takashi kadono / Mbed OS Nucleo446_SSD1331

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Dependencies:   ssd1331

mbed-os/features/lwipstack/lwip/doc/mdns.txt@3:f3764f852aa8, 2018-10-11 (annotated)

Committer:
kadonotakashi
Date:
Thu Oct 11 02:27:46 2018 +0000
Revision:
3:f3764f852aa8
Parent:
0:8fdf9a60065b 
Nucreo 446 + SSD1331 test version;

Who changed what in which revision?

UserRevisionLine numberNew contents of line
kadonotakashi 0:8fdf9a60065b 1 Multicast DNS for lwIP
kadonotakashi 0:8fdf9a60065b 2
kadonotakashi 0:8fdf9a60065b 3 Author: Erik Ekman
kadonotakashi 0:8fdf9a60065b 4
kadonotakashi 0:8fdf9a60065b 5
kadonotakashi 0:8fdf9a60065b 6 Note! The MDNS responder does not have all features required by the standards.
kadonotakashi 0:8fdf9a60065b 7 See notes in src/apps/mdns/mdns.c for what is left. It is however usable in normal
kadonotakashi 0:8fdf9a60065b 8 cases - but watch out if many devices on the same network try to use the same
kadonotakashi 0:8fdf9a60065b 9 host/service instance names.
kadonotakashi 0:8fdf9a60065b 10
kadonotakashi 0:8fdf9a60065b 11
kadonotakashi 0:8fdf9a60065b 12 How to enable:
kadonotakashi 0:8fdf9a60065b 13 ==============
kadonotakashi 0:8fdf9a60065b 14
kadonotakashi 0:8fdf9a60065b 15 MDNS support does not depend on DNS.
kadonotakashi 0:8fdf9a60065b 16 MDNS supports using IPv4 only, v6 only, or v4+v6.
kadonotakashi 0:8fdf9a60065b 17
kadonotakashi 0:8fdf9a60065b 18 To enable MDNS responder, set
kadonotakashi 0:8fdf9a60065b 19 LWIP_MDNS_RESPONDER = 1
kadonotakashi 0:8fdf9a60065b 20 in lwipopts.h and add src/apps/mdns/mdns.c to your list of files to build.
kadonotakashi 0:8fdf9a60065b 21
kadonotakashi 0:8fdf9a60065b 22 The max number of services supported per netif is defined by MDNS_MAX_SERVICES,
kadonotakashi 0:8fdf9a60065b 23 default is 1.
kadonotakashi 0:8fdf9a60065b 24
kadonotakashi 0:8fdf9a60065b 25 Increase MEMP_NUM_UDP_PCB by 1. MDNS needs one PCB.
kadonotakashi 0:8fdf9a60065b 26 Increase LWIP_NUM_NETIF_CLIENT_DATA by 1 (MDNS needs one entry on netif).
kadonotakashi 0:8fdf9a60065b 27
kadonotakashi 0:8fdf9a60065b 28 MDNS with IPv4 requires LWIP_IGMP = 1, and preferably LWIP_AUTOIP = 1.
kadonotakashi 0:8fdf9a60065b 29 MDNS with IPv6 requires LWIP_IPV6_MLD = 1, and that a link-local address is
kadonotakashi 0:8fdf9a60065b 30 generated.
kadonotakashi 0:8fdf9a60065b 31
kadonotakashi 0:8fdf9a60065b 32 The MDNS code puts its structs on the stack where suitable to reduce dynamic
kadonotakashi 0:8fdf9a60065b 33 memory allocation. It may use up to 1kB of stack.
kadonotakashi 0:8fdf9a60065b 34
kadonotakashi 0:8fdf9a60065b 35 MDNS needs a strncasecmp() implementation. If you have one, define
kadonotakashi 0:8fdf9a60065b 36 LWIP_MDNS_STRNCASECMP to it. Otherwise the code will provide an implementation
kadonotakashi 0:8fdf9a60065b 37 for you.
kadonotakashi 0:8fdf9a60065b 38
kadonotakashi 0:8fdf9a60065b 39
kadonotakashi 0:8fdf9a60065b 40 How to use:
kadonotakashi 0:8fdf9a60065b 41 ===========
kadonotakashi 0:8fdf9a60065b 42
kadonotakashi 0:8fdf9a60065b 43 Call mdns_resp_init() during system initialization.
kadonotakashi 0:8fdf9a60065b 44 This opens UDP sockets on port 5353 for IPv4 and IPv6.
kadonotakashi 0:8fdf9a60065b 45
kadonotakashi 0:8fdf9a60065b 46
kadonotakashi 0:8fdf9a60065b 47 To start responding on a netif, run
kadonotakashi 0:8fdf9a60065b 48 mdns_resp_add_netif(struct netif *netif, char *hostname, u32_t dns_ttl)
kadonotakashi 0:8fdf9a60065b 49
kadonotakashi 0:8fdf9a60065b 50 The hostname will be copied. If this returns successfully, the netif will join
kadonotakashi 0:8fdf9a60065b 51 the multicast groups and any MDNS/legacy DNS requests sent unicast or multicast
kadonotakashi 0:8fdf9a60065b 52 to port 5353 will be handled:
kadonotakashi 0:8fdf9a60065b 53 - <hostname>.local type A, AAAA or ANY returns relevant IP addresses
kadonotakashi 0:8fdf9a60065b 54 - Reverse lookups (PTR in-addr.arpa, ip6.arpa) of netif addresses
kadonotakashi 0:8fdf9a60065b 55 returns <hostname>.local
kadonotakashi 0:8fdf9a60065b 56 Answers will use the supplied TTL (in seconds)
