Added option to binary encoder to skip unknown fields.

tests/bindings/lua/BUILD

@@ -16,6 +16,7 @@ cc_test(
     data = [
         "test_upb.lua",
         ":descriptor_proto_lua",
+        ":empty_proto_lua",
         ":test_messages_proto2_proto_lua",
         ":test_messages_proto3_proto_lua",
         ":test_proto_lua",
@@ -49,6 +50,11 @@ lua_proto_library(
     deps = ["@com_google_protobuf//:descriptor_proto"],
 )
 
+lua_proto_library(
+    name = "empty_proto_lua",
+    deps = ["@com_google_protobuf//:empty_proto"],
+)
+
 lua_proto_library(
     name = "test_messages_proto3_proto_lua",
     testonly = 1,

tests/bindings/lua/test_upb.lua

@@ -5,6 +5,7 @@ local upb_test = require "tests.bindings.lua.test_pb"
 local test_messages_proto3 = require "google.protobuf.test_messages_proto3_pb"
 local test_messages_proto2 = require "google.protobuf.test_messages_proto2_pb"
 local descriptor = require "google.protobuf.descriptor_pb"
+local empty = require "google.protobuf.empty_pb"
 
 if _VERSION >= 'Lua 5.2' then
   _ENV = lunit.module("testupb", "seeall")
@@ -664,6 +665,21 @@ function test_descriptor_error()
   assert_nil(symtab:lookup_msg("ABC"))
 end
 
+function test_encode_skipunknown()
+  -- Test that upb.ENCODE_SKIPUNKNOWN does not encode unknown fields.
+  local msg = test_messages_proto3.TestAllTypesProto3{
+    optional_int32 = 10,
+    optional_uint32 = 20,
+    optional_int64 = 30,
+  }
+  local serialized = upb.encode(msg)
+  assert_true(#serialized > 0)
+  local empty_with_unknown = upb.decode(empty.Empty, serialized)
+  assert_true(#upb.encode(empty_with_unknown) > 0)
+  print(upb.encode(empty_with_unknown, upb.ENCODE_SKIPUNKNOWN))
+  assert_true(#upb.encode(empty_with_unknown, {upb.ENCODE_SKIPUNKNOWN}) == 0)
+end
+
 function test_gc()
   local top = test_messages_proto3.TestAllTypesProto3()
   local n = 100

upb/bindings/lua/msg.c

@@ -1030,6 +1030,7 @@ void lupb_msg_registertypes(lua_State *L) {
   lupb_setfieldi(L, "TXTENC_NOSORT", UPB_TXTENC_NOSORT);
 
   lupb_setfieldi(L, "ENCODE_DETERMINISTIC", UPB_ENCODE_DETERMINISTIC);
+  lupb_setfieldi(L, "ENCODE_SKIPUNKNOWN", UPB_ENCODE_SKIPUNKNOWN);
 
   lupb_cacheinit(L);
 }

upb/encode.c

@@ -408,16 +408,17 @@ static void encode_scalarfield(upb_encstate *e, const char *msg,
 static void encode_message(upb_encstate *e, const char *msg,
                            const upb_msglayout *m, size_t *size) {
   size_t pre_len = e->limit - e->ptr;
-  const char *unknown;
-  size_t unknown_size;
   const upb_msglayout_field *f = &m->fields[m->field_count];
   const upb_msglayout_field *first = &m->fields[0];
 
-  unknown = upb_msg_getunknown(msg, &unknown_size);
+  if ((e->options & UPB_ENCODE_SKIPUNKNOWN) == 0) {
+    size_t unknown_size;
+    const char *unknown = upb_msg_getunknown(msg, &unknown_size);
 
     if (unknown) {
       encode_bytes(e, unknown, unknown_size);
     }
+  }
 
   while (f != first) {
     f--;

upb/encode.h

@@ -22,6 +22,9 @@ enum {
    * If your proto contains maps, the encoder will need to malloc()/free()
    * memory during encode. */
   UPB_ENCODE_DETERMINISTIC = 1,
+
+  /* When set, unknown fields are not printed. */
+  UPB_ENCODE_SKIPUNKNOWN = 2,
 };
 
 char *upb_encode_ex(const void *msg, const upb_msglayout *l, int options,