Fix a corner case where createDirectory would fail on windows

The //?/ prefix needs to be added to directories if the length is
greater than MAX_PATH - 12, however the PATHCCH_ALLOW_LONG_PATHS to
PathAllocCanonicalize would only do that if the path was greater than
MAX_PATH. This change uses PATHCCH_ENSURE_IS_EXTENDED_LENGTH_PATH, which
forces it on all the time.  Just needed to remove the prefix in a few
places as it was making it way out into tests as this is suppose to be
transparent to the user.

This also fixes createDirectory() "withIntermediateDirectories: true"
for long paths on Windows.

Author: daveinglis

Sources/FoundationEssentials/FileManager/FileManager+Directories.swift

@@ -271,36 +271,49 @@ extension _FileManagerImpl {
             SECURITY_ATTRIBUTES(nLength: DWORD(MemoryLayout<SECURITY_ATTRIBUTES>.size),
                                 lpSecurityDescriptor: nil,
                                 bInheritHandle: false)
-        // `SHCreateDirectoryExW` creates intermediate directories while `CreateDirectoryW` does not.
+        // `CreateDirectoryW` does not create intermediate directories, so we need to handle that manually.  
+        // Note: `SHCreateDirectoryExW` seems to have issues with long paths.
         if createIntermediates {
-            // `SHCreateDirectoryExW` requires an absolute path while `CreateDirectoryW` works based on the current working
-            // directory.
-            try path.withNTPathRepresentation { pwszPath in
-                let errorCode = SHCreateDirectoryExW(nil, pwszPath, &saAttributes)
-                guard let errorCode = DWORD(exactly: errorCode) else {
-                    // `SHCreateDirectoryExW` returns `Int` but all error codes are defined in terms of `DWORD`, aka
-                    // `UInt`. We received an unknown error code.
-                    throw CocoaError.errorWithFilePath(.fileWriteUnknown, path)
-                }
-                switch errorCode {
-                case ERROR_SUCCESS:
-                    if let attributes {
-                        try? fileManager.setAttributes(attributes, ofItemAtPath: path)
+            // Create intermediate directories recursively
+            func createDirectoryRecursively(at directoryPath: String) throws {
+                // Check if directory already exists
+                var isDirectory: Bool = false
+                if fileExists(atPath: directoryPath, isDirectory: &isDirectory) {
+                    if isDirectory {
+                        return // Directory already exists, nothing to do
+                    } else {
+                        // A file exists at this path, which is an error
+                        throw CocoaError.errorWithFilePath(directoryPath, win32: ERROR_ALREADY_EXISTS, reading: false)
                     }
-                case ERROR_ALREADY_EXISTS:
-                    var isDirectory: Bool = false
-                    if fileExists(atPath: path, isDirectory: &isDirectory), isDirectory {
-                        // A directory already exists at this path, which is not an error if we have
-                        // `createIntermediates == true`.
-                        break
+                }
+                
+                // Get parent directory
+                let parentPath = directoryPath.deletingLastPathComponent()
+                if !parentPath.isEmpty && parentPath != directoryPath {
+                    // Recursively create parent directory first
+                    try createDirectoryRecursively(at: parentPath)
+                }
+                
+                // Create this directory
+                try directoryPath.withNTPathRepresentation { pwszPath in
+                    guard CreateDirectoryW(pwszPath, &saAttributes) else {
+                        let lastError = GetLastError()
+                        // If directory was created by another thread/process between our check and creation, that's OK
+                        if lastError == ERROR_ALREADY_EXISTS {
+                            var isDir: Bool = false
+                            if fileExists(atPath: directoryPath, isDirectory: &isDir), isDir {
+                                return // Directory now exists, success
+                            }
+                        }
+                        throw CocoaError.errorWithFilePath(directoryPath, win32: lastError, reading: false)
                     }
-                    // A file (not a directory) exists at the given path or the file creation failed and the item
-                    // at this path has been deleted before the call to `fileExists`. Throw the original error.
-                    fallthrough
-                default:
-                    throw CocoaError.errorWithFilePath(path, win32: errorCode, reading: false)
                 }
             }
+            
+            try createDirectoryRecursively(at: path)
+            if let attributes {
+                try? fileManager.setAttributes(attributes, ofItemAtPath: path)
+            }
         } else {
             try path.withNTPathRepresentation { pwszPath in
                 guard CreateDirectoryW(pwszPath, &saAttributes) else {
@@ -497,9 +510,14 @@ extension _FileManagerImpl {
         // This is solely to minimize the number of allocations and number of bytes allocated versus starting with a hardcoded value like MAX_PATH.
         // We should NOT early-return if this returns 0, in order to avoid TOCTOU issues.
         let dwSize = GetCurrentDirectoryW(0, nil)
-        return try? FillNullTerminatedWideStringBuffer(initialSize: dwSize >= 0 ? dwSize : DWORD(MAX_PATH), maxSize: DWORD(Int16.max)) {
+        let cwd = try? FillNullTerminatedWideStringBuffer(initialSize: dwSize >= 0 ? dwSize : DWORD(MAX_PATH), maxSize: DWORD(Int16.max)) {
             GetCurrentDirectoryW(DWORD($0.count), $0.baseAddress)
         }
+        
+        // Handle Windows NT object namespace prefix
+        // The \\?\ prefix is used by Windows NT for device paths and may appear
+        // in current working directory paths. We strip it to return a standard path.
+        return cwd?.removingNTPathPrefix()
 #else
         withUnsafeTemporaryAllocation(of: CChar.self, capacity: FileManager.MAX_PATH_SIZE) { buffer in
             guard getcwd(buffer.baseAddress!, FileManager.MAX_PATH_SIZE) != nil else {

