HttpServerUpgradeHandler causing StringIndexOutOfBoundsException

[dpy1123]

We are using netty as a proxy server. And added HttpServerUpgradeHandler incase client wants to talk in h2c.
But with a normal http1 request, we see the following exceptions.

	at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:98)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)
	at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:436)
	at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:324)
	at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:296)
	at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:251)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)
	at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
	at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919)
	at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166)
	at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:714)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:650)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:576)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:493)
	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989)
	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at java.base/java.lang.Thread.run(Thread.java:829)
Caused by: java.lang.StringIndexOutOfBoundsException: String index out of range: -1
	at java.base/java.lang.AbstractStringBuilder.setLength(AbstractStringBuilder.java:275)
	at java.base/java.lang.StringBuilder.setLength(StringBuilder.java:85)
	at io.netty.handler.codec.http.HttpServerUpgradeHandler.upgrade(HttpServerUpgradeHandler.java:297)
	at io.netty.handler.codec.http.HttpServerUpgradeHandler.decode(HttpServerUpgradeHandler.java:239)
	at io.netty.handler.codec.http.HttpServerUpgradeHandler.decode(HttpServerUpgradeHandler.java:40)
	at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:88)
	... 22 more

As far as I can see, it seems like the if conditon should also add isEmpty().

            return false;
        }

netty/codec-http/src/main/java/io/netty/handler/codec/http/HttpServerUpgradeHandler.java

Line 326 in 3f8dab5

if (connectionHeaderValues == null) {

[dpy1123]

Work around can be fond in #11267
Implement your own shouldHandleUpgradeRequest, and check connection header there.

[chrisvest]

@dpy1123 Yeah, a missing isEmpty() looks about right. Would you like to make a PR for this?