feat: support streaming in node JS SDK

[markphelps]

Re: #430

This pull request introduces significant enhancements to the FliptEvaluationClient in the flipt-client-node package, including support for both polling and streaming fetch modes, and refactors to improve code readability and maintainability. The most important changes include modifications to the client initialization, the addition of streaming support, and updates to the testing suite to accommodate these new features.

Enhancements to FliptEvaluationClient:

• Client Initialization:

  • Added support for namespace and fetchMode parameters in the client constructor and initialization method. (flipt-client-node/src/index.ts) [1] [2]
  • Updated the fetcher function to accept a URL and options, including an abort signal. (flipt-client-node/src/index.ts) [1] [2]

• Streaming Support:

  • Introduced methods for starting and stopping streaming updates, including handling of streaming responses and abort signals. (flipt-client-node/src/index.ts) [1] [2]
  • Added new interfaces StreamChunk and StreamResult to handle streaming data. (flipt-client-node/src/internal/models.ts)

Updates to Testing Suite:

• Refactoring Tests:
  • Moved client initialization inside a runTests function to support both polling and streaming fetch modes. (flipt-client-node/__tests__/evaluation.test.ts) [1] [2] [3]
  • Adjusted test teardown to ensure the client is properly closed, including awaiting the close operation. (flipt-client-node/__tests__/evaluation.test.ts)

Additional Changes:

• Interface Updates:
  • Modified IFetcherOptions to include an optional signal property for aborting requests. (flipt-client-node/src/models.ts)
  • Added fetchMode to ClientOptions to specify whether to use polling or streaming. (flipt-client-node/src/models.ts) [1] [2]

These changes improve the flexibility and robustness of the FliptEvaluationClient, allowing it to better handle different use cases and environments.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.09%. Comparing base (40022f7) to head (ae201eb).

Additional details and impacted files

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##             main     #452   +/-   ##
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  Coverage   84.09%   84.09%           
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  Files           8        8           
  Lines        3936     3936           
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  Hits         3310     3310           
  Misses        626      626           

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[erka]

nice!

One thing that worry me is the error handling in startStreamingUpdates. Let's say there is an network error for a minute for any reason and then a recover. What will happen to the Flipt client and how user could recover from it?

[markphelps]

nice!

One thing that worry me is the error handling in startStreamingUpdates. Let's say there is an network error for a minute for any reason and then a recover. What will happen to the Flipt client and how user could recover from it?

yeah good point. we should likely add some reconnect/retry logic for both streaming and polling. it would be great to be smarter about error handling in general, like if its a 401 or 404 error because of bad auth token or invalid URL then it should exit quickly with error. but if its a transient networking error then we should try to reconnect. will look into how we can support this