* MM-25516: Changed to byte slice instead of string for cluster messages
https://mattermost.atlassian.net/browse/MM-25116
Testing:
Manually tested.
Load-tested with Cluster Controller.
I looked into changing the serialization method to use msgpack,
but the ClusterMessage struct was mainly used for only 3 fields
which didn't lead to much of a CPU time improvement, whereas
actually led to more allocations using msgpack. Hence, I chose
to remain with JSON.
```
name old time/op new time/op delta
ClusterMarshal-8 3.51µs ± 1% 3.10µs ± 2% -11.59% (p=0.000 n=9+10)
name old alloc/op new alloc/op delta
ClusterMarshal-8 776B ± 0% 1000B ± 0% +28.87% (p=0.000 n=10+10)
name old allocs/op new allocs/op delta
ClusterMarshal-8 12.0 ± 0% 13.0 ± 0% +8.33% (p=0.000 n=10+10)
```
```release-note
Changed the field type of Data in model.ClusterMessage to []byte from string.
```
* Trigger CI
```release-note
NONE
```
This PR builds up on the pass-through DB driver to a fully functioning DB driver implementation via our RPC layer.
To keep things separate from the plugin RPC API, and have the ability to move fast with changes, a separate field Driver is added to MattermostPlugin. Typically the field which is required to be compatible are the API and Helpers. It would be well-documented that Driver is purely for internal use by Mattermost plugins.
A new Driver interface was created which would have a client and server implementation. Every object (connection, statement, etc.) is created and added to a map on the server side. On the client side, the wrapper structs hold the object id, and communicate via the RPC API using this id.
When the server gets the object id, it picks up the appropriate object from its map and performs the operation, and sends back the data.
Some things that need to be handled are errors. Typical error types like pq.Error and mysql.MySQLError are registered with encoding/gob. But for error variables like sql.ErrNoRows, a special integer is encoded with the ErrorString struct. And on the cilent side, the integer is checked, and the appropriate error variable is returned.
Some pending things:
- Context support. This is tricky. Since context.Context is an interface, it's not possible to marshal it. We have to find a way to get the timeout value from the context and pass it.
- RowsColumnScanType(rowsID string, index int) reflect.Type API. Again, reflect.Type is an interface.
- Master/Replica API support.
* format using `goimports -local github.com/mattermost/mattermost-server/v5 -w`
* added goimports lint check to .golangci.yml
* format using `goimports -local github.com/mattermost/mattermost-server/v5 -w` for a corner case
* make app-layers, *-mocks and store-layers for ci check
Co-authored-by: Mahmudul Haque <mahmudulhaque@protonmail.com>
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
