feat: Add S7Comm server plugin for Siemens S7 protocol communication

[thiagoralves]

Summary

This PR adds a native S7Comm server plugin that enables Siemens S7 protocol communication with OpenPLC. It allows S7-compatible HMIs, SCADA systems, and other clients to read and write OpenPLC I/O buffers using the industry-standard S7 protocol.

Key Features

• S7 Server Implementation: Full Snap7 library integration providing S7-300/400 compatible server
• JSON Configuration: Flexible configuration via JSON file for data blocks, system areas, and server settings
• Double-Buffered Sync: Thread-safe buffer synchronization with shadow buffers to minimize mutex contention
• Bidirectional Data Flow:
  • cycle_start: Copy S7 buffer → OpenPLC (S7 client writes visible to PLC)
  • cycle_end: Copy OpenPLC buffer → S7 (PLC outputs visible to S7 clients)
• Multiple Data Types: Support for bool, int, dint, lint inputs/outputs/memory
• Configurable Data Blocks: Map S7 DBs to OpenPLC buffer locations

Files Added

• core/src/drivers/plugins/native/s7comm/ - Complete plugin implementation
  • s7comm_plugin.cpp/h - Main plugin with buffer sync logic
  • s7comm_config.c/h - JSON configuration parser
  • snap7/ - Snap7 library sources (embedded for portability)
  • cjson/ - cJSON library for configuration parsing
  • docs/ - Implementation plan, JSON schema, user guide
• install.sh - Build system for native plugins
• plugins_default.conf - Default plugin registration

Configuration Example

{
  "server": {
    "enabled": true,
    "port": 102,
    "max_clients": 32
  },
  "data_blocks": [
    {
      "db_number": 1,
      "size_bytes": 128,
      "mapping": {
        "type": "bool_output",
        "start_buffer": 0
      }
    }
  ]
}

Testing

• Verified with Python Snap7 client connecting to runtime at 192.168.1.127
• Confirmed PLC outputs (%QX0.1, %QX0.2, %QX0.5) visible and oscillating correctly via S7 protocol
• Tested bidirectional buffer sync strategy

Test Plan

• Plugin builds successfully on Linux
• S7 server starts and accepts connections on port 102
• S7 clients can read PLC outputs via configured data blocks
• PLC program outputs are correctly synchronized to S7 buffer
• Test with commercial HMI/SCADA software
• Test write operations from S7 client to PLC inputs
• Performance testing under load

Related

• OpenPLC Editor S7Comm configuration UI (separate PR)
• Future: Journal buffer architecture for multi-plugin synchronization

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🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR adds native S7Comm server functionality to OpenPLC Runtime, enabling Siemens S7 protocol communication with compatible HMI and SCADA systems. The implementation integrates the Snap7 library and provides bidirectional synchronization between S7 data areas and OpenPLC I/O buffers through a plugin architecture.

Changes:

• Added complete S7Comm plugin implementation with embedded Snap7 library
• Integrated native plugin build system into install.sh
• Registered s7comm plugin in default configuration files

Reviewed changes

Copilot reviewed 42 out of 44 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
plugins_default.conf	Added s7comm plugin registration entry
plugins.conf	Added s7comm plugin registration entry
install.sh	Added build_native_plugins function to compile CMake-based plugins
core/src/drivers/plugins/native/s7comm/snap7/sys/*.h	Snap7 threading and platform abstraction headers
core/src/drivers/plugins/native/s7comm/snap7/sys/*.cpp	Snap7 threading, utilities, socket, and TCP server implementations
core/src/drivers/plugins/native/s7comm/snap7/lib/*.h	Snap7 library main interface headers
core/src/drivers/plugins/native/s7comm/snap7/lib/*.cpp	Snap7 library main implementation
core/src/drivers/plugins/native/s7comm/snap7/core/*.h	S7 protocol type definitions and class interfaces
core/src/drivers/plugins/native/s7comm/snap7/core/*.cpp	S7 protocol implementations
core/src/drivers/plugins/native/s7comm/s7comm_plugin.h	Plugin interface header with lifecycle function declarations

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[Copilot]

Inconsistent spacing around assignment operator. Should be 'Closed = false;' to match the style on line 74.

Suggested change

	Closed=false;
	Closed = false;

[Copilot]

Missing space after assignment operator. Should be 'ts.tv_nsec = (long)' for consistency.

Suggested change

	ts.tv_nsec =(long)((Delay_ms - ts.tv_sec) * 1000000);
	ts.tv_nsec = (long)((Delay_ms - ts.tv_sec) * 1000000);

[Copilot]

Corrected spelling of 'bacause' to 'because'.

Suggested change

	strcat(S, " clients have been dropped bacause unresponsive");
	strcat(S, " clients have been dropped because unresponsive");