bring in khatru and eventstore.

eventstore/badger/migrations.go

@@ -0,0 +1,66 @@
+package badger
+
+import (
+	"encoding/binary"
+	"fmt"
+
+	"github.com/dgraph-io/badger/v4"
+)
+
+func (b *BadgerBackend) runMigrations() error {
+	return b.Update(func(txn *badger.Txn) error {
+		var version uint16
+
+		item, err := txn.Get([]byte{dbVersionKey})
+		if err == badger.ErrKeyNotFound {
+			version = 0
+		} else if err != nil {
+			return err
+		} else {
+			item.Value(func(val []byte) error {
+				version = binary.BigEndian.Uint16(val)
+				return nil
+			})
+		}
+
+		// do the migrations in increasing steps (there is no rollback)
+		//
+
+		// the 3 first migrations go to trash because on version 3 we need to export and import all the data anyway
+		if version < 3 {
+			// if there is any data in the relay we will stop and notify the user,
+			// otherwise we just set version to 3 and proceed
+			prefix := []byte{indexIdPrefix}
+			it := txn.NewIterator(badger.IteratorOptions{
+				PrefetchValues: true,
+				PrefetchSize:   100,
+				Prefix:         prefix,
+			})
+			defer it.Close()
+
+			hasAnyEntries := false
+			for it.Seek(prefix); it.ValidForPrefix(prefix); it.Next() {
+				hasAnyEntries = true
+				break
+			}
+
+			if hasAnyEntries {
+				return fmt.Errorf("your database is at version %d, but in order to migrate up to version 3 you must manually export all the events and then import again: run an old version of this software, export the data, then delete the database files, run the new version, import the data back in.", version)
+			}
+
+			b.bumpVersion(txn, 3)
+		}
+
+		if version < 4 {
+			// ...
+		}
+
+		return nil
+	})
+}
+
+func (b *BadgerBackend) bumpVersion(txn *badger.Txn, version uint16) error {
+	buf := make([]byte, 2)
+	binary.BigEndian.PutUint16(buf, version)
+	return txn.Set([]byte{dbVersionKey}, buf)
+}