Add support for CommandListeners

[sokomishalov]

Draft for #1382

[codecov]

Codecov Report

Merging #1424 into main will increase coverage by 0.00%.
The diff coverage is 61.78%.

@@            Coverage Diff             @@
##               main    #1424    +/-   ##
==========================================
  Coverage     78.81%   78.82%            
- Complexity     6206     6261    +55     
==========================================
  Files           461      468     +7     
  Lines         20741    21039   +298     
  Branches       2283     2325    +42     
==========================================
+ Hits          16348    16584   +236     
- Misses         3337     3388    +51     
- Partials       1056     1067    +11     

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/io/lettuce/core/CommandListener.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...va/io/lettuce/core/cluster/RedisClusterClient.java	85.62% <0.00%> (-2.15%)	112.00 <0.00> (ø)
...java/io/lettuce/core/resource/ClientResources.java	66.66% <ø> (ø)	2.00 <0.00> (ø)
src/main/java/io/lettuce/core/RedisClient.java	88.28% <33.33%> (-1.42%)	91.00 <0.00> (+1.00)	⬇️
...in/java/io/lettuce/core/CommandListenerWriter.java	54.09% <54.09%> (ø)	6.00 <6.00> (?)
...tuce/core/models/events/CommandSucceededEvent.java	71.42% <71.42%> (ø)	2.00 <2.00> (?)
...o/lettuce/core/models/events/CommandBaseEvent.java	83.33% <83.33%> (ø)	2.00 <2.00> (?)
...va/io/lettuce/core/CommandListenerMulticaster.java	93.75% <93.75%> (ø)	7.00 <7.00> (?)
...lettuce/core/models/events/CommandFailedEvent.java	100.00% <100.00%> (ø)	2.00 <2.00> (?)
...ettuce/core/models/events/CommandStartedEvent.java	100.00% <100.00%> (ø)	2.00 <2.00> (?)
... and 21 more

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[mp911de]

Thanks for looking into this issue. I left a few comments about topics that we should address.

Please also note that we should have copyright headers on each new class with 2020 as inception year.

[mp911de]

Targetting this PR for 6.1 since 6.0 will be released in the next few days.

[sokomishalov]

Ok. Fixed @since javadoc lines for APIs.

[mp911de]

I started working on merging this PR. It provides a lot of value, but the real design challenges surfaced when trying to come up with a configuration model. Listeners aren't tied to ClientOptions or ClientResources. Since AbstractRedisClient already provides a listener API, I decided to add an overload accepting CommandListener.

I also removed generics from the command events to make things simpler. Let's see how this goes. I also noticed that introducing CommandListenerWriter breaks timeout overrides as setTimeout in RedisChannelHandler checks whether the writer is a CommandExpiryWriter.

The changes are exciting and the implementation makes a lot of sense. With the merge some shortcomings of the current implementation of RedisClient become apparent (see #1511). Also, redirected Cluster commands are reported multiple times with started/success events since each connection applies a listener. Not sure how to feel about it yet.

[mp911de]

Thank you for your contribution. That's merged and polished now.