Merge pull request #3977 from gonzaloserrano/feature/go-generic-deserialitzation

Add a generic way to deserialize a flatbuffer in Go.

go/lib.go

+package flatbuffers
+
+// FlatBuffer is the interface that represents a flatbuffer.
+type FlatBuffer interface {
+	Table() Table
+	Init(buf []byte, i UOffsetT)
+}
+
+// GetRootAs is a generic helper to initialize a FlatBuffer with the provided buffer bytes and its data offset.
+func GetRootAs(buf []byte, offset UOffsetT, fb FlatBuffer) {
+	n := GetUOffsetT(buf[offset:])
+	fb.Init(buf, n+offset)
+}

src/idl_gen_go.cpp

@@ -144,6 +144,23 @@ static void InitializeExisting(const StructDef &struct_def,
   code += "}\n\n";
 }
 
+// Implement the table accessor
+static void GenTableAccessor(const StructDef &struct_def,
+                               std::string *code_ptr) {
+  std::string &code = *code_ptr;
+
+  GenReceiver(struct_def, code_ptr);
+  code += " Table() flatbuffers.Table ";
+  code += "{\n";
+
+  if (struct_def.fixed) {
+      code += "\treturn rcv._tab.Table\n";
+  } else {
+      code += "\treturn rcv._tab\n";
+  }
+  code += "}\n\n";
+}
+
 // Get the length of a vector.
 static void GetVectorLen(const StructDef &struct_def,
                          const FieldDef &field,
@@ -591,6 +608,10 @@ static void GenStruct(const StructDef &struct_def,
   // Generate the Init method that sets the field in a pre-existing
   // accessor object. This is to allow object reuse.
   InitializeExisting(struct_def, code_ptr);
+  // Generate _tab accessor
+  GenTableAccessor(struct_def, code_ptr);
+
+  // Generate struct fields accessors
   for (auto it = struct_def.fields.vec.begin();
        it != struct_def.fields.vec.end();
        ++it) {
@@ -601,6 +622,7 @@ static void GenStruct(const StructDef &struct_def,
     GenStructMutator(struct_def, field, code_ptr);
   }
 
+  // Generate builders
   if (struct_def.fixed) {
     // create a struct constructor function
     GenStructBuilder(struct_def, code_ptr);

tests/MyGame/Example/Monster.go

@@ -23,6 +23,10 @@ func (rcv *Monster) Init(buf []byte, i flatbuffers.UOffsetT) {
 	rcv._tab.Pos = i
 }
 
+func (rcv *Monster) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
 func (rcv *Monster) Pos(obj *Vec3) *Vec3 {
 	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
 	if o != 0 {

tests/MyGame/Example/Stat.go

@@ -22,6 +22,10 @@ func (rcv *Stat) Init(buf []byte, i flatbuffers.UOffsetT) {
 	rcv._tab.Pos = i
 }
 
+func (rcv *Stat) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
 func (rcv *Stat) Id() []byte {
 	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
 	if o != 0 {

tests/MyGame/Example/Test.go

@@ -15,6 +15,10 @@ func (rcv *Test) Init(buf []byte, i flatbuffers.UOffsetT) {
 	rcv._tab.Pos = i
 }
 
+func (rcv *Test) Table() flatbuffers.Table {
+	return rcv._tab.Table
+}
+
 func (rcv *Test) A() int16 {
 	return rcv._tab.GetInt16(rcv._tab.Pos + flatbuffers.UOffsetT(0))
 }

tests/MyGame/Example/TestSimpleTableWithEnum.go

@@ -22,6 +22,10 @@ func (rcv *TestSimpleTableWithEnum) Init(buf []byte, i flatbuffers.UOffsetT) {
 	rcv._tab.Pos = i
 }
 
+func (rcv *TestSimpleTableWithEnum) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
 func (rcv *TestSimpleTableWithEnum) Color() int8 {
 	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
 	if o != 0 {

tests/MyGame/Example/Vec3.go

@@ -15,6 +15,10 @@ func (rcv *Vec3) Init(buf []byte, i flatbuffers.UOffsetT) {
 	rcv._tab.Pos = i
 }
 
