HTTP client errors out when sending CONNECT request

[DerGuteMoritz]

Using the HTTP client to directly send a CONNECT request (i.e. not by means of proxy configuration) results in an unhandled decoder error. Reproducer:

;; in aleph.http-test

(defn http-connect
  ([path]
   (http-connect path nil))
  ([path options]
   (http/connect (make-url path) (merge (default-request-options) {:pool *pool*} options))))

(deftest test-connect
  (with-http1-server basic-handler {}
    (is (= string-response
           (bs/to-string (:body @(http-connect "/string")))))))

This fails with

FAIL in (test-connect) (http_test.clj:325)
- http1
expected: (= string-response (bs/to-string (:body (clojure.core/deref (http-connect "/string")))))
  actual: (not (= "String!" ""))

And the following exception is logged:

1142576 tid=624 WARN client - error in HTTP client
java.lang.ClassCastException: io.netty.buffer.PooledUnsafeDirectByteBuf cannot be cast to io.netty.handler.codec.DecoderResultProvider
	at aleph.http.common$decoder_failed_QMARK_.invokeStatic(common.clj:237)
	at aleph.http.common$decoder_failed_QMARK_.invoke(common.clj:237)
	at aleph.http.client$http1_client_handler$reify__19484.channelRead(client.clj:209)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
	at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:436)
	at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:346)
	at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:318)
	at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:251)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
	at io.netty.handler.logging.LoggingHandler.channelRead(LoggingHandler.java:280)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
	at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1357)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:440)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
	at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:868)
	at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166)
	at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:788)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:724)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:650)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:562)
	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:997)
	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at manifold.executor$thread_factory$reify__12656$f__12657.invoke(executor.clj:71)
	at clojure.lang.AFn.run(AFn.java:22)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.lang.Thread.run(Thread.java:750)

It looks like Netty special-cases CONNECT requests somehow so that the message read from the channel is not a DecoderResultProvider but a raw byte buffer instead. It's questionable whether anyone would ever send a CONNECT request directly like this but given that we expose it as a first-class API via aleph.http/connect, we should probably do something about it.