net: dns_sd, mdns: support service type enumeration

Support DNS-SD Service Type Enumeration in the dns_sd library
and mdns_responder sample application.

For more information, please see Section 9, "Service Type
Enumeration" in RFC 6763.

https://datatracker.ietf.org/doc/html/rfc6763

Fixes #38673

Signed-off-by: Christopher Friedt <[email protected]>

Author: cfriedt

include/net/dns_sd.h

@@ -50,6 +50,38 @@ extern "C" {
 /** RFC 1034 Section 3.1, RFC 6763 Section 7.2 */
 #define DNS_SD_DOMAIN_MAX_SIZE 63
 
+/**
+ * Minimum number of segments in a fully-qualified name
+ *
+ * This reqpresents FQN's of the form below
+ * ```
+ * <sn>._tcp.<domain>.
+ * ```
+ * Currently sub-types and service domains are unsupported and only the
+ * "local" domain is supported. Specifically, that excludes the following:
+ * ```
+ * <sub>._sub.<sn>._tcp.<servicedomain>.<parentdomain>.
+ * ```
+ * @see <a href="https://datatracker.ietf.org/doc/html/rfc6763">RFC 6763</a>, Section 7.2.
+ */
+#define DNS_SD_MIN_LABELS 3
+/**
+ * Maximum number of segments in a fully-qualified name
+ *
+ * This reqpresents FQN's of the form below
+ * ```
+ * <instance>.<sn>._tcp.<domain>.
+ * ```
+ *
+ * Currently sub-types and service domains are unsupported and only the
+ * "local" domain is supported. Specifically, that excludes the following:
+ * ```
+ * <sub>._sub.<sn>._tcp.<servicedomain>.<parentdomain>.
+ * ```
+ * @see <a href="https://datatracker.ietf.org/doc/html/rfc6763">RFC 6763</a>, Section 7.2.
+ */
+#define DNS_SD_MAX_LABELS 4
+
 /**
  * @brief Register a service for DNS Service Discovery
  *
@@ -209,6 +241,12 @@ struct dns_sd_rec {
  * @internal
  */
 extern const char dns_sd_empty_txt[1];
+/**
+ * @brief Wildcard Port specifier for DNS-SD
+ *
+ * @internal
+ */
+extern const uint16_t dns_sd_port_zero;
 
 /** @endcond */
 
@@ -223,6 +261,32 @@ static inline size_t dns_sd_txt_size(const struct dns_sd_rec *rec)
 	return rec->text_size;
 }
 
+/**
+ * @brief Check if @a rec is a DNS-SD Service Type Enumeration
+ *
+ * DNS-SD Service Type Enumeration is used by network tooling to
+ * acquire a list of all mDNS-advertised services belonging to a
+ * particular host on a particular domain.
+ *
+ * For example, for the domain '.local', the equivalent query
+ * would be '_services._dns-sd._udp.local'.
+ *
+ * Currently, only the '.local' domain is supported.
+ *
+ * @see <a href="https://datatracker.ietf.org/doc/html/rfc6763#section-9">Service Type Enumeration, RFC 6763</a>.
+ *
+ * @param rec the record to in question
+ * @return true if @a rec is a DNS-SD Service Type Enumeration
+ */
+bool dns_sd_is_service_type_enumeration(const struct dns_sd_rec *rec);
+
+/**
+ * @brief Create a wildcard filter for DNS-SD records
+ *
+ * @param filter a pointer to the filter to use
+ */
+void dns_sd_create_wildcard_filter(struct dns_sd_rec *filter);
+
 /**
  * @}
  */

subsys/net/lib/dns/Kconfig

@@ -159,6 +159,17 @@ config MDNS_RESPONDER_DNS_SD
 	  By doing so, Zephyr network services are discoverable
 	  using e.g. 'avahi-browse -t -r _greybus._tcp'.
 
+if MDNS_RESPONDER_DNS_SD
+config MDNS_RESPONDER_DNS_SD_SERVICE_TYPE_ENUMERATION
+	bool "Enable DNS SD Service Type Enumeration"
+	default y
+	help
+	  Selecting this option ensures that the MDNS Responder
+	  performs DNS-SD Service Type Enumeration according to RFC 6763,
+	  Chapter 9. By doing so, Zephyr network services are discoverable
+	  using e.g. 'avahi-browse -t -r _services._dns-sd._udp.local'.
+endif # MDNS_RESPONDER_DNS_SD
+
 module = MDNS_RESPONDER
 module-dep = NET_LOG
 module-str = Log level for mDNS responder