wal: change io.EOF returned by readFull to io.ErrUnexpectedEOF

Decoder should return error for any broken block including the
one that only contains the length field. We should change io.EOF
to io.ErrUnexpectedEOF before return the error.

wal/decoder.go

@@ -54,6 +54,11 @@ func (d *decoder) decode(rec *walpb.Record) error {
 	}
 	data := make([]byte, l)
 	if _, err = io.ReadFull(d.br, data); err != nil {
+		// ReadFull returns io.EOF only if no bytes were read
+		// the decoder should treat this as an ErrUnexpectedEOF instead.
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
 		return err
 	}
 	if err := rec.Unmarshal(data); err != nil {

wal/record_test.go

@@ -42,6 +42,7 @@ func TestReadRecord(t *testing.T) {
 	}{
 		{infoRecord, &walpb.Record{Type: 1, Crc: crc32.Checksum(infoData, crcTable), Data: infoData}, nil},
 		{[]byte(""), &walpb.Record{}, io.EOF},
+		{infoRecord[:8], &walpb.Record{}, io.ErrUnexpectedEOF},
 		{infoRecord[:len(infoRecord)-len(infoData)-8], &walpb.Record{}, io.ErrUnexpectedEOF},
 		{infoRecord[:len(infoRecord)-len(infoData)], &walpb.Record{}, io.ErrUnexpectedEOF},
 		{infoRecord[:len(infoRecord)-8], &walpb.Record{}, io.ErrUnexpectedEOF},