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