Add multi-database support to EchoVault

[kelvinmwinuka]

This change adds key name spacing using logical database to EchoVault. These name spaces are called databases and can be selected using indexes.

Features

• Key name spaces can be created in both standalone mode and RAFT cluster mode.
• Key name spaces are supported in AOF files and snapshot files. Multiple databases will be saved within the same AOF and snapshot file.
• Name spaces are restored from disk upon startup.
• New commands to interact with databases.

Client-Server Commands

HELLO

HELLO [protover [AUTH username password] [SETNAME clientname]]

The hello commands returns information about the client. The AUTH options allow the client to authenticate itself. The SETNAME sets the alias for the current connection.

Example response with protocol 2:

1) server
2) "echovault"
3) version
4) "0.8.0"
5) proto
6) (integer) 2
7) id
8) (integer) 1
9) mode
10) "standalone"
11) role
12) "master"
13) modules
14)  1) "acl"
       2) "admin"
       3) "connection"
       4) "generic"
       5) "hash"
       6) "list"
       7) "pubsub"
       8) "set"
       9) "sortedset"
      10) "string"

Example response with protocol 3:

1# server => "echovault"
2# version => "0.8.0"
3# proto => (integer) 3
4# id => (integer) 1
5# mode => "standalone"
6# role => "master"
7# modules => 
    1) "acl"
    2) "admin"
    3) "connection"
    4) "generic"
    5) "hash"
    6) "list"
    7) "pubsub"
    8) "set"
    9) "sortedset"
   10) "string"

SELECT

SELECT index

Change the logical database that the current connection is operating from.

SWAPDB

SWAPDB index1 index2

This command swaps two databases,
so that immediately all the clients connected to a given database will see the data of the other database,
and the other way around.

FLUSHALL

FLUSHALL

Delete all the keys in all the existing databases. This command is always synchronous.

FLUSHDB

FLUSHDB

Delete all the keys in the currently selected database. This command is always synchronous.

Embedded API

SetProtocol

echovault.SetProtocol(protocol int) error

This methods sets the protocol that is expected by responses to embedded API calls. This is relevant for the ExecuteCommand methods which returns raw RESP to the caller.

SelectDB

echovault.SelectDB(database int) error

This method sets the database that the embedded client is operating from.

SwapDBs

echovault.SwapDBs(database1, database2 int)

SwapDBs swaps every TCP client connection from database1 over to database2. It also swaps every TCP client connection from database2 over to database1. This only affects TCP connections, it does not swap the logical database currently being used by the embedded API.

Flush

echovault.Flush(database int)

Flush flushes all the data from the database at the specified index. When -1 is passed, all the logical databases are cleared.

[codecov]

Codecov Report

Attention: Patch coverage is 70.73171% with 204 lines in your changes missing coverage. Please review.

Project coverage is 79.88%. Comparing base (d7bcc3a) to head (85e8a68).

Files	Patch %	Lines
echovault/keyspace.go	28.27%	104 Missing ⚠️
internal/aof/log/store.go	59.25%	16 Missing and 6 partials ⚠️
echovault/echovault.go	78.04%	17 Missing and 1 partial ⚠️
internal/modules/connection/commands.go	88.03%	7 Missing and 7 partials ⚠️
internal/aof/engine.go	35.00%	10 Missing and 3 partials ⚠️
internal/aof/preamble/store.go	62.96%	9 Missing and 1 partial ⚠️
internal/snapshot/snapshot.go	50.00%	5 Missing and 2 partials ⚠️
internal/modules/connection/utils.go	82.35%	4 Missing and 2 partials ⚠️
internal/modules/acl/acl.go	69.23%	3 Missing and 1 partial ⚠️
internal/modules/generic/commands.go	93.18%	1 Missing and 2 partials ⚠️
... and 2 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #83      +/-   ##
==========================================
- Coverage   80.39%   79.88%   -0.51%     
==========================================
  Files          48       50       +2     
  Lines        8304     8692     +388     
==========================================
+ Hits         6676     6944     +268     
- Misses       1144     1246     +102     
- Partials      484      502      +18     

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