Sources/FoundationEssentials/FileManager/FileOperations.swift

@@ -366,15 +366,14 @@ enum _FileOperations {
             var stack = [(path, false)]
             while let (directory, checked) = stack.popLast() {
                 try directory.withNTPathRepresentation {
-                    let ntpath = String(decodingCString: $0, as: UTF16.self)
-
-                    guard checked || filemanager?._shouldRemoveItemAtPath(ntpath) ?? true else { return }
+                    let fullpath = String(decodingCString: $0, as: UTF16.self).removingNTObjectNamespacePrefix()
 
+                    guard checked || filemanager?._shouldRemoveItemAtPath(fullpath) ?? true else { return }
                     if RemoveDirectoryW($0) { return }
                     let dwError: DWORD = GetLastError()
                     guard dwError == ERROR_DIR_NOT_EMPTY else {
                         let error = CocoaError.removeFileError(dwError, directory)
-                        guard (filemanager?._shouldProceedAfter(error: error, removingItemAtPath: ntpath) ?? false) else {
+                        guard (filemanager?._shouldProceedAfter(error: error, removingItemAtPath: fullpath) ?? false) else {
                             throw error
                         }
                         return
@@ -383,29 +382,29 @@ enum _FileOperations {
 
                     for entry in _Win32DirectoryContentsSequence(path: directory, appendSlashForDirectory: false, prefix: [directory]) {
                         try entry.fileNameWithPrefix.withNTPathRepresentation {
-                            let ntpath = String(decodingCString: $0, as: UTF16.self)
+                            let fullpath = String(decodingCString: $0, as: UTF16.self).removingNTObjectNamespacePrefix()
 
