Windows: Add support for SYMLINKS

* Both `stat` and `readdir` entry points support returning FILE_TYPE_SYMLINK
* Both `stat` and `readdir` entry points support the "followLink" parameter
* Add a `stat-L` option in the test app (`stat` with `followLink` option)
* Add a `ls-L` option in test app (`ls` with `followLink` option)
* Requires Windows Vista/Windows Server 2008 or later

Author: rpaquay

src/main/cpp/win.cpp

@@ -87,7 +87,19 @@ wchar_t* add_prefix(wchar_t* path, int path_len, wchar_t* prefix) {
     int str_len = path_len + prefix_len;
     wchar_t* str = (wchar_t*)malloc(sizeof(wchar_t) * (str_len + 1));
     wcscpy_s(str, str_len + 1, prefix);
-    wcscat_s(str, str_len + 1, path);
+    wcsncat_s(str, str_len + 1, path, path_len);
+    return str;
+}
+
+//
+// Returns a UTF-16 string that is the concatenation of |path| and |suffix|.
+//
+wchar_t* add_suffix(wchar_t* path, int path_len, wchar_t* suffix) {
+    int suffix_len = wcslen(suffix);
+    int str_len = path_len + suffix_len;
+    wchar_t* str = (wchar_t*)malloc(sizeof(wchar_t) * (str_len + 1));
+    wcsncpy_s(str, str_len + 1, path, path_len);
+    wcscat_s(str, str_len + 1, suffix);
     return str;
 }
 
@@ -127,6 +139,125 @@ wchar_t* java_to_wchar_path(JNIEnv *env, jstring string, jobject result) {
     }
 }
 
