discovery: don't panic on libmdns errors (#1427)

On panic, the discovery task crashes, but the main program is not
notified of this. Returning an error will result in the Discovery stream
yielding None, serving as notification to the application (which might
shutdown with error, for example, if no other means of authentication is
available).

CHANGELOG.md

@@ -29,7 +29,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   on Android platform.
 - [core] Fix "Invalid Credentials" when using a Keymaster access token and
   client ID on Android platform.
-= [connect] Fix "play" command not handled if missing "offset" property
+- [connect] Fix "play" command not handled if missing "offset" property
+- [discovery] Fix libmdns zerconf setup errors not propagating to the main task.
 
 ### Removed
 

discovery/src/lib.rs

@@ -396,17 +396,17 @@ fn launch_libmdns(
 
     let task_handle = tokio::task::spawn_blocking(move || {
         let inner = move || -> Result<(), DiscoveryError> {
-            let svc = if !zeroconf_ip.is_empty() {
+            let responder = if !zeroconf_ip.is_empty() {
                 libmdns::Responder::spawn_with_ip_list(
                     &tokio::runtime::Handle::current(),
                     zeroconf_ip,
                 )
             } else {
                 libmdns::Responder::spawn(&tokio::runtime::Handle::current())
             }
-            .map_err(|e| DiscoveryError::DnsSdError(Box::new(e)))
-            .unwrap()
-            .register(
+            .map_err(|e| DiscoveryError::DnsSdError(Box::new(e)))?;
+
+            let svc = responder.register(
                 DNS_SD_SERVICE_NAME.to_owned(),
                 name.into_owned(),
                 port,