[HTTPCLIENT-2120] Support HTTP/2 (TLS) Tunneling over HTTP-Proxy

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 5.0.3
• Fix Version/s: 5.2-alpha1
• Component/s: HttpClient (async)
• Labels: http2 proxy
• Assignee: Unassigned
• Reporter: synth3
• Created: 19/Oct/20 12:04
• Updated: 28/Sep/21 17:32
• Resolved: 09/Sep/21 13:05

Description

First of all:

• Are there plans for supporting HTTP/2 (with TLS) connections via corporate HTTP-proxies?
  • If yes: is there a schedule?
• Could you please add documentation to "https://hc.apache.org" that makes it clear that the HTTP/2 implementation does currently not support HTTP-proxies?
  • This alone could save people hours of programming something that has no chance to work and debugging afterwards
  • The only clear statement I found regarding that topic was at a migration guide ("https://ok2c.github.io/httpclient-migration-guide/migration-to-async-http2.html")

Observations while trying to establish a HTTP/2 connection via proxy:

The observations can be made using the following minimal example with [proxy_ip]:[proxy_port] replaced with host and port of an actual HTTP-Proxy:

CloseableHttpAsyncClient client = HttpAsyncClients.custom()
    .setVersionPolicy(HttpVersionPolicy.FORCE_HTTP_2)
    .setProxy(HttpHost.create("[proxy_ip]:[proxy_port]")).build();
client.start();
// throws org.apache.hc.core5.http.ConnectionClosedException
client.execute(SimpleHttpRequests.get("https://http2.pro/client"), null).get();

The above code throws the following Exception:

Exception in thread "main" java.util.concurrent.ExecutionException: org.apache.hc.core5.http.ConnectionClosedException: Connection is closed
	at org.apache.hc.core5.concurrent.BasicFuture.getResult(BasicFuture.java:72)
	at org.apache.hc.core5.concurrent.BasicFuture.get(BasicFuture.java:85)
	at com.test.MinimalProxyTest.basicTest(MinimalProxyTest.java:41)
	at com.test.MinimalProxyTest.main(MinimalProxyTest.java:23)
Caused by: org.apache.hc.core5.http.ConnectionClosedException: Connection is closed
	at org.apache.hc.core5.http2.impl.nio.AbstractH2StreamMultiplexer.onException(AbstractH2StreamMultiplexer.java:661)
	at org.apache.hc.core5.http2.impl.nio.AbstractH2IOEventHandler.exception(AbstractH2IOEventHandler.java:91)
	at org.apache.hc.core5.http2.impl.nio.ClientH2IOEventHandler.exception(ClientH2IOEventHandler.java:39)
	at org.apache.hc.core5.reactor.InternalDataChannel.onException(InternalDataChannel.java:162)
	at org.apache.hc.core5.reactor.InternalChannel.handleIOEvent(InternalChannel.java:55)
	at org.apache.hc.core5.reactor.SingleCoreIOReactor.processEvents(SingleCoreIOReactor.java:179)
	at org.apache.hc.core5.reactor.SingleCoreIOReactor.doExecute(SingleCoreIOReactor.java:128)
	at org.apache.hc.core5.reactor.AbstractSingleCoreIOReactor.execute(AbstractSingleCoreIOReactor.java:85)
	at org.apache.hc.core5.reactor.IOReactorWorker.run(IOReactorWorker.java:44)
	at java.base/java.lang.Thread.run(Thread.java:832)

• There is no exception thrown that makes clear that this constellation (HTTP/2 + Proxy) is not supported
  • Even though I found org.apache.hc.client5.http.impl.async.InternalHttpAsyncClient.determineRoute(HttpHost, HttpClientContext) with throw new HttpException("HTTP/2 tunneling not supported") which is not triggered because HttpClientContext.getProtocolVersion() returns HTTP-1.1
• Looking at the Logs I see that the HTTP/2 request was tried to be performed unencrypted and the Proxy sends HTTP/1.0 400 Bad Request and closes the connection
• Also in the logs I can see Code FRAME_SIZE_ERROR and Frame size exceeds maximum which might be caused by trying to consume the HTTP-1.1 proxy response as HTTP/2
  • The associated Exception (H2ConnectionException: Frame size exceeds maximum) is omitted in org.apache.hc.core5.http2.impl.nio.AbstractH2StreamMultiplexer.onException(Exception) where ((ExecutableCommand) command).failed(new ConnectionClosedException()) is called

What can be done?

If I wanted to support you in implementing the HTTP/2 via proxy support where would I have to start?

• When I understand the situation right then we are almost there and the only problem is that the HTTP/2 request is tried to be performed without encryption