+func (rcv *Vec3) Table() flatbuffers.Table {
+	return rcv._tab.Table
+}
+
 func (rcv *Vec3) X() float32 {
 	return rcv._tab.GetFloat32(rcv._tab.Pos + flatbuffers.UOffsetT(0))
 }

tests/MyGame/Example2/Monster.go

@@ -22,6 +22,10 @@ func (rcv *Monster) Init(buf []byte, i flatbuffers.UOffsetT) {
 	rcv._tab.Pos = i
 }
 
+func (rcv *Monster) Table() flatbuffers.Table {
+	return rcv._tab
+}
+
 func MonsterStart(builder *flatbuffers.Builder) {
 	builder.StartObject(0)
 }

tests/go_test.go

@@ -78,6 +78,7 @@ func TestAll(t *testing.T) {
 
 	// Verify that GetRootAs works for non-root tables
 	CheckGetRootAsForNonRootTable(t.Fatalf)
+	CheckTableAccessors(t.Fatalf)
 
 	// Verify that using the generated Go code builds a buffer without
 	// returning errors:
@@ -137,8 +138,11 @@ func TestAll(t *testing.T) {
 // CheckReadBuffer checks that the given buffer is evaluated correctly
 // as the example Monster.
 func CheckReadBuffer(buf []byte, offset flatbuffers.UOffsetT, fail func(string, ...interface{})) {
-	monster := example.GetRootAsMonster(buf, offset)
-
+	// try the two ways of generating a monster
+	monster1 := example.GetRootAsMonster(buf, offset)
+	monster2 := &example.Monster{}
+	flatbuffers.GetRootAs(buf, offset, monster2)
+	for _, monster := range []*example.Monster{monster1, monster2} {
 		if got := monster.Hp(); 80 != got {
 			fail(FailString("hp", 80, got))
 		}
@@ -287,6 +291,7 @@ func CheckReadBuffer(buf []byte, offset flatbuffers.UOffsetT, fail func(string,
 		if got := monster.Testarrayofstring(1); !bytes.Equal([]byte("test2"), got) {
 			fail(FailString("Testarrayofstring(1)", "test2", got))
 		}
+	}
 }
 
 // CheckMutateBuffer checks that the given buffer can be mutated correctly
@@ -1161,6 +1166,38 @@ func CheckGeneratedBuild(fail func(string, ...interface{})) ([]byte, flatbuffers
 	return b.Bytes, b.Head()
 }
 
+// CheckTableAccessors checks that the table accessors work as expected.
+func CheckTableAccessors(fail func(string, ...interface{})) {
+	// test struct accessor
+	b := flatbuffers.NewBuilder(0)
+	pos := example.CreateVec3(b, 1.0, 2.0, 3.0, 3.0, 4, 5, 6)
+	b.Finish(pos)
+	vec3Bytes := b.FinishedBytes()
+	vec3 := &example.Vec3{}
+	flatbuffers.GetRootAs(vec3Bytes, 0, vec3)
+
+	if bytes.Compare(vec3Bytes, vec3.Table().Bytes) != 0 {
+		fail("invalid vec3 table")
+	}
+
+	// test table accessor
+	b = flatbuffers.NewBuilder(0)
+	str := b.CreateString("MyStat")
+	example.StatStart(b)
+	example.StatAddId(b, str)
+	example.StatAddVal(b, 12345678)
+	example.StatAddCount(b, 12345)
+	pos = example.StatEnd(b)
+	b.Finish(pos)
+	statBytes := b.FinishedBytes()
+	stat := &example.Stat{}
+	flatbuffers.GetRootAs(statBytes, 0, stat)
+
+	if bytes.Compare(statBytes, stat.Table().Bytes) != 0 {
+		fail("invalid stat table")
+	}
+}
+
 // CheckVtableDeduplication verifies that vtables are deduplicated.
 func CheckVtableDeduplication(fail func(string, ...interface{})) {
 	b := flatbuffers.NewBuilder(0)