Add an accessor for context of a fanout channel

Summary: Title

Reviewed By: yfeldblum

Differential Revision: D59761840

fbshipit-source-id: 4de9ce742a215f6d7f5fbf783b3cfa3e8634a956

folly/channels/FanoutChannel-inl.h

@@ -86,6 +86,11 @@ void FanoutChannel<ValueType, ContextType>::close(exception_wrapper ex) && {
   processor_ = nullptr;
 }
 
+template <typename ValueType, typename ContextType>
+ContextType FanoutChannel<ValueType, ContextType>::getContext() const {
+  return processor_->getContext();
+}
+
 namespace detail {
 
 template <typename ValueType, typename ContextType>
@@ -100,6 +105,8 @@ class IFanoutChannelProcessor : public IChannelCallback {
   virtual void closeSubscribers(CloseResult closeResult) = 0;
 
   virtual void destroyHandle(CloseResult closeResult) = 0;
+
+  virtual ContextType getContext() = 0;
 };
 
 /**
@@ -210,6 +217,8 @@ class FanoutChannelProcessor
     return state_.wlock()->fanoutSender.anySubscribers();
   }
 
+  ContextType getContext() { return state_.rlock()->context; }
+
  private:
   /**
    * Called when one of the channels we are listening to has an update (either

folly/channels/FanoutChannel.h

@@ -125,6 +125,11 @@ class FanoutChannel {
    */
   void close(exception_wrapper ex = exception_wrapper()) &&;
 
+  /**
+   * Get the context
+   */
+  ContextType getContext() const;
+
  private:
   TProcessor* processor_;
 };

folly/channels/test/FanoutChannelTest.cpp

@@ -94,6 +94,8 @@ TEST_F(FanoutChannelFixture, ReceiveValue_FanoutBroadcastsValues) {
   sender.write(2);
   executor_.drain();
 
+  EXPECT_EQ(fanoutChannel.getContext().version, 2);
+
   auto [handle3, callback3] = processValues(
       fanoutChannel.subscribe([](const LatestVersion& latestVersion) {
         EXPECT_EQ(latestVersion.numSubscribers, 2);