From 9c6f14583169100b7cd70346c7dc3d13d82806aa Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Sat, 25 Jul 2026 11:25:59 +0200
Subject: kapi: implement interface registry notifications

---
 kernel/kapi/devices/interface_registry.tests.cpp | 131 ++++++++++++++++++++++-
 1 file changed, 127 insertions(+), 4 deletions(-)

(limited to 'kernel/kapi/devices/interface_registry.tests.cpp')

diff --git a/kernel/kapi/devices/interface_registry.tests.cpp b/kernel/kapi/devices/interface_registry.tests.cpp
index 4d2e2097..071b9a6d 100644
--- a/kernel/kapi/devices/interface_registry.tests.cpp
+++ b/kernel/kapi/devices/interface_registry.tests.cpp
@@ -4,6 +4,8 @@
 
 #include <catch2/catch_test_macros.hpp>
 
+#include <cstddef>
+
 namespace
 {
   struct probe_device
@@ -66,6 +68,44 @@ namespace
     const_device * m_const_device;
   };
 
+  struct counting_observer final : kapi::devices::interface_registry_observer
+  {
+    auto on_interface_published(kapi::devices::interface_id, kapi::devices::interface_registry::entry const &)
+        -> void override
+    {
+      ++published;
+    }
+
+    auto on_interface_withdrawn(kapi::devices::interface_id, kapi::devices::device &) -> void override
+    {
+      ++withdrawn;
+    }
+
+    std::size_t published{};
+    std::size_t withdrawn{};
+  };
+
+  struct evil_observer final : kapi::devices::interface_registry_observer
+  {
+    explicit evil_observer(kstd::shared_ptr<counting_observer> & victim)
+        : m_victim{victim}
+    {}
+
+    auto on_interface_published(kapi::devices::interface_id, kapi::devices::interface_registry::entry const &)
+        -> void override
+    {
+      m_victim.reset();
+    }
+
+    auto on_interface_withdrawn(kapi::devices::interface_id, kapi::devices::device &) -> void override
+    {
+      m_victim.reset();
+    }
+
+  private:
+    kstd::shared_ptr<counting_observer> & m_victim;  // NOLINT
+  };
+
 }  // namespace
 
 SCENARIO("Publishing and finding a device", "[kapi][devices][interface_registry]")
@@ -138,7 +178,7 @@ SCENARIO("Publishing and finding a device", "[kapi][devices][interface_registry]
         }
       }
 
-      THEN("find finds the published capability by name")
+      THEN("resolve finds the published capability by name")
       {
         REQUIRE(registry.resolve<probe_device>("probe0"));
       }
@@ -153,14 +193,14 @@ SCENARIO("Publishing and finding a device", "[kapi][devices][interface_registry]
         REQUIRE_FALSE(registry.resolve<unimplemented_device>("probe0"));
       }
 
-      THEN("find for an unpublished device does not find a device")
+      THEN("resolve for an unpublished device does not find a device")
       {
         REQUIRE_FALSE(registry.resolve<probe_device>("probe1"));
       }
 
       THEN("withdrawing an interface for a device removes it from the registry")
       {
-        registry.unpublish(*device, probe_device::id);
+        registry.withdraw(*device, probe_device::id);
         REQUIRE_FALSE(registry.resolve<probe_device>("probe0"));
       }
     }
@@ -175,7 +215,7 @@ SCENARIO("Publishing and finding a device", "[kapi][devices][interface_registry]
         REQUIRE(registry.all(probe_device::id).empty());
       }
 
-      THEN("find() no longer finds it")
+      THEN("resolve() no longer finds it")
       {
         REQUIRE_FALSE(registry.resolve<probe_device>("probe0"));
       }
@@ -204,3 +244,86 @@ SCENARIO("Publishing and finding a device", "[kapi][devices][interface_registry]
     }
   }
 }
+
+SCENARIO("Interface registry notifies subscribers", "[kapi][devices][interface_registry]")
+{
+  GIVEN("a device and a subscribed observer")
+  {
+    auto registry = kapi::devices::interface_registry{};
+    auto free_standing_interface = const_device{};
+    auto device = kstd::make_shared<test_device>(128, free_standing_interface);
+    auto observer = kstd::make_shared<counting_observer>();
+
+    registry.subscribe(observer);
+
+    WHEN("an interface is published for the device")
+    {
+      CHECK(registry.publish(device, "probe0", device->as<probe_device>()));
+
+      THEN("the observer is notified exactly once")
+      {
+        REQUIRE(observer->published == 1);
+        REQUIRE(observer->withdrawn == 0);
+      }
+    }
+
+    WHEN("an interface is published and then withdrawn")
+    {
+      CHECK(registry.publish(device, "probe0", device->as<probe_device>()));
+      registry.withdraw(*device, probe_device::id);
+
+      THEN("the observer is notified of both exactly one")
+      {
+        REQUIRE(observer->published == 1);
+        REQUIRE(observer->withdrawn == 1);
+      }
+    }
+
+    WHEN("the observer is destroyed before anything is published")
+    {
+      observer.reset();
+
+      THEN("publishing afterward does not crash")
+      {
+        REQUIRE_NOTHROW(registry.publish(device, "probe0", device->as<probe_device>()));
+      }
+    }
+
+    WHEN("the observer unsubscribes before anything is published")
+    {
+      registry.unsubscribe(*observer);
+
+      THEN("publishing afterward does not crash")
+      {
+        REQUIRE_NOTHROW(registry.publish(device, "probe0", device->as<probe_device>()));
+      }
+
+      THEN("the subscriber is not notified")
+      {
+        REQUIRE_NOTHROW(registry.publish(device, "probe0", device->as<probe_device>()));
+        REQUIRE_NOTHROW(registry.withdraw(*device, probe_device::id));
+        REQUIRE(observer->published == 0);
+        REQUIRE(observer->withdrawn == 0);
+      }
+    }
+  }
+
+  GIVEN("two subscriber, the first destroying the second")
+  {
+    auto registry = kapi::devices::interface_registry{};
+    auto free_standing_interface = const_device{};
+    auto device = kstd::make_shared<test_device>(128, free_standing_interface);
+
+    auto second = kstd::make_shared<counting_observer>();
+    auto first = kstd::make_shared<evil_observer>(second);
+
+    registry.subscribe(first);
+    registry.subscribe(second);
+
+    THEN("publishing an interface does not crash")
+    {
+      REQUIRE_NOTHROW(registry.publish(device, "probe0", device->as<probe_device>()));
+      REQUIRE(second == nullptr);
+    }
+  }
+}
\ No newline at end of file
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