+//
+// Returns 'true' if a file, given its attributes, is a Windows Symbolic Link.
+//
+bool is_file_symlink(DWORD dwFileAttributes, DWORD reparseTagData) {
+    //
+    // See https://docs.microsoft.com/en-us/windows/desktop/fileio/reparse-point-tags
+    //  IO_REPARSE_TAG_SYMLINK (0xA000000C)
+    //
+    return 
+        ((dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) == FILE_ATTRIBUTE_REPARSE_POINT) &&
+        (reparseTagData == IO_REPARSE_TAG_SYMLINK);
+}
+
+jlong lastModifiedNanos(FILETIME* time) {
+    return ((jlong)time->dwHighDateTime << 32) | time->dwLowDateTime;
+}
+
+jlong lastModifiedNanos(LARGE_INTEGER* time) {
+    return ((jlong)time->HighPart << 32) | time->LowPart;
+}
+
+typedef struct file_stat {
+    int fileType;
+    LONG64 lastModified;
+    LONG64 size;
+} file_stat_t;
+
+//
+// Retrieves the file attributes for the file specified by |pathStr|.
+// If |followLink| is true, symbolic link targets are resolved.
+//
+// * Returns ERROR_SUCCESS if the file exists and file attributes can be retrieved,
+// * Returns ERROR_SUCCESS with a FILE_TYPE_MISSING if the file does not exist,
+// * Returns a Win32 error code in all other cases.
+//
+DWORD get_file_stat(wchar_t* pathStr, jboolean followLink, file_stat_t* pFileStat) {
+#ifdef WINDOWS_MIN
+    WIN32_FILE_ATTRIBUTE_DATA attr;
+    BOOL ok = GetFileAttributesExW(pathStr, GetFileExInfoStandard, &attr);
+    if (!ok) {
+        DWORD error = GetLastError();
+        if (error == ERROR_FILE_NOT_FOUND || error == ERROR_PATH_NOT_FOUND || error == ERROR_NOT_READY) {
+            // Treat device with no media as missing
+            pFileStat->lastModified = 0;
+            pFileStat->size = 0;
+            pFileStat->fileType = FILE_TYPE_MISSING;
+            return ERROR_SUCCESS;
+        }
+        return error;
+    }
+    pFileStat->lastModified = lastModifiedNanos(&attr.ftLastWriteTime);
+    if (attr.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) {
+        pFileStat->size = 0;
+        pFileStat->fileType = FILE_TYPE_DIRECTORY;
+    } else {
+        pFileStat->size = ((LONG64)attr.nFileSizeHigh << 32) | attr.nFileSizeLow;
+        pFileStat->fileType = FILE_TYPE_FILE;
+    }
+    return ERROR_SUCCESS;
+#else //WINDOWS_MIN: Windows Vista+ support for symlinks
+    DWORD dwFlagsAndAttributes = FILE_FLAG_BACKUP_SEMANTICS;
+    if (!followLink) {
+        dwFlagsAndAttributes |= FILE_FLAG_OPEN_REPARSE_POINT;
+    }
+    HANDLE fileHandle = CreateFileW(
+        pathStr, // lpFileName
+        GENERIC_READ, // dwDesiredAccess
+        FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, // dwShareMode
+        NULL, // lpSecurityAttributes
+        OPEN_EXISTING, // dwCreationDisposition
+        dwFlagsAndAttributes, // dwFlagsAndAttributes
+        NULL // hTemplateFile
+        );
+    if (fileHandle == INVALID_HANDLE_VALUE) {
+        DWORD error = GetLastError();
+        if (error == ERROR_FILE_NOT_FOUND || error == ERROR_PATH_NOT_FOUND || error == ERROR_NOT_READY) {
+            // Treat device with no media as missing
+            pFileStat->lastModified = 0;
+            pFileStat->size = 0;
+            pFileStat->fileType = FILE_TYPE_MISSING;
+            return ERROR_SUCCESS;
+        }
+        return error;
+    }
+
+    // This call allows retrieving almost everything except for the reparseTag
+    BY_HANDLE_FILE_INFORMATION fileInfo;
+    BOOL ok = GetFileInformationByHandle(fileHandle, &fileInfo);
+    if (!ok) {
+        DWORD error = GetLastError();
+        CloseHandle(fileHandle);
+        return error;
+    }
+
+    // This call allows retrieving the reparse tag
+    FILE_ATTRIBUTE_TAG_INFO fileTagInfo;
+    ok = GetFileInformationByHandleEx(fileHandle, FileAttributeTagInfo, &fileTagInfo, sizeof(fileTagInfo));
+    if (!ok) {
+        DWORD error = GetLastError();
+        CloseHandle(fileHandle);
+        return error;
+    }
+
+    CloseHandle(fileHandle);
+
+    pFileStat->lastModified = lastModifiedNanos(&fileInfo.ftLastWriteTime);
+    pFileStat->size = 0;
+    if (is_file_symlink(fileTagInfo.FileAttributes, fileTagInfo.ReparseTag)) {
+        pFileStat->fileType = FILE_TYPE_SYMLINK;
+    } else if (fileTagInfo.FileAttributes & FILE_ATTRIBUTE_DIRECTORY) {
+        pFileStat->fileType = FILE_TYPE_DIRECTORY;
+    } else {
+        pFileStat->size = ((LONG64)fileInfo.nFileSizeHigh << 32) | fileInfo.nFileSizeLow;
+        pFileStat->fileType = FILE_TYPE_FILE;
+    }
+    return ERROR_SUCCESS;
+#endif
+}
+
 JNIEXPORT void JNICALL
 Java_net_rubygrapefruit_platform_internal_jni_NativeLibraryFunctions_getSystemInfo(JNIEnv *env, jclass target, jobject info, jobject result) {
     jclass infoClass = env->GetObjectClass(info);
@@ -387,44 +518,28 @@ Java_net_rubygrapefruit_platform_internal_jni_FileEventFunctions_closeWatch(JNIE
     free(details);
 }
 
