feat(http): add custom processing to responses using response steps

include/http_loop.h

@@ -27,9 +27,10 @@ typedef enum http_route_type {
  * Function describing a step in a route's processing.
  *
  * @param conn connection to process
- * @return whether the processing can immediately advance to the next step. A
- * step should return false if it's e.g. waiting for I/O, and can therefore not
- * finish its task in the current cycle of the event loop.
+ * @return whether processing can proceed to the next step without performing
+ * I/O first. For a request step, `false` means more data needs to be read
+ * before the step can finish its processing. For response steps, `false` means
+ * there's new data in the write buffer that needs to be written.
  */
 typedef bool (*step)(event_loop_conn *conn);
 
@@ -44,6 +45,7 @@ typedef struct http_route {
   // starting the http loop
   regex_t *regex;
   step steps[HTTP_LOOP_MAX_STEPS];
+  step steps_res[HTTP_LOOP_MAX_STEPS];
 } http_route;
 
 /**
@@ -116,14 +118,6 @@ typedef struct event_loop http_loop;
  */
 bool http_loop_handle_request(event_loop_conn *conn);
 
-/**
- * Write the HTTP response to the file descriptor. This is the "write_data"
- * function for the event loop.
- *
- * @param conn connection to process
- */
-void http_loop_write_response(event_loop_conn *conn);
-
 /**
  * Try to parse the incoming data as an HTTP request.
  *
@@ -148,6 +142,14 @@ void http_loop_route_request(event_loop_conn *conn);
  */
 void http_loop_process_request(event_loop_conn *conn);
 
+/**
+ * Handles the response processing. This is the `write_data` function for the
+ * event loop.
+ *
+ * @param conn connection to process
+ */
+void http_loop_handle_response(event_loop_conn *conn);
+
 /**
  * Request step that consumes the request body and stores it in a buffer.
  *
@@ -180,6 +182,21 @@ bool http_loop_step_auth(event_loop_conn *conn);
  */
 bool http_loop_step_switch_res(event_loop_conn *conn);
 
+/**
+ * Write the HTTP header back to the connection. If `res->head` is not set, a
+ * header will be generated for you.
+ *
+ * @param conn connection to process
+ */
+bool http_loop_step_write_header(event_loop_conn *conn);
+
+/**
+ * Write the HTTP body back to the connection.
+ *
+ * @param conn connection to process
+ */
+bool http_loop_step_write_body(event_loop_conn *conn);
+
 /**
  * Initialize a new http loop.
  *