Add retry logic of connection lifetime to cluster client and sentinel client

[terut]

This is follow-up PR regarding #727 .

See #727 (comment).

[rueian]

Wow. You are lightning fast, but we still need some test cases for this.

[terut]

@rueian Sure, I'll add the tests. I’m not familiar to cluster and sentinel client, so I wanted to check whether my understanding is correct about what you said.

[rueian]

Yes, I think you are on the right track.

[rueian]

Shouldn't this go back to L526?

[terut]

Fix 3623adc . Is it correct?

[rueian]

ASKING can't be handled this way. It must be sent in every retry.

[terut]

@rueian Does it mean that ASKING needs at head of cmds when retrying due to errConnExpired

[rueian]

Yes, ASKING is only effective in the same connection and applied only to the next command; therefore, we need to re-send ASKING before the target cmd if errConnExpired happens.

[terut]

I see. I will also fix askingMulti and askingMultiCache as same.

[terut]

@rueian Fix ce19729 be811cc

[rueian]

This reminds me that we need to handle the MULTI EXEC pattern correctly: If errConnExpired occurs during the MULTI EXEC, we should retry the entire MULTI EXEC block. This applies to the single client as well, which we overlooked in the previous PR.

[terut]

@rueian Would you check this pull-request #837 ? This is draft so I will fix other methods and add tests after checking the implement.

[rueian]

Yes, the draft looks good to me.

[terut]

Thanks!

[terut]

@rueian Please review #837 .

[terut]

I missed response of Multi command of test data.

I'm writing tests for askingMulti() but I'm not sure why multi has the following commands when calling that method. Any idea?

// Call for unit testing
multi := []Completed{
	client.B().Get().Key("1{t}").Build(),
	client.B().Multi().Build(),
	client.B().Incr().Key("2{t}").Build(),
	client.B().Incr().Key("3{t}").Build(),
	client.B().Exec().Build(),
	client.B().Get().Key("4{t}").Build(),
}
resps := client.DoMulti(context.Background(), multi...)

// multi in askingMulti(). I don't know why there is no [GET 2{t}] [Get 3{t}].
[ASKING]
[GET 1{t}]
[ASKING]
[MULTI]
[EXEC]
[ASKING]
[GET 4{t}]

[terut]

Fix 6362824

[rueian]

Here, we can advance the i by 6 in every iteration and only check the Error of the ExecCmd.

[terut]

Fix 6362824

[rueian]

Thanks @terut!

[terut]

@rueian Thank you for great help for couple of months 😄