feat(mdns): Use internal cache for browser update, and support subtype browsing

components/mdns/CMakeLists.txt

@@ -13,7 +13,7 @@ endif()
 set(MDNS_MEMORY "mdns_mem_caps.c")
 
 set(MDNS_CORE "mdns_responder.c" "mdns_receive.c" "mdns_utils.c" "mdns_debug.c" "mdns_browser.c" "mdns_send.c" "mdns_netif.c"
-                "mdns_querier.c" "mdns_pcb.c" "mdns_service.c")
+                "mdns_querier.c" "mdns_pcb.c" "mdns_service.c" "mdns_cache.c")
 
 idf_build_get_property(target IDF_TARGET)
 if(${target} STREQUAL "linux")

components/mdns/include/mdns.h

@@ -134,35 +134,30 @@ typedef struct mdns_result_s {
     size_t txt_count;                       /*!< number of txt items */
     // A and AAAA
     mdns_ip_addr_t *addr;                   /*!< linked list of IP addresses found */
+    // Browse only
+    char *subtype;                          /*!< browse subtype, or NULL for normal browse */
 } mdns_result_t;
 
 typedef void (*mdns_query_notify_t)(mdns_search_once_t *search);
 
 /**
  * @brief Browse result change notifier
  *
- * Called once per browse result that changed in a given response packet (not
- * once per packet). The @p result argument points at the changed entry, but it
- * remains a live node in the internal browse cache until the callback returns.
+ * Called once for every matching browse result changed by a received response,
+ * or once for every currently cached result when a new browse is registered.
  *
- * @warning @p result->next links other cached instances for this browse, not
- *          necessarily other results that changed in the same packet. For
- *          ordinary add/update notifications, use only @p result; do not walk
- *          @c next, because unchanged instances may appear there.
+ * The @p result is a temporary projection of the internal mDNS cache, which is only valid
+ * during the lifetime of this callback and is freed immediately after the callback returns.
  *
- * @warning Batch PTR TTL=0 ("goodbye") responses (for example when a peer
- *          exits and Bonjour sends many removals in one packet) may invoke the
- *          notifier once while several instances in the cache are updated.
- *          Until this is improved, applications may walk @c next and treat
- *          entries with @c ttl == 0 as removals. Do not assume every node on
- *          @c next changed in the current packet.
+ * @warning @p result->next is always NULL. Other instances cannot be obtained from @p result.
  *
- * @warning If handling is deferred outside this callback, copy @p result first
- *          (including strings and addresses). Goodbye entries may be freed when
- *          the callback returns.
+ * @warning If handling is deferred outside this callback, applications must make a deep copy
+ *          of @p result with all components, including strings, TXT entries, address list, and subtype.
  *
- * @param result  The browse result that changed. See the warnings above for
- *                use of @c result->next.
+ * @warning `mdns_browse_new*` APIs will acquire mDNS service lock, and `mdns_browse_notify_t` runs
+ *          in the mDNS service task. Users must not call `mdns_service_new*` APIs from `mdns_browse_notify_t`.
+ *
+ * @param result  Temporary result of the browse that changed.
  */
 typedef void (*mdns_browse_notify_t)(mdns_result_t *result);
 
@@ -1053,19 +1048,35 @@ esp_err_t mdns_netif_action(esp_netif_t *esp_netif, mdns_event_actions_t event_a
  * @return mdns_browse_t pointer to new browse object if initiated successfully.
  *         NULL otherwise.
  *
- * @note When several service instances share the same SRV target hostname, A/AAAA
- *       addresses from a response are attached only to the first matching browse
- *       result for that hostname (per interface and IP protocol). Other instances
- *       with the same target host are not populated automatically; applications
- *       that need host-level addresses for every instance must resolve or cache
- *       them separately until this behavior is improved.
+ * @note If matching services already present in the internal mDNS cache,
+ *       the notifier will be called once for each cached service after this browse
+ *       is registered.
  *
- * @note If one response packet contains answers for multiple active browses,
- *       only one browse is synchronized for that packet. This should not affect
- *       typical browse traffic, where packets answer one service type.
+ * @note The notifier receives a temporary result that is valid only during the callback.
+ *       See @ref mdns_browse_notify_t for ownership and lifetime details.
  */
 mdns_browse_t *mdns_browse_new(const char *service, const char *proto, mdns_browse_notify_t notifier);
 
+/**
+ * @brief   Browse mDNS for a service subtype `_subtype._sub._service._proto`
+ *          (Selective Instance Enumeration per RFC 6763 Section 7.1).
+ *
+ * @param service  Pointer to the `_service` which will be browsed.
+ * @param proto    Pointer to the `_proto` which will be browsed.
+ * @param subtype  Pointer to the `_subtype` to restrict browsing to. Can be NULL for standard browse.
+ * @param notifier The callback which will be called when the browsing service changed.
+ * @return mdns_browse_t pointer to new browse object if initiated successfully.
+ *         NULL otherwise.
+ *
+ * @note If matching services already present in the internal mDNS cache,
+ *       the notifier will be called once for each cached service after this browse
+ *       is registered.
+ *
+ * @note The notifier receives a temporary result that is valid only during the callback.
+ *       See @ref mdns_browse_notify_t for ownership and lifetime details.
+ */
+mdns_browse_t *mdns_browse_new_with_subtype(const char *service, const char *proto, const char *subtype, mdns_browse_notify_t notifier);
+
 /**
  * @brief   Stop the `_service._proto` browse.
  * @param service  Pointer to the `_service` which will be browsed.
@@ -1077,6 +1088,19 @@ mdns_browse_t *mdns_browse_new(const char *service, const char *proto, mdns_brow
  */
 esp_err_t mdns_browse_delete(const char *service, const char *proto);
 
+
+/**
+ * @brief   Stop the `_subtype._sub._service._proto` browse.
+ * @param service  Pointer to the `_service` which will be browsed.
+ * @param proto    Pointer to the `_proto` which will be browsed.
+ * @param subtype  Pointer to the `_subtype`. Can be NULL to match a browse without subtype.
+ * @return
+ *     - ESP_OK                 success.
+ *     - ESP_ERR_FAIL           mDNS is not running or the browsing was never started.
+ *     - ESP_ERR_NO_MEM         memory error.
+ */
+esp_err_t mdns_browse_delete_with_subtype(const char *service, const char *proto, const char *subtype);
+
 #ifdef __cplusplus
 }
 #endif