Where should I start if Im trying to modify the Geth client to filter transactions by sender to include only specific transactions in the mined blocks ? What files of code should I understand to do it ?
Note: Im playing with a private PoA network if it matters.
Depending on how you want to achieve it I'd suggest two possible places where to start.
validateTx in tx_pool.go: This is evaluated before queuing the transaction into the pending pool, it will not affect transactions in mined blocks.
ApplyTransaction in state_processor: It is used to validate transactions in a block, if you fail the transaction the whole block will be discarded.
