fix: serialize Map and Buffer in Redis ISR handler (fixes #15)

[mrjasonroy]

Summary

• Fixes ISR cache-handler: r.segmentData.get is not a function #15 — r.segmentData.get is not a function when using the Redis ISR cache handler with Next.js 16 APP_PAGE entries
• Next.js 16 stores segmentData as a Map<string, Buffer> and rscData as a Buffer on APP_PAGE cache entries. Plain JSON.stringify converts Maps to {} and loses Buffer identity, so on deserialization segmentData.get() throws
• Adds custom jsonReplacer/jsonReviver to the Redis ISR handler that preserve Map and Buffer types through the serialization round-trip
• Also adds APP_PAGE, APP_ROUTE, PAGES, and REDIRECT to the CacheValue type union to match the full Next.js 16 cache entry vocabulary

Changes

• packages/cache-handler/src/handlers/redis.ts — jsonReplacer / jsonReviver functions; set() uses replacer, get() uses reviver. Also handles backward-compat with Node's native Buffer.toJSON() format for entries stored before this fix
• packages/cache-handler/src/types.ts — adds missing cache value kinds (APP_PAGE, APP_ROUTE, PAGES, REDIRECT)
• packages/cache-handler/src/handlers/redis.test.ts — new test suite covering APP_PAGE with segmentData Map + rscData Buffer round-trip, empty/undefined segmentData, APP_ROUTE with Buffer body, backward compat with old Buffer JSON format, and existing value types

Test plan

• All 86 unit tests pass (pnpm vitest run)
• Lint clean (pnpm lint)
• Types pass (pnpm typecheck)
• Manual test with Next.js 16 app using APP_PAGE cache entries on Redis

🤖 Generated with Claude Code

[gemini-code-assist]

Summary of Changes

Hello @mrjasonroy, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses critical serialization issues within the Redis ISR cache handler, specifically for Next.js 16 applications. It ensures that complex data structures like Map and Buffer instances, commonly found in APP_PAGE and APP_ROUTE cache entries, are correctly preserved when stored in and retrieved from Redis. This enhancement prevents data corruption and runtime errors, improving the reliability and compatibility of the cache handler with modern Next.js features.

Highlights

• Fixes Next.js 16 APP_PAGE serialization issue: Resolved the r.segmentData.get is not a function error occurring when using the Redis ISR cache handler with Next.js 16 APP_PAGE entries, which store segmentData as Map<string, Buffer> and rscData as Buffer.
• Custom JSON serialization for Map and Buffer: Introduced custom jsonReplacer and jsonReviver functions to the Redis ISR handler to correctly serialize and deserialize Map and Buffer types, preserving their identity across the serialization round-trip.
• Backward compatibility for Buffer serialization: The jsonReviver now includes logic to handle backward compatibility with Node's native Buffer.toJSON() format for cache entries stored prior to this fix.
• Updated CacheValue types: Expanded the CacheValue type union to include APP_PAGE, APP_ROUTE, PAGES, and REDIRECT to align with the full Next.js 16 cache entry vocabulary.
• Comprehensive test coverage: Added a new, extensive test suite covering APP_PAGE with segmentData Map and rscData Buffer round-trips, APP_ROUTE with Buffer bodies, and backward compatibility for old Buffer JSON formats, ensuring robust serialization.

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Changelog

• packages/cache-handler/src/handlers/redis.test.ts
  • Added a new test file for RedisCacheHandler.
  • Implemented a FakeRedis class to mock ioredis for isolated testing.
  • Added tests for APP_PAGE serialization with segmentData (Map) and rscData (Buffer) round-trips.
  • Added tests for APP_PAGE with undefined and empty segmentData.
  • Added tests for backward compatibility with Node's native Buffer JSON format.
  • Added tests for APP_ROUTE serialization with Buffer body round-trips.
  • Confirmed existing FETCH and PAGE value types still function correctly after changes.
• packages/cache-handler/src/handlers/redis.ts
  • Added jsonReplacer function to serialize Map and Buffer instances into a custom format.
  • Added jsonReviver function to deserialize custom Map and Buffer formats, including backward compatibility for Node's native Buffer.toJSON() format.
  • Modified set() method to use jsonReplacer for serialization.
  • Modified get() method to use jsonReviver for deserialization.
• packages/cache-handler/src/types.ts
  • Extended CacheValue type union to include APP_PAGE with rscData (Buffer) and segmentData (Map<string, Buffer>).
  • Extended CacheValue type union to include APP_ROUTE with body (Buffer).
  • Extended CacheValue type union to include PAGES.
  • Extended CacheValue type union to include REDIRECT.

Activity

• The pull request was created to fix a specific issue (ISR cache-handler: r.segmentData.get is not a function #15) related to Redis ISR handler and Next.js 16 APP_PAGE entries.
• The author provided a detailed summary of the problem, the proposed solution, and the specific files changed.
• The author included a test plan outlining unit tests, linting, type checking, and a manual test for verification.

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[gemini-code-assist]

Code Review

This pull request effectively addresses the serialization issue with Map and Buffer types when using the Redis ISR cache handler. The introduction of custom jsonReplacer and jsonReviver functions is a solid approach, and the implementation correctly handles serialization to and from a string format suitable for Redis. I appreciate the backward compatibility support for the old Buffer JSON format. The type definitions have been correctly expanded to include new Next.js 16 cache entry kinds, and the new test suite is comprehensive, covering the new functionality, edge cases, and regression testing. I have a couple of suggestions to improve the robustness of the jsonReviver function against malformed cache data.

[gemini-code-assist]

For improved robustness, you could add a check to ensure obj.entries contains valid key-value pairs before attempting to create a Map. This makes the reviver more defensive against malformed cache data, which could prevent runtime errors if the cache is ever manually edited or corrupted.

Suggested change

	if (obj.__serialized_type === "Map" && Array.isArray(obj.entries)) {
	if (obj.__serialized_type === "Map" && Array.isArray(obj.entries) && obj.entries.every(e => Array.isArray(e) && e.length === 2)) {

[gemini-code-assist]

Similar to the Map deserialization, you could make the backward-compatible Buffer revival more robust by checking if obj.data is an array of numbers before passing it to Buffer.from(). This would make the parsing more defensive against malformed data.

Suggested change

	if (obj.type === "Buffer" && Array.isArray(obj.data)) {
	if (obj.type === "Buffer" && Array.isArray(obj.data) && obj.data.every(n => typeof n === "number")) {