[ntcore] Add API to get and set user data on NT_Topic (#8962)

Theres many uses where we need to attach data to a topic, and doing it
this way can make it really easy and efficient.

ntcore/src/main/native/cpp/LocalStorage.hpp

@@ -106,6 +106,22 @@ class LocalStorage final : public net::ILocalStorage {
     }
   }
 
+  void* GetTopicUserData(NT_Topic topicHandle) {
+    std::scoped_lock lock{m_mutex};
+    if (auto topic = m_impl.GetTopicByHandle(topicHandle)) {
+      return topic->userData;
+    } else {
+      return nullptr;
+    }
+  }
+
+  void SetTopicUserData(NT_Topic topicHandle, void* userData) {
+    std::scoped_lock lock{m_mutex};
+    if (auto topic = m_impl.GetTopicByHandle(topicHandle)) {
+      topic->userData = userData;
+    }
+  }
+
   NT_Type GetTopicType(NT_Topic topicHandle) {
     std::scoped_lock lock{m_mutex};
     if (auto topic = m_impl.GetTopicByHandle(topicHandle)) {

ntcore/src/main/native/cpp/local/LocalTopic.hpp

@@ -100,6 +100,8 @@ struct LocalTopic {
   VectorSet<LocalEntry*> entries;
   VectorSet<NT_Listener> listeners;
 
+  void* userData{nullptr};
+
  private:
   // update flags from properties
   void RefreshFlags();

ntcore/src/main/native/cpp/ntcore_c.cpp

@@ -274,6 +274,14 @@ void NT_GetTopicName(NT_Topic topic, struct WPI_String* name) {
   wpi::nt::ConvertToC(wpi::nt::GetTopicName(topic), name);
 }
 
+void* NT_GetTopicUserData(NT_Topic topic) {
+  return wpi::nt::GetTopicUserData(topic);
+}
+
+void NT_SetTopicUserData(NT_Topic topic, void* userData) {
+  wpi::nt::SetTopicUserData(topic, userData);
+}
+
 NT_Type NT_GetTopicType(NT_Topic topic) {
   return wpi::nt::GetTopicType(topic);
 }

ntcore/src/main/native/cpp/ntcore_cpp.cpp

@@ -217,6 +217,19 @@ std::string GetTopicName(NT_Topic topic) {
     return {};
   }
 }
+void* GetTopicUserData(NT_Topic topic) {
+  if (auto ii = InstanceImpl::GetTyped(topic, Handle::TOPIC)) {
+    return ii->localStorage.GetTopicUserData(topic);
+  } else {
+    return nullptr;
+  }
+}
+
+void SetTopicUserData(NT_Topic topic, void* userData) {
+  if (auto ii = InstanceImpl::GetTyped(topic, Handle::TOPIC)) {
+    ii->localStorage.SetTopicUserData(topic, userData);
+  }
+}
 
 NT_Type GetTopicType(NT_Topic topic) {
   if (auto ii = InstanceImpl::GetTyped(topic, Handle::TOPIC)) {

ntcore/src/main/native/include/wpi/nt/Topic.hpp

@@ -60,6 +60,23 @@ class Topic {
    */
   std::string GetName() const { return ::wpi::nt::GetTopicName(m_handle); }
 
+  /**
+   * Gets the user data associated with the topic.
+   *
+   * @return User data pointer, or nullptr if no user data is associated.
+   */
+  void* GetUserData() const { return ::wpi::nt::GetTopicUserData(m_handle); }
+
+  /**
+   * Sets the user data associated with the topic. User data is not used by
+   * ntcore and is for the user's convenience. It is not automatically freed.
+   *
+   * @param userData User data pointer to associate with the topic.
+   */
+  void SetUserData(void* userData) {
+    ::wpi::nt::SetTopicUserData(m_handle, userData);
+  }
+
   /**
    * Gets the type of the topic.
    *

ntcore/src/main/native/include/wpi/nt/ntcore_c.h

@@ -654,6 +654,25 @@ NT_Topic NT_GetTopic(NT_Inst inst, const struct WPI_String* name);
  */
 void NT_GetTopicName(NT_Topic topic, struct WPI_String* name);
 
