Maintain outgoing bytes queued count

design.md

@@ -395,7 +395,7 @@ public:
     proto_data->process(data);
   }
 
-  void on_post_batch(std::span<std::unique_ptr<Connection>> batch) override {
+  void on_batch_complete(std::span<std::unique_ptr<Connection>> batch) override {
     // Process a batch of connections
     for (auto& conn_ptr : batch) {
       if (conn_ptr) {

src/commit_request_parser.hpp

@@ -18,7 +18,7 @@ public:
   /**
    * @brief Status returned by streaming parse operations.
    */
-  enum class ParseStatus {
+  enum class [[nodiscard]] ParseStatus {
     Incomplete, ///< Parser needs more data to complete parsing
     Complete,   ///< Successfully parsed a complete commit request
     Error       ///< Parse error occurred (check get_parse_error() for details)
@@ -27,7 +27,7 @@ public:
   /**
    * @brief Result type for one-shot parsing operations.
    */
-  enum class ParseResult {
+  enum class [[nodiscard]] ParseResult {
     Success,      ///< Parsing completed successfully
     InvalidJson,  ///< Invalid JSON format or structure
     MissingField, ///< Required field missing from input

src/connection.cpp

@@ -43,6 +43,7 @@ void Connection::appendMessage(std::string_view s, bool copy_to_arena) {
   } else {
     messages_.push_back(s);
   }
+  outgoing_bytes_queued_ += s.size();
 }
 
 int Connection::readBytes(char *buf, size_t buffer_size) {
@@ -104,6 +105,7 @@ bool Connection::writeBytes() {
 
     // Handle partial writes by updating string_view data/size
     size_t bytes_written = static_cast<size_t>(w);
+    outgoing_bytes_queued_ -= bytes_written;
     while (bytes_written > 0 && !messages_.empty()) {
       auto &front = messages_.front();
 

src/connection.hpp

@@ -178,7 +178,7 @@ struct Connection {
   /**
    * @brief Get the number of bytes queued for transmission.
    *
-   * Calculates and returns the total number of bytes in all messages currently
+   * Returns the total number of bytes in all messages currently
    * queued for transmission to the client. This includes all data added via
    * appendMessage() that has not yet been sent over the network.
    *
@@ -187,8 +187,8 @@ struct Connection {
    * @warning Thread Safety: Only call from the thread that currently owns this
    * connection. Concurrent access to the message queue is not thread-safe.
    *
-   * @note Performance: This method iterates through all queued messages to
-   * calculate the total, so avoid calling it frequently in hot paths.
+   * @note Performance: This method uses an O(1) counter for fast retrieval
+   * in release builds. In debug builds, validates counter accuracy.
    *
    * @note The count decreases as the server sends data via writeBytes() and
    * removes completed messages from the queue.
@@ -210,11 +210,17 @@ struct Connection {
    * ```
    */
   int64_t outgoingBytesQueued() const {
-    int64_t result = 0;
+#ifndef NDEBUG
+    // Debug build: validate counter accuracy
+    int64_t computed_total = 0;
     for (auto s : messages_) {
-      result += s.size();
+      computed_total += s.size();
     }
-    return result;
+    assert(
+        outgoing_bytes_queued_ == computed_total &&
+        "outgoing_bytes_queued_ counter is out of sync with actual queue size");
+#endif
+    return outgoing_bytes_queued_;
   }
 
   /**
@@ -282,6 +288,7 @@ struct Connection {
    */
   void reset() {
     assert(messages_.empty());
+    outgoing_bytes_queued_ = 0;
     arena_.reset();
     messages_ =
         std::deque<std::string_view, ArenaStlAllocator<std::string_view>>{
@@ -345,6 +352,9 @@ private:
   std::deque<std::string_view, ArenaStlAllocator<std::string_view>> messages_{
       ArenaStlAllocator<std::string_view>{&arena_}};
 
+  // Counter tracking total bytes queued for transmission
+  int64_t outgoing_bytes_queued_{0};
+
   // Whether or not to close the connection after completing writing the
   // response
   bool closeConnection_{false};

src/connection_handler.hpp

@@ -107,6 +107,6 @@ public:
    *
    * @param batch A span of unique_ptrs to the connections in the batch.
    */
-  virtual void on_post_batch(std::span<std::unique_ptr<Connection>> /*batch*/) {
-  }
+  virtual void
+  on_batch_complete(std::span<std::unique_ptr<Connection>> /*batch*/) {}
 };

src/http_handler.cpp

@@ -50,7 +50,8 @@ void HttpHandler::on_write_buffer_drained(
   on_connection_established(*conn_ptr);
 }
 
-void HttpHandler::on_post_batch(std::span<std::unique_ptr<Connection>> batch) {
+void HttpHandler::on_batch_complete(
+    std::span<std::unique_ptr<Connection>> batch) {
   int readyCount = 0;
   for (int i = 0; i < int(batch.size()); ++i) {
     readyCount += batch[i] && batch[i]->outgoingBytesQueued() > 0;

src/http_handler.hpp

@@ -103,7 +103,8 @@ struct HttpHandler : ConnectionHandler {
   void on_data_arrived(std::string_view data,
                        std::unique_ptr<Connection> &conn_ptr) override;
   void on_write_buffer_drained(std::unique_ptr<Connection> &conn_ptr) override;
-  void on_post_batch(std::span<std::unique_ptr<Connection>> /*batch*/) override;
+  void on_batch_complete(
+      std::span<std::unique_ptr<Connection>> /*batch*/) override;
 
   // Route parsing (public for testing)
   static HttpRoute parseRoute(std::string_view method, std::string_view url);

src/server.cpp

@@ -535,8 +535,8 @@ void Server::process_connection_batch(
     }
   }
 
-  // Call post-batch handler - handlers can take ownership here
-  handler_.on_post_batch(batch);
+  // Call batch complete handler - handlers can take ownership here
+  handler_.on_batch_complete(batch);
 
   // Transfer all remaining connections back to epoll
   for (auto &conn_ptr : batch) {

style.md

@@ -344,9 +344,10 @@ arena_allocator.reset();  // Reset arena memory
 - **Error messages are human-readable only** - never parse message strings
 - **Consistent error boundaries** - each component defines what it can/cannot recover from
 - **Interface precondition violations are undefined behavior** - acceptable to skip checks for performance in hot paths
+- **Error code types must be nodiscard** - mark error code enums with `[[nodiscard]]` to prevent silent failures
 
 ```cpp
-enum class ParseResult { Success, InvalidJson, MissingField };
+enum class [[nodiscard]] ParseResult { Success, InvalidJson, MissingField };
 
 // System failure - abort immediately
 void* memory = std::malloc(size);