fix(rivetkit): bind handler to Registry in serve

[NathanFlurry]

No description provided.

[railway-app]

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🚅 Deployed to the rivet-pr-3787 environment in rivet-frontend-website-preview

Service	Status	Web	Updated (UTC)
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[NathanFlurry]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• fix(rivetkit): fix default logic for serveManager & advertiseEndpoint #3789
• fix(rivetkit): bind handler to Registry in serve #3787 👈 (View in Graphite)
• chore(ci): update pkg.pr.new for shared packages #3786
• main

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[claude]

PR Review: fix(rivetkit): bind handler to Registry in serve

Summary

This PR fixes a critical bug where the this context was lost when the handler method was passed through serve(). The fix properly binds the method to the Registry instance.

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Changes Overview

• Line 95: Added .bind(this) to ensure proper this context when handler is called
• Lines 242-248: Simplified conditional logic (removed unnecessary intermediate variable)

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Code Quality ✅

Primary Fix (Line 95): The addition of .bind(this) is the correct solution. Without this binding, when registry.serve() is used like export default registry.serve(), the handler method loses its this context, which would cause runtime errors when trying to access this.#ensureServerlessInitialized() at line 82.

Consistent Pattern: This fix aligns with existing patterns in the codebase:

• Line 111: fetch: router.fetch.bind(router) - binds to router
• Line 338: fetch: this.handler.bind(this) - same pattern in legacy code path

Secondary Refactor (Lines 242-248): The removal of the shouldShowEndpoint variable simplifies the code. The condition now directly checks:

• config.serveManager OR
• (kind === 'serverless' AND config.serverless.spawnEngine)

This is cleaner since config.serverless.advertiseEndpoint is only used inside the conditional block anyway, so checking it beforehand was redundant.

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Technical Analysis

Why This Bug Occurred:
When you do export default registry.serve(), the returned object contains a reference to the handler method, but that reference doesn't maintain the binding to the registry instance. When the serverless runtime (e.g., Cloudflare Workers, Vercel) calls fetch(request), this would be undefined (in strict mode) or the global object, causing a crash.

Impact:

• Without this fix: Runtime error: TypeError: Cannot read private member #ensureServerlessInitialized from an object whose class did not declare it
• With this fix: Proper binding ensures this refers to the Registry instance

Example Usage (from examples/chat-room/src/server.ts:4):

export default registry.serve();

This is the exact pattern that requires the fix.

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Best Practices ✅

Method Binding Approach: The .bind() solution is appropriate here. Alternative approaches would be:

1. Arrow function in constructor - more invasive, requires constructor changes
2. Arrow property - changes the method signature, affects inheritance
3. Current solution with .bind() - minimal, clear, and idiomatic ✅

Code Simplification: Removing the shouldShowEndpoint variable improves readability without changing behavior.

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Performance ✅

The .bind() call has negligible performance impact - it's called once during initialization, not per-request.

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Security ✅

No security concerns. This is a pure bug fix that improves reliability.

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Testing Observations ⚠️

Current State: No test files found for the Registry class.

Recommendation: Consider adding a test case to prevent regression:

test('serve() returns bound handler', async () => {
  const registry = setup({ use: {} });
  const { fetch } = registry.serve();
  // Verify fetch can be called without the registry context
  const response = await fetch(new Request('http://localhost/health'));
  expect(response).toBeDefined();
});

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Potential Issues

None identified. The changes are minimal, targeted, and correct.

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Verdict: APPROVED ✅

This is a well-targeted bug fix that solves a real production issue with minimal changes. Both changes are correct:

1. Critical fix: The .bind(this) prevents runtime crashes in serverless deployments
2. Code cleanup: Removing the intermediate variable improves code clarity

The fix follows existing patterns in the codebase and has no negative side effects.

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Minor Suggestions (not blocking):

• Add unit tests for the serve() method to prevent regression
• Consider adding a test that verifies the handler works when destructured: const { fetch } = registry.serve()

[pkg-pr-new]

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rivetkit

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@rivetkit/sql-loader

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@rivetkit/virtual-websocket

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@rivetkit/engine-runner

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@rivetkit/engine-runner-protocol

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commit: b2b13ca

[graphite-app]

Merge activity

• Jan 8, 9:33 PM UTC: NathanFlurry added this pull request to the Graphite merge queue.
• Jan 8, 9:34 PM UTC: CI is running for this pull request on a draft pull request (#3795) due to your merge queue CI optimization settings.
• Jan 8, 9:34 PM UTC: Merged by the Graphite merge queue via draft PR: #3795.