Add a setting via render_app.conf.dist to set static files from

webwork2_files to be cached by the browser, and to expire a set amount
of time in the future. This should reduce server load regarding static
files which are used by multiple problems, but still makes it reasonable
to roll out updated files in a reasonable manner.

At present, we only add the response header settings to support
browser caching for files under webwork2_files. However, we set expired
times for those whose URL contains a match to tmp/renderer as files
which were generated for a specific problem may be dangerous to cache,
in case they get updated in any manner on a subsequent call.

lib/RenderApp.pm

@@ -69,6 +69,37 @@ sub startup {
 		});
 	}
 
+	# Add Cache-Control and Expires headers to static content from webwork2_files
+	if (my $STATIC_EXPIRES = $self->config('STATIC_EXPIRES')) {
+	    $STATIC_EXPIRES = int( $STATIC_EXPIRES );
+	    my $cache_control_setting = "max-age=$STATIC_EXPIRES";
+	    my $no_cache_setting = "max-age=1, no-cache";
+	    $self->hook(after_dispatch => sub {
+		my $c = shift;
+
+		# Only process if file requested is under webwork2_files
+		unless ( $c->req->url->path =~ '^/webwork2_files' ) {
+		    return;
+		}
+
+		if ( $c->req->url->path =~ '/tmp/renderer' ) {
+		    # Treat problem generated files as already expired.
+		    # They should not be cached.
+		    $c->res->headers->cache_control( $no_cache_setting );
+		    $c->res->headers->header(Expires =>
+		        Mojo::Date->new(time - 86400) # expired 24 hours ago
+		    );
+		} else {
+		    # Standard "static" files.
+		    # They can be cached
+		    $c->res->headers->cache_control( $cache_control_setting );
+		    $c->res->headers->header(Expires =>
+		        Mojo::Date->new(time + $STATIC_EXPIRES)
+			);
+		}
+	    });
+	}
+
 	# Models
 	$self->helper(newProblem => sub { shift; RenderApp::Model::Problem->new(@_) });
 

render_app.conf.dist

@@ -6,6 +6,7 @@
   webworkJWTsecret => 'private',
   SITE_HOST => 'http://localhost:3000',
   CORS_ORIGIN => '*',
+  STATIC_EXPIRES => 86400,
   STRICT_JWT => 0,
   hypnotoad => {
     listen => ['http://*:3000'],