feat: read total slots header for serverless

[MasterPtato]

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Project	Deployment	Preview	Comments	Updated (UTC)
rivetkit-serverless	Ready	Preview	Comment	Oct 1, 2025 4:42am

[MasterPtato]

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.
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• feat: read total slots header for serverless #1319 👈 (View in Graphite)
• fix: make serverless use bare #1318
• chore: bump engine runner #1316
• fix(serverless): read x-rivet-token from start endpoint #1315 : 2 other dependent PRs (#1317 , #1320 )
• main

---

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[claude]

Claude finished @MasterPtato's task —— View job

---

Code Review Complete ✅

Todo List:

• Read repository guidelines (CLAUDE.md)
• Analyze changed files for code quality
• Check for potential bugs and issues
• Review performance considerations
• Assess security concerns
• Evaluate test coverage needs
• Provide comprehensive feedback

---

Review Summary

This PR implements support for reading the x-rivetkit-total-slots header in serverless mode, allowing dynamic configuration of slot capacity at runtime. The changes are well-structured and follow the existing codebase patterns.

🟢 Code Quality & Best Practices

Positive aspects:

• Consistent parameter naming (totalSlots) across all components
• Proper fallback handling with config.totalSlots as default
• Follows existing patterns for header-based configuration (similar to x-rivet-token)
• Type safety maintained with proper TypeScript annotations
• Clean separation of concerns between client config, manager router, and actor driver

🟡 Minor Issues Found

1. Type Coercion (Line 122 in router.ts):

   let totalSlots: number | undefined = parseInt(c.req.header("x-rivetkit-total-slots") as any);

   The as any cast is needed here because c.req.header() returns string | undefined, but it's not ideal. Consider:

   const totalSlotsHeader = c.req.header("x-rivetkit-total-slots");
   let totalSlots: number | undefined = totalSlotsHeader ? parseInt(totalSlotsHeader) : undefined;

2. Input Validation:
   The code only checks for isNaN() but doesn't validate if the parsed number is positive or within reasonable bounds. Consider adding:

   if (isNaN(totalSlots) || totalSlots <= 0) totalSlots = undefined;

🟢 Security Considerations

• No security concerns identified
• Header-based input is properly parsed and validated
• No sensitive data exposure risks
• Follows existing security patterns used for token handling

🟢 Performance Considerations

• Minimal performance impact
• Header parsing is lightweight
• parseInt() call is acceptable for this use case
• No memory leaks or performance bottlenecks introduced

🟡 Test Coverage Recommendations

Missing test scenarios that should be added:

1. Header parsing tests:

   • Valid numeric values
   • Invalid/non-numeric values
   • Missing header (undefined case)
   • Negative numbers
   • Zero values
   • Very large numbers

2. Integration tests:

   • Serverless endpoint with x-rivetkit-total-slots header
   • Fallback to config value when header is missing
   • Override behavior when both header and config are present

🟢 Architecture & Design

The implementation properly follows the existing architecture:

• ClientConfig → RunConfig → EngineActorDriver flow is maintained
• Serverless-specific handling isolated in router
• Consistent with existing token parameter handling

Recommendations

1. Improve type safety in header parsing (see issue Test #1 above)
2. Add input validation for reasonable slot limits
3. Add comprehensive tests for the new functionality
4. Consider documenting the new header in API documentation

Files & Lines Referenced

• packages/rivetkit/src/client/config.ts:22 - New totalSlots field
• packages/rivetkit/src/drivers/engine/actor-driver.ts:84,87 - Priority logic for token/totalSlots
• packages/rivetkit/src/manager/router.ts:108,122-123 - Header parsing and function signature update
• packages/rivetkit/src/registry/mod.ts:218,220-221 - Serverless builder function update

Overall, this is a solid implementation that extends the existing patterns appropriately. The minor issues identified are easily addressable and don't block the functionality.

---

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commit: 128cee0

[graphite-app]

Merge activity

• Oct 1, 4:30 AM UTC: NathanFlurry added this pull request to the Graphite merge queue.
• Oct 1, 4:31 AM UTC: The Graphite merge queue removed this pull request due to downstack failures on PR #1316.
• Oct 1, 4:31 AM UTC: The Graphite merge queue removed this pull request due to downstack failures on PR #1316.
• Oct 1, 4:40 AM UTC: NathanFlurry added this pull request to the Graphite merge queue.
• Oct 1, 4:40 AM UTC: CI is running for this pull request on a draft pull request (#1322) due to your merge queue CI optimization settings.
• Oct 1, 4:41 AM UTC: Merged by the Graphite merge queue via draft PR: #1322.

[claude]

Claude finished @MasterPtato's task —— View job

---

PR Review: feat: read total slots header for serverless

Todo List:

• Read repository guidelines (CLAUDE.md)
• Analyze changed files for code quality
• Check for potential bugs and issues
• Review performance considerations
• Assess security concerns
• Evaluate test coverage needs
• Provide comprehensive feedback

---

Review Summary

This PR implements support for reading the x-rivetkit-total-slots header in serverless mode, allowing dynamic configuration of slot capacity at runtime. The changes are well-structured and follow the existing codebase patterns.

