Fix wrong dbnum showed in cli after client reconnected

[vitahlin]

When the server restarts while the CLI is connecting, the reconnection does not automatically select the previous db.
This may lead users to believe they are still in the previous db, in fact, they are in db0.

This PR will automatically reset the current dbnum and cliSelect() again when reconnecting.

Steps for reproducing bug

1. start server and client:

./src/valkey-server
./src/valkey-cli

2. set value in db0 and db5:

127.0.0.1:6379> set a 0
OK
127.0.0.1:6379> get a
"0"
127.0.0.1:6379> select 5
OK
127.0.0.1:6379[5]> set a 5
OK
127.0.0.1:6379[5]> get a
"5"
127.0.0.1:6379[5]> 

3. Ctrl+C to stop server:

127.0.0.1:6379[5]> get a
Error: Connection reset by peer
not connected> 

4. restart server then in valkey-cli:

not connected> get a
"0"
127.0.0.1:6379[5]> 

The valkey-cli run command at db0 but showed db5.

Solution

valkey-cli will re-select db5 after reconnected:

127.0.0.1:6379> get a
"0"
127.0.0.1:6379> select 5
OK
127.0.0.1:6379[5]> get a
"5"
127.0.0.1:6379[5]> get a
Error: Connection reset by peer
not connected> get a
"5"
127.0.0.1:6379[5]> 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.77%. Comparing base (3df609e) to head (5cd9b3c).

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #1382      +/-   ##
============================================
- Coverage     70.78%   70.77%   -0.02%     
============================================
  Files           118      118              
  Lines         63497    63499       +2     
============================================
- Hits          44945    44939       -6     
- Misses        18552    18560       +8     

Files with missing lines	Coverage Δ
src/valkey-cli.c	55.54% <100.00%> (+0.08%)	⬆️

... and 12 files with indirect coverage changes

[zuiderkwast]

Reconnect can happen in a few places in the code so I think it's better that cliSelect() is done inside cliConnect().

I see now that inside cliConnect() with the CC_FORCE flag, we already set config.dbnum = 0 and we call cliSelect() and a few other things, such as

        /* Do AUTH, select the right DB, switch to RESP3 if needed. */
        if (cliAuth(context, config.conn_info.user, config.conn_info.auth) != REDIS_OK) return REDIS_ERR;
        if (cliSelect() != REDIS_OK) return REDIS_ERR;
        if (cliSwitchProto() != REDIS_OK) return REDIS_ERR;

I wonder why that doesn't work as intended.