HPCC-32877 Fix abort in esp when accessing secrets from a vault

[ghalliday]

The vault secret code uses httplib to request entries
from a vault. The default compilation mode is to use select() rather
than poll(), but select() has a limit of 1024 sockets. That means
that if a process has a large number of sockets (or files?) open
the select based code will fail.

This commit defines CPPHTTPLIB_USE_POLL which enables the use of poll()

Type of change:

• This change is a bug fix (non-breaking change which fixes an issue).
• This change is a new feature (non-breaking change which adds functionality).
• This change improves the code (refactor or other change that does not change the functionality)
• This change fixes warnings (the fix does not alter the functionality or the generated code)
• This change is a breaking change (fix or feature that will cause existing behavior to change).
• This change alters the query API (existing queries will have to be recompiled)

Checklist:

• My code follows the code style of this project.
  • My code does not create any new warnings from compiler, build system, or lint.
• The commit message is properly formatted and free of typos.
  • The commit message title makes sense in a changelog, by itself.
  • The commit is signed.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly, or...
  • I have created a JIRA ticket to update the documentation.
  • Any new interfaces or exported functions are appropriately commented.
• I have read the CONTRIBUTORS document.
• The change has been fully tested:
  • I have added tests to cover my changes.
  • All new and existing tests passed.
  • I have checked that this change does not introduce memory leaks.
  • I have used Valgrind or similar tools to check for potential issues.
• I have given due consideration to all of the following potential concerns:
  • Scalability
  • Performance
  • Security
  • Thread-safety
  • Cloud-compatibility
  • Premature optimization
  • Existing deployed queries will not be broken
  • This change fixes the problem, not just the symptom
  • The target branch of this pull request is appropriate for such a change.
• There are no similar instances of the same problem that should be addressed
  • I have addressed them here
  • I have raised JIRA issues to address them separately
• This is a user interface / front-end modification
  • I have tested my changes in multiple modern browsers
  • The component(s) render as expected

Smoketest:

• Send notifications about my Pull Request position in Smoketest queue.
• Test my draft Pull Request.

Testing:

[ghalliday]

@mckellyln I do not know which version to target with this fix.
I think 9.6.x is safe - and this is potentially a problem for roxie as well as esp.
A separate question is why this started causing problems recently.

[github-actions]

Jira Issue: https://hpccsystems.atlassian.net//browse/HPCC-32877

Jirabot Action Result:
Changing assignee from: [email protected] to: [email protected]
Workflow Transition To: Merge Pending
Updated PR

[jakesmith]

Looks fine, but not clear how/why switching to epoll is related to accessing secrets, maybe needs fuller description in PR/JIRA.

[ghalliday]

Force push to improve the commit comment.

[mckellyln]

Looks good.

[github-actions]

Jirabot Action Result:
Added fix version: 9.6.60
Added fix version: 9.8.34
Workflow Transition: 'Resolve issue'