189 lines
6.3 KiB
ReStructuredText
189 lines
6.3 KiB
ReStructuredText
mDNS Service
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============
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:link_to_translation:`zh_CN:[中文]`
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Overview
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--------
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mDNS is a multicast UDP service that is used to provide local network service and host discovery.
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mDNS is installed by default on most operating systems or is available as separate package. On ``Mac OS`` it is installed by default and is called ``Bonjour``. Apple releases an installer for ``Windows`` that can be found `on Apple's support page <https://support.apple.com/downloads/bonjour%2520for%2520windows>`_. On ``Linux``, mDNS is provided by `avahi <https://github.com/lathiat/avahi>`_ and is usually installed by default.
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mDNS Properties
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^^^^^^^^^^^^^^^
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* ``hostname``: the hostname that the device will respond to. If not set, the ``hostname`` will be read from the interface. Example: ``my-esp32`` will resolve to ``my-esp32.local``
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* ``default_instance``: friendly name for your device, like ``Jhon's ESP32 Thing``. If not set, ``hostname`` will be used.
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Example method to start mDNS for the STA interface and set ``hostname`` and ``default_instance``:
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.. highlight:: c
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::
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void start_mdns_service()
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{
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//initialize mDNS service
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esp_err_t err = mdns_init();
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if (err) {
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printf("MDNS Init failed: %d\n", err);
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return;
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}
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//set hostname
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mdns_hostname_set("my-esp32");
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//set default instance
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mdns_instance_name_set("Jhon's ESP32 Thing");
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}
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mDNS Services
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^^^^^^^^^^^^^
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mDNS can advertise information about network services that your device offers. Each service is defined by a few properties.
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* ``instance_name``: friendly name for your service, like ``Jhon's ESP32 Web Server``. If not defined, ``default_instance`` will be used.
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* ``service_type``: (required) service type, prepended with underscore. Some common types can be found `here <http://www.dns-sd.org/serviceTypes.html>`_.
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* ``proto``: (required) protocol that the service runs on, prepended with underscore. Example: ``_tcp`` or ``_udp``
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* ``port``: (required) network port that the service runs on
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* ``txt``: ``{var, val}`` array of strings, used to define properties for your service
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Example method to add a few services and different properties::
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void add_mdns_services()
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{
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//add our services
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mdns_service_add(NULL, "_http", "_tcp", 80, NULL, 0);
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mdns_service_add(NULL, "_arduino", "_tcp", 3232, NULL, 0);
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mdns_service_add(NULL, "_myservice", "_udp", 1234, NULL, 0);
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//NOTE: services must be added before their properties can be set
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//use custom instance for the web server
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mdns_service_instance_name_set("_http", "_tcp", "Jhon's ESP32 Web Server");
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mdns_txt_item_t serviceTxtData[3] = {
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{"board","esp32"},
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{"u","user"},
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{"p","password"}
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};
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//set txt data for service (will free and replace current data)
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mdns_service_txt_set("_http", "_tcp", serviceTxtData, 3);
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//change service port
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mdns_service_port_set("_myservice", "_udp", 4321);
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}
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mDNS Query
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^^^^^^^^^^
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mDNS provides methods for browsing for services and resolving host's IP/IPv6 addresses.
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Results for services are returned as a linked list of ``mdns_result_t`` objects.
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Example method to resolve host IPs::
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void resolve_mdns_host(const char * host_name)
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{
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printf("Query A: %s.local", host_name);
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struct ip4_addr addr;
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addr.addr = 0;
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esp_err_t err = mdns_query_a(host_name, 2000, &addr);
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if(err){
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if(err == ESP_ERR_NOT_FOUND){
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printf("Host was not found!");
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return;
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}
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printf("Query Failed");
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return;
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}
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printf(IPSTR, IP2STR(&addr));
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}
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Example method to resolve local services::
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static const char * if_str[] = {"STA", "AP", "ETH", "MAX"};
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static const char * ip_protocol_str[] = {"V4", "V6", "MAX"};
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void mdns_print_results(mdns_result_t * results){
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mdns_result_t * r = results;
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mdns_ip_addr_t * a = NULL;
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int i = 1, t;
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while(r){
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printf("%d: Interface: %s, Type: %s\n", i++, if_str[r->tcpip_if], ip_protocol_str[r->ip_protocol]);
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if(r->instance_name){
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printf(" PTR : %s\n", r->instance_name);
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}
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if(r->hostname){
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printf(" SRV : %s.local:%u\n", r->hostname, r->port);
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}
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if(r->txt_count){
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printf(" TXT : [%u] ", r->txt_count);
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for(t=0; t<r->txt_count; t++){
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printf("%s=%s; ", r->txt[t].key, r->txt[t].value);
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}
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printf("\n");
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}
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a = r->addr;
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while(a){
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if(a->addr.type == IPADDR_TYPE_V6){
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printf(" AAAA: " IPV6STR "\n", IPV62STR(a->addr.u_addr.ip6));
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} else {
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printf(" A : " IPSTR "\n", IP2STR(&(a->addr.u_addr.ip4)));
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}
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a = a->next;
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}
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r = r->next;
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}
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}
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void find_mdns_service(const char * service_name, const char * proto)
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{
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ESP_LOGI(TAG, "Query PTR: %s.%s.local", service_name, proto);
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mdns_result_t * results = NULL;
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esp_err_t err = mdns_query_ptr(service_name, proto, 3000, 20, &results);
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if(err){
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ESP_LOGE(TAG, "Query Failed");
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return;
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}
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if(!results){
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ESP_LOGW(TAG, "No results found!");
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return;
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}
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mdns_print_results(results);
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mdns_query_results_free(results);
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}
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Example of using the methods above::
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void my_app_some_method(){
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//search for esp32-mdns.local
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resolve_mdns_host("esp32-mdns");
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//search for HTTP servers
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find_mdns_service("_http", "_tcp");
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//or file servers
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find_mdns_service("_smb", "_tcp"); //windows sharing
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find_mdns_service("_afpovertcp", "_tcp"); //apple sharing
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find_mdns_service("_nfs", "_tcp"); //NFS server
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find_mdns_service("_ftp", "_tcp"); //FTP server
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//or networked printer
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find_mdns_service("_printer", "_tcp");
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find_mdns_service("_ipp", "_tcp");
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}
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Application Example
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-------------------
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mDNS server/scanner example: :example:`protocols/mdns`.
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API Reference
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-------------
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.. include:: /_build/inc/mdns.inc
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