chore(test): bitswap limit tests

[LesnyRumcajs]

Summary of changes

Changes introduced in this pull request:

• follow-up tests for fix: limit bitswap requests #7440, the coverage gain is small but it tests edge cases that wouldn't surface in the coverage report
• moved the random cid helper so that it can be re-used in different test modules.

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

Outside contributions

• This pull request is based on an issue that a maintainer has accepted (see Before Opening a Pull Request).
• I have read and agree to the CONTRIBUTING document.
• I have read and agree to the AI Policy document. I understand that failure to comply with the guidelines will lead to rejection of the pull request.

Summary by CodeRabbit

• Bug Fixes

  • Improved handling of inbound wantlists by enforcing per-request entry limits.
  • Prevented excessive concurrent wantlist serving and correctly ignored empty wantlists.

• Tests

  • Added coverage for wantlist limits, concurrency saturation, blocked reads, and response behavior.
  • Standardized test CID generation for more consistent test scenarios.

[coderabbitai]

Walkthrough

The request manager exposes inbound serving limits within the Bitswap crate. New tests validate wantlist size limits, concurrency saturation, permit retention, and empty wantlists. Manifest tests now use a shared random CID helper.

Changes

Bitswap serving limits

Layer / File(s)	Summary
Serving limit visibility src/libp2p_bitswap/request_manager.rs, src/libp2p_bitswap/tests/request_manager.rs	The request manager exposes the maximum wantlist size and concurrent inbound serve count within the Bitswap crate. Tests import these limits.
Serving behavior validation src/libp2p_bitswap/tests/request_manager.rs	Tests verify response limits, blocked reads, dropped serves when concurrency is saturated, and empty wantlist handling.
Shared random CID test support src/utils/rand/mod.rs, src/shim/machine/manifest.rs	A test-only random CID helper is added. Manifest tests use the shared helper instead of local CID generation.

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

Possibly related PRs

• ChainSafe/forest#7440: Introduces the same inbound Bitswap wantlist-serving limits that this PR exposes and tests.

Suggested reviewers: akaladarshi, eclesiomelojunior, hanabi1224

🚥 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 identifies the main change: adding Bitswap limit tests.
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

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• Create stacked PR
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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch add-bitswap-tests

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch add-bitswap-tests

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[coderabbitai]

🧹 Nitpick comments (1)

src/libp2p_bitswap/tests/request_manager.rs (1)

123-144: 🩺 Stability & Availability | 🔵 Trivial | ⚡ Quick win

Make the saturation test independent of the Tokio runtime blocking-thread limit by using a small test-local capacity.

The test depends on each of the first cap spawn_blocking tasks executing and blocking in GatedStore::contains() while holding permits. If FOREST_MAX_CONCURRENT_INBOUND_WANTLIST_SERVES is set above the runtime's blocking-thread limit (default 512), excess tasks remain queued and cannot signal entered_rx. The loop at line 139 then times out. Use a test-local constant for the cap (e.g., 4) instead of reading the global variable, or explicitly configure the test runtime to guarantee sufficient blocking capacity:

#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
async fn serve_drops_when_concurrency_saturated() {
    let cap = 4; // test-local, independent of global config
    // ... rest of test

This ensures the test remains deterministic regardless of how the global cap is set.

🤖 Prompt for 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.

In `@src/libp2p_bitswap/tests/request_manager.rs` around lines 123 - 144, Update
the saturation test around serve_drops_when_concurrency_saturated to use a small
test-local capacity, such as 4, instead of dereferencing
MAX_CONCURRENT_INBOUND_WANTLIST_SERVES. Keep the existing saturation and
entered_rx synchronization logic unchanged so the test remains deterministic
regardless of the configured global limit.

🤖 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.

Nitpick comments:
In `@src/libp2p_bitswap/tests/request_manager.rs`:
- Around line 123-144: Update the saturation test around
serve_drops_when_concurrency_saturated to use a small test-local capacity, such
as 4, instead of dereferencing MAX_CONCURRENT_INBOUND_WANTLIST_SERVES. Keep the
existing saturation and entered_rx synchronization logic unchanged so the test
remains deterministic regardless of the configured global limit.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

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Run ID: b3c7a370-5b42-42c7-b6fd-addd11073473

📥 Commits

Reviewing files that changed from the base of the PR and between a188092 and 25d02ef.

📒 Files selected for processing (4)

• src/libp2p_bitswap/request_manager.rs
• src/libp2p_bitswap/tests/request_manager.rs
• src/shim/machine/manifest.rs
• src/utils/rand/mod.rs

🔗 Linked repositories identified

CodeRabbit considers these linked repositories for cross-repo context during reviews:

• filecoin-project/lotus (manual)