                             if entry.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY == FILE_ATTRIBUTE_DIRECTORY,
                                     entry.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT != FILE_ATTRIBUTE_REPARSE_POINT {
-                                if filemanager?._shouldRemoveItemAtPath(ntpath) ?? true {
-                                    stack.append((ntpath, true))
+                                if filemanager?._shouldRemoveItemAtPath(fullpath) ?? true {
+                                    stack.append((fullpath, true))
                                 }
                             } else {
                                 if entry.dwFileAttributes & FILE_ATTRIBUTE_READONLY == FILE_ATTRIBUTE_READONLY {
                                     guard SetFileAttributesW($0, entry.dwFileAttributes & ~FILE_ATTRIBUTE_READONLY) else {
-                                        throw CocoaError.removeFileError(GetLastError(), ntpath)
+                                        throw CocoaError.removeFileError(GetLastError(), entry.fileName)
                                     }
                                 }
                                 if entry.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY == FILE_ATTRIBUTE_DIRECTORY {
-                                    guard filemanager?._shouldRemoveItemAtPath(ntpath) ?? true else { return }
+                                    guard filemanager?._shouldRemoveItemAtPath(fullpath) ?? true else { return }
                                     if !RemoveDirectoryW($0) {
                                         let error = CocoaError.removeFileError(GetLastError(), entry.fileName)
                                         guard (filemanager?._shouldProceedAfter(error: error, removingItemAtPath: entry.fileNameWithPrefix) ?? false) else {
                                             throw error
                                         }
                                     }
                                 } else {
-                                    guard filemanager?._shouldRemoveItemAtPath(ntpath) ?? true else { return }
+                                    guard filemanager?._shouldRemoveItemAtPath(fullpath) ?? true else { return }
                                     if !DeleteFileW($0) {
                                         let error = CocoaError.removeFileError(GetLastError(), entry.fileName)
                                         guard (filemanager?._shouldProceedAfter(error: error, removingItemAtPath: entry.fileNameWithPrefix) ?? false) else {

Sources/FoundationEssentials/String/String+Internals.swift

@@ -66,7 +66,8 @@ extension String {
                 // 2. Canonicalize the path.
                 // This will add the \\?\ prefix if needed based on the path's length.
                 var pwszCanonicalPath: LPWSTR?
-                let flags: ULONG = PATHCCH_ALLOW_LONG_PATHS
+                // Alway add the long path prefix since we don't know if this is a directory.
+                let flags: ULONG =  PATHCCH_ENSURE_IS_EXTENDED_LENGTH_PATH
                 let result = PathAllocCanonicalize(pwszFullPath.baseAddress, flags, &pwszCanonicalPath)
                 if let pwszCanonicalPath {
                     defer { LocalFree(pwszCanonicalPath) }
@@ -79,6 +80,32 @@ extension String {
             }
         }
     }
+    /// Removes the Windows NT prefix for long file paths if present.
+    /// The \\?\ prefix is used by Windows NT for device paths and may appear
+    /// in paths returned by system APIs. This method provides a clean way to
+    /// normalize such paths to standard format.
+    ///
+    /// - Returns: A string with the NT object namespace prefix removed, or the original string if no prefix is found.
+    package func removingNTPathPrefix() -> String {
+        // Use Windows API PathCchStripPrefix for robust prefix handling
+        return withCString(encodedAs: UTF16.self) { pwszPath in
+            // Calculate required buffer size (original path length should be sufficient)
+            let length = wcslen(pwszPath) + 1 // include null terminator
+            
+            return withUnsafeTemporaryAllocation(of: WCHAR.self, capacity: Int(length)) { buffer  in
+                // Copy the original path to the buffer
+                _ = buffer.initialize(from: UnsafeBufferPointer(start: pwszPath, count: Int(length)))
+
+                // Call PathCchStripPrefix (modifies buffer in place)
+                _ = PathCchStripPrefix(buffer.baseAddress, buffer.count)                
+
+                // Return the result regardless of success/failure
+                // PathCchStripPrefix modifies the buffer in-place and returns S_OK on success
+                // If it fails, the original path remains unchanged, which is the desired fallback
+                return String(decodingCString: buffer.baseAddress!, as: UTF16.self)
+            }
+        }
+    }
 }
 #endif
 