kadonotakashi 0:8fdf9a60065b 57 MDNS allows UTF-8 names, but it is recommended to stay within ASCII,
kadonotakashi 0:8fdf9a60065b 58 since the default case-insensitive comparison assumes this.
kadonotakashi 0:8fdf9a60065b 59
kadonotakashi 0:8fdf9a60065b 60 It is recommended to call this function after an IPv4 address has been set,
kadonotakashi 0:8fdf9a60065b 61 since there is currently no check if the v4 address is valid.
kadonotakashi 0:8fdf9a60065b 62
kadonotakashi 0:8fdf9a60065b 63 Call mdns_resp_netif_settings_changed() every time the IP address
kadonotakashi 0:8fdf9a60065b 64 on the netif has changed.
kadonotakashi 0:8fdf9a60065b 65
kadonotakashi 0:8fdf9a60065b 66 To stop responding on a netif, run
kadonotakashi 0:8fdf9a60065b 67 mdns_resp_remove_netif(struct netif *netif)
kadonotakashi 0:8fdf9a60065b 68
kadonotakashi 0:8fdf9a60065b 69
kadonotakashi 0:8fdf9a60065b 70 Adding services:
kadonotakashi 0:8fdf9a60065b 71 ================
kadonotakashi 0:8fdf9a60065b 72
kadonotakashi 0:8fdf9a60065b 73 The netif first needs to be registered. Then run
kadonotakashi 0:8fdf9a60065b 74 mdns_resp_add_service(struct netif *netif, char *name, char *service,
kadonotakashi 0:8fdf9a60065b 75 u16_t proto, u16_t port, u32_t dns_ttl,
kadonotakashi 0:8fdf9a60065b 76 service_get_txt_fn_t txt_fn, void *txt_userdata);
kadonotakashi 0:8fdf9a60065b 77
kadonotakashi 0:8fdf9a60065b 78 The name and service pointers will be copied. Name refers to the name of the
kadonotakashi 0:8fdf9a60065b 79 service instance, and service is the type of service, like _http
kadonotakashi 0:8fdf9a60065b 80 proto can be DNSSD_PROTO_UDP or DNSSD_PROTO_TCP which represent _udp and _tcp.
kadonotakashi 0:8fdf9a60065b 81 If this call returns successfully, the following queries will be answered:
kadonotakashi 0:8fdf9a60065b 82 - _services._dns-sd._udp.local type PTR returns <service>.<proto>.local
kadonotakashi 0:8fdf9a60065b 83 - <service>.<proto>.local type PTR returns <name>.<service>.<proto>.local
kadonotakashi 0:8fdf9a60065b 84 - <name>.<service>.<proto>.local type SRV returns hostname and port of service
kadonotakashi 0:8fdf9a60065b 85 - <name>.<service>.<proto>.local type TXT builds text strings by calling txt_fn
kadonotakashi 0:8fdf9a60065b 86 with the supplied userdata. The callback adds strings to the reply by calling
kadonotakashi 0:8fdf9a60065b 87 mdns_resp_add_service_txtitem(struct mdns_service *service, char *txt,
kadonotakashi 0:8fdf9a60065b 88 int txt_len). Example callback method:
kadonotakashi 0:8fdf9a60065b 89
kadonotakashi 0:8fdf9a60065b 90 static void srv_txt(struct mdns_service *service, void *txt_userdata)
kadonotakashi 0:8fdf9a60065b 91 {
kadonotakashi 0:8fdf9a60065b 92 res = mdns_resp_add_service_txtitem(service, "path=/", 6);
kadonotakashi 0:8fdf9a60065b 93 LWIP_ERROR("mdns add service txt failed\n", (res == ERR_OK), return);
kadonotakashi 0:8fdf9a60065b 94 }
kadonotakashi 0:8fdf9a60065b 95
kadonotakashi 0:8fdf9a60065b 96 Since a hostname struct is used for TXT storage each single item can be max
kadonotakashi 0:8fdf9a60065b 97 63 bytes long, and the total max length (including length bytes for each
kadonotakashi 0:8fdf9a60065b 98 item) is 255 bytes.
kadonotakashi 0:8fdf9a60065b 99
kadonotakashi 0:8fdf9a60065b 100 If your device runs a webserver on port 80, an example call might be:
kadonotakashi 0:8fdf9a60065b 101
kadonotakashi 0:8fdf9a60065b 102 mdns_resp_add_service(netif, "myweb", "_http"
kadonotakashi 0:8fdf9a60065b 103 DNSSD_PROTO_TCP, 80, 3600, srv_txt, NULL);
kadonotakashi 0:8fdf9a60065b 104
kadonotakashi 0:8fdf9a60065b 105 which will publish myweb._http._tcp.local for any hosts looking for web servers,
kadonotakashi 0:8fdf9a60065b 106 and point them to <hostname>.local:80
kadonotakashi 0:8fdf9a60065b 107
kadonotakashi 0:8fdf9a60065b 108 Relevant information will be sent as additional records to reduce number of
kadonotakashi 0:8fdf9a60065b 109 requests required from a client.
kadonotakashi 0:8fdf9a60065b 110
kadonotakashi 0:8fdf9a60065b 111 Removing services is currently not supported. Services are removed when the
kadonotakashi 0:8fdf9a60065b 112 netif is removed.
kadonotakashi 0:8fdf9a60065b 113