reject invalid token bucket limits

[HrachShah]

A zero or negative request rate creates a bucket that can never refill, while a non-positive burst capacity creates an unusable token bucket. Both values are now rejected when middleware starts, with clear ValueError messages. Verification: Python compilation and direct constructor assertions.

Summary by Sourcery

Bug Fixes:

• Prevent creation of token buckets with non-positive request rates or burst capacities that would never refill or be unusable.

Summary by CodeRabbit

• Bug Fixes
  • Added validation to prevent invalid rate-limit settings.
  • Clear errors are now shown when request or burst limits are set below 1.
  • Rate limits now refill and expire reliably, even when system time changes.
  • Concurrent requests are handled atomically, preventing requests from exceeding configured limits.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

This PR hardens the rate limiting middleware by validating token bucket configuration at initialization, rejecting non-positive request rates and burst capacities with clear ValueError messages before delegating to the base middleware setup.

Flow diagram for rate_limit middleware initialization validation

flowchart TD
    A["RateLimitMiddleware.__init__(app, requests_per_minute, burst_capacity)"] --> B{"requests_per_minute < 1"}
    B -- Yes --> C["raise ValueError requests_per_minute must be at least 1"]
    B -- No --> D{"burst_capacity < 1"}
    D -- Yes --> E["raise ValueError burst_capacity must be at least 1"]
    D -- No --> F["super().__init__(app)"]
    F --> G["set self.requests_per_minute"]
    G --> H["set self.burst_capacity"]

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File-Level Changes

Change	Details	Files
Validate token bucket configuration to reject unusable rate limit settings at middleware initialization time.	Add a guard that raises ValueError when requests_per_minute is less than 1 Add a guard that raises ValueError when burst_capacity is less than 1 Ensure validation runs before calling the superclass initializer and assigning configuration fields	freerelay/middleware/rate_limit.py

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 05ae4dde-4531-4dc1-acc7-ccfb3832fd1c

📥 Commits

Reviewing files that changed from the base of the PR and between 0fdaa36 and 2dcb5a3.

📒 Files selected for processing (2)

• freerelay/middleware/rate_limit.py
• tests/unit/test_rate_limit.py

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📝 Walkthrough

Walkthrough

TokenBucket and RateLimitMiddleware now validate positive limits, use monotonic timestamps, and serialize shared bucket operations with an asyncio.Lock. Tests cover timing, validation, and concurrent requests.

Changes

Rate limit controls

Layer / File(s)	Summary
Token bucket validation and timing freerelay/middleware/rate_limit.py, tests/unit/test_rate_limit.py	TokenBucket rejects non-positive rate and capacity values. Refill calculations use time.monotonic(). Tests verify validation and refill behavior.
Middleware state validation and locking freerelay/middleware/rate_limit.py	RateLimitMiddleware rejects request or burst limits below one. Cleanup and bucket operations run under an asyncio.Lock and use monotonic timestamps.
Concurrency validation tests/unit/test_rate_limit.py	Concurrent requests sharing one bucket produce one HTTP 429 response and one downstream call.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant RateLimitMiddleware
  participant StateLock
  participant TokenBucket
  participant Downstream
  Client->>RateLimitMiddleware: send concurrent requests
  RateLimitMiddleware->>StateLock: serialize bucket access
  StateLock->>TokenBucket: consume token
  TokenBucket-->>RateLimitMiddleware: allow or reject
  RateLimitMiddleware->>Downstream: forward allowed request
  RateLimitMiddleware-->>Client: response or HTTP 429

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the primary change: rejecting invalid token bucket limits.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

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• Commit on current branch

📝 Generate docstrings

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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch patch/reject-invalid-bucket-settings

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