mDNS 服务¶
概述¶
mDNS 是一种组播 UDP 服务,用来提供本地网络服务和主机发现。
绝大多数的操作系统默认都会安装 mDNS 服务,或者提供单独的安装包。Mac OS
默认会安装名为 Bonjour
的服务(该服务基于 mDNS),此外 Apple 还发布了适用于 Windows 系统的安装程序,可以在 官方支持 找到。在 Linux
上,mDNS 服务由 avahi 提供,通常也会被默认安装。
mDNS 属性¶
hostname
:设备会去响应的主机名,如果没有设置,会根据设备的网络接口名定义hostname
。例如,my-esp32
会被解析为my-esp32.local
。
default_instance
:默认实例名(即易记的设备名),例如Jhon's ESP32 Thing
。如果没有设置,将会使用hostname
。
以下为 STA 接口启动 mDNS 服务并设置 hostname
和 default_instance
的示例方法:
void start_mdns_service()
{
// 初始化 mDNS 服务
esp_err_t err = mdns_init();
if (err) {
printf("MDNS Init failed: %d\n", err);
return;
}
// 设置 hostname
mdns_hostname_set("my-esp32");
// 设置默认实例
mdns_instance_name_set("Jhon's ESP32 Thing");
}
mDNS 服务¶
mDNS 可以广播设备能够提供的网络服务的相关信息,每个服务会由以下属性构成。
instance_name
:实例名(即易记的服务名),例如Jhon's ESP32 Web Server
。如果没有定义,会使用default_instance
。
service_type
:(必需)服务类型,以下划线为前缀,这里 列出了常见的类型。
proto
:(必需)服务运行所依赖的协议,以下划线为前缀,例如_tcp
或者_udp
。
port
:(必需)服务运行所用的端口号。
txt
:形如{var, val}
的字符串数组,用于定义服务的属性。
添加一些服务和不同属性的示例方法:
void add_mdns_services()
{
// 添加服务
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);
// 注意:必须先添加服务,然后才能设置其属性
// web 服务器使用自定义的实例名
mdns_service_instance_name_set("_http", "_tcp", "Jhon's ESP32 Web Server");
mdns_txt_item_t serviceTxtData[3] = {
{"board","esp32"},
{"u","user"},
{"p","password"}
};
// 设置服务的文本数据(会释放并替换当前数据)
mdns_service_txt_set("_http", "_tcp", serviceTxtData, 3);
// 修改服务端口号
mdns_service_port_set("_myservice", "_udp", 4321);
}
mDNS 查询¶
mDNS 提供查询服务和解析主机 IP/IPv6 地址的方法。
服务查询的结果会作为 mdns_result_t
类型对象的链表返回。
解析主机 IP 地址的示例方法:
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));
}
解析本地服务的示例方法:
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);
}
使用上述方法的示例:
void my_app_some_method(){
// 搜索 esp32-mdns.local
resolve_mdns_host("esp32-mdns");
// 搜索 HTTP 服务器
find_mdns_service("_http", "_tcp");
// 或者搜索文件服务器
find_mdns_service("_smb", "_tcp"); // Windows 系统的共享服务
find_mdns_service("_afpovertcp", "_tcp"); // Apple AFP 文件共享服务
find_mdns_service("_nfs", "_tcp"); // NFS 服务器
find_mdns_service("_ftp", "_tcp"); // FTP 服务器
// 或者网络打印机
find_mdns_service("_printer", "_tcp");
find_mdns_service("_ipp", "_tcp");
}
应用示例¶
有关 mDNS 服务器和查询器的应用示例请参考 protocols/mdns。
API 参考¶
Header File¶
Functions¶
-
esp_err_t
mdns_init
(void)¶ Initialize mDNS on given interface.
- Return
ESP_OK on success
ESP_ERR_INVALID_STATE when failed to register event handler
ESP_ERR_NO_MEM on memory error
ESP_FAIL when failed to start mdns task
-
void
mdns_free
(void)¶ Stop and free mDNS server.
-
esp_err_t
mdns_hostname_set
(const char *hostname)¶ Set the hostname for mDNS server required if you want to advertise services.
- Return
ESP_OK success
ESP_ERR_INVALID_ARG Parameter error
ESP_ERR_NO_MEM memory error
- Parameters
hostname
: Hostname to set
-
esp_err_t
mdns_instance_name_set
(const char *instance_name)¶ Set the default instance name for mDNS server.
- Return
ESP_OK success
ESP_ERR_INVALID_ARG Parameter error
ESP_ERR_NO_MEM memory error
- Parameters
instance_name
: Instance name to set
-
esp_err_t
mdns_service_add
(const char *instance_name, const char *service_type, const char *proto, uint16_t port, mdns_txt_item_t txt[], size_t num_items)¶ Add service to mDNS server.