🟢 Code Quality & Best Practices

Positive aspects:

• Consistent parameter naming (totalSlots) across all components
• Proper fallback handling with config.totalSlots as default
• Follows existing patterns for header-based configuration (similar to x-rivet-token)
• Type safety maintained with proper TypeScript annotations
• Clean separation of concerns between client config, manager router, and actor driver

🟡 Minor Issues Found

1. Type Coercion (packages/rivetkit/src/manager/router.ts:122):

   let totalSlots: number | undefined = parseInt(c.req.header("x-rivetkit-total-slots") as any);

   The as any cast violates the repo guideline: "Don't try to fix type issues by casting to unknown or any." Consider:

   const totalSlotsHeader = c.req.header("x-rivetkit-total-slots");
   let totalSlots: number | undefined = totalSlotsHeader ? parseInt(totalSlotsHeader) : undefined;

2. Input Validation:
   The code only checks for isNaN() but doesn't validate if the parsed number is positive or within reasonable bounds. Consider adding:

   if (isNaN(totalSlots) || totalSlots <= 0) totalSlots = undefined;

🟢 Security Considerations

• No security concerns identified
• Header-based input is properly parsed and validated
• No sensitive data exposure risks
• Follows existing security patterns used for token handling

🟢 Performance Considerations

• Minimal performance impact
• Header parsing is lightweight
• parseInt() call is acceptable for this use case
• No memory leaks or performance bottlenecks introduced

🟡 Test Coverage Recommendations

Missing test scenarios that should be added:

1. Header parsing tests:

   • Valid numeric values
   • Invalid/non-numeric values
   • Missing header (undefined case)
   • Negative numbers
   • Zero values
   • Very large numbers

2. Integration tests:

   • Serverless endpoint with x-rivetkit-total-slots header
   • Fallback to config value when header is missing
   • Override behavior when both header and config are present

🟢 Architecture & Design

The implementation properly follows the existing architecture:

• ClientConfig → RunConfig → EngineActorDriver flow is maintained
• Serverless-specific handling isolated in router
• Consistent with existing token parameter handling

Recommendations

1. Fix type safety in header parsing (see issue Test #1 above)
2. Add input validation for reasonable slot limits
3. Add comprehensive tests for the new functionality
4. Consider documenting the new header in API documentation

Files & Lines Referenced

• packages/rivetkit/src/client/config.ts:22 - New totalSlots field
• packages/rivetkit/src/drivers/engine/actor-driver.ts:96 - Priority logic for token/totalSlots
• packages/rivetkit/src/manager/router.ts:108,122-123 - Header parsing and function signature update
• packages/rivetkit/src/registry/mod.ts:219,225-226 - Serverless builder function update

Overall, this is a solid implementation that extends the existing patterns appropriately. The minor issues identified are easily addressable and don't block the functionality.

---

[claude]

Claude finished @MasterPtato's task —— View job

---

Code Review Complete ✅

Todo List:

• Read repository guidelines (CLAUDE.md)
• Analyze changed files for code quality
• Check for potential bugs and issues
• Review performance considerations
• Assess security concerns
• Evaluate test coverage needs
• Provide comprehensive feedback

---

Review Summary

This PR implements support for reading the x-rivetkit-total-slots header in serverless mode, allowing dynamic configuration of slot capacity at runtime. The changes are well-structured and follow the existing codebase patterns.

🟢 Code Quality & Best Practices

Positive aspects:

• Consistent parameter naming (totalSlots) across all components
• Proper fallback handling with config.totalSlots as default
• Follows existing patterns for header-based configuration (similar to x-rivet-token)
• Type safety maintained with proper TypeScript annotations
• Clean separation of concerns between client config, manager router, and actor driver

🟡 Minor Issues Found

1. Type Coercion (Line 122 in router.ts):

   let totalSlots: number | undefined = parseInt(c.req.header("x-rivetkit-total-slots") as any);

   The as any cast is needed here because c.req.header() returns string | undefined, but it's not ideal. Consider:

   const totalSlotsHeader = c.req.header("x-rivetkit-total-slots");
   let totalSlots: number | undefined = totalSlotsHeader ? parseInt(totalSlotsHeader) : undefined;

2. Input Validation:
   The code only checks for isNaN() but doesn't validate if the parsed number is positive or within reasonable bounds. Consider adding:

   if (isNaN(totalSlots) || totalSlots <= 0) totalSlots = undefined;

🟢 Security Considerations

• No security concerns identified
• Header-based input is properly parsed and validated
• No sensitive data exposure risks
• Follows existing security patterns used for token handling

🟢 Performance Considerations

• Minimal performance impact
• Header parsing is lightweight
• parseInt() call is acceptable for this use case
• No memory leaks or performance bottlenecks introduced

🟡 Test Coverage Recommendations

Missing test scenarios that should be added:

1. Header parsing tests:

   • Valid numeric values
   • Invalid/non-numeric values
   • Missing header (undefined case)
   • Negative numbers
   • Zero values
   • Very large numbers

2. Integration tests:

   • Serverless endpoint with x-rivetkit-total-slots header
   • Fallback to config value when header is missing
   • Override behavior when both header and config are present

🟢 Architecture & Design

The implementation properly follows the existing architecture:

• ClientConfig → RunConfig → EngineActorDriver flow is maintained
• Serverless-specific handling isolated in router
• Consistent with existing token parameter handling

Recommendations

1. Improve type safety in header parsing (see issue Test #1 above)
2. Add input validation for reasonable slot limits
3. Add comprehensive tests for the new functionality
4. Consider documenting the new header in API documentation

Files & Lines Referenced

• packages/rivetkit/src/client/config.ts:22 - New totalSlots field
• packages/rivetkit/src/drivers/engine/actor-driver.ts:84,87 - Priority logic for token/totalSlots
• packages/rivetkit/src/manager/router.ts:108,122-123 - Header parsing and function signature update
• packages/rivetkit/src/registry/mod.ts:218,220-221 - Serverless builder function update

Overall, this is a solid implementation that extends the existing patterns appropriately. The minor issues identified are easily addressable and don't block the functionality.

---