feat(runner): add -mp/-metrics-port for the -stats metrics server

[mazzz3r]

Summary

-stats served its metrics on 127.0.0.1:63636 with no way to change the port, and moved to a random port without saying so when 63636 was taken. The runner built its client with clistats.New(), which hands clistats a pointer to the package-level clistats.DefaultOptions, so that fallback port was also written into the defaults of any other clistats user in the same process.

Changes

• -mp, -metrics-port (default 63636) sets the port, under the same name as the nuclei flag. ValidateOptions rejects values outside 0-65535; 0 keeps the default, for library callers that leave the field unset.
• The runner starts clistats with a copy of clistats.DefaultOptions. After Start() it prints the port in use when the requested one is taken, at info level so that it shows without -v, and logs the metrics address in verbose mode.
• README flag list updated.

Testing

• TestOptions_ValidateMetricsPort: -1 and 65536 are rejected; 0, 8080 and 65535 pass.
• TestOptions_metricsPort: a port left at 0, as library callers do, means the clistats default, so a busy default port is reported for them too.
• TestRunner_metricsPort: /metrics answers on the requested port, a busy port falls back to another one, and clistats.DefaultOptions.ListenPort stays 63636 in both cases.
• go test -race ./runner/ passes except TestRunner_probeall_targets, which resolves one.one.one.one and fails the same way on dev here. The metrics port tests also pass with -race in a golang:1.27.1 container without network. golangci-lint run ./runner/...: 0 issues.
• In a container without network:

$ httpx -l targets.txt -stats -si 1 -mp 19200 &
$ curl -s 127.0.0.1:19200/metrics
{"duration":"0:00:02","rps":"1","hosts":2,"requests":2,"totalHosts":4,...}

$ httpx -u http://127.0.0.1:18091 -stats -mp 19201     # 19201 in use
[INF] Metrics port 19201 is not available, using 39479

$ httpx -u http://127.0.0.1:18091 -mp 70000
[FTL] invalid metrics port 70000, must be between 0 and 65535

On dev, -mp stops with flag provided but not defined: -mp.

Closes #2665

Checklist

• Pull request is created against the dev branch
• All checks passed (lint, unit/integration/regression tests etc.) with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Summary by CodeRabbit

• New Features
  • Added a configurable port for the HTTP metrics server. Set it with -metrics-port or -mp; the default is 63636. If the requested port is unavailable, the server reports the port it is using.
• Documentation
  • Updated the README’s debug options to include the metrics port setting.

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between de2627e and 44be896.

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📒 Files selected for processing (3)

• runner/metrics_port_test.go
• runner/options.go
• runner/runner.go

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Walkthrough

The runner adds a -metrics-port/-mp option, validates port values, and uses the configured port when starting clistats. It reports the actual metrics address. Tests cover validation, available and occupied ports, and the /metrics endpoint.

Changes

Metrics port configuration

Layer / File(s)	Summary
Port option and validation runner/options.go, runner/metrics_port_test.go, README.md	Adds the MetricsPort option and flag, validates values from 0 through 65535, and documents the flag. Tests cover rejected and accepted values.
Metrics listener startup runner/runner.go, runner/metrics_port_test.go	The runner passes a copy of clistats.DefaultOptions to clistats.NewWithOptions and overrides the listen port when MetricsPort is positive. After startup, it logs port mismatches and the metrics server address. Tests check available and occupied ports and request /metrics.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Feature · Severity of issue fixed: Medium

Sequence Diagram(s)

sequenceDiagram
  participant Runner
  participant clistatsNewWithOptions
  participant Statistics
  participant HTTPClient
  Runner->>clistatsNewWithOptions: pass options with selected ListenPort
  clistatsNewWithOptions-->>Runner: return statistics client
  Runner->>Statistics: start statistics
  HTTPClient->>Statistics: GET /metrics
  Statistics-->>HTTPClient: return HTTP 200

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Suggested reviewers: mzack9999

Merge Risk: ⚪ Minimal · up to 44be8

When the default metrics port is occupied, the runner reports the fallback port even if the caller left the port unset. No actionable merge-blocking risk remains after normal checks.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 44be8

The change preserves default loopback binding and isolates listener configuration between instances. No introduced security issue was established, but deployment-specific exposure and concurrent startup behavior were not fully verified.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — With dependency defaults intact, the changed exposure is another selectable port in the process’s local network namespace, not a new externally bound service. Selecting the port does not itself grant additional operating-system authority.

Trust Boundaries and Controls

• observed — Port configuration comes from CLI configuration or a library caller, rather than metrics-request content. The runner still inherits ListenHost from mutable package defaults, so loopback binding is conditional on those defaults not being changed by embedding code; that condition predates this PR.

Resilience and Maintainability Implications

• inferred — Copying listener options reduces cross-instance configuration drift. Concurrent same-port allocation can still race between availability probing and the actual bind, and polling still follows a startup warning; these failure-containment limitations use the unchanged dependency and runner paths and are not established as worsened by this PR.

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Pre-merge checks | 4 | 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 6 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check		Issue [#2665] requires -mp, -metrics-port, selectable metrics ports, fallback reporting, and protection of clistats.DefaultOptions. The diff registers both flags with default 63636, validates port…
Out of Scope Changes check		The changes are limited to issue-related option handling, metrics startup and logging, README documentation, and supporting tests. No unrelated production behavior or unrelated files appear in the who…
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly identifies the main change: adding the -mp/-metrics-port option for the -stats metrics server.

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_{A rabbit set a port with care,
And checked the metrics waiting there.
A busy port? The tests made clear,
The listener chose a different sphere.
/metrics answered, crisp and bright,
Then bunny hopped away at night.}

_{Comment @coderabbitai help to get the list of available commands.}

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @runner/runner.go:
- Around line 626-627: Update the metrics-port comparison in the runner setup to
use the effective requested port: use r.options.MetricsPort when nonzero,
otherwise use clistats.DefaultOptions.ListenPort. Keep the Info-level notice
when stats.Options.ListenPort differs from that effective port so fallback ports
are reported when MetricsPort is unset.

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⚙️ Run configuration

• Configuration used: Organization UI
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📥 Commits

Reviewing files that changed from the base of the PR and between 482ce7b and de2627e.

📒 Files selected for processing (4)

• README.md
• runner/metrics_port_test.go
• runner/options.go
• runner/runner.go

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