feat(lnm): implement event loop state switching

lnm/src/http/lnm_http_loop_process.c

@@ -264,6 +264,25 @@ void (*process_fns[])(lnm_http_conn *conn) = {
     lnm_http_loop_process_finish,
 };
 
+lnm_loop_state state_map[] = {
+    // parse_req
+    lnm_loop_state_req,
+    // route
+    lnm_loop_state_req,
+    // parse_headers
+    lnm_loop_state_req,
+    // steps
+    lnm_loop_state_req,
+    // write_status_line
+    lnm_loop_state_res,
+    // write_headers
+    lnm_loop_state_res,
+    // write_body
+    lnm_loop_state_res,
+    // finish
+    lnm_loop_state_res,
+};
+
 void lnm_http_loop_process(lnm_http_conn *conn) {
   const lnm_http_loop_ctx *ctx = conn->ctx;
 
@@ -271,13 +290,20 @@ void lnm_http_loop_process(lnm_http_conn *conn) {
   lnm_loop_state loop_state = conn->state;
 
   // We stop processing if:
-  // - the event loop state has changed, as we need to switch to the other I/O
-  // loop
+  // - the event loop state has been explicitely changed inside the executed
+  // step, as we need to switch to the other I/O loop
+  // - the event loop state needs to be changed because the next step should be
+  // run in another event loop state
   // - the process fn returned without changing the HTTP loop state, indicating
   // it's waiting for I/O
   do {
     http_loop_state = ctx->state;
 
     process_fns[http_loop_state](conn);
-  } while ((conn->state == loop_state) && (http_loop_state != ctx->state));
+  } while ((conn->state == loop_state) &&
+           (conn->state == state_map[loop_state]) &&
+           (http_loop_state != ctx->state));
+
+  // Check required to prevent overwriting manually set event loop state
+  conn->state = conn->state == loop_state ? state_map[loop_state] : conn->state;
 }