lua-mdns

Multicast DNS (mDNS) service browser implemented in pure Lua. mDNS provides the ability to provide and find DNS names for local devices. For more information on mDNS and DNS Service discovery, see http://www.dns-sd.org.

Installing

Prerequisites

Lua 5.2 or later
LuaSocket 2.1 or later (currently tested on 3.0rc1)

Installation using LuaRocks package manager

$ luarocks make mdns-2.0-1.rockspec

Example Usage

The code below queries all mDNS services available on the local network.

local mdns = require('mdns')

-- DNS service discovery (defaults: all services, 2 seconds timeout)
local res = mdns.query()
if (res) then
    for k,v in pairs(res) do
        -- output key name
        print(k)
        local function print_table(t, indent) 
            for k,v in pairs(t) do
                -- output service descriptor fields
                if (type(v) == 'table') then
                    print(string.rep('  ',indent)..k..':')
                    print_table(v, indent + 1)
                else
                    print(string.rep('  ',indent)..k..': '..v)
                end
            end
        end
        print_table(v, 1)
    end
else
    print('no result')
end

If called without parameters, mdns.query returns all available services after the default timeout of 2 seconds. Additional examples can be found in the examples subdirectory.

Reference

The only exported function is mdns.query.

mdns.query

Usage

result = mdns.query([<service>, [<timeout>]])

Parameters

mdns.query takes up to two parameters:

service: mDNS service name (e.g. _printers._tcp.local). The .local suffix may be omitted. If this parameter is missing or if it evaluates to nil, mdns.query queries all available mDNS services by using enumerating the _services._dns-sd._udp.local service.
timeout: Timeout in seconds waiting for mDNS responses. If this parameter is missing or if it evaluates to nil, mdns.query uses the dafault timeout of 2 seconds.

Return value

If mdns.resolve succeeds, an associateve array of service descriptors is returned as a Lua table. Please note that the array may be empty if there is no mDNS service available on the local network. In case of error, the function either asserts, or it returns nil.

Service descriptors returned by mdns.query may contain a combination of the following fields:

name: mDNS service name (e.g. HP Laserjet 4L @ server.example.com)
service: mDNS service type (e.g. _ipps._tcp.local)
hostname: hostname
port: port number
ipv4: IPv4 address
ipv6: IPv6 address
text: Table of text record(s)

mdns.resolve returns whatever information the mDNS daemons provide. The presence of certain fields doesn't imply that the system running lua-mdns supports all features. For example, an IPv6 address may be returned even though the LuaSocket library installed on the system may not support IPv6. Resolving such potetial mismatches is beyond the scope of lua-mdns.

License

lua-mdns is released under the MIT license.