Only backfill dead links if at least one on first page was not dead

[sarayourfriend]

Fixes

Fixes #855 by @sarayourfriend

Description

If after validating dead links, there are zero results, assume any subsequent deeper paginations of the same query will not yield better returns. The lines changed is a lie: it's like 97% changes in the unit tests. The actual change required to make this work is two SLOC with some explanatory comments.

Testing Instructions

Check out the unit tests. To test this locally the best thing to do would be to use OpenSnitch or some other firewall to block outbound requests to Flickr. Then observe the logs and ensure that only a single query is sent to Elasticsearch. Note: this will be hard to do if on Linux with Docker as root (you'll need to mess with a bunch of iptables configurations). Instead, you can just modify the code to set the status code on the responses manually using this patch:

diff --git a/api/catalog/api/utils/validate_images.py b/api/catalog/api/utils/validate_images.py
index 6ad23f6f..c4dcbb42 100644
--- a/api/catalog/api/utils/validate_images.py
+++ b/api/catalog/api/utils/validate_images.py
@@ -58,7 +58,7 @@ def validate_images(query_hash, start_slice, results, image_urls):
         # Response didn't arrive in time. Try again later.
         else:
             status = -1
-        to_cache[cache_key] = status
+        to_cache[cache_key] = 404
 
     thirty_minutes = 60 * 30
     twenty_four_hours_seconds = 60 * 60 * 24
@@ -83,7 +83,7 @@ def validate_images(query_hash, start_slice, results, image_urls):
     for idx, url in enumerate(to_verify):
         cache_idx = to_verify[url]
         if verified[idx] is not None:
-            cached_statuses[cache_idx] = verified[idx].status_code
+            cached_statuses[cache_idx] = 404
         else:
             cached_statuses[cache_idx] = -1

Then you can make any request and all links will get cached as dead. You should get responses back that have empty results now from queries that previously gave back results with the local data (like source=flickr).

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the default branch of the repository (main) or a parent feature branch.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.

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[sarayourfriend]

This change is to facilitate mocking the cached statuses in the test. Mostly this is to avoid the status cache being prepopulated based on other tests request/response cycle.

[krysal]

It's also welcome modularization!

[github-actions]

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[AetherUnbound]

@krysal do you mind reviewing this in my stead while I run MSR this week?

[krysal]

Tests look good to me 👍 We could also try with some of the problematic providers (e.g. EOL).

[krysal]

It's also welcome modularization!

[zackkrida]

I believe I'm seeing the correct behavior! I ran this query:

http http://localhost:8000/v1/images/\?source\=flickr\&page\=5

before and after applying the patch to validate_images.py, and the later resulted in a single ES query followed by many Deleting broken image from results id=... status=404 calls.