feat: support passing existing Redis client to ISR handler

[mrjasonroy]

Summary

• Allows RedisCacheHandler to accept a pre-existing ioredis client instance via the redis option
• Uses duck typing instead of instanceof Redis to detect existing clients (avoids fragility across package versions/bundlers)
• Tracks didCreateClient to skip error listeners and close() for shared clients
• Added 5 tests covering existing client detection, lifecycle management, and error listener behavior

Based on #23 by @Antignote, reworked to address review feedback:

• Replaced instanceof Redis with duck typing
• Used didCreateClient consistently for both error listener and close
• Added tests (original PR had none)
• Rebased onto current main (which has significant changes from fix: serialize Map and Buffer in Redis ISR handler (fixes #15) #29)

Supersedes #23

Test plan

• All 95 unit tests pass (16 Redis handler tests, 5 new)
• Existing client stores/retrieves values correctly
• No error listener added for shared clients
• Error listener added for internally created clients
• close() skips shared clients, disconnects created clients
• Lint, format, typecheck all pass

🤖 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 enhances the RedisCacheHandler by introducing the capability to utilize an already instantiated ioredis client. This change provides more control over Redis connection management, particularly in environments where a single Redis client might be shared across multiple components. The implementation focuses on robust client identification and careful resource handling to ensure that shared clients are not inadvertently closed or modified by the cache handler.

Highlights

• Existing Redis Client Support: The RedisCacheHandler now accepts a pre-existing ioredis client instance via the redis option, allowing for greater flexibility in managing Redis connections.
• Robust Client Detection: Client detection has been improved by using duck typing (checking for get, set, del methods) instead of instanceof Redis. This avoids fragility issues that can arise from different package versions or bundler setups.
• Lifecycle Management: A new didCreateClient flag tracks whether the handler internally created the Redis client. This ensures that error listeners are only attached, and the close() method only calls quit(), for clients managed by the handler, preventing unintended side effects on shared client instances.
• Comprehensive Testing: Five new tests were added to cover existing client detection, proper lifecycle management (error listeners and close() behavior), and ensure correct functionality when a shared client is provided.

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Changelog

• packages/cache-handler/src/handlers/redis.test.ts
  • Added quitCalled property and quit method to FakeRedis class to facilitate testing of client disconnection behavior.
  • Updated a comment for clarity regarding cache entry simulation.
  • Introduced a new test suite for 'existing Redis client support' with five new tests covering client acceptance, error listener behavior, and close() method functionality for both shared and internally created clients.
• packages/cache-handler/src/handlers/redis.ts
  • Modified the RedisCacheHandlerOptions interface to allow the redis property to accept an existing ioredis client instance.
  • Updated JSDoc examples to illustrate how to pass an existing Redis client to the handler.
  • Refactored the constructor to implement duck typing for detecting existing Redis client instances, assigning them directly if found, and setting a didCreateClient flag accordingly.
  • Conditionalized the attachment of the Redis error listener, ensuring it is only added if the client was internally created by the handler.
  • Modified the close() method to conditionally call redis.quit(), ensuring that only internally created clients are disconnected, while shared clients remain active.

Activity

• The pull request is a rework of a previous submission (feat: add support for redis client #23 by @Antignote) to address review feedback.
• The original instanceof Redis check was replaced with more robust duck typing for client detection.
• The didCreateClient flag was consistently applied for both error listener management and the close() method.
• Comprehensive tests were added, as the original PR lacked them.
• The branch was rebased onto the current main, incorporating significant changes from fix: serialize Map and Buffer in Redis ISR handler (fixes #15) #29.

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[gemini-code-assist]

Code Review

This pull request introduces a valuable feature by allowing an existing Redis client instance to be passed to the RedisCacheHandler. The implementation correctly uses duck typing to detect the client and manages the client's lifecycle (error listeners, closing connection) based on whether it was created internally or provided externally. The accompanying tests are comprehensive and validate the new behavior thoroughly. I have one suggestion to improve the robustness of the duck-typing check.

[gemini-code-assist]

The current duck-typing for an existing Redis client is not fully robust. It checks for the existence of get, set, and del properties, but only confirms that get is a function. This could lead to runtime errors if an object is passed where set or del are properties but not functions.

A more robust approach is to verify that all three methods (get, set, del) are indeed functions. This also simplifies the condition by making the in checks redundant.

      options.redis &&
      typeof options.redis === "object" &&
      typeof (options.redis as Redis).get === "function" &&
      typeof (options.redis as Redis).set === "function" &&
      typeof (options.redis as Redis).del === "function"

[mrjasonroy]

Closing in favor of pushing updates directly to #23