From 06c068bdfb0bc3c8e11d285b09eda759af17b56d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pablo=20I=C3=B1igo=20Blasco?= <pablo.inigo@ibrobotics.com>
Date: Wed, 6 May 2026 14:02:03 +0200
Subject: [PATCH] feat(pj_datastore): add ObjectStore::findTopic(dataset_id,
 name)
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Add a pure-lookup API to `ObjectStore`:

  std::optional<ObjectTopicId>
  ObjectStore::findTopic(DatasetId, std::string_view) const noexcept;

Returns the existing handle if a topic with the given
`(dataset_id, topic_name)` is registered, `nullopt` otherwise. Does not
mutate the store.

`registerTopic` keeps its strict semantics: it still returns
`unexpected("topic already registered: ...")` when a duplicate is
attempted. Callers that need find-or-register semantics compose the
two explicitly.

Why
---
`OBJECT_STORE_DESIGN.md` documents that DataSource plugins register
object topics on the source-side path (`pj.source_object_write.v1`),
and host-side runtime code resolves an existing id when binding parser-
side write surfaces (`pj.parser_object_write.v1`) — i.e. the source
owns registration; the host looks up.

Without a lookup-only API the host had to call `registerTopic` from its
parser-binding flow. When a source had already registered the same
topic via its own service, the second caller failed with
`"topic already registered: ..."`, the source-side `pushLazy` path went
silently unwired, and blob channels lost retention.

`findTopic` lets the host honour the documented contract: bind to an
existing id without creating one.

Tests
-----
- `FindTopicReturnsRegisteredId` — happy path lookup after register.
- `FindTopicMissingReturnsNullopt` — explicit miss returns nullopt.
- `DuplicateRegistrationFails` (existing) is left untouched —
  `registerTopic`'s strict contract is preserved.
---
 .../include/pj_datastore/object_store.hpp         |  6 ++++++
 pj_datastore/src/object_store.cpp                 | 11 +++++++++++
 pj_datastore/tests/object_store_test.cpp          | 15 +++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/pj_datastore/include/pj_datastore/object_store.hpp b/pj_datastore/include/pj_datastore/object_store.hpp
index 37e4507..9dca500 100644
--- a/pj_datastore/include/pj_datastore/object_store.hpp
+++ b/pj_datastore/include/pj_datastore/object_store.hpp
@@ -9,6 +9,7 @@
 #include <optional>
 #include <shared_mutex>
 #include <string>
+#include <string_view>
 #include <utility>
 #include <variant>
 #include <vector>
@@ -91,6 +92,11 @@ class ObjectStore {
 
   Expected<ObjectTopicId> registerTopic(const ObjectTopicDescriptor& descriptor);
 
+  // Resolve a topic id by (dataset_id, topic_name) without registering. Returns
+  // nullopt if no topic with that key exists. Used by hosts that need to bind a
+  // parser-side write surface to a topic the source already registered.
+  std::optional<ObjectTopicId> findTopic(DatasetId dataset_id, std::string_view topic_name) const;
+
   const ObjectTopicDescriptor& descriptor(ObjectTopicId id) const;
 
   std::vector<ObjectTopicId> listTopics() const;
diff --git a/pj_datastore/src/object_store.cpp b/pj_datastore/src/object_store.cpp
index 60a8f13..e53f85c 100644
--- a/pj_datastore/src/object_store.cpp
+++ b/pj_datastore/src/object_store.cpp
@@ -21,6 +21,17 @@ Expected<ObjectTopicId> ObjectStore::registerTopic(const ObjectTopicDescriptor&
   return id;
 }
 
+std::optional<ObjectTopicId> ObjectStore::findTopic(
+    DatasetId dataset_id, std::string_view topic_name) const {
+  std::shared_lock lock(store_mutex_);
+  for (const auto& [tid, series] : topics_) {
+    if (series->descriptor.dataset_id == dataset_id && series->descriptor.topic_name == topic_name) {
+      return tid;
+    }
+  }
+  return std::nullopt;
+}
+
 const ObjectTopicDescriptor& ObjectStore::descriptor(ObjectTopicId id) const {
   std::shared_lock lock(store_mutex_);
   const auto* s = findSeries(id);
diff --git a/pj_datastore/tests/object_store_test.cpp b/pj_datastore/tests/object_store_test.cpp
index f2f4492..65dddc6 100644
--- a/pj_datastore/tests/object_store_test.cpp
+++ b/pj_datastore/tests/object_store_test.cpp
@@ -48,6 +48,21 @@ TEST(ObjectStoreTest, SameNameDifferentDatasetOk) {
   EXPECT_NE(id1.id, id2_or->id);
 }
 
+TEST(ObjectStoreTest, FindTopicReturnsRegisteredId) {
+  ObjectStore store;
+  auto id = registerTestTopic(store, "cam/image");
+  auto found = store.findTopic(1, "cam/image");
+  ASSERT_TRUE(found.has_value());
+  EXPECT_EQ(found->id, id.id);
+}
+
+TEST(ObjectStoreTest, FindTopicMissingReturnsNullopt) {
+  ObjectStore store;
+  registerTestTopic(store, "cam/image");
+  EXPECT_FALSE(store.findTopic(1, "other/topic").has_value());
+  EXPECT_FALSE(store.findTopic(99, "cam/image").has_value());
+}
+
 TEST(ObjectStoreTest, ListTopics) {
   ObjectStore store;
   auto id1 = registerTestTopic(store, "topic_a");