libnetwork/resolvconf: add new KeepHostSearches/Options

[Luap99]

Using one KeepHostServers that controls the override of nameservers, search domains and options is not good enough.

With netavark 1.15 we dropped the dns.podman search domain[1] as this always overwrote the host search domains which was not correct. However that in turn caused a new issue[2] that a container name might now get resolved to a search domain from the host first.
To fix that we either need to revert the dns.podman change or add the ndots:0 option in resolv.conf. Whatever we end up doing we will need one of KeepHostSearches or KeepHostOptions in podman to populate resolv.conf correctly so that we don't overwrite the host domains/options but still can overwrite the nameservers as we want to force aardvark-dns only as nameserver so resolvers cannot bypass it.

[1] containers/netavark#1214
[2] containers/podman#26198

Summary by Sourcery

Add dedicated flags to preserve host search domains and DNS options when generating resolv.conf and update the generation logic and tests accordingly.

New Features:

• Introduce KeepHostSearches flag to retain host search domains.
• Introduce KeepHostOptions flag to retain host DNS options.

Enhancements:

• Update New() logic to respect the new flags and only append host content when requested.

Tests:

• Extend unit tests to cover all combinations of KeepHostServers, KeepHostSearches, and KeepHostOptions.

[sourcery-ai]

Reviewer's Guide

Introduces two new parameters to control preserving host DNS search domains and options when generating resolv.conf, updates the builder logic to respect these flags, and extends unit tests to validate the new behavior.

File-Level Changes

Change	Details	Files
Enhance Params with new KeepHostSearches and KeepHostOptions flags and update resolv.conf generation logic	Add KeepHostSearches and KeepHostOptions fields to Params struct with documentation Modify short-circuit condition in New() to include the new flags Adjust search and options append logic to use KeepHostSearches and KeepHostOptions instead of only KeepHostServers	libnetwork/resolvconf/resolv.go
Extend TestNew unit tests to cover the new flags	Add keepHostSearches and keepHostOptions fields to the test struct Insert test cases for scenarios with each flag and both flags set Update expected outputs to reflect preserved host searches and options	libnetwork/resolvconf/resolv_test.go

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[Luap99]

@mheon @baude PTAL

[sourcery-ai]

Hey @Luap99 - I've reviewed your changes and they look great!

Here's what I looked at during the review

• 🟡 General issues: 1 issue found
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

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[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Luap99, sourcery-ai[bot]

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• OWNERS [Luap99]

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[mheon]

LGTM