Add HTTP Last-Modified header for TEI resources

controller.xql

@@ -40,6 +40,13 @@ console:log('exist:path: ' || $exist:path)
 ,
 :)
 
+let $if-modified-since := request:get-header("If-Modified-Since")
+return
+    if ($if-modified-since) then
+        request:set-attribute("if-modified-since", $if-modified-since)
+    else
+        (),
+
 if ($exist:path eq '') then
     <dispatch xmlns="http://exist.sourceforge.net/NS/exist">
         <redirect url="{local:get-uri()}/"/>

modules/app.xqm

@@ -1,4 +1,4 @@
-xquery version "3.0";
+xquery version "3.1";
 
 module namespace app="http://history.state.gov/ns/site/hsg/templates";
 
@@ -151,6 +151,20 @@ function app:handle-error($node as node(), $model as map(*), $code as xs:int?) {
             ()
 };
 
+declare function app:format-http-date($dateTime as xs:dateTime) as xs:string {
+    $dateTime
+    => adjust-dateTime-to-timezone(xs:dayTimeDuration("PT0H"))
+    => format-dateTime("[FNn,*-3], [D01] [MNn,*-3] [Y0001] [H01]:[m01]:[s01] [Z0000]", "en", (), ())
+};
+
+declare function app:set-last-modified($last-modified as xs:dateTime) {
+    response:set-header("Last-Modified", app:format-http-date($last-modified))
+};
+
+declare function app:set-created($created as xs:dateTime) {
+    response:set-header("Created", app:format-http-date($created))
+};
+
 declare function app:uri($node as node(), $model as map(*)) {
     <code>{request:get-attribute("hsg-shell.path")}</code>
 };