1Multicast DNS for lwIP 2 3Author: Erik Ekman 4 5 6Note! The MDNS responder does not have all features required by the standards. 7See notes in src/apps/mdns/mdns.c for what is left. It is however usable in normal 8cases - but watch out if many devices on the same network try to use the same 9host/service instance names. 10 11 12How to enable: 13============== 14 15MDNS support does not depend on DNS. 16MDNS supports using IPv4 only, v6 only, or v4+v6. 17 18To enable MDNS responder, set 19 LWIP_MDNS_RESPONDER = 1 20in lwipopts.h and add src/apps/mdns/mdns.c to your list of files to build. 21 22The max number of services supported per netif is defined by MDNS_MAX_SERVICES, 23default is 1. 24 25Increase MEMP_NUM_UDP_PCB by 1. MDNS needs one PCB. 26Increase LWIP_NUM_NETIF_CLIENT_DATA by 1 (MDNS needs one entry on netif). 27 28MDNS with IPv4 requires LWIP_IGMP = 1, and preferably LWIP_AUTOIP = 1. 29MDNS with IPv6 requires LWIP_IPV6_MLD = 1, and that a link-local address is 30generated. 31 32The MDNS code puts its structs on the stack where suitable to reduce dynamic 33memory allocation. It may use up to 1kB of stack. 34 35MDNS (like other apps) needs a strncasecmp() implementation. If you have one, define 36'lwip_strnicmp' to it. Otherwise the code will provide an implementation 37for you. 38 39 40How to use: 41=========== 42 43Call mdns_resp_init() during system initialization. 44This opens UDP sockets on port 5353 for IPv4 and IPv6. 45 46 47To start responding on a netif, run 48 mdns_resp_add_netif(struct netif *netif, const char *hostname) 49 50The hostname will be copied. If this returns successfully, the netif will join 51the multicast groups and any MDNS/legacy DNS requests sent unicast or multicast 52to port 5353 will be handled: 53- <hostname>.local type A, AAAA or ANY returns relevant IP addresses 54- Reverse lookups (PTR in-addr.arpa, ip6.arpa) of netif addresses 55 returns <hostname>.local 56MDNS allows UTF-8 names, but it is recommended to stay within ASCII, 57since the default case-insensitive comparison assumes this. 58 59Call mdns_resp_announce() every time the IP address on the netif has changed. 60 61Call mdns_resp_restart() every time the network interface comes up after being 62down, for example cable connected after being disconnected, administrative 63interface comes up after being down, or the device wakes up from sleep. 64 65To stop responding on a netif, run 66 mdns_resp_remove_netif(struct netif *netif) 67 68 69Adding services: 70================ 71 72The netif first needs to be registered. Then run 73 mdns_resp_add_service(struct netif *netif, const char *name, const char *service, 74 enum mdns_sd_proto proto, u16_t port, 75 service_get_txt_fn_t txt_fn, void *txt_userdata); 76 77The name and service pointers will be copied. Name refers to the name of the 78service instance, and service is the type of service, like _http 79proto can be DNSSD_PROTO_UDP or DNSSD_PROTO_TCP which represent _udp and _tcp. 80If this call returns successfully, the following queries will be answered: 81- _services._dns-sd._udp.local type PTR returns <service>.<proto>.local 82- <service>.<proto>.local type PTR returns <name>.<service>.<proto>.local 83- <name>.<service>.<proto>.local type SRV returns hostname and port of service 84- <name>.<service>.<proto>.local type TXT builds text strings by calling txt_fn 85 with the supplied userdata. The callback adds strings to the reply by calling 86 mdns_resp_add_service_txtitem(struct mdns_service *service, char *txt, 87 int txt_len). Example callback method: 88 89 static void srv_txt(struct mdns_service *service, void *txt_userdata) 90 { 91 res = mdns_resp_add_service_txtitem(service, "path=/", 6); 92 LWIP_ERROR("mdns add service txt failed\n", (res == ERR_OK), return); 93 } 94 95 Since a hostname struct is used for TXT storage each single item can be max 96 63 bytes long, and the total max length (including length bytes for each 97 item) is 255 bytes. 98 99If your device runs a webserver on port 80, an example call might be: 100 101 mdns_resp_add_service(netif, "myweb", "_http" 102 DNSSD_PROTO_TCP, 80, srv_txt, NULL); 103 104which will publish myweb._http._tcp.local for any hosts looking for web servers, 105and point them to <hostname>.local:80 106 107Relevant information will be sent as additional records to reduce number of 108requests required from a client. 109 110To remove a service from a netif, run 111 mdns_resp_del_service(struct netif *netif, u8_t slot) 112