core, ethdb, tests, trie: introduce database snapshot (#24486)

ethdb/dbtest/testsuite.go

@@ -313,6 +313,68 @@ func TestDatabaseSuite(t *testing.T, New func() ethdb.KeyValueStore) {
 		}
 	})
 
+	t.Run("Snapshot", func(t *testing.T) {
+		db := New()
+		defer db.Close()
+
+		initial := map[string]string{
+			"k1": "v1", "k2": "v2", "k3": "", "k4": "",
+		}
+		for k, v := range initial {
+			db.Put([]byte(k), []byte(v))
+		}
+		snapshot, err := db.NewSnapshot()
+		if err != nil {
+			t.Fatal(err)
+		}
+		for k, v := range initial {
+			got, err := snapshot.Get([]byte(k))
+			if err != nil {
+				t.Fatal(err)
+			}
+			if !bytes.Equal(got, []byte(v)) {
+				t.Fatalf("Unexpected value want: %v, got %v", v, got)
+			}
+		}
+
+		// Flush more modifications into the database, ensure the snapshot
+		// isn't affected.
+		var (
+			update = map[string]string{"k1": "v1-b", "k3": "v3-b"}
+			insert = map[string]string{"k5": "v5-b"}
+			delete = map[string]string{"k2": ""}
+		)
+		for k, v := range update {
+			db.Put([]byte(k), []byte(v))
+		}
+		for k, v := range insert {
+			db.Put([]byte(k), []byte(v))
+		}
+		for k := range delete {
+			db.Delete([]byte(k))
+		}
+		for k, v := range initial {
+			got, err := snapshot.Get([]byte(k))
+			if err != nil {
+				t.Fatal(err)
+			}
+			if !bytes.Equal(got, []byte(v)) {
+				t.Fatalf("Unexpected value want: %v, got %v", v, got)
+			}
+		}
+		for k := range insert {
+			got, err := snapshot.Get([]byte(k))
+			if err == nil || len(got) != 0 {
+				t.Fatal("Unexpected value")
+			}
+		}
+		for k := range delete {
+			got, err := snapshot.Get([]byte(k))
+			if err != nil || len(got) == 0 {
+				t.Fatal("Unexpected deletion")
+			}
+		}
+	})
 }
 
 func iterateKeys(it ethdb.Iterator) []string {