fs: improve ChunkedReader

- make Close permanent and return errors afterwards
- use RangeSeek from the wrapped reader if present
- add a limit to chunk growth
- correct RangeSeek interface behavior
- add tests

fstest/mockobject/mockobject.go

@@ -2,7 +2,9 @@
 package mockobject
 
 import (
+	"bytes"
 	"errors"
+	"fmt"
 	"io"
 	"time"
 
@@ -15,6 +17,11 @@ var errNotImpl = errors.New("not implemented")
 // Object is a mock fs.Object useful for testing
 type Object string
 
+// New returns mock fs.Object useful for testing
+func New(name string) Object {
+	return Object(name)
+}
+
 // String returns a description of the Object
 func (o Object) String() string {
 	return string(o)
@@ -69,3 +76,105 @@ func (o Object) Update(in io.Reader, src fs.ObjectInfo, options ...fs.OpenOption
 func (o Object) Remove() error {
 	return errNotImpl
 }
+
+// SeekMode specifies the optional Seek interface for the ReadCloser returned by Open
+type SeekMode int
+
+const (
+	// SeekModeNone specifies no seek interface
+	SeekModeNone SeekMode = iota
+	// SeekModeRegular specifies the regular io.Seek interface
+	SeekModeRegular
+	// SeekModeRange specifies the fs.RangeSeek interface
+	SeekModeRange
+)
+
+// SeekModes contains all valid SeekMode's
+var SeekModes = []SeekMode{SeekModeNone, SeekModeRegular, SeekModeRange}
+
+type contentMockObject struct {
+	Object
+	content  []byte
+	seekMode SeekMode
+}
+
+// WithContent returns a fs.Object with the given content.
+func (o Object) WithContent(content []byte, mode SeekMode) fs.Object {
+	return &contentMockObject{
+		Object:   o,
+		content:  content,
+		seekMode: mode,
+	}
+}
+
+func (o *contentMockObject) Open(options ...fs.OpenOption) (io.ReadCloser, error) {
+	var offset, limit int64 = 0, -1
+	for _, option := range options {
+		switch x := option.(type) {
+		case *fs.SeekOption:
+			offset = x.Offset
+		case *fs.RangeOption:
+			offset, limit = x.Decode(o.Size())
+		default:
+			if option.Mandatory() {
+				return nil, fmt.Errorf("Unsupported mandatory option: %v", option)
+			}
+		}
+	}
+	if limit == -1 || offset+limit > o.Size() {
+		limit = o.Size() - offset
+	}
+
+	var r *bytes.Reader
+	if o.seekMode == SeekModeNone {
+		r = bytes.NewReader(o.content[offset : offset+limit])
+	} else {
+		r = bytes.NewReader(o.content)
+		_, err := r.Seek(offset, io.SeekStart)
+		if err != nil {
+			return nil, err
+		}
+	}
+	switch o.seekMode {
+	case SeekModeNone:
+		return &readCloser{r}, nil
+	case SeekModeRegular:
+		return &readSeekCloser{r}, nil
+	case SeekModeRange:
+		return &readRangeSeekCloser{r}, nil
+	default:
+		return nil, errors.New(o.seekMode.String())
+	}
+}
+func (o *contentMockObject) Size() int64 {
+	return int64(len(o.content))
+}
+
+type readCloser struct{ io.Reader }
+
+func (r *readCloser) Close() error { return nil }
+
+type readSeekCloser struct{ io.ReadSeeker }
+
+func (r *readSeekCloser) Close() error { return nil }
+
+type readRangeSeekCloser struct{ io.ReadSeeker }
+
+func (r *readRangeSeekCloser) RangeSeek(offset int64, whence int, length int64) (int64, error) {
+	return r.ReadSeeker.Seek(offset, whence)
+}
+
+func (r *readRangeSeekCloser) Close() error { return nil }
+
+func (m SeekMode) String() string {
+	switch m {
+	case SeekModeNone:
+		return "SeekModeNone"
+	case SeekModeRegular:
+		return "SeekModeRegular"
+	case SeekModeRange:
+		return "SeekModeRange"
+	default:
+		return fmt.Sprintf("SeekModeInvalid(%d)", m)
+	}
+}