Sources/FoundationEssentials/String/String+Path.swift

@@ -741,15 +741,7 @@ extension String {
                 guard GetFinalPathNameByHandleW(hFile, $0.baseAddress, dwLength, VOLUME_NAME_DOS) == dwLength - 1 else {
                     return nil
                 }
-
-                let pathBaseAddress: UnsafePointer<WCHAR>
-                if Array($0.prefix(4)) == Array(#"\\?\"#.utf16) {
-                    // When using `VOLUME_NAME_DOS`, the returned path uses `\\?\`.
-                    pathBaseAddress = UnsafePointer($0.baseAddress!.advanced(by: 4))
-                } else {
-                    pathBaseAddress = UnsafePointer($0.baseAddress!)
-                }
-                return String(decodingCString: pathBaseAddress, as: UTF16.self)
+                return String(decodingCString: UnsafePointer($0.baseAddress!), as: UTF16.self).removingNTPathPrefix()
             }
         }
         #else // os(Windows)

Sources/FoundationEssentials/WinSDK+Extensions.swift

@@ -229,6 +229,10 @@ package var PATHCCH_ALLOW_LONG_PATHS: ULONG {
     ULONG(WinSDK.PATHCCH_ALLOW_LONG_PATHS.rawValue)
 }
 
+package var PATHCCH_ENSURE_IS_EXTENDED_LENGTH_PATH: ULONG {
+    ULONG(WinSDK.PATHCCH_ENSURE_IS_EXTENDED_LENGTH_PATH.rawValue)
+}
+
 package var RRF_RT_REG_SZ: DWORD {
     DWORD(WinSDK.RRF_RT_REG_SZ)
 }

Tests/FoundationEssentialsTests/FileManager/FileManagerTests.swift

@@ -1133,6 +1133,12 @@ private struct FileManagerTests {
             let fileName = UUID().uuidString
             let cwd = fileManager.currentDirectoryPath
 
+            #expect(fileManager.changeCurrentDirectoryPath(cwd))
+            #expect(cwd == fileManager.currentDirectoryPath)
+
+            let nearLimitDir = cwd + "/" + String(repeating: "A", count: 255 - cwd.count)
+            #expect(throws: Never.self) { try fileManager.createDirectory(at: URL(fileURLWithPath: nearLimitDir), withIntermediateDirectories: false) }
+
             #expect(fileManager.createFile(atPath: dirName + "/" + fileName, contents: nil))
 
             let dirURL = URL(filePath: dirName, directoryHint: .checkFileSystem)
@@ -1171,12 +1177,6 @@ private struct FileManagerTests {
 
             #expect(throws: Never.self) { try fileManager.createDirectory(at: URL(fileURLWithPath: dirName + "/" + "subdir1"), withIntermediateDirectories: false) }
 
-            // SHCreateDirectoryExW's path argument is limited to 248 characters, and the \\?\ prefix doesn't help.
-            // https://learn.microsoft.com/en-us/windows/win32/api/shlobj_core/nf-shlobj_core-shcreatedirectoryexw
-            #expect(throws: (any Error).self) {
-                try fileManager.createDirectory(at: URL(fileURLWithPath: dirName + "/" + "subdir2" + "/" + "subdir3"), withIntermediateDirectories: true)
-            }
-
             // SetCurrentDirectory seems to be limited to MAX_PATH unconditionally, counter to the documentation.
             // https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-setcurrentdirectory
             // https://github.com/MicrosoftDocs/feedback/issues/1441
@@ -1195,8 +1195,12 @@ private struct FileManagerTests {
 
             #expect((cwd + "/" + dirName + "/" + "lnk").resolvingSymlinksInPath == (cwd + "/" + dirName + "/" + fileName).resolvingSymlinksInPath)
 
