release: 0.1.0: Phases 0-11: panel, Postfix/DKIM, milter, backup, Docker image

Initial feature-complete implementation of the v1.0 specification (phases 0-11 of `docs/implementation-plan.md`).
Added:
  - Panel (Go, single static binary) with SQLite persistence, one-time
  - Domain management with per-domain DKIM (RSA-2048, generated in pure Go) and
  - Application (sender identity) management: SASL credentials via `sasldb2`,
  - Full Postfix relay config generated from env at container start: SMTPS 465,
  - Journal milter (pure Go, `go-milter`) recording every send to `send_log`;
  … (6 more in CHANGELOG)

Full detail: CHANGELOG.md (0.1.0).

internal/health/socket.go

@@ -0,0 +1,56 @@
+package health
+
+import (
+	"fmt"
+	"os"
+)
+
+// Socket is the state of one milter socket Postfix connects to.
+type Socket struct {
+	Name    string
+	Path    string
+	Present bool
+	Status  Status
+	Detail  string
+}
+
+// CheckSocket stats a milter socket. required distinguishes the two milters:
+// OpenDKIM runs with default_action=tempfail, so a missing socket stops mail
+// leaving the server, while the journal-milter fails open — mail still goes out,
+// only the send log stops being written.
+func CheckSocket(name, path string, required bool) Socket {
+	s := Socket{Name: name, Path: path}
+	if path == "" {
+		s.Status = StatusUnknown
+		s.Detail = "No socket path is configured."
+		return s
+	}
+	fi, err := os.Stat(path)
+	switch {
+	case err != nil:
+		s.Status = missingStatus(required)
+		s.Detail = missingDetail(name, required)
+	case fi.Mode()&os.ModeSocket == 0:
+		s.Status = missingStatus(required)
+		s.Detail = fmt.Sprintf("%s exists but is not a socket.", path)
+	default:
+		s.Present = true
+		s.Status = StatusOK
+		s.Detail = "Listening."
+	}
+	return s
+}
+
+func missingStatus(required bool) Status {
+	if required {
+		return StatusError
+	}
+	return StatusWarn
+}
+
+func missingDetail(name string, required bool) string {
+	if required {
+		return fmt.Sprintf("The %s socket is missing. Postfix rejects mail with a temporary error until it is back.", name)
+	}
+	return fmt.Sprintf("The %s socket is missing. Mail still goes out, but the send log is not being written.", name)
+}