checker-srv/checker/discover.go

package checker

import (
	"fmt"

	sdk "git.happydns.org/checker-sdk-go/checker"
	tlsct "git.happydns.org/checker-tls/contract"
)

// directTLSServices enumerates SRV service names (the "service" part of
// _service._proto.domain) that by convention mean "direct TLS on connect",
// as opposed to STARTTLS or plaintext.
//
// Matching on the service name is more authoritative than matching on the
// port: port 636 could carry anything, but _ldaps._tcp unambiguously
// designates LDAP over TLS — even on a non-standard port.
var directTLSServices = map[string]bool{
	"https":        true,
	"ftps":         true, // FTPS implicit
	"smtps":        true, // SMTP over TLS (legacy port 465 semantics)
	"submissions":  true, // RFC 8314: SMTP submission over TLS
	"imaps":        true,
	"pop3s":        true,
	"nntps":        true,
	"ircs":         true,
	"telnets":      true,
	"ldaps":        true,
	"sips":         true,
	"ipps":         true, // IPP over TLS (printing)
	"xmpps-client": true, // XMPP client over direct TLS
	"xmpps-server": true, // XMPP server-to-server over direct TLS
	"mqtts":        true,
	"coaps":        true,
	"stuns":        true,
	"turns":        true,
}

// starttlsSpec describes how to surface a STARTTLS-capable SRV service in
// the TLS endpoint contract: the upgrade protocol name (which feeds
// tlsct.TLSEndpoint.STARTTLS) and whether the protocol treats STARTTLS as
// mandatory.
type starttlsSpec struct {
	// Proto is the STARTTLS upgrade protocol name. It follows the SRV
	// service-name convention agreed with the TLS checker (see
	// checker-tls/contract) — e.g. "smtp", "imap", "xmpp-client". When two
	// SRV services share the same wire upgrade (submission/smtp both do
	// ESMTP STARTTLS), Proto is the canonical one.
	Proto string

	// Required is true when STARTTLS is mandatory per spec; false when
	// opportunistic (e.g. SMTP on port 25, s2s XMPP). It is mapped to
	// TLSEndpoint.RequireSTARTTLS so the consumer can pick the right
	// severity when the server does not advertise STARTTLS.
	Required bool
}

// starttlsServices enumerates SRV service names that speak plaintext on
// connect and then negotiate TLS via a protocol-specific STARTTLS handshake.
//
// The Proto follows the tls.endpoint.v1 contract's vocabulary; the SDK
// itself has no opinion on these values, they belong to checker-tls.
var starttlsServices = map[string]starttlsSpec{
	"submission":  {"smtp", true},  // RFC 8314: STARTTLS required
	"smtp":        {"smtp", false}, // port 25: opportunistic
	"imap":        {"imap", true},
	"pop3":        {"pop3", true},
	"xmpp-client": {"xmpp-client", true},  // RFC 7590
	"xmpp-server": {"xmpp-server", false}, // s2s: opportunistic
	"ldap":        {"ldap", false},
	"nntp":        {"nntp", false},
	"ftp":         {"ftp", false},
	"sieve":       {"sieve", true},
	"postgresql":  {"postgres", false},
}

// DiscoverEntries is invoked right after Collect. It publishes
// DiscoveryEntry records carrying the TLS endpoint contract
// (tls.endpoint.v1) for:
//
//   - direct-TLS services whose SRV service name is listed in
//     directTLSServices (e.g. _ldaps, _sips, _https),
//   - STARTTLS-capable services whose SRV service name is listed in
//     starttlsServices (e.g. _submission, _imap, _xmpp-client).
//
// Unknown service names produce no entries: we lean on the SRV naming
// convention rather than guessing from the port, since a port alone
// conveys no protocol semantics.
func (p *srvProvider) DiscoverEntries(data any) ([]sdk.DiscoveryEntry, error) {
	d, ok := data.(*SRVData)
	if !ok {
		return nil, fmt.Errorf("unexpected data type %T", data)
	}
	var out []sdk.DiscoveryEntry
	for _, r := range d.Records {
		if r.IsNullTarget || r.Target == "" {
			continue
		}

		if directTLSServices[r.Service] {
			e, err := tlsct.NewEntry(tlsct.TLSEndpoint{
				Host: r.Target,
				Port: r.Port,
				SNI:  r.Target,
			})
			if err != nil {
				return nil, fmt.Errorf("build tls entry for %s:%d: %w", r.Target, r.Port, err)
			}
			out = append(out, e)
			continue
		}

		if spec, ok := starttlsServices[r.Service]; ok {
			e, err := tlsct.NewEntry(tlsct.TLSEndpoint{
				Host:            r.Target,
				Port:            r.Port,
				SNI:             r.Target,
				STARTTLS:        spec.Proto,
				RequireSTARTTLS: spec.Required,
			})
			if err != nil {
				return nil, fmt.Errorf("build starttls entry for %s:%d: %w", r.Target, r.Port, err)
			}
			out = append(out, e)
		}
	}
	return out, nil
}