Support for Golang GRPC (Experimental) (#4082)

* support for grpc golang

* refactored grpc go generator

* added grpc-go test and refactored

* refactored idl_gen_grpc.cpp

* fixed grpc generate method name

* refactored flatc and fixed line length issue

* added codec to go lib and fixed formatting issues

* fixed spacing issues

grpc/tests/go_test.go

@@ -0,0 +1,94 @@
+package testing
+
+import (
+	"../../tests/MyGame/Example"
+
+	"net"
+	"testing"
+
+	"github.com/google/flatbuffers/go"
+	"golang.org/x/net/context"
+	"google.golang.org/grpc"
+)
+
+type server struct{}
+
+// test used to send and receive in grpc methods
+var test string = "Flatbuffers"
+var addr string = "0.0.0.0:50051"
+
+// gRPC server store method
+func (s *server) Store(context context.Context, in *Example.Monster) (*flatbuffers.Builder, error) {
+	b := flatbuffers.NewBuilder(0)
+	i := b.CreateString(test)
+	Example.StatStart(b)
+	Example.StatAddId(b, i)
+	b.Finish(Example.StatEnd(b))
+	return b, nil
+
+}
+
+// gRPC server retrieve method
+func (s *server) Retrieve(context context.Context, in *Example.Stat) (*flatbuffers.Builder, error) {
+	b := flatbuffers.NewBuilder(0)
+	i := b.CreateString(test)
+	Example.MonsterStart(b)
+	Example.MonsterAddName(b, i)
+	b.Finish(Example.MonsterEnd(b))
+	return b, nil
+}
+
+func StoreClient(c Example.MonsterStorageClient, t *testing.T) {
+	b := flatbuffers.NewBuilder(0)
+	i := b.CreateString(test)
+	Example.MonsterStart(b)
+	Example.MonsterAddName(b, i)
+	b.Finish(Example.MonsterEnd(b))
+	out, err := c.Store(context.Background(), b)
+	if err != nil {
+		t.Fatal("Store client failed: %v", err)
+	}
+	if string(out.Id()) != test {
+		t.Errorf("StoreClient failed: expected=%s, got=%s\n", test, out.Id())
+		t.Fail()
+	}
+}
+
+func RetrieveClient(c Example.MonsterStorageClient, t *testing.T) {
+	b := flatbuffers.NewBuilder(0)
+	i := b.CreateString(test)
+	Example.StatStart(b)
+	Example.StatAddId(b, i)
+	b.Finish(Example.StatEnd(b))
+	out, err := c.Retrieve(context.Background(), b)
+	if err != nil {
+		t.Fatal("Retrieve client failed: %v", err)
+	}
+	if string(out.Name()) != test {
+		t.Errorf("RetrieveClient failed: expected=%s, got=%s\n", test, out.Name())
+		t.Fail()
+	}
+}
+
+func TestGRPC(t *testing.T) {
+	lis, err := net.Listen("tcp", addr)
+	if err != nil {
+		t.Fatalf("Failed to listen: %v", err)
+	}
+	ser := grpc.NewServer(grpc.CustomCodec(flatbuffers.FlatbuffersCodec{}))
+	Example.RegisterMonsterStorageServer(ser, &server{})
+	go func() {
+		if err := ser.Serve(lis); err != nil {
+			t.Fatalf("Failed to serve: %v", err)
+			t.FailNow()
+		}
+	}()
+	conn, err := grpc.Dial(addr, grpc.WithInsecure(), grpc.WithCodec(flatbuffers.FlatbuffersCodec{}))
+	if err != nil {
+		t.Fatal("Failed to connect: %v", err)
+	}
+	defer conn.Close()
+	client := Example.NewMonsterStorageClient(conn)
+	StoreClient(client, t)
+	RetrieveClient(client, t)
+}