Ensure that fixed32 and fixed64 data are little endian regardless

of the host endianness.

conformance/binary_json_conformance_suite.cc

@@ -35,6 +35,7 @@
 #include <utility>
 #include <vector>
 
+#include "google/protobuf/endian.h"
 #include "google/protobuf/text_format.h"
 #include "google/protobuf/util/json_util.h"
 #include "google/protobuf/util/type_resolver_util.h"
@@ -58,6 +59,7 @@ using google::protobuf::Descriptor;
 using google::protobuf::FieldDescriptor;
 using google::protobuf::Message;
 using google::protobuf::internal::WireFormatLite;
+using google::protobuf::internal::little_endian::FromHost;
 using google::protobuf::util::NewTypeResolverForDescriptorPool;
 using proto2_messages::TestAllTypesProto2;
 using protobuf_test_messages::proto3::TestAllTypesProto3;
@@ -117,9 +119,18 @@ string longvarint(uint64_t x, int extra) {
   return string(buf, len);
 }
 
-// TODO: proper byte-swapping for big-endian machines.
-string fixed32(void* data) { return string(static_cast<char*>(data), 4); }
-string fixed64(void* data) { return string(static_cast<char*>(data), 8); }
+string fixed32(void* data) {
+  uint32_t data_le;
+  std::memcpy(&data_le, data, 4);
+  data_le = FromHost(data_le);
+  return string(reinterpret_cast<char*>(&data_le), 4);
+}
+string fixed64(void* data) {
+  uint64_t data_le;
+  std::memcpy(&data_le, data, 8);
+  data_le = FromHost(data_le);
+  return string(reinterpret_cast<char*>(&data_le), 8);
+}
 
 string delim(const string& buf) {
   return absl::StrCat(varint(buf.size()), buf);