Hi i use netty on Android to host a webserver and ...

# ktor

[Kilian]

Hi i use netty on Android to host a webserver and would like to use ssl.
I created a certificate as shown here https://github.com/myfreax/android-ssl-certificate
I added it to ktor and the server starts and isn’t available on http anymore as expected.
Code:

sslConnector(
            keyStore = keystore,
            keyAlias = keyAlias,
            keyStorePassword = { keyStorePassword.toCharArray() },
            privateKeyPassword = { keyPassword.toCharArray() },
        ) {
            // this.host = "0.0.0.0"
            this.keyStorePath = file
            this.port = port
        }

Unfortunately i get a crash

[eventLoopGroupProxy-3-1] WARN io.netty.channel.DefaultChannelPipeline - An exceptionCaught() event was fired, and it reached at the tail of the pipeline. It usually means the last handler in the pipeline did not handle the exception.
io.netty.handler.codec.DecoderException: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.isEmpty()' on a null object reference
	at io.netty.handler.codec.ByteToMessageDecoder.callDecode(Unknown Source:103)
	at io.netty.handler.codec.ByteToMessageDecoder.channelRead(Unknown Source:53)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(SourceFile:2)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(SourceFile:1)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(SourceFile:1)
	at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(Unknown Source:0)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(SourceFile:2)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(SourceFile:1)
	at io.netty.channel.DefaultChannelPipeline.fireChannelRead(SourceFile:2)
	at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(Unknown Source:101)
	at io.netty.channel.nio.NioEventLoop.processSelectedKey(SourceFile:1)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(Unknown Source:24)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeys(Unknown Source:4)
	at io.netty.channel.nio.NioEventLoop.run(Unknown Source:131)
	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(Unknown Source:41)
	at io.netty.util.internal.ThreadExecutorMap$2.run(Unknown Source:8)
	at io.ktor.server.netty.EventLoopGroupProxy$Companion.create$lambda$1$lambda$0(Unknown Source:5)
	at io.ktor.server.netty.EventLoopGroupProxy$Companion.$r8$lambda$XgnKz7L6tCWRUaIAa7SVURwtFE4(SourceFile:1)
	at androidx.core.app.ActivityCompat$$ExternalSyntheticLambda0.run(SourceFile:31)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(Unknown Source:2)
	at java.lang.Thread.run(Thread.java:1012)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.isEmpty()' on a null object reference
	at io.netty.handler.ssl.JdkAlpnSslEngine$AlpnSelector.checkUnsupported(Unknown Source:11)
	at io.netty.handler.ssl.JdkAlpnSslEngine.verifyProtocolSelection(Unknown Source:41)
	at io.netty.handler.ssl.JdkAlpnSslEngine.wrap(SourceFile:3)
	at io.netty.handler.ssl.SslHandler.wrap(SourceFile:1)
	at io.netty.handler.ssl.SslHandler.wrapNonAppData(Unknown Source:30)
	at io.netty.handler.ssl.SslHandler.unwrap(Unknown Source:169)
	at io.netty.handler.ssl.SslHandler.decodeJdkCompatible(Unknown Source:39)
	at io.netty.handler.ssl.SslHandler.decode(Unknown Source:13)
	at io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(Unknown Source:5)
	at io.netty.handler.codec.ByteToMessageDecoder.callDecode(Unknown Source:33)
	... 20 more

seems like in JdkAlpnSslEngine String protocol = getApplicationProtocol(); produces a null value. Any idea how to fix it?

[Kilian]

i found this on youtrack https://youtrack.jetbrains.com/issue/KTOR-5065/Netty-Android-Failed-to-select-the-application-level-protocol-error-for-HTTPS-requests-via-HTTP-1

[Kilian]

My workaround for now is to downgrade to 2.1.0. I'll still see the erros in the log but socket won't hang up

[Pim]

Hey @Kilian did you ever manage to fix it without downgrading? I’m having the same issue on an Android 10 device using Ktor version 2.3.13.

[Kilian]

i actually don’t remember. Did you try upgrading to Ktor3 ?

[Pim]

Thanks for your reply! I was about to try that out. But was curious to find out if there was a fix without migrating to 3.x.x. Let me give upgrading a try, I’ll let you know.

[Pim]

The issue was also present on 3.x.x. However I found out it works when I disable http2 using enableHttp2 = false on the NettyApplicationEngine.Configuration. Not sure how that’s connected though.