Initial commit

Generic SRV records checker for happyDomain.

For each SRV record attached to an svcs.UnknownSRV service, the checker
resolves every target and probes reachability:

  - DNS resolution (A/AAAA), CNAME detection (RFC 2782 violation),
    null-target detection (RFC 2782 "service explicitly unavailable")
  - TCP connect to target:port for _tcp SRVs
  - UDP probe for _udp SRVs, using ICMP port-unreachable detection

The checker also publishes TLS endpoints (host, port, SNI) for every
SRV target hitting a well-known direct-TLS port (443, 465, 636, 853,
993, 995, 5061, 5223, …) via the EndpointDiscoverer SDK interface, so
a downstream TLS checker can pick them up.

The HTML report groups records as cards and surfaces the most common
failure scenarios (DNS failure, CNAME target, TCP unreachable,
null-target) at the top with remediation guidance.

checker/collect_standalone.go

@@ -0,0 +1,85 @@
+// This file is part of the happyDomain (R) project.
+// Copyright (c) 2020-2026 happyDomain
+// Authors: Pierre-Olivier Mercier, et al.
+//
+// This program is offered under a commercial and under the AGPL license.
+// For commercial licensing, contact us at <contact@happydomain.org>.
+//
+// For AGPL licensing:
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+//go:build standalone
+
+package checker
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"strings"
+
+	sdk "git.happydns.org/checker-sdk-go/checker"
+)
+
+// collectFallback queries DNS for SRV records directly when no upstream
+// service payload is available (standalone CLI/HTTP mode).
+func (p *srvProvider) collectFallback(ctx context.Context, opts sdk.CheckerOptions) (any, error) {
+	subdomain, _ := sdk.GetOption[string](opts, "subdomain")
+	domain, _ := sdk.GetOption[string](opts, "domain")
+
+	serviceDomain := strings.TrimSuffix(subdomain, ".")
+	if domain != "" {
+		if serviceDomain != "" {
+			serviceDomain += "." + strings.TrimSuffix(domain, ".")
+		} else {
+			serviceDomain = strings.TrimSuffix(domain, ".")
+		}
+	}
+	if serviceDomain == "" {
+		return nil, fmt.Errorf("missing 'domain' option")
+	}
+
+	// Empty service/proto tells the resolver to query the literal name as-is,
+	// preserving _svc._proto labels already encoded in serviceDomain.
+	_, srvs, err := net.DefaultResolver.LookupSRV(ctx, "", "", serviceDomain)
+	if err != nil {
+		return nil, fmt.Errorf("SRV lookup for %s: %w", serviceDomain, err)
+	}
+	if len(srvs) == 0 {
+		return nil, fmt.Errorf("no SRV records at %s", serviceDomain)
+	}
+
+	tcpTimeout := durationOpt(opts, "tcpTimeout", 3000)
+	udpTimeout := durationOpt(opts, "udpTimeout", 2000)
+
+	svc, proto := parseOwner(serviceDomain, serviceDomain)
+	data := &SRVData{
+		ServiceDomain: serviceDomain,
+		Records:       make([]SRVRecord, 0, len(srvs)),
+	}
+	for _, s := range srvs {
+		rec := SRVRecord{
+			Service:  svc,
+			Proto:    proto,
+			Owner:    serviceDomain,
+			Target:   strings.TrimSuffix(s.Target, "."),
+			Port:     s.Port,
+			Priority: s.Priority,
+			Weight:   s.Weight,
+		}
+		resolveAndProbe(ctx, &rec, tcpTimeout, udpTimeout)
+		data.Records = append(data.Records, rec)
+	}
+	return data, nil
+}