python: add framed transport packet logging

[wdfk-prog]

Pull request

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Describe the pull request

Add optional packet logging support for Python framed transports.

This PR introduces an environment-variable driven packet logger for Python eRPC framed transports. It can log TX/RX frames from existing Python clients or servers without application source changes.

Main changes:

• Add erpc.log packet logging helpers.
• Hook framed transport TX/RX paths to emit packet log records.
• Support console, text file and JSON/JSONL packet log output.
• Decode framed transport metadata, CRC status and BasicCodec message headers.
• Optionally enrich logs with generated Python IDL metadata, including service/method names, request arguments and matching reply reference outputs when generated server.py and client.py modules are available.
• Add transport instance ID to IDL reply matching so multiple transports do not share the same reply cache key.
• Add pretty JSON output for manual inspection through ERPC_PYTHON_PACKET_LOG_PRETTY=1.
• Update erpc_python/README.md with configuration examples and environment variable documentation.

Packet logging is disabled by default. Existing behavior is unchanged unless ERPC_PYTHON_PACKET_LOG is configured.

To Reproduce

For console logging:

ERPC_PYTHON_PACKET_LOG=stdout python examples/matrix_multiply_python/matrix_multiply.py --client --serial /dev/ttyS1 --baud 115200

PowerShell example:

$env:ERPC_PYTHON_PACKET_LOG = "stdout"
python examples\matrix_multiply_python\matrix_multiply.py --client --serial COM17 --baud 115200

For JSON file logging:

ERPC_PYTHON_PACKET_LOG=erpc-uart.jsonl ERPC_PYTHON_PACKET_LOG_APPEND=0 \
    python examples/matrix_multiply_python/matrix_multiply.py --client --serial /dev/ttyS1 --baud 115200

For IDL-aware decode:

PYTHONPATH=erpc_python:examples/matrix_multiply_python \
ERPC_PYTHON_PACKET_LOG=erpc-uart.jsonl \
ERPC_PYTHON_PACKET_LOG_IDL=service.erpc_matrix_multiply \
    python examples/matrix_multiply_python/matrix_multiply.py --client --serial /dev/ttyS1 --baud 115200

Expected behavior

When packet logging is disabled, Python eRPC framed transports behave as before.

When packet logging is enabled:

• TX and RX framed packets are logged.
• Frame bytes, framed header fields, payload bytes, message length and CRC fields are recorded.
• BasicCodec message headers are decoded by default.
• If generated Python IDL modules are configured, logs include best-effort service/method names, request arguments and matching reply reference output values.
• JSON output defaults to strict JSON Lines, one compact JSON object per packet.
• Pretty JSON output can be enabled for manual inspection with ERPC_PYTHON_PACKET_LOG_PRETTY=1.
• Decode/logging errors are contained in the packet log record and do not affect normal RPC transport behavior.

Screenshots

Not applicable.

Desktop (please complete the following information):

• OS: Windows / Linux
• eRPC Version: current development branch

Steps you didn't forgot to do

• I checked if other PR isn't solving this issue.
• I read Contribution details and did appropriate actions.
• PR code is tested.
• PR code is formatted.
• Allow edits from maintainers pull request option is set (recommended).

Additional context

This is intended to simplify debugging Python eRPC links over framed transports such as serial, TCP, SPI and I2C. The logger is configured entirely through environment variables, so existing examples and user applications can capture packet-level diagnostics without source changes.

IDL reply decoding depends on the logger observing the matching invocation first. The request cache key includes transport instance ID, service ID, request ID and sequence number to avoid collisions when multiple transports are active.