Add S7CommPlus protocol scaffolding for S7-1200/1500

[gijzelaerr]

Summary

Adds the snap7.s7commplus package for S7CommPlus protocol support, targeting S7-1200/1500 PLCs across all protocol versions (V1/V2/V3/TLS). Includes a functional server emulator, sync client, async client, and 111 passing tests.

Architecture

Module	Description	Status
protocol.py	Protocol constants: opcodes, function codes, data types, element IDs, soft data types	Complete
vlq.py	Variable-Length Quantity encoding/decoding (32/64-bit, signed/unsigned)	Complete
codec.py	Frame headers, request/response headers, typed value serialization	Complete
server.py	PLC emulator with data blocks, named variables, session management, multi-client	Complete (V1)
client.py	Sync client: db_read, db_write, db_read_multi, explore	Complete (V1)
async_client.py	Async client with asyncio.Lock for concurrent safety	Complete (V1)
connection.py	Multi-version connection with COTP/TPKT transport	Complete (V1)

Server emulator

The server emulates an S7-1200/1500 PLC with:

• Data blocks with named variables and type metadata (register_db())
• Thread-safe memory model with per-block locking
• S7CommPlus protocol handling: CreateObject, DeleteObject, Explore, GetMultiVariables, SetMultiVariables
• Multi-client support (threaded, each client gets a unique session ID)
• CPU state management (Run/Stop)

server = S7CommPlusServer()
server.register_db(1, {
    "temperature": ("Real", 0),
    "pressure": ("Real", 4),
    "running": ("Bool", 8),
})
server.start(port=11020)

Protocol version support

Version	Target PLCs	Authentication	Status
V1	S7-1200 FW V4.0+	Trivial anti-replay	Working
V2	S7-1200/1500 older FW	Proprietary HMAC-SHA256/AES	Planned
V3	S7-1200/1500 pre-V17	ECC key exchange	Planned
V3+TLS	TIA Portal V17+	Standard TLS 1.3	Planned

The wire protocol (VLQ, data types, object model) is identical across all versions -- only the session authentication layer differs.

Tests (111 total)

• 62 VLQ tests: Boundary values, roundtrips, signed/unsigned, 32/64-bit
• 24 codec tests: Frame headers, request headers, fixed-width, typed values, strings
• 7 server unit tests: Data blocks, named variables, CPU state, edge cases
• 11 sync client integration tests: Connect, read, write, multi-read, explore, persistence, concurrent clients
• 7 async client integration tests: Connect, read, write, concurrent reads with Lock

Test plan

• 111 passing tests (VLQ, codec, server unit, sync integration, async integration)
• Ruff lint passes
• Existing test suite unaffected
• Server handles multiple concurrent clients with unique sessions
• Data persists across client sessions
• Async Lock serializes concurrent reads correctly

🤖 Generated with Claude Code