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.

Makefile

@@ -0,0 +1,28 @@
+CHECKER_NAME := checker-srv
+CHECKER_IMAGE := happydomain/$(CHECKER_NAME)
+CHECKER_VERSION ?= custom-build
+
+CHECKER_SOURCES := main.go $(wildcard checker/*.go)
+
+GO_LDFLAGS := -X main.Version=$(CHECKER_VERSION)
+
+.PHONY: all plugin docker test clean
+
+all: $(CHECKER_NAME)
+
+$(CHECKER_NAME): $(CHECKER_SOURCES)
+	go build -tags standalone -ldflags "$(GO_LDFLAGS)" -o $@ .
+
+plugin: $(CHECKER_NAME).so
+
+$(CHECKER_NAME).so: $(CHECKER_SOURCES) $(wildcard plugin/*.go)
+	go build -buildmode=plugin -ldflags "$(GO_LDFLAGS)" -o $@ ./plugin/
+
+docker:
+	docker build --build-arg CHECKER_VERSION=$(CHECKER_VERSION) -t $(CHECKER_IMAGE) .
+
+test:
+	go test -tags standalone ./...
+
+clean:
+	rm -f $(CHECKER_NAME) $(CHECKER_NAME).so