boost::beast::http::request Sending a file as multipart/form-data - boost-beast

Question

Just getting in to this using http_client_sync.cpp. I added a little bit of code to use the
http::file_body type.
I can't seem to figure out how to get the multipart boundaries inserted. Is there something in particular I need to do to make that happen? When I look at the POST in wireshark, the entire multipart/form data is in one big part. Relevant (I hope) snippet below. Modified from oroginal http_client_sync.cpp.
// Set up an HTTP POST request message
http::request<http::file_body> req{http::verb::post, target, version};
// use the full host:port here
req.set(http::field::host, fullhost.c_str());
req.set(http::field::user_agent, BOOST_BEAST_VERSION_STRING);
req.set(http::field::accept,"*/*");
req.set(http::field::content_length,contentLen);
req.set(http::field::content_type,"multipart/form-data; boundary=fd1c38d86c0a42ac933e7319e51882fd");
req.body() = std::move(body);
http::request_serializer<http::file_body, http::fields> sr{req};
// Send the HTTP request to the remote host
http::write(socket, sr);
I did also try this, but the result was the same
size_t len = http::write_header(socket, sr);
while(len!=0)
{
len = http::write_some(socket, sr);
}
The server I'm talking to is expecting multiple parts.
Many Thanks

Answer 1

Ok it turns out this is possible, and cured my issue. Probably not the "right" way to do it, but it works.
size_t len = http::write_header(socket, sr);
// where multipart header is a string containing the first boundary
// and the content disposition
boost::asio::write(socket,boost::asio::buffer( multipartHeader));
while(len!=0)
{
len = http::write_some(socket, sr);
}
// where multipart trailer is a string containing the final boundary
boost::asio::write(socket,boost::asio::buffer( multipartTrailer));
Happy to hear better solutions.