Crate simple_mdns

Simple mDNS

Pure Rust implementation for mDNS and DNS-SD protocols

This crate provides two versions of service discovery, the sync version is located in the module sync_discovery and the async counterpart in async_discovery.

Features

It is necessary to enable at least one of the features to use service discovery

• sync: Provides sync_discovery module
• async-tokio: Provides async_discovery module using tokio runtime

ServiceDiscovery

Advertise registered addresses and query for available instances on the same network.
It is necessary to provide instance and service name

    use simple_mdns::sync_discovery::ServiceDiscovery;
    use simple_mdns::InstanceInformation;
    use std::str::FromStr;

    let mut discovery = ServiceDiscovery::new(
        InstanceInformation::new("a".into()).with_socket_address("192.168.1.22:8090".parse().expect("Invalid socket address")),
        "_mysrv._tcp.local", 
        60
    ).expect("Failed to start service discovery");

    // Removing service from discovery
    discovery.remove_service_from_discovery();

OneShotMdnsResolver (Legacy mDNS)

One shot resolvers are considered legacy and not fully compliant with the mDNS protocol, but they are handy for service discovery if you have (or need) only one service instance

How it works

One shot resolvers or queries send a multicast DNS question to discover available services in the network.

• Only the IP address is necessary (port is fixed or already known), a A or AAAA question is sent.
• IP address and port are necessary, a SRV question is sent.

Since mDNS is a well known protocol, you can register your service in any mDNS responder inside your network, and they should be able to reply the requested information about your service.

Query example:

    use simple_mdns::sync_discovery::OneShotMdnsResolver;
    let resolver = OneShotMdnsResolver::new().expect("Failed to create resolver");
    // querying for IP Address
    let answer = resolver.query_service_address("_myservice._tcp.local").expect("Failed to query service address");
    println!("{:?}", answer);
    // IpV4Addr or IpV6Addr, depending on what was returned
    
    let answer = resolver.query_service_address_and_port("_myservice._tcp.local").expect("Failed to query service address and port");
    println!("{:?}", answer);
    // SocketAddr, "127.0.0.1:8080", with a ipv4 or ipv6

SimpleMdnsResponder

In case you don’t have a mDNS responder in your network, or for some reason don’t want to use the ones available.

This responder will list for any mDNS query in the network via Multicast and will reply only to the resources that were added.

This struct relies on simple-dns crate and the same must be added as a dependency

    use simple_mdns::sync_discovery::SimpleMdnsResponder;
    use simple_dns::{Name, CLASS, ResourceRecord, rdata::{RData, A, SRV}};
    use std::net::Ipv4Addr;


    let mut responder = SimpleMdnsResponder::new(10);
    let srv_name = Name::new_unchecked("_srvname._tcp.local");

    responder.add_resource(ResourceRecord::new(
        srv_name.clone(),
        CLASS::IN,
        10,
        RData::A(A { address: Ipv4Addr::LOCALHOST.into() }),
    ));

    responder.add_resource(ResourceRecord::new(
        srv_name.clone(),
        CLASS::IN,
        10,
        RData::SRV(SRV {
            port: 8080,
            priority: 0,
            weight: 0,
            target: srv_name
        })
    ));

IPV6

IPV6 is now supported by using the NetworkScope enum.

    use simple_mdns::sync_discovery::ServiceDiscovery;
    use simple_mdns::{NetworkScope, InstanceInformation};
    use std::str::FromStr;

    let mut discovery = ServiceDiscovery::new_with_scope(
        InstanceInformation::new("a".into()), 
        "_mysrv._tcp.local", 
        60, 
        None, 
        NetworkScope::V6,
    ).expect(" Service Name");

Note: It is not tested on MacOS.

Modules

• async_discovery
  Contains the async (tokio) version of service discovery
• conversion_utils
  Provides helper functions to convert net addresses to resource records
• sync_discovery
  Contains the sync (blocking) version of service discovery

Structs

• InstanceInformation
  Represents a single instance of the service. Notice that it is not possible to associate a port to a single ip address, due to limitations of the DNS protocol

Enums

• NetworkScope
  Network scope to be used by service discovery Default scope for services is to use IPV4 protocol
• SimpleMdnsError
  Error types for simple-mdns