-jlong lastModifiedNanos(FILETIME* time) {
-    return ((jlong)time->dwHighDateTime << 32) | time->dwLowDateTime;
-}
-
 JNIEXPORT void JNICALL
-Java_net_rubygrapefruit_platform_internal_jni_WindowsFileFunctions_stat(JNIEnv *env, jclass target, jstring path, jobject dest, jobject result) {
+Java_net_rubygrapefruit_platform_internal_jni_WindowsFileFunctions_stat(JNIEnv *env, jclass target, jstring path, jboolean followLink, jobject dest, jobject result) {
     jclass destClass = env->GetObjectClass(dest);
     jmethodID mid = env->GetMethodID(destClass, "details", "(IJJ)V");
     if (mid == NULL) {
         mark_failed_with_message(env, "could not find method", result);
         return;
     }
 
-    WIN32_FILE_ATTRIBUTE_DATA attr;
     wchar_t* pathStr = java_to_wchar_path(env, path, result);
-    BOOL ok = GetFileAttributesExW(pathStr, GetFileExInfoStandard, &attr);
+    file_stat_t fileStat;
+    DWORD errorCode = get_file_stat(pathStr, followLink, &fileStat);
     free(pathStr);
-    if (!ok) {
-        DWORD error = GetLastError();
-        if (error == ERROR_FILE_NOT_FOUND || error == ERROR_PATH_NOT_FOUND || error == ERROR_NOT_READY) {
-            // Treat device with no media as missing
-            env->CallVoidMethod(dest, mid, (jint)FILE_TYPE_MISSING, (jlong)0, (jlong)0);
-            return;
-        }
-        mark_failed_with_errno(env, "could not file attributes", result);
+    if (errorCode != ERROR_SUCCESS) {
+        mark_failed_with_code(env, "could not file attributes", errorCode, NULL, result);
         return;
     }
-    jlong lastModified = lastModifiedNanos(&attr.ftLastWriteTime);
-    if (attr.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) {
-        env->CallVoidMethod(dest, mid, (jint)FILE_TYPE_DIRECTORY, (jlong)0, lastModified);
-    } else {
-        jlong size = ((jlong)attr.nFileSizeHigh << 32) | attr.nFileSizeLow;
-        env->CallVoidMethod(dest, mid, (jint)FILE_TYPE_FILE, size, lastModified);
-    }
+    env->CallVoidMethod(dest, mid, fileStat.fileType, fileStat.size, fileStat.lastModified);
 }
 
 JNIEXPORT void JNICALL
-Java_net_rubygrapefruit_platform_internal_jni_WindowsFileFunctions_readdir(JNIEnv *env, jclass target, jstring path, jobject contents, jobject result) {
+Java_net_rubygrapefruit_platform_internal_jni_WindowsFileFunctions_readdir(JNIEnv *env, jclass target, jstring path, jboolean followLink, jobject contents, jobject result) {
     jclass contentsClass = env->GetObjectClass(contents);
     jmethodID mid = env->GetMethodID(contentsClass, "addFile", "(Ljava/lang/String;IJJ)V");
     if (mid == NULL) {
@@ -434,29 +549,55 @@ Java_net_rubygrapefruit_platform_internal_jni_WindowsFileFunctions_readdir(JNIEn
 
     WIN32_FIND_DATAW entry;
     wchar_t* pathStr = java_to_wchar_path(env, path, result);
-    HANDLE dirHandle = FindFirstFileW(pathStr, &entry);
+    wchar_t* patternStr = add_suffix(pathStr, wcslen(pathStr), L"\\*");
     free(pathStr);
+    HANDLE dirHandle = FindFirstFileW(patternStr, &entry);
     if (dirHandle == INVALID_HANDLE_VALUE) {
         mark_failed_with_errno(env, "could not open directory", result);
+        free(patternStr);
         return;
     }
 
