Module validate 

Server-side request validation helpers.

Implements the validation state diagrams from Spec V1.1b3 §6.1–6.18. These are pure functions — no I/O.

Validation order matters (per §4.5 Figure 9 and per-FC state diagrams):

1. Data value: quantity in range, byte count matches → IllegalDataValue (0x03)
2. Data address: address + quantity must not overflow → IllegalDataAddress (0x02)

Functions

validate_mask_write_address

Validate a mask write register (FC 16) address.

validate_read_coils

Validate a read coils (FC 01) request.

validate_read_discrete_inputs

Validate a read discrete inputs (FC 02) request.

validate_read_registers

Validate a read holding/input registers (FC 03/04) request.

validate_read_write_registers

Validate a read/write multiple registers (FC 17) request.

validate_write_coils

Validate a write multiple coils (FC 0F) request.

validate_write_registers

Validate a write multiple registers (FC 10) request.

validate_write_single_coil

Validate a write single coil (FC 05) request.