spdy: WINDOW_UPDATE sent on data receiving to allow big HTTP bodies

src/microspdy/internal.h

@@ -28,14 +28,24 @@
 #include "platform.h"
 #include "microspdy.h"
 
-/* size of read buffers for each connection
- * must be at least the size of SPDY_MAX_SUPPORTED_FRAME_SIZE */
+/**
+ * size of read buffers for each connection
+ * must be at least the size of SPDY_MAX_SUPPORTED_FRAME_SIZE
+ */
 #define SPDYF_BUFFER_SIZE 8192
 
-/* number of frames written to the socket at once. After X frames
+/**
+ * initial size of window for each stream (this is for the data
+ * within data frames that can be handled)
+ */
+#define SPDYF_INITIAL_WINDOW_SIZE 65536
+
+/**
+ * number of frames written to the socket at once. After X frames
  * everything should be run again. In this way the application can
  * response to more important requests while a big file is still
- * being transmitted to the client  */
+ * being transmitted to the client
+ */
 #define SPDYF_NUM_SENT_FRAMES_AT_ONCE 10
 
 

src/microspdy/session.c

@@ -380,7 +380,9 @@ spdyf_handler_read_data (struct SPDY_Session *session)
                                       frame->length,
                                       0 == (SPDY_DATA_FLAG_FIN & frame->flags));
         
-    session->read_buffer_beginning += frame->length;   
+    session->read_buffer_beginning += frame->length;
+    
+    stream->window_size -= frame->length;  
          
     //TODO close in and send rst maybe
     SPDYF_ASSERT(SPDY_YES == ret, "Cancel POST data is not yet implemented");
@@ -389,6 +391,20 @@ spdyf_handler_read_data (struct SPDY_Session *session)
     {
       stream->is_in_closed = true;
     }
+    else if(stream->window_size < SPDYF_INITIAL_WINDOW_SIZE / 2)
+    {
+      //very simple implementation of flow control
+      //when the window's size is under the half of the initial value,
+      //increase it again up to the initial value
+      
+      //prepare WINDOW_UPDATE
+      if(SPDY_YES == SPDYF_prepare_window_update(session, stream,
+            SPDYF_INITIAL_WINDOW_SIZE - stream->window_size))
+      {
+        stream->window_size = SPDYF_INITIAL_WINDOW_SIZE;
+      }
+      //else: do it later
+    }
     session->status = SPDY_SESSION_STATUS_WAIT_FOR_HEADER;
     free(frame);
 	}
@@ -751,6 +767,47 @@ SPDYF_handler_write_rst_stream (struct SPDY_Session *session)
 	return SPDY_YES;
 }
 
+		   
+int
+SPDYF_handler_write_window_update (struct SPDY_Session *session)
+{
+	struct SPDYF_Response_Queue *response_queue = session->response_queue_head;
+	struct SPDYF_Control_Frame control_frame;
+	size_t total_size;
+	
+	SPDYF_ASSERT(NULL == session->write_buffer, "the function is called not in the correct moment");
+	
+	memcpy(&control_frame, response_queue->control_frame, sizeof(control_frame));
+	
+	total_size = sizeof(struct SPDYF_Control_Frame) //SPDY header
+		+ 4 // stream id as "subheader"
+		+ 4; // delta-window-size as "subheader"
+
+	if(NULL == (session->write_buffer = malloc(total_size)))
+	{
+		return SPDY_NO;
+	}
+	session->write_buffer_beginning = 0;
+	session->write_buffer_offset = 0;
+	session->write_buffer_size = total_size;
+	
+	control_frame.length = 8; // always for WINDOW_UPDATE
+	SPDYF_CONTROL_FRAME_HTON(&control_frame);
+	
+	//put frame headers to write buffer
+	memcpy(session->write_buffer + session->write_buffer_offset,&control_frame,sizeof(struct SPDYF_Control_Frame));
+	session->write_buffer_offset +=  sizeof(struct SPDYF_Control_Frame);
+	
+	//put stream id and delta-window-size to write buffer
+	memcpy(session->write_buffer + session->write_buffer_offset, response_queue->data, 8);
+	session->write_buffer_offset +=  8;
+	
+	SPDYF_ASSERT(0 == session->write_buffer_beginning, "bug1");
+	SPDYF_ASSERT(session->write_buffer_offset == session->write_buffer_size, "bug2");
+
+	return SPDY_YES;
+}
+
 