     do {
         if (wcscmp(L".", entry.cFileName) == 0 || wcscmp(L"..", entry.cFileName) == 0) {
             continue;
         }
+
+        // If entry is a symbolic link, we may have to get the attributes of the link target
+        bool isSymLink = is_file_symlink(entry.dwFileAttributes, entry.dwReserved0);
+        file_stat_t fileInfo;
+        if (isSymLink && followLink) {
+            // We use patternStr minus the last character ("*") to create the absolute path of the child entry
+            wchar_t* childPathStr = add_suffix(patternStr, wcslen(patternStr) - 1, entry.cFileName);
+            DWORD errorCode = get_file_stat(childPathStr, true, &fileInfo);
+            free(childPathStr);
+            if (errorCode != ERROR_SUCCESS) {
+                // If we can't dereference the symbolic link, create a "missing file" entry
+                fileInfo.fileType = FILE_TYPE_MISSING;
+                fileInfo.size = 0;
+                fileInfo.lastModified = 0;
+            }
+        } else {
+            fileInfo.fileType = isSymLink ?
+                    FILE_TYPE_SYMLINK :
+                    (entry.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) ?
+                    FILE_TYPE_DIRECTORY :
+                    FILE_TYPE_FILE;
+            fileInfo.lastModified = lastModifiedNanos(&entry.ftLastWriteTime);
+            fileInfo.size = ((jlong)entry.nFileSizeHigh << 32) | entry.nFileSizeLow;
+        }
+
+        // Add entry
         jstring childName = wchar_to_java(env, entry.cFileName, wcslen(entry.cFileName), result);
-        jint type = (entry.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) ? FILE_TYPE_DIRECTORY : FILE_TYPE_FILE;
-        jlong lastModified = lastModifiedNanos(&entry.ftLastWriteTime);
-        jlong size = ((jlong)entry.nFileSizeHigh << 32) | entry.nFileSizeLow;
-        env->CallVoidMethod(contents, mid, childName, type, size, lastModified);
+        env->CallVoidMethod(contents, mid, childName, fileInfo.fileType, fileInfo.size, fileInfo.lastModified);
     } while (FindNextFileW(dirHandle, &entry) != 0);
 
     DWORD error = GetLastError();
     if (error != ERROR_NO_MORE_FILES ) {
         mark_failed_with_errno(env, "could not read next directory entry", result);
     }
 
+    free(patternStr);
     FindClose(dirHandle);
 }
 

src/main/java/net/rubygrapefruit/platform/file/WindowsFiles.java

@@ -29,4 +29,9 @@ public interface WindowsFiles extends Files, NativeIntegration {
      * {@inheritDoc}
      */
     WindowsFileInfo stat(File file) throws NativeException;
+
+    /**
+     * {@inheritDoc}
+     */
+    WindowsFileInfo stat(File file, boolean linkTarget) throws NativeException;
 }

src/main/java/net/rubygrapefruit/platform/internal/DefaultWindowsFiles.java

@@ -28,30 +28,30 @@
 
 public class DefaultWindowsFiles extends AbstractFiles implements WindowsFiles {
     public WindowsFileInfo stat(File file) throws NativeException {
+        return stat(file, false);
+    }
+
+    public WindowsFileInfo stat(File file, boolean linkTarget) throws NativeException {
         FunctionResult result = new FunctionResult();
         WindowsFileStat stat = new WindowsFileStat(file.getPath());
-        WindowsFileFunctions.stat(file.getPath(), stat, result);
+        WindowsFileFunctions.stat(file.getPath(), linkTarget, stat, result);
         if (result.isFailed()) {
             throw new NativeException(String.format("Could not get file details of %s: %s", file, result.getMessage()));
         }
         return stat;
     }
 
-    public FileInfo stat(File file, boolean linkTarget) throws NativeException {
-        return stat(file);
-    }
-
-    public List<? extends DirEntry> listDir(File dir) throws NativeException {
+    public List<? extends DirEntry> listDir(File dir, boolean linkTarget) throws NativeException {
         FunctionResult result = new FunctionResult();
         WindowsDirList dirList = new WindowsDirList();
-        WindowsFileFunctions.readdir(dir.getPath() + "\\*", dirList, result);
+        WindowsFileFunctions.readdir(dir.getPath(), linkTarget, dirList, result);
         if (result.isFailed()) {
             throw listDirFailure(dir, result);
         }
         return dirList.files;
     }
 
