lwIP 2.1.1 Lightweight IP stack

Modules | Macros | Functions
MDNS
Applications

## Modules
| Options

## Macros
#define | mdns_resp_netif_settings_changed(netif) mdns_resp_announce(netif)

## Functions
err_t | mdns_resp_add_netif (struct netif *netif, const char *hostname, u32_t dns_ttl)
err_t | mdns_resp_remove_netif (struct netif *netif)
err_t | mdns_resp_rename_netif (struct netif *netif, const char *hostname)
s8_t | mdns_resp_add_service (struct netif *netif, const char *name, const char *service, enum mdns_sd_proto proto, u16_t port, u32_t dns_ttl, service_get_txt_fn_t txt_fn, void *txt_data)
err_t | mdns_resp_del_service (struct netif *netif, s8_t slot)
err_t | mdns_resp_rename_service (struct netif *netif, s8_t slot, const char *name)
err_t | mdns_resp_add_service_txtitem (struct mdns_service *service, const char *txt, u8_t txt_len)
void | mdns_resp_announce (struct netif *netif)
void | mdns_resp_restart (struct netif *netif)
void | mdns_resp_init (void)

## Detailed Description

RFC 6762 - Multicast DNS
RFC 6763 - DNS-Based Service Discovery

    Multicast DNS for lwIP

    Author: Erik Ekman

    Note! The MDNS responder does not have all features required by the standards.
    See notes in src/apps/mdns/mdns.c for what is left. It is however usable in normal
    cases - but watch out if many devices on the same network try to use the same
    host/service instance names.

    How to enable:
    ==============

    MDNS support does not depend on DNS.
    MDNS supports using IPv4 only, v6 only, or v4+v6.

    To enable MDNS responder, set
      LWIP_MDNS_RESPONDER = 1
    in lwipopts.h and add src/apps/mdns/mdns.c to your list of files to build.

    The max number of services supported per netif is defined by MDNS_MAX_SERVICES,
    default is 1.

    Increase MEMP_NUM_UDP_PCB by 1. MDNS needs one PCB.
    Increase LWIP_NUM_NETIF_CLIENT_DATA by 1 (MDNS needs one entry on netif).

    MDNS with IPv4 requires LWIP_IGMP = 1, and preferably LWIP_AUTOIP = 1.
    MDNS with IPv6 requires LWIP_IPV6_MLD = 1, and that a link-local address is
    generated.

    The MDNS code puts its structs on the stack where suitable to reduce dynamic
    memory allocation. It may use up to 1kB of stack.

    MDNS (like other apps) needs a strncasecmp() implementation. If you have one, define
    'lwip_strnicmp' to it. Otherwise the code will provide an implementation
    for you.

    How to use:
    ===========

    Call mdns_resp_init() during system initialization.
    This opens UDP sockets on port 5353 for IPv4 and IPv6.

    To start responding on a netif, run
      mdns_resp_add_netif(struct netif *netif, char *hostname, u32_t dns_ttl)

    The hostname will be copied. If this returns successfully, the netif will join
    the multicast groups and any MDNS/legacy DNS requests sent unicast or multicast
    to port 5353 will be handled:
    - <hostname>.local type A, AAAA or ANY returns relevant IP addresses
    - Reverse lookups (PTR in-addr.arpa, ip6.arpa) of netif addresses
      returns <hostname>.local
    Answers will use the supplied TTL (in seconds)
    MDNS allows UTF-8 names, but it is recommended to stay within ASCII,
    since the default case-insensitive comparison assumes this.

    Call mdns_resp_announce() every time the IP address on the netif has changed.

    Call mdns_resp_restart() every time the network interface comes up after being
    down, for example cable connected after being disconnected, administrative
    interface comes up after being down, or the device wakes up from sleep.

    To stop responding on a netif, run
      mdns_resp_remove_netif(struct netif *netif)

    Adding services:
    ================

    The netif first needs to be registered. Then run
      mdns_resp_add_service(struct netif *netif, char *name, char *service,
          u16_t proto, u16_t port, u32_t dns_ttl,
          service_get_txt_fn_t txt_fn, void *txt_userdata);

    The name and service pointers will be copied. Name refers to the name of the
    service instance, and service is the type of service, like _http
    proto can be DNSSD_PROTO_UDP or DNSSD_PROTO_TCP which represent _udp and _tcp.
    If this call returns successfully, the following queries will be answered:
    - _services._dns-sd._udp.local type PTR returns <service>.<proto>.local
    - <service>.<proto>.local type PTR returns <name>.<service>.<proto>.local
    - <name>.<service>.<proto>.local type SRV returns hostname and port of service
    - <name>.<service>.<proto>.local type TXT builds text strings by calling txt_fn
      with the supplied userdata. The callback adds strings to the reply by calling
      mdns_resp_add_service_txtitem(struct mdns_service *service, char *txt,
       int txt_len). Example callback method:

       static void srv_txt(struct mdns_service *service, void *txt_userdata)
       {
         res = mdns_resp_add_service_txtitem(service, "path=/", 6);
         LWIP_ERROR("mdns add service txt failed\n", (res == ERR_OK), return);
       }

      Since a hostname struct is used for TXT storage each single item can be max
      63 bytes long, and  the total max length (including length bytes for each
      item) is 255 bytes.

    If your device runs a webserver on port 80, an example call might be:

      mdns_resp_add_service(netif, "myweb", "_http"
          DNSSD_PROTO_TCP, 80, 3600, srv_txt, NULL);

    which will publish myweb._http._tcp.local for any hosts looking for web servers,
    and point them to <hostname>.local:80

    Relevant information will be sent as additional records to reduce number of
    requests required from a client.

