For both HTTP/1.1 and HTTP/2, HttpClient very slow if downloading a 160M file with TLS, it spends only 2 seconds for 8M, but much more time than 2 * (160 / 8) seconds to download the 160M file. And if we use legacy HttpsURLConnection, it spends about 20 seconds.

The following tes will fail with timeout:
import static jdk.incubator.http.HttpClient.Version.HTTP_2;
import static jdk.incubator.http.HttpClient.Version.HTTP_1_1;

import java.io.InputStream;
import java.net.URI;
import java.net.URL;
import java.security.GeneralSecurityException;
import java.security.cert.X509Certificate;

import javax.net.ssl.HttpsURLConnection;
import javax.net.ssl.SSLContext;
import javax.net.ssl.TrustManager;
import javax.net.ssl.X509TrustManager;

import org.testng.annotations.Test;

import jdk.incubator.http.HttpClient;
import jdk.incubator.http.HttpClient.Version;
import jdk.incubator.http.HttpRequest;
import jdk.incubator.http.HttpResponse;

/*
 * @test
 * @compile HttpTestUtils.java
 * @modules jdk.incubator.httpclient
 * @run testng/othervm Test1
 */
public class Test1 {//-Djdk.internal.httpclient.debug=true
    @Test
    public void testLegacy() throws Exception {
        TrustManager[] trustAllCerts = new TrustManager[] { new X509TrustManager() {
            public java.security.cert.X509Certificate[] getAcceptedIssuers() {
                return new X509Certificate[0];
            }

            public void checkClientTrusted(java.security.cert.X509Certificate[] certs,
                    String authType) {
            }

            public void checkServerTrusted(java.security.cert.X509Certificate[] certs,
                    String authType) {
            }
        } };

        try {
            SSLContext sc = SSLContext.getInstance("SSL");
            sc.init(null, trustAllCerts, new java.security.SecureRandom());
            HttpsURLConnection.setDefaultSSLSocketFactory(sc.getSocketFactory());
        } catch (GeneralSecurityException e) {
        }

        InputStream in = new URL("https://<host>/yc/data/d1.data").openStream();
        System.out.println(in.readAllBytes().length);
        in.close();
    }
    
    @Test
    public void test1() throws Exception {
        test(HTTP_1_1);
    }
    
    @Test
    public void test2() throws Exception {
        System.setProperty("jdk.httpclient.connectionWindowSize", String.valueOf(1024*1024*32));
        System.setProperty("jdk.httpclient.windowsize", String.valueOf(1024*1024*16));
        test(HTTP_2);
    }

    private static HttpClient getClient(Version v) {
        return HttpTestUtils.clientBuilder().version(v).build();
    }

    private void test(Version v) throws Exception {
        HttpClient client = getClient(v);

        client.sendAsync(HttpRequest
                .newBuilder(new URI("https://<host>/yc/data/d1.data")).GET().build(),
                    HttpResponse.BodyHandler.asByteArray())
                .get();
    }
}