+/**
+ * Gets the user data pointer for the specified topic.
+ * Returns nullptr if the handle is invalid or no user data is associated.
+ * The user data pointer is not used by ntcore and is for the caller's use.
+ *
+ * @param topic     topic handle
+ * @return User data pointer
+ */
+void* NT_GetTopicUserData(NT_Topic topic);
+
+/**
+ * Sets the user data pointer for the specified topic.  The user data pointer
+ * is not used by ntcore and is for the caller's use.
+ *
+ * @param topic     topic handle
+ * @param userData  user data pointer to associate with the topic
+ */
+void NT_SetTopicUserData(NT_Topic topic, void* userData);
+
 /**
  * Gets the type for the specified topic, or unassigned if non existent.
  *

ntcore/src/main/native/include/wpi/nt/ntcore_cpp.hpp

@@ -647,6 +647,28 @@ NT_Topic GetTopic(NT_Inst inst, std::string_view name);
  */
 std::string GetTopicName(NT_Topic topic);
 
+/**
+ * Gets the user data associated with the specified topic.
+ * Returns nullptr if the handle is invalid or no user data is associated.
+ * User data is not used by ntcore and is for the user's convenience.  It is not
+ * inherited by subscribers/publishers of the topic, and is not automatically
+ * freed.
+ *
+ * @param topic   topic handle
+ * @return User data pointer
+ */
+void* GetTopicUserData(NT_Topic topic);
+
+/**
+ * Sets the user data associated with the specified topic.  User data is not
+ * used by ntcore and is for the user's convenience.  It is not inherited by
+ * subscribers/publishers of the topic, and is not automatically freed.
+ *
+ * @param topic   topic handle
+ * @param userData User data pointer to associate with the topic
+ */
+void SetTopicUserData(NT_Topic topic, void* userData);
+
 /**
  * Gets the type for the specified topic, or unassigned if non existent.
  *

ntcore/src/main/python/semiwrap/Topic.yml

@@ -15,6 +15,10 @@ classes:
         ignore: true
       GetInstance:
       GetName:
+      GetUserData:
+        ignore: true
+      SetUserData:
+        ignore: true
       GetType:
       GetTypeString:
       SetPersistent:

ntcore/src/test/native/cpp/TopicTest.cpp

@@ -0,0 +1,60 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include "wpi/nt/Topic.hpp"
+
+#include <gtest/gtest.h>
+
+#include "wpi/nt/NetworkTableInstance.hpp"
+
+class TopicTest : public ::testing::Test {
+ public:
+  TopicTest() : m_inst{wpi::nt::NetworkTableInstance::Create()} {}
+  ~TopicTest() override { wpi::nt::NetworkTableInstance::Destroy(m_inst); }
+
+ protected:
+  wpi::nt::NetworkTableInstance m_inst;
+};
+
+TEST_F(TopicTest, UserDataDefaultsToNull) {
+  auto topic = m_inst.GetTopic("foo");
+
+  EXPECT_EQ(nullptr, topic.GetUserData());
+}
+
+TEST_F(TopicTest, UserDataRoundTrip) {
+  auto topic = m_inst.GetTopic("foo");
+  int data = 5;
+
+  topic.SetUserData(&data);
+
+  EXPECT_EQ(&data, topic.GetUserData());
+}
+
+TEST_F(TopicTest, UserDataCanBeReplacedAndCleared) {
+  auto topic = m_inst.GetTopic("foo");
+  auto sameTopic = m_inst.GetTopic("foo");
+  int data1 = 5;
+  int data2 = 10;
+
+  topic.SetUserData(&data1);
+  EXPECT_EQ(&data1, sameTopic.GetUserData());
+
+  sameTopic.SetUserData(&data2);
+  EXPECT_EQ(&data2, topic.GetUserData());
+
+  topic.SetUserData(nullptr);
+  EXPECT_EQ(nullptr, sameTopic.GetUserData());
+}
+
+TEST_F(TopicTest, UserDataInvalidTopic) {
+  wpi::nt::Topic topic;
+  int data = 5;
+
+  EXPECT_EQ(nullptr, topic.GetUserData());
+
+  topic.SetUserData(&data);
+
+  EXPECT_EQ(nullptr, topic.GetUserData());
+}