Support creating empty directories. (#5049)

Every so often we get requirements for creating
directories/prefixes and we end up rejecting
such requirements. This PR implements this and
allows empty directories without any new file
addition to backend.

Existing lower APIs themselves are leveraged to provide
this behavior. Only FS backend supports this for
the time being as desired.

cmd/fs-v1-helpers.go

@@ -37,12 +37,7 @@ func fsRemoveFile(filePath string) (err error) {
 	}
 
 	if err = os.Remove((filePath)); err != nil {
-		if os.IsNotExist(err) {
-			return traceError(errFileNotFound)
-		} else if os.IsPermission(err) {
-			return traceError(errFileAccessDenied)
-		}
-		return traceError(err)
+		return osErrToFSFileErr(err)
 	}
 
 	return nil
@@ -94,6 +89,24 @@ func fsRemoveDir(dirPath string) (err error) {
 	return nil
 }
 
+// Creates a new directory, parent dir is also recursively created
+// if it doesn't exist.
+func fsMkdirAll(dirPath string) (err error) {
+	if dirPath == "" {
+		return traceError(errInvalidArgument)
+	}
+
+	if err = checkPathLength(dirPath); err != nil {
+		return traceError(err)
+	}
+
+	if err = os.MkdirAll(dirPath, 0777); err != nil {
+		return traceError(err)
+	}
+
+	return nil
+}
+
 // Creates a new directory, parent dir should exist
 // otherwise returns an error. If directory already
 // exists returns an error. Windows long paths
@@ -126,6 +139,11 @@ func fsMkdir(dirPath string) (err error) {
 	return nil
 }
 
+// fsStat is a low level call which validates input arguments
+// and checks input length upto supported maximum. Does
+// not perform any higher layer interpretation of files v/s
+// directories. For higher level interpretation look at
+// fsStatFileDir, fsStatFile, fsStatDir.
 func fsStat(statLoc string) (os.FileInfo, error) {
 	if statLoc == "" {
 		return nil, traceError(errInvalidArgument)
@@ -141,10 +159,9 @@ func fsStat(statLoc string) (os.FileInfo, error) {
 	return fi, nil
 }
 
-// Lookup if directory exists, returns directory
-// attributes upon success.
-func fsStatDir(statDir string) (os.FileInfo, error) {
-	fi, err := fsStat(statDir)
+// Lookup if volume exists, returns volume attributes upon success.
+func fsStatVolume(volume string) (os.FileInfo, error) {
+	fi, err := fsStat(volume)
 	if err != nil {
 		err = errorCause(err)
 		if os.IsNotExist(err) {
@@ -162,21 +179,47 @@ func fsStatDir(statDir string) (os.FileInfo, error) {
 	return fi, nil
 }
 
-// Lookup if file exists, returns file attributes upon success
+// Is a one place function which converts all os.PathError
+// into a more FS object layer friendly form, converts
+// known errors into their typed form for top level
+// interpretation.
+func osErrToFSFileErr(err error) error {
+	if err == nil {
+		return nil
+	}
+	err = errorCause(err)
+	if os.IsNotExist(err) {
+		return traceError(errFileNotFound)
+	}
+	if os.IsPermission(err) {
+		return traceError(errFileAccessDenied)
+	}
+	if isSysErrNotDir(err) {
+		return traceError(errFileAccessDenied)
+	}
+	if isSysErrPathNotFound(err) {
+		return traceError(errFileNotFound)
+	}
+	return err
+}
+
+// Lookup if directory exists, returns directory attributes upon success.
+func fsStatDir(statDir string) (os.FileInfo, error) {
+	fi, err := fsStat(statDir)
+	if err != nil {
+		return nil, osErrToFSFileErr(err)
+	}
+	if !fi.IsDir() {
+		return nil, traceError(errFileAccessDenied)
+	}
+	return fi, nil
+}
+
+// Lookup if file exists, returns file attributes upon success.
 func fsStatFile(statFile string) (os.FileInfo, error) {
 	fi, err := fsStat(statFile)
 	if err != nil {
-		err = errorCause(err)
-		if os.IsNotExist(err) {
-			return nil, traceError(errFileNotFound)
-		} else if os.IsPermission(err) {
-			return nil, traceError(errFileAccessDenied)
-		} else if isSysErrNotDir(err) {
-			return nil, traceError(errFileAccessDenied)
-		} else if isSysErrPathNotFound(err) {
-			return nil, traceError(errFileNotFound)
-		}
-		return nil, traceError(err)
+		return nil, osErrToFSFileErr(err)
 	}
 	if fi.IsDir() {
 		return nil, traceError(errFileAccessDenied)
@@ -196,18 +239,7 @@ func fsOpenFile(readPath string, offset int64) (io.ReadCloser, int64, error) {
 
 	fr, err := os.Open((readPath))
 	if err != nil {
-		if os.IsNotExist(err) {
-			return nil, 0, traceError(errFileNotFound)
-		} else if os.IsPermission(err) {
-			return nil, 0, traceError(errFileAccessDenied)
-		} else if isSysErrNotDir(err) {
-			// File path cannot be verified since one of the parents is a file.
-			return nil, 0, traceError(errFileAccessDenied)
-		} else if isSysErrPathNotFound(err) {
-			// Add specific case for windows.
-			return nil, 0, traceError(errFileNotFound)
-		}
-		return nil, 0, traceError(err)
+		return nil, 0, osErrToFSFileErr(err)
 	}
 
 	// Stat to get the size of the file at path.
@@ -253,11 +285,7 @@ func fsCreateFile(filePath string, reader io.Reader, buf []byte, fallocSize int6
 
 	writer, err := os.OpenFile((filePath), os.O_CREATE|os.O_WRONLY, 0666)
 	if err != nil {
-		// File path cannot be verified since one of the parents is a file.
-		if isSysErrNotDir(err) {
-			return 0, traceError(errFileAccessDenied)
-		}
-		return 0, err
+		return 0, osErrToFSFileErr(err)
 	}
 	defer writer.Close()
 
@@ -346,17 +374,7 @@ func fsRenameFile(sourcePath, destPath string) error {
 	}
 	// Verify if source path exists.
 	if _, err := os.Stat((sourcePath)); err != nil {
-		if os.IsNotExist(err) {
-			return traceError(errFileNotFound)
-		} else if os.IsPermission(err) {
-			return traceError(errFileAccessDenied)
-		} else if isSysErrPathNotFound(err) {
-			return traceError(errFileNotFound)
-		} else if isSysErrNotDir(err) {
-			// File path cannot be verified since one of the parents is a file.
-			return traceError(errFileAccessDenied)
-		}
-		return traceError(err)
+		return osErrToFSFileErr(err)
 	}
 	if err := os.MkdirAll(pathutil.Dir(destPath), 0777); err != nil {
 		return traceError(err)