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/types.go

@@ -0,0 +1,52 @@
+// Package checker implements the generic SRV records checker for happyDomain.
+//
+// TLS/certificate testing is intentionally out of scope: it is handled by a
+// dedicated TLS checker.
+package checker
+
+import (
+	sdk "git.happydns.org/checker-sdk-go/checker"
+)
+
+const ObservationKeySRV sdk.ObservationKey = "srv_records"
+
+const (
+	protoTCP = "tcp"
+	protoUDP = "udp"
+)
+
+type SRVRecord struct {
+	Service  string `json:"service"`
+	Proto    string `json:"proto"`
+	Owner    string `json:"owner"`
+	Target   string `json:"target"`
+	Port     uint16 `json:"port"`
+	Priority uint16 `json:"priority"`
+	Weight   uint16 `json:"weight"`
+
+	IsNullTarget bool     `json:"isNullTarget,omitempty"` // target == "." means "no service"
+	IsCNAME      bool     `json:"isCNAME,omitempty"`      // RFC 2782: MUST NOT be CNAME
+	CNAMEChain   []string `json:"cnameChain,omitempty"`
+	Addresses    []string `json:"addresses,omitempty"`
+	ResolveError string   `json:"resolveError,omitempty"`
+
+	Probes []ProbeResult `json:"probes,omitempty"`
+}
+
+type ProbeResult struct {
+	Address string `json:"address"`
+	Proto   string `json:"proto"`
+	// Connected reports whether the probe should be treated as reachable.
+	// For TCP this is a true handshake. For UDP, where silent drops are
+	// indistinguishable from a working service, a timeout also sets
+	// Connected=true and populates Error with an explanatory note: the
+	// rule treats "no ICMP unreachable" as best-effort reachable.
+	Connected bool    `json:"connected"`
+	LatencyMs float64 `json:"latencyMs,omitempty"`
+	Error     string  `json:"error,omitempty"`
+}
+
+type SRVData struct {
+	ServiceDomain string      `json:"serviceDomain"`
+	Records       []SRVRecord `json:"records"`
+}