Implement memory efficient readdir for windows (#6247)

Fixes #6164

cmd/posix-list-dir_plan9.go

@@ -1,7 +1,7 @@
-// +build !linux,!darwin,!openbsd,!freebsd,!netbsd
+// +build plan9
 
 /*
- * Minio Cloud Storage, (C) 2016 Minio, Inc.
+ * Minio Cloud Storage, (C) 2016, 2017, 2018 Minio, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.

cmd/posix-list-dir_unix.go

@@ -1,7 +1,7 @@
-// +build linux darwin freebsd netbsd openbsd
+// +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
 
 /*
- * Minio Cloud Storage, (C) 2016 Minio, Inc.
+ * Minio Cloud Storage, (C) 2016, 2017, 2018 Minio, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -90,9 +90,9 @@ func parseDirents(dirPath string, buf []byte) (entries []string, err error) {
 				return nil, err
 			}
 			if fi.IsDir() {
-				entries = append(entries, fi.Name()+slashSeparator)
+				entries = append(entries, name+slashSeparator)
 			} else if fi.Mode().IsRegular() {
-				entries = append(entries, fi.Name())
+				entries = append(entries, name)
 			}
 		default:
 			// Skip entries which are not file or directory.

cmd/posix-list-dir_windows.go

@@ -0,0 +1,111 @@
+// +build windows
+
+/*
+ * Minio Cloud Storage, (C) 2016, 2017, 2018 Minio, Inc.
+ *
+ * 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.
+ */
+
+package cmd
+
+import (
+	"os"
+	"path"
+	"strings"
+	"syscall"
+)
+
+// Return all the entries at the directory dirPath.
+func readDir(dirPath string) (entries []string, err error) {
+	return readDirN(dirPath, -1)
+}
+
+// Return N entries at the directory dirPath. If count is -1, return all entries
+func readDirN(dirPath string, count int) (entries []string, err error) {
+	d, err := os.Open(dirPath)
+	if err != nil {
+		// File is really not found.
+		if os.IsNotExist(err) {
+			return nil, errFileNotFound
+		}
+
+		// File path cannot be verified since one of the parents is a file.
+		if strings.Contains(err.Error(), "not a directory") {
+			return nil, errFileNotFound
+		}
+		return nil, err
+	}
+	defer d.Close()
+
+	st, err := d.Stat()
+	if err != nil {
+		return nil, err
+	}
+	// Not a directory return error.
+	if !st.IsDir() {
+		return nil, errFileAccessDenied
+	}
+
+	data := &syscall.Win32finddata{}
+
+	remaining := count
+	done := false
+	for !done {
+		e := syscall.FindNextFile(syscall.Handle(d.Fd()), data)
+		if e != nil {
+			if e == syscall.ERROR_NO_MORE_FILES {
+				break
+			} else {
+				err = &os.PathError{
+					Op:   "FindNextFile",
+					Path: dirPath,
+					Err:  e,
+				}
+				return
+			}
+		}
+		name := syscall.UTF16ToString(data.FileName[0:])
+		if name == "." || name == ".." { // Useless names
+			continue
+		}
+		switch {
+		case data.FileAttributes&syscall.FILE_ATTRIBUTE_REPARSE_POINT != 0:
+			// If its symbolic link, follow the link using os.Stat()
+			var fi os.FileInfo
+			fi, err = os.Stat(path.Join(dirPath, name))
+			if err != nil {
+				// If file does not exist, we continue and skip it.
+				// Could happen if it was deleted in the middle while
+				// this list was being performed.
+				if os.IsNotExist(err) {
+					continue
+				}
+				return nil, err
+			}
+			if fi.IsDir() {
+				entries = append(entries, name+slashSeparator)
+			} else if fi.Mode().IsRegular() {
+				entries = append(entries, name)
+			}
+		case data.FileAttributes&syscall.FILE_ATTRIBUTE_DIRECTORY != 0:
+			entries = append(entries, name+slashSeparator)
+		default:
+			entries = append(entries, name)
+		}
+		if remaining > 0 {
+			remaining--
+			done = remaining == 0
+		}
+	}
+	return entries, nil
+}