 @@ static bool DeleteRecursively(PathBuffer* path) {
     return false;
   }
   // All content deleted succesfully, try to delete directory.
-  path->Reset(path_length - 1);  // Drop the "\" from the end of the path.
-  return RemoveDirectoryW(path->AsStringW()) != 0;
+  prefixed_path.Reset(path_length -
+                      1);  // Drop the "\" from the end of the path.
+  return RemoveDirectoryW(prefixed_path.AsStringW()) != 0;
 }
 
 static Directory::ExistsResult ExistsHelper(const wchar_t* dir_name) {
@@ -349,7 +355,8 @@ static Directory::ExistsResult ExistsHelper(const wchar_t* dir_name) {
 
 Directory::ExistsResult Directory::Exists(Namespace* namespc,
                                           const char* dir_name) {
-  Utf8ToWideScope system_name(dir_name);
+  const char* prefixed_dir_name = PrefixLongDirectoryPath(dir_name);
+  Utf8ToWideScope system_name(prefixed_dir_name);
   return ExistsHelper(system_name.wide());
 }
 
@@ -369,7 +376,8 @@ char* Directory::CurrentNoScope() {
 }
 
 bool Directory::Create(Namespace* namespc, const char* dir_name) {
-  Utf8ToWideScope system_name(dir_name);
+  const char* prefixed_dir_name = PrefixLongDirectoryPath(dir_name);
+  Utf8ToWideScope system_name(prefixed_dir_name);
   int create_status = CreateDirectoryW(system_name.wide(), NULL);
   // If the directory already existed, treat it as a success.
   if ((create_status == 0) && (GetLastError() == ERROR_ALREADY_EXISTS) &&
@@ -475,10 +483,11 @@ const char* Directory::CreateTemp(Namespace* namespc, const char* prefix) {
 bool Directory::Delete(Namespace* namespc,
                        const char* dir_name,
                        bool recursive) {
+  const char* prefixed_dir_name = PrefixLongDirectoryPath(dir_name);
   bool result = false;
-  Utf8ToWideScope system_dir_name(dir_name);
+  Utf8ToWideScope system_dir_name(prefixed_dir_name);
   if (!recursive) {
-    if (File::GetType(namespc, dir_name, true) == File::kIsDirectory) {
+    if (File::GetType(namespc, prefixed_dir_name, true) == File::kIsDirectory) {
       result = (RemoveDirectoryW(system_dir_name.wide()) != 0);
     } else {
       SetLastError(ERROR_FILE_NOT_FOUND);
@@ -495,18 +504,20 @@ bool Directory::Delete(Namespace* namespc,
 bool Directory::Rename(Namespace* namespc,
                        const char* path,
                        const char* new_path) {
-  Utf8ToWideScope system_path(path);
-  Utf8ToWideScope system_new_path(new_path);
+  const char* prefixed_dir = PrefixLongDirectoryPath(path);
+  Utf8ToWideScope system_path(prefixed_dir);
   ExistsResult exists = ExistsHelper(system_path.wide());
   if (exists != EXISTS) {
     return false;
   }
+  const char* prefixed_new_dir = PrefixLongDirectoryPath(new_path);
+  Utf8ToWideScope system_new_path(prefixed_new_dir);
   ExistsResult new_exists = ExistsHelper(system_new_path.wide());
   // MoveFile does not allow replacing existing directories. Therefore,
   // if the new_path is currently a directory we need to delete it
   // first.
   if (new_exists == EXISTS) {
-    bool success = Delete(namespc, new_path, true);
+    bool success = Delete(namespc, prefixed_new_dir, true);
     if (!success) {
       return false;
     }