HttpsServer causes 100% CPU load with curl

I've created a minimal application around Java's HttpsServer.

I've installed an HttpHandler that replies to a request with a short text message:

return exchange -> {
    try {
        OutputStream responseBodyStream = exchange.getResponseBody();

        byte[] response = "Trouble with HTTPS and curl\n"
                .getBytes(StandardCharsets.UTF_8);

        exchange.getResponseHeaders().set("Content-Type", "text/plain");

        exchange.sendResponseHeaders(200, response.length);

        responseBodyStream.write(response);

        responseBodyStream.close();

        // Note that exchange.close() also closes the exchange's input stream
        // and output stream

    } catch (Exception e) {
        log.warn("Could not handle request", e);
    }
};

When connecting to the server with curl, the server responds but the Java process keeps using an entire core, thus rendering the server unresponsive.

It's this line that triggers the issue:

responseBodyStream.close();

If we remove the line, the server keeps on working.

From the docs:

In order to correctly terminate each exchange, the output stream must be closed, even if no response body is being sent.

I've created a project to reproduce the issue.

Some potential clues I've found up till now:

• High CPU usage only occurs when connecting to the server with curl. When connecting with Firefox, CPU usage stays low
• The issue does not occur with curl when using a regular HTTP server without TLS
• Data gathered using Flight Recorder indicate that SSLEngineImpl#writeRecord in the thread HTTP-Dispatcher allocates a lot of objects

I'm on Arch Linux 5.1.7 using OpenJDK 12.0.1+12. The version of curl is 7.65.1.

Is this a bug in the JDK? Or am I using HttpsServer the wrong way?