PDF export hangs in Confluence when external image URL destination is not accessible

Issue Summary

When exporting a page to PDF, the export process may hang up to 16 minutes before completing the export.

This is reproducible on Data Center: Yes

Steps to Reproduce

1. Create a page in Confluence
2. Add image URL links to the page and ensure the URLs are not reachable from Confluence
3. From the ellipsis menu, choose "Export to PDF"

Expected Results

While export times are expected to be variable, the PDF export should complete sooner than 16 minutes.

Actual Results

The PDF export takes 16 minutes to complete. If multiple exports are triggered at the same time, it can lead to significant performance degradation. This occurs because of a stuck thread in the export process that hangs due to an inaccessible image link

The below exception is thrown in the atlassian-confluence.log file:

ERROR [http-nio-8090-exec-1] [extra.flyingpdf.impl.ConfluenceExportUserAgent] log Can't get image resource for urihttps://<confluence_hostname>/download/attachments/123456789/image_title.png?&api=v2, error: Unknown image format

Workaround

Remove the bad image link URLs and retry the PDF export