fix: Zemu.checkAndPullImage should reliably reject

[turbocrime]

if the network request made by checkAndPullImage fails for any reason, sometimes the promise stalls forever.

this PR attempts to make promise rejection more reliable.

relevant to #564

Summary by CodeRabbit

• Bug Fixes

  • Improved error handling during image pulling to ensure errors are properly reported and prevent potential runtime issues.

• Tests

  • Added new tests to verify correct error handling when pulling invalid images.

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Walkthrough

The EmuContainer.checkAndPullImage method in src/emulator.ts was refactored to improve error handling by using Promise rejection instead of direct error throwing and by adding checks for stream validity. Additionally, a new test suite was introduced in tests/check-and-pull-image.test.ts to verify error handling in both EmuContainer and Zemu when image pulling fails.

Changes

Cohort / File(s)	Change Summary
Error Handling Refactor in EmuContainer src/emulator.ts	Refactored checkAndPullImage to use Promise rejection for errors, updated callback parameter types, and added a check for stream validity before proceeding.
Unit Tests for Image Pull Failure tests/check-and-pull-image.test.ts	Added tests to verify that checkAndPullImage in both EmuContainer and Zemu correctly handle and propagate errors when image pulling fails.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~7 minutes

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📜 Recent review details

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📥 Commits

Reviewing files that changed from the base of the PR and between 1ba263d and 4eb1f03.

📒 Files selected for processing (2)

• src/emulator.ts (2 hunks)
• tests/check-and-pull-image.test.ts (1 hunks)

🔇 Additional comments (8)

src/emulator.ts (5)

73-73: LGTM! Proper Promise constructor usage.

The Promise constructor now correctly uses both resolve and reject parameters, which is essential for proper error handling and addresses the core issue where promises could stall indefinitely.

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74-74: LGTM! Proper callback parameter handling.

The callback signature correctly handles both error and stream parameters from the docker.pull operation, supporting the improved error handling flow.

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82-87: LGTM! Critical fix for promise rejection in callback.

Changing from throw err to reject(err) in the onFinished callback is essential. Previously, throwing an error in this nested callback wouldn't properly reject the outer Promise, causing it to hang indefinitely. Now errors are correctly propagated as Promise rejections.

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89-92: LGTM! Consistent error handling for immediate failures.

Using reject(err) instead of throw err for immediate docker.pull errors maintains consistency with the callback error handling and ensures the Promise is properly rejected rather than throwing synchronously.

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94-96: LGTM! Good defensive programming for stream validation.

Adding a check for stream existence before calling docker.modem.followProgress prevents potential runtime errors. This is a solid defensive programming practice.

Consider: Should there be an else clause to handle the case where stream is falsy? Currently, if stream is null/undefined, the promise would resolve without any progress tracking, which might be the intended behavior, but it's worth confirming.

tests/check-and-pull-image.test.ts (3)

1-8: LGTM! Well-structured test setup.

The imports, test suite structure, and constant definition for the invalid image name are well-organized and follow good testing practices.

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9-11: LGTM! Direct test of error handling.

This test directly verifies that EmuContainer.checkAndPullImage properly rejects when given an invalid image name, which validates the core promise rejection fix implemented in the source code.

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13-22: LGTM! Comprehensive test of error propagation through delegation.

This test effectively verifies that:

1. Zemu.checkAndPullImage properly delegates to EmuContainer.checkAndPullImage
2. The expected DEFAULT_EMU_IMG parameter is passed
3. Error propagation works correctly through the delegation layer

The mock implementation is well-designed, intercepting the call to verify the parameter and then forwarding to trigger the error condition.

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[turbocrime]

i encountered the issue due to network errors, but it seems like simply requesting an invalid image name can activate the same conditions.