import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse.BodyHandlers;
import java.nio.file.Path;

public class MultipartBodyPublisherRawTest {

    static final String CRLF = "\r\n";
    static final String BOUNDARY = "gc0p4Jq0M2Yt08jU534c0p";
    static final String BOUNDARY_START = "--";
    static final String BOUNDARY_END = "--";

    public static void main(String... args) throws Exception {

        // # using raw concat only !
        var publisher = HttpRequest.BodyPublishers.concat(
                // preamble
                HttpRequest.BodyPublishers.ofString(CRLF + BOUNDARY_START + BOUNDARY + CRLF + "Content-Type: text/plain; charset=us-ascii" + CRLF),
                HttpRequest.BodyPublishers.ofFile(Path.of("/tmp/xxyy")),
                HttpRequest.BodyPublishers.ofString(CRLF + BOUNDARY_START + BOUNDARY + BOUNDARY_END)
                // epilogue
        );

        var client = HttpClient.newHttpClient();
        var request = HttpRequest.newBuilder()
                .uri(URI.create("http://foo.com/"))
                .header("Content-Type", "multipart/mixed; boundary=" + BOUNDARY)
                .POST(publisher)
                .build();
        client.send(request, BodyHandlers.ofString());
    }
}