-    public List<? extends DirEntry> listDir(File dir, boolean linkTarget) throws NativeException {
-        return listDir(dir);
+    public List<? extends DirEntry> listDir(File dir) throws NativeException {
+        return listDir(dir, false);
     }
 }

src/main/java/net/rubygrapefruit/platform/internal/jni/WindowsFileFunctions.java

@@ -21,7 +21,7 @@
 import net.rubygrapefruit.platform.internal.WindowsFileStat;
 
 public class WindowsFileFunctions {
-    public static native void stat(String file, WindowsFileStat stat, FunctionResult result);
+    public static native void stat(String file, boolean followLink, WindowsFileStat stat, FunctionResult result);
 
-    public static native void readdir(String path, DirList dirList, FunctionResult result);
+    public static native void readdir(String path, boolean followLink, DirList dirList, FunctionResult result);
 }

test-app/src/main/java/net/rubygrapefruit/platform/test/Main.java

@@ -41,7 +41,9 @@ public static void main(String[] args) throws IOException {
         optionParser.accepts("cache-dir", "The directory to cache native libraries in").withRequiredArg();
         optionParser.accepts("ansi", "Force the use of ANSI escape sequences for terminal output");
         optionParser.accepts("stat", "Display details about the specified file or directory").withRequiredArg();
+        optionParser.accepts("stat-L", "Display details about the specified file or directory, following symbolic links").withRequiredArg();
         optionParser.accepts("ls", "Display contents of the specified directory").withRequiredArg();
+        optionParser.accepts("ls-L", "Display contents of the specified directory, following symbolic links").withRequiredArg();
         optionParser.accepts("long-paths", "Test support for long (i.e. >= 260 characters) paths");
         optionParser.accepts("watch", "Watches for changes to the specified file or directory").withRequiredArg();
         optionParser.accepts("machine", "Display details about the current machine");
@@ -70,11 +72,21 @@ public static void main(String[] args) throws IOException {
             return;
         }
 
+        if (result.has("stat-L")) {
+            statFollowLinks((String) result.valueOf("stat-L"));
+            return;
+        }
+
         if (result.has("ls")) {
             ls((String) result.valueOf("ls"));
             return;
         }
 
+        if (result.has("ls-L")) {
+            lsFollowLinks((String) result.valueOf("ls-L"));
+            return;
+        }
+
         if (result.has("long-paths")) {
             longPaths();
             return;
@@ -382,10 +394,18 @@ public void run() {
     }
 
     private static void ls(String path) {
+        ls(path, false);
+    }
+
+    private static void lsFollowLinks(String path) {
+        ls(path, true);
+    }
+
+    private static void ls(String path, boolean followLinks) {
         File dir = new File(path);
 
         Files files = Native.get(Files.class);
-        List<? extends DirEntry> entries = files.listDir(dir);
+        List<? extends DirEntry> entries = files.listDir(dir, followLinks);
         for (DirEntry entry : entries) {
             System.out.println();
             System.out.println("* Name: " + entry.getName());
@@ -463,10 +483,18 @@ private static File createTempDirectory() throws IOException {
     }
 
     private static void stat(String path) {
+        stat(path, false);
+    }
+
+    private static void statFollowLinks(String path) {
+        stat(path, true);
+    }
+
+    private static void stat(String path, boolean linkTarget) {
         File file = new File(path);
 
         Files files = Native.get(Files.class);
-        FileInfo stat = files.stat(file);
+        FileInfo stat = files.stat(file, linkTarget);
         System.out.println();
         System.out.println("* File: " + file);
         System.out.println("* Type: " + stat.getType());