WIP

src/connection_handler.hpp

@@ -3,9 +3,22 @@
 #include <span>
 #include <string_view>
 
-// Forward declaration to avoid circular dependency
+// Forward declarations to avoid circular dependency
 struct Connection;
 
+// Include Arena header since PendingResponse uses Arena by value
+#include "arena.hpp"
+
+/**
+ * Represents a response queued by pipeline threads for protocol processing.
+ * Contains JSON response data that can be wrapped by any protocol.
+ */
+struct PendingResponse {
+  void *protocol_context;         // Arena-allocated protocol-specific context
+  std::string_view response_json; // JSON response body (arena-allocated)
+  Arena arena;                    // Arena containing response data and context
+};
+
 /**
  * Abstract interface for handling connection data processing.
  *
@@ -89,4 +102,20 @@ public:
    * @note Called from this connection's io thread.
    */
   virtual void on_batch_complete(std::span<Connection *const> /*batch*/) {}
+
+  /**
+   * Called before processing outgoing writes on a connection.
+   *
+   * This hook allows protocol handlers to process queued responses
+   * before actual socket writes occur. Used for response ordering,
+   * serialization, and other preprocessing.
+   *
+   * @param conn Connection about to write data
+   * @param pending_responses Responses queued by pipeline threads
+   * @note Called from this connection's io thread.
+   * @note Called when EPOLLOUT event occurs
+   */
+  virtual void
+  on_preprocess_writes(Connection &conn,
+                       std::span<PendingResponse> pending_responses) {}
 };