Feature: Add timeout option

[proost]

When use redis with rueidis, i set timeout to context.Context. but rueidis can handle this, so that many rueidis user do not have to set timeout to context.Context.

http.Client supports timeout, and lettuce in Java supports timeout. if rueidis support timeout option, then it can be more convenient.

[rueian]

Hi @proost, rueidis does have a default timeout option: option.ConnWriteTimeout. It is 10s by default.

[proost]

There is something confused me.

	if dlOk {
		p.conn.SetDeadline(dl)
	} else if p.timeout > 0 && !cmd.IsBlock() {
		p.conn.SetDeadline(time.Now().Add(p.timeout))
	} else {
		p.conn.SetDeadline(time.Time{})
	}

setting timeout logic likes above,

1. if a context.Context has deadline, whether some commands are blocking or not, always set timeout.
2. if a context.Context has not deadline, ConnWriteTimeout is configured and all commands is not block, set timeout.

I think, these logic feels like inconsistent. Because if one of commands is blocking, always ignore pipe.timeout and deadline in context.Context or respect pipe.timeout and deadline in context.Context both. why respect only deadline in context.Context? what are reasons?

[rueian]

Consider the following two use cases:

func case1() {
	client, _ := rueidis.NewClient(rueidis.ClientOption{InitAddress: []string{"127.0.0.1:6379"}})
	defer client.Close()

	client.Do(context.Background(), client.B().Blpop().Key("list").Timeout(0).Build())
}

func case2() {
	client, _ := rueidis.NewClient(rueidis.ClientOption{InitAddress: []string{"127.0.0.1:6379"}})
	defer client.Close()

	ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
	defer cancel()
	client.Do(ctx, client.B().Blpop().Key("list").Timeout(0).Build())
}

Users who write the case1 will want the BLPOP block indefinitely, therefore no deadline is applied.

Users who write the case2 will want the BLPOP block for at most 1 minute, therefore 1 minute deadline is applied.

[proost]

Yes, I agree. we should avoid block indefinitely. so if pipe.timeout is configured, no deadline in context.Context and blocking command is given, we should set deadline too.

[rueian]

Uh, no, that is not what I mean.

I mean users want to block indefinitely in the first case, so we should not apply pipe.timeout.

[proost]

Oh, I understand.

[proost]

Solved by:
#470
#469