[coro_http_server][feat]Support multipart

[qicosmos]

Why

coro_http_server support multipart upload.

What is changing

Example

  coro_http_server server(1, 8090);
  server.set_http_handler<cinatra::PUT, cinatra::POST>(
      "/multipart_upload",
      [](coro_http_request &req,
         coro_http_response &resp) -> async_simple::coro::Lazy<void> {
        assert(req.get_content_type() == content_type::multipart);
        auto boundary = req.get_boundary();

        while (true) {
          auto part_head = co_await req.get_conn()->read_part_head();
          if (part_head.ec) {
            co_return;
          }

          std::cout << part_head.name << "\n";
          std::cout << part_head.filename << "\n";

          std::shared_ptr<coro_io::coro_file> file;
          std::string filename;
          if (!part_head.filename.empty()) {
            file = std::make_shared<coro_io::coro_file>();
            filename = std::to_string(
                std::chrono::system_clock::now().time_since_epoch().count());

            size_t pos = part_head.filename.rfind('.');
            if (pos != std::string::npos) {
              auto extent = part_head.filename.substr(pos);
              filename += extent;
            }

            std::cout << filename << "\n";
            co_await file->async_open(filename, coro_io::flags::create_write);
            if (!file->is_open()) {
              resp.set_status_and_content(status_type::internal_server_error,
                                          "file open failed");
              co_return;
            }
          }

          auto part_body = co_await req.get_conn()->read_part_body(boundary);
          if (part_body.ec) {
            co_return;
          }

          if (!filename.empty()) {
            auto ec = co_await file->async_write(part_body.data.data(),
                                                 part_body.data.size());
            if (ec) {
              co_return;
            }

            file->close();
          }
          else {
            std::cout << part_body.data << "\n";
          }

          if (part_body.eof) {
            break;
          }
        }

        resp.set_status_and_content(status_type::ok, "ok");
      });

  server.async_start();