Fix race condition in Unsplash search that causes mixed results

[niranjan-uma-shankar]

This PR fixes a race condition in the Unsplash search flow where results from an intermediate search term (e.g., "germ") may appear alongside the final term (e.g., "germany") when users pause briefly while typing.

Fixes: #24584

Root cause

The race condition occurs due to the combination of:

1. A debounce in _search() delaying API calls.

2. The updateSearch() method triggering a UI reset too early, before this.photos is populated.

3. No mechanism to discard results from outdated search terms.

I could consistently reproduce results on a ~50Mbps connection:

• Type "germany" with a brief ~1s pause after "m".
• "germ" triggers a search.
• Before that request completes, the user continues typing to "germany", triggering a new search.
• Since both API calls resolve asynchronously, the results from "germ" are populated, followed by the results from "germany" being appended to the previous results, leading to incorrect UI state.

Changes made

The fix adds validation to ensure that search results are only applied if the returned term matches the current user input. Each _makeRequest() call captures the term at the time it was made, and the response handler checks if it still matches the latest search term. If not, the results are discarded.

Before

• Typing "Germany" with a brief pause shows results for "Germ" at the top.
• Network requests shows search fired for both "germ" and "germany".

Screen.Recording.2025-08-02.at.3.47.40.PM.mp4

After

• Typing "Germany" with a brief pause at "Germ" discards the old search results, ensuring that the relevant result for "Germany" appears at the top.
• Network requests shows search fired for both "germ" and "germany". The fix ensures that only the results for "germany" are included in the results.

Screen.Recording.2025-08-02.at.3.50.05.PM.mp4

Testing Instructions

1. Throttle your network to ~50Mbps.
2. Open the editor for either a post or page.
3. Click on "Add feature image".
4. In the Unsplash search bar, type a term slowly with a pause in the middle (e.g., "para" → pause → "chute").
5. Ensure that only results for the final input (e.g., "parachute") are shown.
6. Try with other terms and varying pause durations to confirm consistent behaviour.
7. Ensure that other behaviours (such as lazy loading paginated content in Unsplash results) remain unaffected.

[coderabbitai]

Walkthrough

The code modifies the Unsplash image search service to prevent stale search results from being appended when the user changes the search term during an asynchronous request. It introduces a mechanism to track the search term at the time of the request and ensures that only results matching the latest search term are processed. This involves updating the _search task to capture the search term, passing it through _makeRequest, and updating _addPhotosFromResponse to check for term consistency before adding photos.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Assessment against linked issues

Objective	Addressed	Explanation
Prevent race condition in Unsplash search causing mixed/incorrect results (#24584)	✅
Ensure only results for the latest search term are appended in Unsplash search (#24584)	✅

Assessment against linked issues: Out-of-scope changes

No out-of-scope changes were found.

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📥 Commits

Reviewing files that changed from the base of the PR and between b5dedb0 and ce8db6c.

📒 Files selected for processing (1)

• ghost/admin/app/services/unsplash.js (2 hunks)

🧰 Additional context used

🧠 Learnings (1)

📓 Common learnings

Learnt from: niranjan-uma-shankar
PR: TryGhost/Ghost#24557
File: apps/admin-x-settings/src/components/settings/general/TimeZone.tsx:7-7
Timestamp: 2025-08-01T12:44:07.467Z
Learning: In Ghost development, PRs may depend on unpublished changes from SDK packages. When this occurs, TypeScript compilation errors for missing exports are expected and documented in the PR description until the dependency packages are published and updated. This is normal workflow for cross-repository feature development.

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• GitHub Check: Unit tests (Node 22.13.1)
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• GitHub Check: Admin tests - Chrome

🔇 Additional comments (4)

ghost/admin/app/services/unsplash.js (4)

112-118: LGTM! Race condition fix correctly implemented.

The search term is properly captured after the debounce timeout and passed to the request. This ensures that only results matching the final search term (after user stops typing) are processed, effectively preventing the race condition where intermediate search results could mix with final results.

---

120-126: Excellent race condition prevention logic.

The guard clause effectively prevents stale search results from being added when the search term has changed during the asynchronous request. The validation logic is correct and the comments clearly explain the purpose.

---

201-201: Parameter passing correctly implemented.

The captured search term is properly forwarded through the promise chain to _addPhotosFromResponse, completing the race condition fix implementation.

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114-126: Complete solution effectively addresses the race condition.

The implementation successfully solves the Unsplash search race condition described in the PR objectives. By capturing the search term at request time and validating it before adding photos, the fix ensures that only results matching the current search term are displayed, preventing mixed results from intermediate searches.

The solution is well-designed with:

• Minimal code changes that don't affect existing functionality
• Clear parameter flow from search initiation to result processing
• Proper handling of both search and non-search requests
• Good code documentation explaining the fix

Also applies to: 201-201

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[9larsons]

@niranjan-uma-shankar Thanks for this! I think there's still some gaps in the logic, though this ought to improve the gap here. Ultimately, we're moving to React and we'll need to rebuild all of this.