- Return
ESP_OK success
ESP_ERR_INVALID_ARG Parameter error
ESP_ERR_NO_MEM memory error
ESP_FAIL failed to add service
- Parameters
instance_name
: instance name to set. If NULL, global instance name or hostname will be usedservice_type
: service type (_http, _ftp, etc)proto
: service protocol (_tcp, _udp)port
: service porttxt
: string array of TXT data (eg. {{“var”,”val”},{“other”,”2”}})num_items
: number of items in TXT data
-
esp_err_t
mdns_service_remove
(const char *service_type, const char *proto)¶ Remove service from mDNS server.
- Return
ESP_OK success
ESP_ERR_INVALID_ARG Parameter error
ESP_ERR_NOT_FOUND Service not found
ESP_ERR_NO_MEM memory error
- Parameters
service_type
: service type (_http, _ftp, etc)proto
: service protocol (_tcp, _udp)
-
esp_err_t
mdns_service_instance_name_set
(const char *service_type, const char *proto, const char *instance_name)¶ Set instance name for service.
- Return
ESP_OK success
ESP_ERR_INVALID_ARG Parameter error
ESP_ERR_NOT_FOUND Service not found
ESP_ERR_NO_MEM memory error
- Parameters
service_type
: service type (_http, _ftp, etc)proto
: service protocol (_tcp, _udp)instance_name
: instance name to set
-
esp_err_t
mdns_service_port_set
(const char *service_type, const char *proto, uint16_t port)¶ Set service port.
- Return
ESP_OK success
ESP_ERR_INVALID_ARG Parameter error
ESP_ERR_NOT_FOUND Service not found
ESP_ERR_NO_MEM memory error
- Parameters
service_type
: service type (_http, _ftp, etc)proto
: service protocol (_tcp, _udp)port
: service port
-
esp_err_t
mdns_service_txt_set
(const char *service_type, const char *proto, mdns_txt_item_t txt[], uint8_t num_items)¶ Replace all TXT items for service.
- Return
ESP_OK success
ESP_ERR_INVALID_ARG Parameter error
ESP_ERR_NOT_FOUND Service not found
ESP_ERR_NO_MEM memory error
- Parameters
service_type
: service type (_http, _ftp, etc)proto
: service protocol (_tcp, _udp)txt
: array of TXT data (eg. {{“var”,”val”},{“other”,”2”}})num_items
: number of items in TXT data
-
esp_err_t
mdns_service_txt_item_set
(const char *service_type, const char *proto, const char *key, const char *value)¶ Set/Add TXT item for service TXT record.
- Return
ESP_OK success
ESP_ERR_INVALID_ARG Parameter error
ESP_ERR_NOT_FOUND Service not found
ESP_ERR_NO_MEM memory error
- Parameters
service_type
: service type (_http, _ftp, etc)proto
: service protocol (_tcp, _udp)key
: the key that you want to add/updatevalue
: the new value of the key
-
esp_err_t
mdns_service_txt_item_remove
(const char *service_type, const char *proto, const char *key)¶ Remove TXT item for service TXT record.
- Return
ESP_OK success
ESP_ERR_INVALID_ARG Parameter error
ESP_ERR_NOT_FOUND Service not found
ESP_ERR_NO_MEM memory error
- Parameters
service_type
: service type (_http, _ftp, etc)proto
: service protocol (_tcp, _udp)key
: the key that you want to remove
-
esp_err_t
mdns_service_remove_all
(void)¶ Remove and free all services from mDNS server.
- Return
ESP_OK success
ESP_ERR_INVALID_ARG Parameter error
-
esp_err_t
mdns_query
(const char *name, const char *service_type, const char *proto, uint16_t type, uint32_t timeout, size_t max_results, mdns_result_t **results)¶ Query mDNS for host or service All following query methods are derived from this one.
- Return
ESP_OK success
ESP_ERR_INVALID_STATE mDNS is not running
ESP_ERR_NO_MEM memory error
ESP_ERR_INVALID_ARG timeout was not given
- Parameters
name
: service instance or host name (NULL for PTR queries)service_type
: service type (_http, _arduino, _ftp etc.) (NULL for host queries)proto
: service protocol (_tcp, _udp, etc.) (NULL for host queries)type
: type of query (MDNS_TYPE_*)timeout
: time in milliseconds to wait for answers.max_results
: maximum results to be collectedresults
: pointer to the results of the query results must be freed using mdns_query_results_free below
-
void
mdns_query_results_free
(mdns_result_t *results)¶ Free query results.
- Parameters
results
: linked list of results to be freed
-
esp_err_t
mdns_query_ptr
(const char *service_type, const char *proto, uint32_t timeout, size_t max_results, mdns_result_t **results)¶ Query mDNS for service.
