* Add once_received plugin (by dmx)

* Fix read_callback to avoid double freeing of task object

src/plugins/lua/once_received.lua

+-- 0 or 1 received: = spam
+
+local metric = 'default'
+local symbol = 'ONCE_RECEIVED'
+
+function check_quantity_received (task)
+	local recvh = task:get_received_headers()
+	if table.maxn(recvh) <= 1 then
+		task:insert_result(metric, symbol, 1)
+	end
+end
+
+-- Register symbol's callback
+local m = rspamd_config:get_metric(metric)
+m:register_symbol(symbol, 1.0, 'check_quantity_received')

src/worker.c

 			task->state = WRITE_ERROR;
 		}
 		if (task->state == WRITE_REPLY || task->state == WRITE_ERROR) {
-			write_socket (task);
+			return write_socket (task);
 		}
 		break;
 	case READ_MESSAGE:
 			task->last_error = "MIME processing error";
 			task->error_code = RSPAMD_FILTER_ERROR;
 			task->state = WRITE_ERROR;
-			write_socket (task);
+			return write_socket (task);
 		}
 		if (task->cmd == CMD_OTHER) {
 			/* Skip filters */
 			task->state = WRITE_REPLY;
-			write_socket (task);
-			return TRUE;
+			return write_socket (task);
 		}
 		r = process_filters (task);
 		if (r == -1) {
 			task->last_error = "Filter processing error";
 			task->error_code = RSPAMD_FILTER_ERROR;
 			task->state = WRITE_ERROR;
-			write_socket (task);
+			return write_socket (task);
 		}
 		else if (r == 0) {
 			task->state = WAIT_FILTER;
 		}
 		else {
 			process_statfiles (task);
-			write_socket (task);
+			return write_socket (task);
 		}
 		break;
 	default: