From dfb592e256b5121ec897e1516ccaf3b87c5d0de5 Mon Sep 17 00:00:00 2001
From: Paulus Schoutsen <balloob@gmail.com>
Date: Wed, 21 Oct 2026 18:04:22 -0400
Subject: [PATCH 1/2] Report every browsed instance on macOS

The dns_sd backend reported an instance from its address callback only
when kDNSServiceFlagsMoreComing was clear. All operations share one
connection, and on a shared connection that flag covers the replies of
every operation. So when an instance's last address came with the flag
set, and another operation's reply ended the batch, the instance was
never reported and the server never dialed it. On a network with five
`_sendspin._tcp` speakers, the server reported three on every start.

The address callback now marks the instance as updated. The run loop
reports the updated instances after it handles a reply and no other
reply is left to read on the connection.

The host tests never use the system's mDNS, so they cannot reach this
backend. Checked against the five speakers: all five are reported on
each of three starts.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 src/discovery/dns_sd_discovery.cpp | 36 +++++++++++++++++++++++-------
 1 file changed, 28 insertions(+), 8 deletions(-)

diff --git a/src/discovery/dns_sd_discovery.cpp b/src/discovery/dns_sd_discovery.cpp
index cedd643..0ebf1b5 100644
--- a/src/discovery/dns_sd_discovery.cpp
+++ b/src/discovery/dns_sd_discovery.cpp
@@ -200,6 +200,7 @@ class DnsSdDiscovery final : public DiscoveryProvider {
             }
         }
         this->instances_.clear();
+        this->updated_.clear();
     }
 
     void run() {
@@ -241,12 +242,15 @@ class DnsSdDiscovery final : public DiscoveryProvider {
             }
             // The socket is invalid or mDNSResponder went away (kDNSServiceErr_ServiceNotRunning):
             // connect again
-            if (count == 2 && fds[1].revents != 0 &&
-                ((fds[1].revents & POLLNVAL) != 0 ||
-                 DNSServiceProcessResult(this->connection_) != kDNSServiceErr_NoError)) {
-                this->disconnect();
-                reported_unavailable = true;
-                this->sink_->on_unavailable();
+            if (count == 2 && fds[1].revents != 0) {
+                if ((fds[1].revents & POLLNVAL) != 0 ||
+                    DNSServiceProcessResult(this->connection_) != kDNSServiceErr_NoError) {
+                    this->disconnect();
+                    reported_unavailable = true;
+                    this->sink_->on_unavailable();
+                } else {
+                    this->report_updated();
+                }
             }
         }
     }
@@ -269,6 +273,7 @@ class DnsSdDiscovery final : public DiscoveryProvider {
             this->connection_ = nullptr;
         }
         this->instances_.clear();
+        this->updated_.clear();
         for (int& fd : this->wake_) {
             if (fd >= 0) {
                 close(fd);
@@ -336,6 +341,7 @@ class DnsSdDiscovery final : public DiscoveryProvider {
         }
         const bool reported = instance.reported;
         const std::string lost = instance.name;
+        this->updated_.erase(&instance);
         stop_operation(instance.resolve);
         stop_operation(instance.lookup);
         this->instances_.erase(it);
@@ -398,9 +404,21 @@ class DnsSdDiscovery final : public DiscoveryProvider {
                 addresses.erase(it);
             }
         }
-        if ((flags & kDNSServiceFlagsMoreComing) == 0) {
-            instance->owner->report(*instance);
+        instance->owner->updated_.insert(instance);
+    }
+
+    /// Reports the instances whose addresses changed once no reply is left to read. On the
+    /// shared connection kDNSServiceFlagsMoreComing covers every operation's replies, so an
+    /// instance's last address can come with it set and another operation's reply end the batch.
+    void report_updated() {
+        pollfd fd{DNSServiceRefSockFD(this->connection_), POLLIN, 0};
+        if (poll(&fd, 1, 0) != 0) {
+            return;
+        }
+        for (Instance* instance : this->updated_) {
+            this->report(*instance);
         }
+        this->updated_.clear();
     }
 
     /// Reports instance once it has a path and an address: IPv4 first, then IPv6, link-local
@@ -436,6 +454,8 @@ class DnsSdDiscovery final : public DiscoveryProvider {
     /// Set by stop() before it writes to the wake pipe
     std::atomic<bool> stopping_{false};
     std::map<std::string, std::unique_ptr<Instance>> instances_;
+    /// Instances whose addresses changed since report_updated() last reported
+    std::set<Instance*> updated_;
     std::thread thread_;
 };
 

From f2b533a69ec8153b29ba76c5ee78e5d7e2b22d0d Mon Sep 17 00:00:00 2001
From: Kevin Ahrendt <kahrendt@gmail.com>
Date: Wed, 28 Oct 2026 07:53:58 -0400
Subject: [PATCH 2/2] Report updated instances when the check for pending
 replies fails

---
 src/discovery/dns_sd_discovery.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/discovery/dns_sd_discovery.cpp b/src/discovery/dns_sd_discovery.cpp
index 0ebf1b5..8488269 100644
--- a/src/discovery/dns_sd_discovery.cpp
+++ b/src/discovery/dns_sd_discovery.cpp
@@ -412,7 +412,7 @@ class DnsSdDiscovery final : public DiscoveryProvider {
     /// instance's last address can come with it set and another operation's reply end the batch.
     void report_updated() {
         pollfd fd{DNSServiceRefSockFD(this->connection_), POLLIN, 0};
-        if (poll(&fd, 1, 0) != 0) {
+        if (poll(&fd, 1, 0) > 0) {
             return;
         }
         for (Instance* instance : this->updated_) {