fix: fallback to all targets when host discovery finds no hosts

[dogancanbakir]

Summary

• When ARP or other host discovery methods find no live hosts (e.g., due to network configuration, firewall rules, or container environments), naabu now falls back to scanning all original targets instead of exiting with an error
• Adds a warning message to inform users when this fallback occurs

Fixes

Closes #1194

Test plan

• Test with host discovery enabled on a network where ARP fails (e.g., container/VM without proper network access)
• Verify that port scanning proceeds with all original targets
• Verify warning message is displayed when fallback occurs

Summary by CodeRabbit

• Bug Fixes
  • Improved host discovery behavior: when no live hosts are discovered, the scanner now includes all targets in the scan instead of limiting to discovery results, with a warning message.

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[coderabbitai]

Walkthrough

The change modifies the host discovery callback selection in RunEnumeration to check whether the discovery found live hosts. If no hosts are detected, the function falls back to scanning all targets instead of relying on empty results, with a warning log emitted for this scenario.

Changes

Cohort / File(s)	Summary
Host Discovery Fallback Logic pkg/runner/runner.go	Made ipsCallback selection conditional: verifies if scanner.HostDiscoveryResults.HasIPS() before using getHostDiscoveryIps; falls back to preprocessed IPs and logs warning "Host discovery found no live hosts, scanning all targets" when no live hosts detected

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A rabbit once sought hosts upon the wire,
But when the path grew dark and silence deep,
It hopped back to the safer, broader way,
With warnings whispered to the watchers near—
No failure now, just prudent fallback fare! 🥕

Pre-merge checks and finishing touches

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The pull request title 'fix: fallback to all targets when host discovery finds no hosts' clearly summarizes the main change: implementing fallback behavior when host discovery yields no results.
Linked Issues check	✅ Passed	The code changes implement the exact requirement from issue #1194: when host discovery finds no live hosts, the scanner now falls back to scanning all original targets instead of failing with an error.
Out of Scope Changes check	✅ Passed	All changes are directly related to the linked issue objectives. The modification to RunEnumeration adds conditional logic for host discovery fallback and warning logging, which aligns precisely with the stated requirements.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing touches

• 📝 Generate docstrings

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📜 Recent review details

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📥 Commits

Reviewing files that changed from the base of the PR and between 9976c32 and d1df30e.

📒 Files selected for processing (1)

• pkg/runner/runner.go

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🔇 Additional comments (1)

pkg/runner/runner.go (1)

486-490: Good fix for the host discovery fallback issue!

The conditional check correctly addresses the problem described in issue #1194. When host discovery finds no live hosts (e.g., due to ARP failures in containers or restricted network environments), the code now falls back to scanning all original targets instead of proceeding with an empty result set. The warning message appropriately informs users about this fallback behavior.

The logic is sound:

• Defaults to scanning preprocessed IPs (line 484)
• Only uses host discovery results if they contain IPs (line 486)
• Falls back gracefully with a clear warning when discovery yields nothing

The HasIPS() method is correctly implemented on the Result type and properly returns a boolean indicating whether IPs were discovered.

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