Reject transactions with negative fees

[Jiyacodex]

Addressed Issues:

Fixes #108

Screenshots/Recordings:

Not applicable. This PR modifies transaction validation logic and adds regression tests.

Additional Notes:

This PR adds validation to reject transactions with negative fees before state execution and includes a regression test to prevent this issue from recurring. The changes were tested locally.

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Checklist

• My PR addresses a single issue, fixes a single bug or makes a single improvement.
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Summary by CodeRabbit

• Bug Fixes

  • Improved transaction validation to reject invalid fee and nonce values, including negative and non-integer inputs.
  • Prevented rejected transactions from affecting account balance or nonce.
  • Kept valid zero and positive-fee transactions working as expected.

• Tests

  • Added coverage for negative, non-integer, and large invalid fee cases.
  • Added checks to confirm valid transactions are accepted and processed correctly.

• Chores

  • Added a new ignore rule for local virtual environment files.

[coderabbitai]

Walkthrough

State.validate_and_apply gains explicit type and range checks for fee and tx.nonce, returning None for non-integer or negative values, replacing a prior placeholder comment. A new test module covers these rejection and acceptance cases. A .venv/ entry is added to .gitignore.

Changes

Fee and Nonce Validation

Layer / File(s)	Summary
validate_and_apply checks + tests minichain/state.py, tests/test_negative_fee.py, .gitignore	validate_and_apply now rejects transactions with non-integer or negative fee/nonce values by returning None. The new TestNegativeFeePrevention suite covers negative fees, large negative fees, balance/nonce immutability on rejection, float fees, zero fee acceptance, positive fee deduction, and negative nonce rejection. .venv/ is added to .gitignore.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Suggested labels

Python Lang

Poem

🐇 A negative fee? Not on my watch!
The nonce must be whole, not a fractional notch.
I validate, check, and return None with care,
While .venv stays hidden — no longer laid bare.
Hop hop, the chain stays clean and fair! 🌟

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly matches the main change: adding validation to reject transactions with negative fees.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@minichain/state.py`:
- Around line 95-105: The numeric validation in the state transaction checks
still accepts booleans because `isinstance(..., int)` matches `bool`; update the
guards in the transaction validation logic to explicitly reject `True`/`False`.
In the code around the `tx.amount`, `fee`, and `tx.nonce` checks, switch to
exact integer-type validation so only real integers pass, keeping the existing
non-negative constraints unchanged.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: dfb1d7ce-cabc-465f-aed0-5f61b9070be3

📥 Commits

Reviewing files that changed from the base of the PR and between 3ea9909 and fcafe37.

📒 Files selected for processing (3)

• .gitignore
• minichain/state.py
• tests/test_negative_fee.py