Can not get response from LwM2M clients when using CoAP+TCP (java-coap)

[max-pv]

Version(s)

2.0.0-M16

Which components

leshan-lwm2m-server

Tested With

Leshan Client Demo, Anjay Demo

What happened

When running a Leshan demo a server with a RegistrationListener from Wiki and using Leshan Client (or another LwM2M client) with CoAP+TCP server address, the server timeouts and throws the error from the "relevant output" section.

It works fine when using plain CoAP provider (just coap:// scheme)

How to reproduce

1. Copy the changes from this diff to LeshanDemoServer.java
2. Run mvn clean install
3. Run the Leshan server: java -jar ./leshan-demo-server/target/leshan-demo-server-*-SNAPSHOT-jar-with-dependencies.jar -vvv
4. Run the Leshan client with CoAP+TCP scheme (in a separate terminal session): java -jar leshan-demo-client/target/leshan-demo-client-*-SNAPSHOT-jar-with-dependencies.jar -u coap+tcp://localhost:5683 -n tcp-device-1
5. Wait for some time, the server will not get a response from client
6. After around 2-3 minutes, the server terminal will show the error from "relevant output"

Relevant Output

2024-11-19 15:32:51,172 LeshanServerDemo     [ERROR] Unexpected error while reading device time  
java.lang.NullPointerException: Cannot invoke "org.eclipse.leshan.core.response.ReadResponse.isSuccess()" because "response" is null
	at org.eclipse.leshan.demo.server.LeshanServerDemo$1.registered(LeshanServerDemo.java:150)
	at org.eclipse.leshan.server.registration.RegistrationServiceImpl.fireRegistered(RegistrationServiceImpl.java:74)
	at org.eclipse.leshan.server.registration.RegistrationHandler$1.run(RegistrationHandler.java:126)
	at org.eclipse.leshan.core.response.SendableResponse.sent(SendableResponse.java:47)
	at org.eclipse.leshan.transport.javacoap.server.resource.RegistrationResource.handleRegister(RegistrationResource.java:171)
	at org.eclipse.leshan.transport.javacoap.server.resource.RegistrationResource.handlePOST(RegistrationResource.java:89)
	at org.eclipse.leshan.transport.javacoap.resource.LwM2mCoapResource.handleRequest(LwM2mCoapResource.java:78)
	at org.eclipse.leshan.transport.javacoap.resource.LwM2mCoapResource.apply(LwM2mCoapResource.java:63)
	at org.eclipse.leshan.transport.javacoap.resource.LwM2mCoapResource.apply(LwM2mCoapResource.java:42)
	at com.mbed.coap.server.RouterService.apply(RouterService.java:68)
	at com.mbed.coap.server.RouterService.apply(RouterService.java:33)
	at com.mbed.coap.utils.Filter$1.apply(Filter.java:69)
	at com.mbed.coap.utils.Filter.lambda$null$0(Filter.java:33)
	at com.mbed.coap.server.block.BlockWiseIncomingFilter.apply(BlockWiseIncomingFilter.java:55)
	at com.mbed.coap.server.block.BlockWiseIncomingFilter.apply(BlockWiseIncomingFilter.java:38)
	at com.mbed.coap.utils.Filter.lambda$null$0(Filter.java:33)
	at com.mbed.coap.server.CriticalOptionVerifier.apply(CriticalOptionVerifier.java:34)
	at com.mbed.coap.server.CriticalOptionVerifier.apply(CriticalOptionVerifier.java:27)
	at com.mbed.coap.utils.Filter.lambda$null$0(Filter.java:33)
	at com.mbed.coap.server.RescueFilter.apply(RescueFilter.java:35)
	at com.mbed.coap.server.RescueFilter.apply(RescueFilter.java:29)
	at com.mbed.coap.utils.Filter.lambda$andThen$1(Filter.java:34)
	at com.mbed.coap.utils.Filter.lambda$andThen$1(Filter.java:34)
	at com.mbed.coap.utils.Filter.lambda$andThen$1(Filter.java:34)
	at com.mbed.coap.utils.Filter.lambda$then$3(Filter.java:53)
	at com.mbed.coap.server.messaging.CoapTcpDispatcher.handle(CoapTcpDispatcher.java:73)
	at com.mbed.coap.server.CoapServer.handle(CoapServer.java:76)
	at java.base/java.util.concurrent.CompletableFuture.uniWhenComplete(CompletableFuture.java:863)
	at java.base/java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:841)
	at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:510)
	at java.base/java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:2147)
	at org.eclipse.leshan.transport.javacoap.server.coaptcp.transport.NettyCoapTcpTransport$DispatchHandler.channelRead(NettyCoapTcpTransport.java:167)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
	at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:346)
	at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:318)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
	at io.netty.handler.timeout.IdleStateHandler.channelRead(IdleStateHandler.java:289)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
	at io.netty.channel.DefaultChannelPipeline$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 io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.base/java.lang.Thread.run(Thread.java:840)

[sbernard31]

Thx for taking time to reporting that. 🙏

Glad to see that you are testing coap+tcp experimental feature.

I will try to look at this but maybe not today 😬

Some remarks waiting I take time to look at this deeper :

"org.eclipse.leshan.core.response.ReadResponse.isSuccess()" because "response" is null

a null response with synchronous send API means that the request timeout.
Why it times-out ? I don't know for now.

ReadResponse response = lwm2mServer.send(registration, new ReadRequest(3, 0, 13));

I see you are using synchronous send API in registered event.
This is not advised, see javadoc :

/**
 * Listen for client registration events.
 * <p>
 * Those methods are called by the protocol stage thread pool, this means that execution MUST be done in a short delay,
 * if you need to do long time processing use a dedicated thread pool.
 */

Could you try with async send API ?

[max-pv]

Thank you! I will try that sometime later. Instead of doing CoAP over TCP, for now I've decided to try if WebSocket proxy would work, as defined in Section 4 of RFC 8323.