Possible fix for #22

Add sparse support for fragments (undocumented)

reader_frag.go

@@ -1,6 +1,7 @@
 package squashfs
 
 import (
+	"bytes"
 	"io"
 
 	"github.com/CalebQ42/squashfs/internal/toreader"
@@ -12,8 +13,11 @@ type fragEntry struct {
 	_     uint32
 }
 
-func (r Reader) fragReader(index uint32) (io.Reader, error) {
+func (r Reader) fragReader(index uint32, fragSize uint32) (io.Reader, error) {
 	realSize := r.fragEntries[index].Size &^ (1 << 24)
+	if realSize == 0 {
+		return bytes.NewReader(make([]byte, fragSize)), nil
+	}
 	rdr := io.LimitReader(toreader.NewReader(r.r, int64(r.fragEntries[index].Start)), int64(realSize))
 	if realSize != r.fragEntries[index].Size {
 		return rdr, nil

reader_inode.go

@@ -59,7 +59,7 @@ func (r Reader) getReaders(i inode.Inode) (full *data.FullReader, rdr *data.Read
 	if fragInd != 0xFFFFFFFF {
 		full.AddFragment(func() (io.Reader, error) {
 			var fragRdr io.Reader
-			fragRdr, err = r.fragReader(fragInd)
+			fragRdr, err = r.fragReader(fragInd, fragSize)
 			if err != nil {
 				return nil, err
 			}
@@ -75,7 +75,7 @@ func (r Reader) getReaders(i inode.Inode) (full *data.FullReader, rdr *data.Read
 			return fragRdr, nil
 		})
 		var fragRdr io.Reader
-		fragRdr, err = r.fragReader(fragInd)
+		fragRdr, err = r.fragReader(fragInd, fragSize)
 		if err != nil {
 			return nil, nil, err
 		}