Fix Modbus TCP protocol ID validation in FramerSocket #2830
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Add protocol ID check in FramerSocket to reject non-zero values, and include a test to verify that invalid messages produce empty results.
Updated two test vectors that previously used fixed, nonzero protocol IDs. Now the vectors use Protocol ID = 0, in compliance with the Modbus TCP specification
…t to 0x1234 and did not follow standard
janiversen
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Dec 17, 2025
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LGTM, Thanks.
Good catch, looking forward to see more PRs.
janiversen
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Dec 17, 2025
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The changes are ok, but you have a pylint problem and a pytest problem that you need to solve.
Use ./check_ci.sh to run the tests locally or push to github.
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Summary
This PR adds validation for the Modbus TCP Protocol ID in
FramerSocketand ensures only compliant frames (Protocol ID = 0) are accepted.
Changes
FramerSocketto reject non-zero valuesRationale
According to the Modbus TCP specification, the Protocol ID field must be
set to
0. Previously, non-zero values were accepted and some tests usedinvalid protocol IDs, which could mask malformed input.
This change enforces spec compliance and improves robustness when handling
invalid Modbus TCP frames.
Testing