The idea of this feature is from @4ertus2, we discussed it today.

Capture network interaction (requests and responses) from clickhouse-server.
Make clickhouse-mock server that will use this dump to provide the same responses to the same requests.
Use it for backward compatibility checks in distributed setups.

Tricks and caveats:

• it should reply with the best suitable response based on the history of requests;
• it should track connection identifier to allow to keep a chain of requests and responses;
• it will not take into account all timing issues;
• real requests can be slightly different from expected... for example, by client name.

Possible way of implementation:

• hook into send/recv functions and dump data into system.network_dump table;
• mock server can load the data from dump in any supported format, keep it in memory and find the best response based on search by a tree of previously seen requests at the same connection.