- Return
ESP_OK success
ESP_ERR_INVALID_STATE mDNS is not running
ESP_ERR_NO_MEM memory error
ESP_ERR_INVALID_ARG parameter error
- Parameters
service_type
: service type (_http, _arduino, _ftp etc.)proto
: service protocol (_tcp, _udp, etc.)timeout
: time in milliseconds to wait for answer.max_results
: maximum results to be collectedresults
: pointer to the results of the query
-
esp_err_t
mdns_query_srv
(const char *instance_name, const char *service_type, const char *proto, uint32_t timeout, mdns_result_t **result)¶ Query mDNS for SRV record.
- Return
ESP_OK success
ESP_ERR_INVALID_STATE mDNS is not running
ESP_ERR_NO_MEM memory error
ESP_ERR_INVALID_ARG parameter error
- Parameters
instance_name
: service instance nameservice_type
: service type (_http, _arduino, _ftp etc.)proto
: service protocol (_tcp, _udp, etc.)timeout
: time in milliseconds to wait for answer.result
: pointer to the result of the query
-
esp_err_t
mdns_query_txt
(const char *instance_name, const char *service_type, const char *proto, uint32_t timeout, mdns_result_t **result)¶ Query mDNS for TXT record.
- Return
ESP_OK success
ESP_ERR_INVALID_STATE mDNS is not running
ESP_ERR_NO_MEM memory error
ESP_ERR_INVALID_ARG parameter error
- Parameters
instance_name
: service instance nameservice_type
: service type (_http, _arduino, _ftp etc.)proto
: service protocol (_tcp, _udp, etc.)timeout
: time in milliseconds to wait for answer.result
: pointer to the result of the query
-
esp_err_t
mdns_query_a
(const char *host_name, uint32_t timeout, esp_ip4_addr_t *addr)¶ Query mDNS for A record.
- Return
ESP_OK success
ESP_ERR_INVALID_STATE mDNS is not running
ESP_ERR_NO_MEM memory error
ESP_ERR_INVALID_ARG parameter error
- Parameters
host_name
: host name to look fortimeout
: time in milliseconds to wait for answer.addr
: pointer to the resulting IP4 address
-
esp_err_t
mdns_query_aaaa
(const char *host_name, uint32_t timeout, esp_ip6_addr_t *addr)¶ Query mDNS for A record.
- Return
ESP_OK success
ESP_ERR_INVALID_STATE mDNS is not running
ESP_ERR_NO_MEM memory error
ESP_ERR_INVALID_ARG parameter error
- Parameters
host_name
: host name to look fortimeout
: time in milliseconds to wait for answer. If 0, max_results needs to be definedaddr
: pointer to the resulting IP6 address
-
esp_err_t
mdns_handle_system_event
(void *ctx, system_event_t *event)¶ System event handler This method controls the service state on all active interfaces and applications are required to call it from the system event handler for normal operation of mDNS service.
- Parameters
ctx
: The system event contextevent
: The system event
Structures¶
-
struct
mdns_txt_item_t
¶ mDNS basic text item structure Used in mdns_service_add()
-
struct
mdns_ip_addr_s
¶ mDNS query linked list IP item
Public Members
-
esp_ip_addr_t
addr
¶ IP address
-
struct mdns_ip_addr_s *
next
¶ next IP, or NULL for the last IP in the list
-
esp_ip_addr_t
-
struct
mdns_result_s
¶ mDNS query result structure
Public Members
-
struct mdns_result_s *
next
¶ next result, or NULL for the last result in the list
-
mdns_ip_protocol_t
ip_protocol
¶ ip_protocol type of the interface (v4/v6)
-
char *
instance_name
¶ instance name
-
char *
hostname
¶ hostname
-
uint16_t
port
¶ service port
-
mdns_txt_item_t *
txt
¶ txt record
-
size_t
txt_count
¶ number of txt items
-
mdns_ip_addr_t *
addr
¶ linked list of IP addresses found
-
struct mdns_result_s *
Macros¶
-
MDNS_TYPE_A
¶
-
MDNS_TYPE_PTR
¶
-
MDNS_TYPE_TXT
¶
-
MDNS_TYPE_AAAA
¶
-
MDNS_TYPE_SRV
¶
-
MDNS_TYPE_OPT
¶
-
MDNS_TYPE_NSEC
¶
-
MDNS_TYPE_ANY
¶
Type Definitions¶
-
typedef struct mdns_ip_addr_s
mdns_ip_addr_t
¶ mDNS query linked list IP item
-
typedef enum mdns_if_internal
mdns_if_t
¶
-
typedef struct mdns_result_s
mdns_result_t
¶ mDNS query result structure