segment/findEntry: do not consider offset 0 as an invalid read value

commitlog/segment.go

@@ -216,14 +216,13 @@ func (s *Segment) findEntry(offset int64) (e *Entry, err error) {
 	e = &Entry{}
 	n := int(s.Index.bytes / entryWidth)
 	idx := sort.Search(n, func(i int) bool {
-		_ = s.Index.ReadEntryAtFileOffset(e, int64(i*entryWidth))
-		return e.Offset >= offset || e.Offset == 0
+		err = s.Index.ReadEntryAtFileOffset(e, int64(i*entryWidth))
+		return e.Offset >= offset || err != nil
 	})
 	if idx == n {
 		return nil, errors.New("entry not found")
 	}
-	_ = s.Index.ReadEntryAtFileOffset(e, int64(idx*entryWidth))
-	return e, nil
+	return e, s.Index.ReadEntryAtFileOffset(e, int64(idx*entryWidth))
 }
 
 // Delete closes the segment and then deletes its log and index files.

commitlog/segment_test.go

@@ -1,6 +1,7 @@
 package commitlog_test
 
 import (
+	"io"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -29,3 +30,39 @@ func TestSegmentScanner(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, msgSets[0], ms)
 }
+func TestSegmentReader(t *testing.T) {
+	var err error
+
+	l := setupWithOptions(t, commitlog.Options{
+		MaxSegmentBytes: 1024,
+		MaxLogBytes:     1024,
+	})
+	defer cleanup(t, l)
+
+	message := []byte("one")
+	nb := 12
+	for i := 0; i < nb; i++ {
+		_, err = l.Append(commitlog.NewMessageSet(uint64(i), message))
+		require.NoError(t, err)
+	}
+	t.Run("must read 1 message from offset 11", mustRead(l, 11, 1, message))
+}
+
+func mustRead(l *commitlog.CommitLog, offset int64, messagesNumber int, message []byte) func(t *testing.T) {
+	return func(t *testing.T) {
+		r, err := l.NewReader(offset, 0)
+		require.NoError(t, err)
+		buf := make([]byte, len(message)+12)
+
+		for messagesNumber > 0 {
+			n, err := r.Read(buf)
+			require.NoError(t, err)
+			require.Equal(t, message, buf[12:])
+			require.Equal(t, 15, n)
+			messagesNumber--
+		}
+		n, err := r.Read(buf)
+		require.Equal(t, 0, n)
+		require.Equal(t, io.EOF, err)
+	}
+}