esp-idf/docs/en/api-reference/protocols/mdns.rst
2019-11-14 13:28:04 +08:00

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