httpd: ssi: support selecting ssi files by file flags, not by extension (at runtime) only

src/apps/httpd/httpd.c

@@ -2234,8 +2234,16 @@ http_find_file(struct http_state *hs, const char *uri, int is_09)
     } else {
       file = http_get_404_file(hs, &uri);
     }
-#if LWIP_HTTPD_SSI && LWIP_HTTPD_SSI_BY_FILE_EXTENSION
-    tag_check = http_uri_is_ssi(file, uri);
+#if LWIP_HTTPD_SSI
+    if (file != NULL) {
+      if (file->flags & FS_FILE_FLAGS_SSI) {
+        tag_check = 1;
+      } else {
+#if LWIP_HTTPD_SSI_BY_FILE_EXTENSION
+        tag_check = http_uri_is_ssi(file, uri);
+#endif /* LWIP_HTTPD_SSI_BY_FILE_EXTENSION */
+      }
+    }
 #endif /* LWIP_HTTPD_SSI */
   }
   if (file == NULL) {

src/include/lwip/apps/fs.h

@@ -52,6 +52,8 @@ struct fsdata_chksum {
 
 #define FS_FILE_FLAGS_HEADER_INCLUDED     0x01
 #define FS_FILE_FLAGS_HEADER_PERSISTENT   0x02
+#define FS_FILE_FLAGS_HEADER_KEEPALIVE    0x04
+#define FS_FILE_FLAGS_SSI                 0x08
 
 /** Define FS_FILE_EXTENSION_T_DEFINED if you have typedef'ed to your private
  * pointer type (defaults to 'void' so the default usage is 'void*')