 void
 SPDYF_handler_ignore_frame (struct SPDY_Session *session)
@@ -1638,3 +1695,55 @@ SPDYF_prepare_rst_stream (struct SPDY_Session *session,
 
 	return SPDY_YES;
 }
+
+
+int
+SPDYF_prepare_window_update (struct SPDY_Session *session,
+					struct SPDYF_Stream * stream,
+					int32_t delta_window_size)
+{
+	struct SPDYF_Response_Queue *response_to_queue;
+	struct SPDYF_Control_Frame *control_frame;
+	uint32_t *data;
+	
+  SPDYF_ASSERT(NULL != stream, "stream cannot be NULL");
+  
+	if(NULL == (response_to_queue = malloc(sizeof(struct SPDYF_Response_Queue))))
+	{
+		return SPDY_NO;
+	}
+	memset(response_to_queue, 0, sizeof(struct SPDYF_Response_Queue));
+	
+	if(NULL == (control_frame = malloc(sizeof(struct SPDYF_Control_Frame))))
+	{
+		free(response_to_queue);
+		return SPDY_NO;
+	}
+	memset(control_frame, 0, sizeof(struct SPDYF_Control_Frame));
+	
+	if(NULL == (data = malloc(8)))
+	{
+		free(control_frame);
+		free(response_to_queue);
+		return SPDY_NO;
+	}
+	*(data) = HTON31(stream->stream_id);
+	*(data + 1) = HTON31(delta_window_size);
+	
+	control_frame->control_bit = 1;
+	control_frame->version = SPDY_VERSION;
+	control_frame->type = SPDY_CONTROL_FRAME_TYPES_WINDOW_UPDATE;
+	control_frame->flags = 0;
+	
+	response_to_queue->control_frame = control_frame;
+	response_to_queue->process_response_handler = &SPDYF_handler_write_window_update;
+	response_to_queue->data = data;
+	response_to_queue->data_size = 8;
+	response_to_queue->stream = stream;
+	
+	SPDYF_queue_response (response_to_queue,
+						session,
+						-1);
+
+	return SPDY_YES;
+}

src/microspdy/session.h

@@ -171,6 +171,23 @@ SPDYF_prepare_rst_stream (struct SPDY_Session *session,
 					enum SPDY_RST_STREAM_STATUS status);
 
 
+/**
+ * Prepares WINDOW_UPDATE frame to tell the other party that more
+ * data can be sent on the stream. The frame will be put at the head of
+ * the queue.
+ * 
+ * @param session SPDY session
+ * @param stream stream to which the changed window will apply
+ * @param delta_window_size how much the window grows
+ * @return SPDY_NO on memory error or
+ * 			SPDY_YES on success
+ */
+int
+SPDYF_prepare_window_update (struct SPDY_Session *session,
+					struct SPDYF_Stream * stream,
+					int32_t delta_window_size);
+          
+
 /**
  * Handler called by session_write to fill the write buffer according to
  * the data frame waiting in the response queue.
@@ -232,6 +249,20 @@ int
 SPDYF_handler_write_rst_stream (struct SPDY_Session *session);
 
 
+/**
+ * Handler called by session_write to fill the write buffer based on the
+ * control frame (WINDOW_UPDATE) waiting in the response queue.
+ * 
+ * @param session SPDY session
+ * @return SPDY_NO on error (not enough memory). If
+ *         the error is unrecoverable the handler changes session's
+ *         status.
+ * 			SPDY_YES on success
+ */			
+int
+SPDYF_handler_write_window_update (struct SPDY_Session *session);
+
+
 /**
  * Carefully ignore the full size of frames which are not yet supported
  * by the lib.

src/microspdy/stream.c

@@ -104,6 +104,7 @@ SPDYF_stream_new (struct SPDY_Session *session)
 	stream->flag_unidirectional = (frame->flags & SPDY_SYN_STREAM_FLAG_UNIDIRECTIONAL) != 0;
 	stream->is_out_closed = stream->flag_unidirectional;
 	stream->is_server_initiator = false;
+	stream->window_size = SPDYF_INITIAL_WINDOW_SIZE;
 	
 	//put the stream to the list of streams for the session
 	DLL_insert(session->streams_head, session->streams_tail, stream);

src/microspdy/structures.h

@@ -553,6 +553,11 @@ struct SPDYF_Stream
 	 */
 	uint32_t assoc_stream_id;
 	
+	/**
+	 * The window of the data within data frames.
+	 */
+	uint32_t window_size;
+	
 	/**
 	 * Stream priority. 0 is the highest, 7 is the lowest.
 	 */