mDNS 服务

[English]

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 used
  • service_type: service type (_http, _ftp, etc)
  • proto: service protocol (_tcp, _udp)
  • port: service port
  • txt: 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/update
  • value: 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 collected
  • results: 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 collected
  • results: 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 name
  • service_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 name
  • service_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 for
  • timeout: 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 for
  • timeout: time in milliseconds to wait for answer. If 0, max_results needs to be defined
  • addr: 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 context
  • event: The system event

Structures

struct mdns_txt_item_t

mDNS basic text item structure Used in mdns_service_add()

Public Members

const char *key

item key name

const char *value

item value string

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

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_if_t tcpip_if

interface index

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

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

Enumerations

enum mdns_ip_protocol_t

mDNS enum to specify the ip_protocol type

Values:

MDNS_IP_PROTOCOL_V4
MDNS_IP_PROTOCOL_V6
MDNS_IP_PROTOCOL_MAX
enum mdns_if_internal

Values:

MDNS_IF_STA = 0
MDNS_IF_AP = 1
MDNS_IF_ETH = 2
MDNS_IF_MAX

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