output/httpd: keep track of queue size

Don't iterate the std::list each time.

src/output/HttpdClient.cxx

@@ -197,6 +197,7 @@ HttpdClient::HttpdClient(HttpdOutput &_httpd, int _fd, EventLoop &_loop,
 	:BufferedSocket(_fd, _loop),
 	 httpd(_httpd),
 	 state(REQUEST),
+	 queue_size(0),
 	 head_method(false),
 	 dlna_streaming_requested(false),
 	 metadata_supported(_metadata_supported),
@@ -207,18 +208,6 @@ HttpdClient::HttpdClient(HttpdOutput &_httpd, int _fd, EventLoop &_loop,
 {
 }
 
-size_t
-HttpdClient::GetQueueSize() const
-{
-	if (state != RESPONSE)
-		return 0;
-
-	size_t size = 0;
-	for (auto page : pages)
-		size += page->size;
-	return size;
-}
-
 void
 HttpdClient::CancelQueue()
 {
@@ -228,6 +217,7 @@ HttpdClient::CancelQueue()
 	for (auto page : pages)
 		page->Unref();
 	pages.clear();
+	queue_size = 0;
 
 	if (current_page == nullptr)
 		CancelWrite();
@@ -278,6 +268,9 @@ HttpdClient::TryWrite()
 		current_page = pages.front();
 		pages.pop_front();
 		current_position = 0;
+
+		assert(queue_size >= current_page->size);
+		queue_size -= current_page->size;
 	}
 
 	const ssize_t bytes_to_write = GetBytesTillMetaData();
@@ -380,6 +373,7 @@ HttpdClient::PushPage(Page *page)
 
 	page->Ref();
 	pages.push_back(page);
+	queue_size += page->size;
 
 	ScheduleWrite();
 }

src/output/HttpdClient.hxx

@@ -55,6 +55,11 @@ class HttpdClient final : BufferedSocket {
 	 */
 	std::list<Page *> pages;
 
+	/**
+	 * The sum of all page sizes in #pages.
+	 */
+	size_t queue_size;
+
 	/**
 	 * The #page which is currently being sent to the client.
 	 */
@@ -140,7 +145,9 @@ public:
 	 * Returns the total size of this client's page queue.
 	 */
 	gcc_pure
-	size_t GetQueueSize() const;
+	size_t GetQueueSize() const {
+		return queue_size;
+	}
 
 	/**
 	 * Clears the page queue.