Initial commit

Adds a happyDomain checker that probes STUN/TURN servers end-to-end:
DNS/SRV discovery, UDP/TCP/TLS/DTLS dial, STUN binding + reflexive-addr
sanity, open-relay detection, authenticated TURN Allocate (long-term
creds or REST-API HMAC), public-relay check, CreatePermission + Send
round-trip through the relay, and optional ChannelBind.

Failing sub-tests carry a remediation string (`Fix`) that the HTML
report surfaces as a yellow headline callout and inline next to each
row. Mapping covers the most common coturn misconfigurations
(external-ip, relay-ip, lt-cred-mech, min-port/max-port, cert issues,
401 nonce drift, 441/442/486/508 allocation errors).

Implements sdk.EndpointDiscoverer (checker/discovery.go): every
stuns:/turns:/DTLS endpoint observed during Collect is published as a
DiscoveredEndpoint{Type: "tls"|"dtls"} so a downstream TLS checker can
verify certificates without re-parsing the observation.

Backed by pion/stun/v3 + pion/turn/v4 + pion/dtls/v3; SDK pinned to a
local replace until the EndpointDiscoverer interface ships in a tagged
release.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

checker/types.go

@@ -0,0 +1,132 @@
+// Package checker implements the STUN/TURN checker for happyDomain.
+//
+// The checker drives a target server through the STUN binding and TURN
+// allocation/relay protocols (RFC 5389, RFC 5766) using the Pion libraries,
+// then exposes a structured observation and a rich HTML report including
+// remediation guidance for the most common deployment mistakes.
+package checker
+
+import (
+	"time"
+
+	sdk "git.happydns.org/checker-sdk-go/checker"
+)
+
+// ObservationKeyStunTurn is the observation key for STUN/TURN test data.
+const ObservationKeyStunTurn sdk.ObservationKey = "stun_turn"
+
+// Transport identifies the L4/L4-secure transport used to reach an endpoint.
+type Transport string
+
+const (
+	TransportUDP  Transport = "udp"
+	TransportTCP  Transport = "tcp"
+	TransportTLS  Transport = "tls"
+	TransportDTLS Transport = "dtls"
+)
+
+// Endpoint is a single resolved server target to probe.
+type Endpoint struct {
+	URI       string    `json:"uri"`
+	Host      string    `json:"host"`
+	Port      uint16    `json:"port"`
+	Transport Transport `json:"transport"`
+	Secure    bool      `json:"secure"`
+	IsTURN    bool      `json:"is_turn"` // false: STUN-only scheme, true: TURN scheme
+	Source    string    `json:"source"`  // "uri" or "srv:_turn._udp.example.com"
+}
+
+// SubTestStatus mirrors sdk.Status as a string for JSON friendliness.
+type SubTestStatus string
+
+const (
+	SubTestOK      SubTestStatus = "ok"
+	SubTestInfo    SubTestStatus = "info"
+	SubTestWarn    SubTestStatus = "warn"
+	SubTestCrit    SubTestStatus = "crit"
+	SubTestSkipped SubTestStatus = "skipped"
+	SubTestError   SubTestStatus = "error"
+)
+
+// SubTest is one fine-grained test executed against an endpoint.
+type SubTest struct {
+	Name       string        `json:"name"`
+	Status     SubTestStatus `json:"status"`
+	DurationMs int64         `json:"duration_ms"`
+	Detail     string        `json:"detail,omitempty"`
+	Error      string        `json:"error,omitempty"`
+	Fix        string        `json:"fix,omitempty"`
+}
+
+// EndpointReport gathers all sub-tests run against a single endpoint.
+type EndpointReport struct {
+	Endpoint Endpoint  `json:"endpoint"`
+	SubTests []SubTest `json:"sub_tests"`
+}
+
+// Worst returns the worst sub-test status of the endpoint.
+func (e EndpointReport) Worst() SubTestStatus {
+	worst := SubTestOK
+	for _, t := range e.SubTests {
+		if statusRank(t.Status) > statusRank(worst) {
+			worst = t.Status
+		}
+	}
+	return worst
+}
+
+// FirstFailure returns the first non-OK/Info/Skipped sub-test.
+func (e EndpointReport) FirstFailure() *SubTest {
+	for i := range e.SubTests {
+		s := e.SubTests[i].Status
+		if s != SubTestOK && s != SubTestInfo && s != SubTestSkipped {
+			return &e.SubTests[i]
+		}
+	}
+	return nil
+}
+
+// StunTurnData is the JSON-serializable observation payload.
+type StunTurnData struct {
+	Zone        string           `json:"zone,omitempty"`
+	Mode        string           `json:"mode,omitempty"`
+	CollectedAt time.Time        `json:"collected_at"`
+	Endpoints   []EndpointReport `json:"endpoints"`
+	GlobalError string           `json:"global_error,omitempty"`
+}
+
+// statusRank converts a SubTestStatus to an orderable severity.
+func statusRank(s SubTestStatus) int {
+	switch s {
+	case SubTestOK:
+		return 0
+	case SubTestSkipped:
+		return 1
+	case SubTestInfo:
+		return 2
+	case SubTestWarn:
+		return 3
+	case SubTestCrit:
+		return 4
+	case SubTestError:
+		return 5
+	}
+	return -1
+}
+
+// toSDKStatus converts the worst SubTestStatus seen to an sdk.Status.
+func toSDKStatus(s SubTestStatus) sdk.Status {
+	switch s {
+	case SubTestOK:
+		return sdk.StatusOK
+	case SubTestInfo, SubTestSkipped:
+		return sdk.StatusInfo
+	case SubTestWarn:
+		return sdk.StatusWarn
+	case SubTestCrit:
+		return sdk.StatusCrit
+	case SubTestError:
+		return sdk.StatusError
+	}
+	return sdk.StatusUnknown
+}