Add DNS-SD service discovery

build.rs

@@ -51,6 +51,11 @@ fn main() {
         .allowlist_type("ipp_.*")
         .allowlist_var("IPP_.*");
 
+    // Lets wrapper.h include cups/dnssd.h, which only CUPS 3 has.
+    if cups_cfg == "cups3" {
+        builder = builder.clang_arg("-DCUPS_RS_CUPS3");
+    }
+
     for include_path in library.include_paths {
         builder = builder.clang_arg(format!("-I{}", include_path.display()));
     }

examples/discover_system_services.rs

@@ -0,0 +1,53 @@
+// DNS-SD is built on cups/dnssd.h, a CUPS 3-only addition; nothing to run under CUPS 2.
+#[cfg(not(cups3))]
+fn main() {
+    eprintln!("discover_system_services requires CUPS 3; skipping under CUPS 2.");
+}
+
+#[cfg(cups3)]
+use cups_rs::Dnssd;
+#[cfg(cups3)]
+use std::sync::mpsc;
+#[cfg(cups3)]
+use std::time::{Duration, Instant};
+
+#[cfg(cups3)]
+fn main() -> cups_rs::Result<()> {
+    let (error_sender, error_receiver) = mpsc::channel();
+    let (browse_sender, browse_receiver) = mpsc::channel();
+    let dnssd = Dnssd::new(error_sender)?;
+    let _ipp = dnssd.browse("_ipp-system._tcp", None, browse_sender.clone())?;
+    let _ipps = dnssd.browse("_ipps-system._tcp", None, browse_sender)?;
+    let mut resolvers = Vec::new();
+    let deadline = Instant::now() + Duration::from_secs(5);
+
+    while Instant::now() < deadline {
+        while let Ok(service) = browse_receiver.try_recv() {
+            if service.added {
+                resolvers.push(dnssd.resolve_service(&service)?);
+            }
+        }
+        for resolver in &mut resolvers {
+            if let Some(resolved) = resolver.try_recv()? {
+                let service = resolved.service;
+                println!(
+                    "{} {}:{} ({}) addresses={:?}",
+                    service.name,
+                    service.hostname,
+                    service.port,
+                    service.service_type,
+                    resolved.addresses
+                );
+                for (name, value) in service.txt {
+                    println!("  {name}={value}");
+                }
+            }
+        }
+        while let Ok(error) = error_receiver.try_recv() {
+            eprintln!("DNS-SD error: {error}");
+        }
+        std::thread::sleep(Duration::from_millis(20));
+    }
+
+    Ok(())
+}