Binary entity (de)-serialization

Author: mlange-42

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## [[unpublished]](https://github.com/mlange-42/ark/compare/v0.6.4...v0.6.5)
+
+### Features
+
+- Provides binary serialization and de-serialization of entities for networking (#453)
+
 ## [[v0.6.4]](https://github.com/mlange-42/ark/compare/v0.6.3...v0.6.4)
 
 ### Bugfixes

ecs/entity.go

@@ -1,7 +1,9 @@
 package ecs
 
 import (
+	"encoding/binary"
 	"encoding/json"
+	"fmt"
 	"reflect"
 )
 
@@ -82,6 +84,26 @@ func (e *Entity) UnmarshalJSON(data []byte) error {
 	return nil
 }
 
+// MarshalBinary returns a binary representation of the entity, for serialization and networking purposes.
+func (e *Entity) MarshalBinary() []byte {
+	buf := make([]byte, 8)
+	binary.BigEndian.PutUint32(buf[0:4], uint32(e.id))
+	binary.BigEndian.PutUint32(buf[4:8], e.gen)
+	return buf
+}
+
+// UnmarshalBinary into an entity.
+//
+// For serialization and networking purposes only. Do not use this to create entities!
+func (e *Entity) UnmarshalBinary(data []byte) error {
+	if len(data) != 8 {
+		return fmt.Errorf("invalid data length: expected 8 bytes, got %d", len(data))
+	}
+	e.id = entityID(binary.BigEndian.Uint32(data[0:4]))
+	e.gen = binary.BigEndian.Uint32(data[4:8])
+	return nil
+}
+
 // entityIndex denotes an entity's location by table and row index.
 type entityIndex struct {
 	table tableID

ecs/entity_test.go

@@ -50,3 +50,23 @@ func TestEntityMarshal(t *testing.T) {
 	err = e2.UnmarshalJSON([]byte("pft"))
 	expectNotNil(t, err)
 }
+
+func TestEntityMarshalBinary(t *testing.T) {
+	e := Entity{2, 3}
+
+	binData, err := json.Marshal(&e)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	e2 := Entity{}
+	err = json.Unmarshal(binData, &e2)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	expectEqual(t, e2, e)
+
+	err = e2.UnmarshalJSON(make([]byte, 9))
+	expectNotNil(t, err)
+}