Merge pull request #3 from alldroll/issue2

Inverted index version validation

Author: alldroll

pkg/index/index_reader.go

@@ -71,6 +71,10 @@ func (ir *Reader) readHeader() (*header, error) {
 		return nil, fmt.Errorf("Failed to retrieve header: %v", err)
 	}
 
+	if header.Version != IndexVersion {
+		return nil, fmt.Errorf("Index version mismatch, expected %s version", IndexVersion)
+	}
+
 	if err = closeIfRequired(headerReader); err != nil {
 		return nil, fmt.Errorf("Failed to close header file: %v", err)
 	}

pkg/index/indexer_writer.go

@@ -10,6 +10,9 @@ import (
 	"github.com/alldroll/suggest/pkg/compression"
 )
 
+// IndexVersion tells that the inverted index structure has the provided below version
+const IndexVersion = "v1"
+
 // Writer creates and maintains an inverted index
 type Writer struct {
 	directory Directory
@@ -46,6 +49,7 @@ var (
 
 // header struct that store terms descriptions and indices count
 type header struct {
+	Version string
 	Indices uint32
 	Terms   []termDescription
 }
@@ -102,6 +106,7 @@ func (iw *Writer) Commit() error {
 
 	// header struct that should be loaded on Load
 	header := header{
+		Version: IndexVersion,
 		Terms:   []termDescription{},
 		Indices: uint32(len(iw.indices)),
 	}