http_serializer with buffer_body emits zero-sized chunk surprisingly, breaking HTTP framing

[pgit]

When finishing a chunked body like this:

message.body().data = <non-null-ptr>
message.body().size = 0;
message.body().more = false;

TWO zero-sized chunks are emitted, breaking HTTP framing. Only if data is actually set to nullptr, this works.

My usecase is serializing a sequence of std::string_view, using an empty one as EOM marker. An empty string view may have a non-null data pointer. Only if I do

message.body().data = sv.size() ? const_cast<void*>(sv.data()) : nullptr;
message.body().size = sv.size();
message.body().more = sv.size() != 0; // empty sv --> EOM

this becomes safe. One could argue that beast is so low-level that the caller has to know about this subtle difference, but as the 0-sized chunk has a very specific meaning in HTTP, IMO a safeguard against this could be warranted.

[vinniefalco]

if size==0 then beast should ignore data

[pgit]

Godbolt: Working example Simpler, sync version

   using Serializer = http::response_serializer<http::buffer_body>;
   using Message = std::remove_const_t<typename Serializer::value_type>;
   Message message;
   Serializer serializer{message};

   message.chunked(true);

   error_code ec;
   auto text = asio::buffer("Hello, World!"sv);
   message.body().data = const_cast<void*>(text.data());
   message.body().size = text.size();
   message.body().more = true;
   http::write(stream, serializer, ec);
   assert(ec == http::error::need_buffer);

   if (with_nullptr)
      message.body().data = nullptr;
   message.body().size = 0;
   message.body().more = false;
   http::write(stream, serializer, ec);
   assert(!ec);

with_nullptr = true

HTTP/1.1 200 OK
Transfer-Encoding: chunked

d
Hello, World!
0

with_nullptr = false

HTTP/1.1 200 OK
Transfer-Encoding: chunked

d
Hello, World!
0

0