UnsupportedOperationException from ListSubscriber during hrandfieldWithvalues

[mshinn]

Bug Report

Current Behavior

I'm consistently seeing the following exception when calling hrandfieldWithvalues when there is only a single result returned. If multiple results are returned, the call succeeds.

Stack trace

java.lang.UnsupportedOperationException
	at java.base/java.util.AbstractList.add(AbstractList.java:153)
	at java.base/java.util.AbstractList.add(AbstractList.java:111)
	at io.lettuce.core.output.ListSubscriber.onNext(ListSubscriber.java:49)
	at io.lettuce.core.output.KeyValueListOutput.set(KeyValueListOutput.java:76)
	at io.lettuce.core.protocol.RedisStateMachine.safeSet(RedisStateMachine.java:809)
	at io.lettuce.core.protocol.RedisStateMachine.handleBytes(RedisStateMachine.java:596)
	at io.lettuce.core.protocol.RedisStateMachine$State$Type.handle(RedisStateMachine.java:206)
	at io.lettuce.core.protocol.RedisStateMachine.doDecode(RedisStateMachine.java:358)
	at io.lettuce.core.protocol.RedisStateMachine.decode(RedisStateMachine.java:319)
	at io.lettuce.core.protocol.CommandHandler.decode(CommandHandler.java:840)
	at io.lettuce.core.protocol.CommandHandler.decode0(CommandHandler.java:791)
	at io.lettuce.core.protocol.CommandHandler.decode(CommandHandler.java:765)
	at io.lettuce.core.protocol.CommandHandler.decode(CommandHandler.java:657)
	at io.lettuce.core.protocol.CommandHandler.channelRead(CommandHandler.java:597)
	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)

Input Code

Input Code

String key = "myKey";
redisClusterCommands.hset(key, "field1", "value1");
redisClusterCommands.hset(key, "field2", "value2");
//Collection<KeyValue<String, String>> values1 = redisClusterCommands.hrandfieldWithvalues(key, 2); //works fine!
Collection<KeyValue<String, String>> values2 = redisClusterCommands.hrandfieldWithvalues(key, 1); //throws exception

Expected behavior/code

no exception :)

Environment

• Lettuce version(s): 6.3.2.RELEASE
• Redis version: 7.4.2

Possible Solution

Additional context

Looks similar to #711 although that bug report indicates they ran into the error during an mget call.

I believe the bug is here in the multi method:
https://github.com/redis/lettuce/blob/main/src/main/java/io/lettuce/core/output/KeyValueListOutput.java#L77





If the count argument is one, and keys is null, the output field ends up as an immutable empty list and the UnsupportedOperationException is thrown when the code attempts to add an element to the list.

[tishun]

Thanks for the report!

Yes you are more than certainly right and this seems like a bug in the KeyValueListOutput
The team will try to get this sorted out with the 6.6.0 release

[tishun]

MRE available here