Support IP lookup for `dnnsd` (Bonjour) services

[kriswuollett]

Functionality for being able to look up the IP address of a service on a dnssd system is needed. The documentation for DNSServiceRegister says that the application is responsible for using DNSServiceRegisterRecord to create an address record, otherwise it won't exist.

I sort of expected that functionality to be optionally automatically chained, because the browser does the same for DNSServiceBrowse, DNSServiceResolve, then the DNSServiceGetAddrInfo callbacks.

Possible solutions

Patching options:

• add DNSServiceRegisterRecord as part of the service registration mechanism
• resolve why the domain when set did not appear in dns-sd -L for the updated example code, perhaps from item above

Other way of structuring API (same for avahi):

• pay the cost of copying the record data and break up the callback chain re-passing some of the raw pointers
• add other missing needed callback wrappers, e.g., DNSServiceRegisterRecord
• use the wrappers to build up things like browse and service

Details

I added some extra command line args to the service example and added more tracing to debug this, e.g., added service-name parameter so I could use myservice in this example, while the other device is a soundbar:

% RUST_LOG=info cargo run --bin zeroconf-service-example -- --service-name myservice  --hostname myservice --domain local
[2024-10-28T12:23:22Z INFO  zeroconf_service_example] Starting loop for: BonjourMdnsService { service: Mutex { data: ManagedDNSServiceRef(0x0), poisoned: false, .. }, kind: "_http._tcp", port: 8080, name: Some("myservice"), domain: Some("local"), host: Some("myservice"), interface_index: 0, txt_record: Some(TxtRecord { data: {"foo": "bar"} }), context: BonjourServiceContext { user_context: Some(Any { .. }) } }
[2024-10-28T12:23:23Z INFO  zeroconf_service_example] Service registered: ServiceRegistration { name: "myservice", service_type: ServiceType { name: "http", protocol: "tcp", sub_types: [] }, domain: "local" }
[2024-10-28T12:23:23Z INFO  zeroconf_service_example] Context: Mutex { data: Context { service_name: "myservice" }, poisoned: false, .. }

% dns-sd -B _http                                               
Browsing for _http._tcp
DATE: ---Mon 28 Oct 2024---
 7:23:37.741  ...STARTING...
Timestamp     A/R    Flags  if Domain               Service Type         Instance Name
 7:23:37.742  Add        3  11 local.               _http._tcp.          9x25 MobileAP MDNS
 7:23:37.742  Add        3   1 local.               _http._tcp.          myservice
 7:23:37.742  Add        2  11 local.               _http._tcp.          myservice

% dns-sd -L "9x25 MobileAP MDNS" _http._tcp. local.
Lookup 9x25 MobileAP MDNS._http._tcp..local.
DATE: ---Mon 28 Oct 2024---
 7:26:19.239  ...STARTING...
 7:26:19.535  9x25\032MobileAP\032MDNS._http._tcp.local. can be reached at Bose-[UUID REDACTED].local.:80 (interface 11)

% dns-sd -Gv4v6 Bose-[UUID REDACTED].local.
DATE: ---Mon 28 Oct 2024---
 7:03:23.276  ...STARTING...
Timestamp     A/R  Flags         IF  Hostname                               Address                                      TTL
 7:26:59.146  Add  40000003      11  Bose-[UUID REDACTED].local. [IPV6 REDACTED]%<0>  120
 7:26:59.146  Add  40000002      11  Bose-[UUID REDACTED].local. [IPV4 REDACTED]                                  120

While curiously the local. part of the domain is left off of zerfoconf-rs service example:

% dns-sd -L myservice _http._tcp. local.   
Lookup myservice._http._tcp..local.
DATE: ---Mon 28 Oct 2024---
 7:28:45.173  ...STARTING...
 7:28:45.174  myservice._http._tcp.local. can be reached at myservice.:8080 (interface 1) Flags: 1
 foo=bar
 7:28:45.174  myservice._http._tcp.local. can be reached at myservice.:8080 (interface 11)
 foo=bar

There is no record for the IP address for myservice:

% dns-sd -Gv4v6 myservice.                                      
DATE: ---Mon 28 Oct 2024---
 7:30:02.258  ...STARTING...
Timestamp     A/R  Flags         IF  Hostname                               Address                                      TTL
 7:30:02.264  Add  2              0  myservice.                             0000:0000:0000:0000:0000:0000:0000:0000%<0>  77   No Such Record
 7:30:02.265  Add  2              0  myservice.                             0.0.0.0                                      77   No Such Record

While dns-sd -L saying myservice had domain local, dns-sd -L said it didn't, so as "expected", dns-sd -Gv4v6 returns not even a null record:

% dns-sd -Gv4v6 myservice.local.
DATE: ---Mon 28 Oct 2024---
 7:30:18.096  ...STARTING...

[kriswuollett]

IPv6 would probably be needed too. The (*address).sin_family is not checked:

zeroconf-rs/zeroconf/src/bonjour/browser.rs

Lines 268 to 284 in 7129d3e

	// on macOS the bytes are swapped for the ip
	#[cfg(target_vendor = "apple")]
	let ip = {
	let address = address as *const sockaddr_in;
	assert_not_null!(address);
	let s_addr = (*address).sin_addr.s_addr.to_le_bytes();
	IpAddr::from(s_addr).to_string()
	};
	#[cfg(target_vendor = "pc")]
	let ip = {
	let address = address as *const sockaddr_in;
	assert_not_null!(address);
	let s_un = (*address).sin_addr.S_un.S_un_b;
	let s_addr = [s_un.s_b1, s_un.s_b2, s_un.s_b3, s_un.s_b4];
	IpAddr::from(s_addr).to_string()
	};

Assumes only one result:

zeroconf-rs/zeroconf/src/bonjour/browser.rs

Lines 246 to 255 in 7129d3e

	unsafe fn handle_get_address_info(
	ctx: &mut BonjourBrowserContext,
	error: DNSServiceErrorType,
	address: *const bonjour_sys::sockaddr,
	hostname: *const c_char,
	) -> Result<()> {
	// this callback runs multiple times for some reason
	if ctx.resolved_name.is_none() {
	return Ok(());
	}

The BonjourBrowserContext does not seem to be forked/branched, so results have possibility of overwriting each other?

When using DNSServiceGetAddrInfo directly from bonjour_sys I get 10 results from my mac due to multiple interfaces and a VPN. The last one of a query does not have the flag kDNSServiceFlagsMoreComing set.