Add unit tests for httpmirror package

[Copilot]

Adds test coverage for the httpmirror HTTP reverse proxy and caching server. No tests existed prior.

Coverage Added

fetch.go (HTTP operations):

• httpHead() / httpGet() - success, HTTP errors (404/500), context cancellation
• fileInfo type - all fs.FileInfo methods including edge cases (missing/invalid Last-Modified headers)

mirror.go (request handling):

• isValidDomain() - 28 cases covering RFC compliance, special characters, length limits
• getBlobName() - MD5 hash generation consistency
• MirrorHandler.ServeHTTP() - method validation, path filtering, suffix blocking, domain validation, BaseDomain filtering, HostFromFirstPath mode, custom NotFound handler

Stats

• 720 LOC across 2 test files
• 32.9% statement coverage
• Table-driven tests following Go conventions

Example test structure:

func TestIsValidDomain(t *testing.T) {
    tests := []struct {
        name     string
        domain   string
        expected bool
    }{
        {"valid domain", "example.com", true},
        {"starts with dash", "-example.com", false},
        {"special characters", "exam@ple.com", false},
    }
    // ...
}

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• cdn
  • Triggering command: /tmp/go-build3332974897/b525/httpmirror.test -test.testlogfile=/tmp/go-build3332974897/b525/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true (dns block)
  • Triggering command: /tmp/go-build2702711329/b525/httpmirror.test -test.testlogfile=/tmp/go-build2702711329/b525/testlog.txt -test.paniconexit0 -test.gocoverdir=/tmp/go-build2702711329/b525/gocoverdir -test.timeout=10m0s (dns block)
  • Triggering command: /tmp/go-build1754526662/b525/httpmirror.test -test.testlogfile=/tmp/go-build1754526662/b525/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.short=true (dns block)
• example.com
  • Triggering command: /tmp/go-build17724911/b525/httpmirror.test -test.testlogfile=/tmp/go-build17724911/b525/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true (dns block)
  • Triggering command: /tmp/go-build3332974897/b525/httpmirror.test -test.testlogfile=/tmp/go-build3332974897/b525/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true (dns block)
  • Triggering command: /tmp/go-build2702711329/b525/httpmirror.test -test.testlogfile=/tmp/go-build2702711329/b525/testlog.txt -test.paniconexit0 -test.gocoverdir=/tmp/go-build2702711329/b525/gocoverdir -test.timeout=10m0s (dns block)
• mirror.example.com
  • Triggering command: /tmp/go-build17724911/b525/httpmirror.test -test.testlogfile=/tmp/go-build17724911/b525/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true (dns block)
  • Triggering command: /tmp/go-build3332974897/b525/httpmirror.test -test.testlogfile=/tmp/go-build3332974897/b525/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true (dns block)
  • Triggering command: /tmp/go-build2702711329/b525/httpmirror.test -test.testlogfile=/tmp/go-build2702711329/b525/testlog.txt -test.paniconexit0 -test.gocoverdir=/tmp/go-build2702711329/b525/gocoverdir -test.timeout=10m0s (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Add unit test</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add unit test #6

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