-            #expect(throws: Never.self) { try fileManager.createDirectory(at: URL(fileURLWithPath: dirName + "/" + "subdir2"), withIntermediateDirectories: false) }
-            #expect(throws: Never.self) { try fileManager.createDirectory(at: URL(fileURLWithPath: dirName + "/" + "subdir2" + "/" + "subdir3"), withIntermediateDirectories: false) }
+            #expect(throws: Never.self) {
+                try fileManager.createDirectory(at: URL(fileURLWithPath: dirName + "/" + "subdir2" + "/" + "subdir3"), withIntermediateDirectories: true)
+            }
+            #expect(throws: Never.self) { try fileManager.createDirectory(at: URL(fileURLWithPath: dirName + "/" + "subdir4"), withIntermediateDirectories: false) }
+            #expect(throws: Never.self) { try fileManager.createDirectory(at: URL(fileURLWithPath: dirName + "/" + "subdir4" + "/" + "subdir5"), withIntermediateDirectories: false) }
+
             #expect(throws: Never.self) { try Data().write(to: URL(fileURLWithPath: dirName + "/" + "subdir2" + "/" + "subdir3" + "/" + "somefile")) }
             #expect(throws: Never.self) { try Data().write(to: URL(fileURLWithPath: dirName + "/" + "subdir2" + "/" + "subdir3" + "/" + "somefile2")) }
             #expect(throws: Never.self) { try fileManager.moveItem(atPath: dirName + "/" + "subdir2" + "/" + "subdir3" + "/" + "somefile2", toPath: dirName + "/" + "subdir2" + "/" + "subdir3" + "/" + "somefile3") }

Tests/FoundationEssentialsTests/String/StringNTPathTests.swift

@@ -0,0 +1,75 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2023 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#if os(Windows)
+
+import Testing
+
+#if FOUNDATION_FRAMEWORK
+import Foundation
+#else
+import FoundationEssentials
+#endif
+
+@Suite("String NT Path Tests")
+struct StringNTPathTests {
+
+    @Test("Normal drive path, no prefix")
+    func noPrefix() {
+        let path = "C:\\Windows\\System32"
+        #expect(path.removingNTPathPrefix() == "C:\\Windows\\System32")
+    }
+
+    @Test("Extended-length path prefix (\\\\?\\)")
+    func extendedPrefix() {
+        let path = #"\\?\C:\Windows\System32"#
+        #expect(path.removingNTPathPrefix() == "C:\\Windows\\System32")
+    }
+
+    @Test("UNC path with extended prefix (\\\\?\\UNC\\)")
+    func uncExtendedPrefix() {
+        let path = #"\\?\UNC\Server\Share\Folder"#
+        #expect(path.removingNTPathPrefix() == #"\\Server\Share\Folder"#)
+    }
+
+    @Test("UNC path without extended prefix")
+    func uncNormal() {
+        let path = #"\\Server\Share\Folder"#
+        #expect(path.removingNTPathPrefix() == #"\\Server\Share\Folder"#)
+    }
+
+    @Test("Empty string should stay empty")
+    func emptyString() {
+        let path = ""
+        #expect(path.removingNTPathPrefix() == "")
+    }
+
+    @Test("Path with only prefix should return empty")
+    func prefixOnly() {
+        let path = #"\\?\C:\"#
+        #expect(path.removingNTPathPrefix() == #"C:\"#)
+    }
+
+    @Test("Path longer than MAX_PATH (260 chars)")
+    func longPathBeyondMaxPath() {
+        // Create a folder name repeated to exceed 260 chars
+        let longComponent = String(repeating: "A", count: 280)
+        let rawPath = #"\\?\C:\Test\"# + longComponent
+
+        // After stripping, it should drop the \\?\ prefix but keep the full long component
+        let expected = "C:\\Test\\" + longComponent
+
+        let stripped = rawPath.removingNTPathPrefix()
+        #expect(stripped == expected)
+    }    
+}
+#endif