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fix: reject empty I2C reads before device commands - #312
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YashAnand69 wants to merge 2 commits into
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Reviewer's GuideReject empty or reversed I²C read slices before device commands or transactions begin, while preserving existing behavior for valid reads. New tests cover buffer types, both read APIs, bus-state safety, and ACK/NACK/STOP sequencing. Sequence diagram for preflight validation of I2C readssequenceDiagram
participant Caller
participant I2C
participant Device
Caller->>I2C: readfrom_into(address, buffer, start, end)
I2C->>I2C: Calculate bytes_to_read
alt bytes_to_read < 1
I2C-->>Caller: ValueError
Note over I2C,Device: No transaction or device command begins
else bytes_to_read >= 1
I2C->>Device: _start(address, 1)
I2C->>Device: _read(bytes_to_read)
I2C->>Device: _stop()
I2C-->>Caller: None
end
Caller->>I2C: writeto_then_readfrom(address, buffer_out, buffer_in, in_start, in_end)
I2C->>I2C: Calculate bytes_to_read
alt bytes_to_read < 1
I2C-->>Caller: ValueError
Note over I2C,Device: No write, restart, or read transaction begins
else bytes_to_read >= 1
I2C->>Device: _start(address, 0)
I2C->>Device: _send(buffer_out)
I2C->>Device: _restart(address, 1)
I2C->>Device: _read(bytes_to_read)
I2C->>Device: _stop()
I2C-->>Caller: Buffer populated
end
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info
📝 Walkthrough
Merge Risk: ⚪ Minimal · up to The reviewed read paths reject empty selections and preserve the selected destination slice for nonempty reads. No actionable merge-blocking risk remains after normal checks. Security Architecture Review
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| Check name | Status | Explanation | Resolution |
|---|---|---|---|
| Docstring Coverage |  |
Docstring coverage is 54.55% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 11 functions across 2 files. | Write docstrings for the functions missing them to satisfy the coverage threshold. |
✅ Passed checks (4 passed)
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Check name Status Explanation Description Check Check skipped - CodeRabbit’s high-level summary is enabled. Title check The title clearly and concisely describes the main change: rejecting empty I2C reads before device commands. Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request.
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Hey - I've found 1 issue
Prompt for AI Agents
Please address the comments from this code review:
## Individual Comments
### Comment 1
<location path="pslab/bus/busio.py" line_range="124" />
<code_context>
end = len(buffer) if end is None else end
bytes_to_read = end - start
+
+ if bytes_to_read < 1:
+ raise ValueError("Read buffer must contain at least one byte.")
+
</code_context>
<issue_to_address>
**Clipped reads consume sensor data**
When explicit read bounds have a positive width but Python clips the selected buffer slice to empty or shorter than that width, `bytes_to_read` stays positive, so the guard passes and `readfrom_into` or `writeto_then_readfrom` starts the I2C transaction and consumes sensor bytes. Assignment can grow a bytearray or raise for a memoryview before `_stop`; the combined method also sends its output bytes before the failure.
Validate the selected slice length against `bytes_to_read` and reject mismatched bounds before starting the transaction.
Also at `pslab/bus/busio.py:199-200`.
</issue_to_address>Sourcery assessment
Approval pending. 1 finding to address first.
Blocking findings: pslab/bus/busio.py:124
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Actionable comments posted: 1
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Inline comments:
Review comments at @pslab/bus/busio.py:
- Around line 123-126: Update the buffer-length checks in readfrom_into and
writeto_then_readfrom to use the effective length of each selected Python slice,
rather than subtracting the start and end indices. Keep the existing ValueError
behavior so an empty slice is rejected before either method starts an I2C
transaction.
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📒 Files selected for processing (2)
pslab/bus/busio.pytests/test_i2c_empty_reads.py
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Empty CircuitPython-compatible I²C reads currently consume one sensor byte. A bytearray grows despite an empty selected slice, and a memoryview raises only after the bus transaction has begun.
Reject empty or reversed read slices before starting the transaction or writing the register address, matching CircuitPython's requirement for at least one input byte. Nonempty reads retain their ACK/NACK and STOP sequence. Both
readfrom_intoandwriteto_then_readfromare covered.Validation: eight regression cases fail on unchanged main; four positive controls pass. The fixed branch passes all 12 new cases and 33 existing hardware-independent CLI, Pico and gas-sensor tests (45 total). Configured Black, Flake8, Bandit and pydocstyle checks, package and Sphinx builds pass; seven existing Sphinx warnings remain. No physical PSLab/sensor or full hardware-suite validation was performed. Developed and tested with Codex assistance.
Reference: CircuitPython I²C API. No matching claimed issue or overlapping open PR found.
Summary by Sourcery
Prevent empty I²C reads from starting device transactions while retaining existing behavior for valid reads.
Bug Fixes:
Enhancements:
Tests:
Summary by CodeRabbit
ValueErrorbefore starting an I2C transfer.