    To remove a service from a netif, run
      mdns_resp_del_service(struct netif *netif, s8_t slot)

## Things left to implement:

- Tiebreaking for simultaneous probing
- Sending goodbye messages (zero ttl) - shutdown, DHCP lease about to expire, DHCP turned off...
- Checking that source address of unicast requests are on the same network
- Limiting multicast responses to 1 per second per resource record
- Fragmenting replies if required
- Handling multi-packet known answers
- Individual known answer detection for all local IPv6 addresses
- Dynamic size of outgoing packet

## Macro Definition Documentation

## ◆ mdns_resp_netif_settings_changed

#define mdns_resp_netif_settings_changed | ( |  | netif | ) | mdns_resp_announce(netif)

Announce IP settings have changed on netif. Call this in your callback registered by netif_set_status_callback(). No need to call this function when LWIP_NETIF_EXT_STATUS_CALLBACK==1, this handled automatically for you.

Parameters

  netif | The network interface where settings have changed.

## Function Documentation

## ◆ mdns_resp_add_netif()

err_t mdns_resp_add_netif | ( | struct netif * | netif,
|  | const char * | hostname,
|  | u32_t | dns_ttl
| ) |  |

Activate MDNS responder for a network interface.

Parameters

  netif | The network interface to activate.
  hostname | Name to use. Queries for <hostname>.local will be answered with the IP addresses of the netif. The hostname will be copied, the given pointer can be on the stack.
  dns_ttl | Validity time in seconds to send out for IP address data in DNS replies

Returns
  ERR_OK if netif was added, an err_t otherwise

## ◆ mdns_resp_add_service()

s8_t mdns_resp_add_service | ( | struct netif * | netif,
|  | const char * | name,
|  | const char * | service,
|  | enum mdns_sd_proto | proto,
|  | u16_t | port,
|  | u32_t | dns_ttl,
|  | service_get_txt_fn_t | txt_fn,
|  | void * | txt_data
| ) |  |

Add a service to the selected network interface.

Parameters

  netif | The network interface to publish this service on
  name | The name of the service
  service | The service type, like "_http"
  proto | The service protocol, DNSSD_PROTO_TCP for TCP ("_tcp") and DNSSD_PROTO_UDP for others ("_udp")
  port | The port the service listens to
  dns_ttl | Validity time in seconds to send out for service data in DNS replies
  txt_fn | Callback to get TXT data. Will be called each time a TXT reply is created to allow dynamic replies.
  txt_data | Userdata pointer for txt_fn

Returns
  service_id if the service was added to the netif, an err_t otherwise

## ◆ mdns_resp_add_service_txtitem()

err_t mdns_resp_add_service_txtitem | ( | struct mdns_service * | service,
|  | const char * | txt,
|  | u8_t | txt_len
| ) |  |

Call this function from inside the service_get_txt_fn_t callback to add text data. Buffer for TXT data is 256 bytes, and each field is prefixed with a length byte.

Parameters

  service | The service provided to the get_txt callback
  txt | String to add to the TXT field.
  txt_len | Length of string

Returns
  ERR_OK if the string was added to the reply, an err_t otherwise

## ◆ mdns_resp_announce()

void mdns_resp_announce | ( | struct netif * | netif | ) |

Send unsolicited answer containing all our known data

Parameters

  netif | The network interface to send on

## ◆ mdns_resp_del_service()

err_t mdns_resp_del_service | ( | struct netif * | netif,
|  | s8_t | slot
| ) |  |

Delete a service on the selected network interface.

Parameters

  netif | The network interface on which service should be removed
  slot | The service slot number returned by mdns_resp_add_service

Returns
  ERR_OK if the service was removed from the netif, an err_t otherwise

## ◆ mdns_resp_init()

void mdns_resp_init | ( | void |  | ) |

Initiate MDNS responder. Will open UDP sockets on port 5353

## ◆ mdns_resp_remove_netif()

err_t mdns_resp_remove_netif | ( | struct netif * | netif | ) |

Stop responding to MDNS queries on this interface, leave multicast groups, and free the helper structure and any of its services.

Parameters

  netif | The network interface to remove.

Returns
  ERR_OK if netif was removed, an err_t otherwise

## ◆ mdns_resp_rename_netif()

err_t mdns_resp_rename_netif | ( | struct netif * | netif,
|  | const char * | hostname
| ) |  |

Update MDNS hostname for a network interface.

Parameters

  netif | The network interface to activate.
  hostname | Name to use. Queries for <hostname>.local will be answered with the IP addresses of the netif. The hostname will be copied, the given pointer can be on the stack.

Returns
  ERR_OK if name could be set on netif, an err_t otherwise

## ◆ mdns_resp_rename_service()

err_t mdns_resp_rename_service | ( | struct netif * | netif,
|  | s8_t | slot,
|  | const char * | name
| ) |  |

Update name for an MDNS service.

Parameters

  netif | The network interface to activate.
  slot | The service slot number returned by mdns_resp_add_service
  name | The new name for the service

Returns
  ERR_OK if name could be set on service, an err_t otherwise

## ◆ mdns_resp_restart()

void mdns_resp_restart | ( | struct netif * | netif | ) |

Restart mdns responder. Call this when cable is connected after being disconnected or administrative interface is set up after being down

Parameters

  netif | The network interface to send on