PDF export hangs in Confluence when external image URL destination connection hangs

Issue Summary

PDF export hangs in Confluence when external image URL destination connection hangs

Steps to Reproduce

1. Install Jira in AWS
2. Add an image from web to a Confluence page pointing to an image URL in Jira: http://jira.ec2.address:8080/images/icons/issuetypes/health.png
3. Confirm the image loads in Confluence
4. Edit security groups in AWS, and remove access on 8080
5. Confirm image can no longer be reached - URL should hang when trying to load the image
6. Export Confluence space containing the page with this image URL (Export to PDF)

Expected Results

Connection should fail quickly and export should continue

Actual Results

Export hangs on the connection until it times out

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

2020-12-11 10:46:30,311 ERROR [Long running task: PDF Space Export] [extra.flyingpdf.impl.ConfluenceExportUserAgent] log Can't get image resource for urihttp://10.125.91.86:34929/jira853/images/icons/issuetypes/health.png, error: null
 -- url: /c773/spaces/flyingpdf/doflyingpdf.action | referer: http://localhost:6773/c773/spaces/flyingpdf/flyingpdf.action?key=ADMIN | traceId: a894c7b0bbb2ccc8 | userName: admin | action: doflyingpdf

Export eventually continues, but seems to hang for 1 minute per image that cannot connect. Some high CPU usage was noted, which could cause issues in larger sites.

Workaround

Ensure that Confluence can reach the Jira destination, or attach the image directly to Confluence.