MDL-38627 force byteserving abort on error

It is weird, but Chrome PDF viewer keeps retrying byteserving requests for anything but 407. This commit also normalises response headers on all error pages.

lib/moodlelib.php

@@ -2817,6 +2817,11 @@ function get_login_url() {
 function require_login($courseorid = NULL, $autologinguest = true, $cm = NULL, $setwantsurltome = true, $preventredirect = false) {
     global $CFG, $SESSION, $USER, $PAGE, $SITE, $DB, $OUTPUT;
 
+    // Must not redirect when byteserving already started.
+    if (!empty($_SERVER['HTTP_RANGE'])) {
+        $preventredirect = true;
+    }
+
     // setup global $COURSE, themes, language and locale
     if (!empty($courseorid)) {
         if (is_object($courseorid)) {

lib/outputrenderers.php

@@ -2317,12 +2317,16 @@ EOD;
             }
             error_reporting($CFG->debug);
 
-            // Header not yet printed
-            if (isset($_SERVER['SERVER_PROTOCOL'])) {
-                // server protocol should be always present, because this render
-                // can not be used from command line or when outputting custom XML
-                @header($_SERVER['SERVER_PROTOCOL'] . ' 404 Not Found');
+            // Output not yet started.
+            $protocol = (isset($_SERVER['SERVER_PROTOCOL']) ? $_SERVER['SERVER_PROTOCOL'] : 'HTTP/1.0');
+            if (empty($_SERVER['HTTP_RANGE'])) {
+                @header($protocol . ' 404 Not Found');
+            } else {
+                // Must stop byteserving attempts somehow,
+                // this is weird but Chrome PDF viewer can be stopped only with 407!
+                @header($protocol . ' 407 Proxy Authentication Required');
             }
+
             $this->page->set_context(null); // ugly hack - make sure page context is set to something, we do not want bogus warnings here
             $this->page->set_url('/'); // no url
             //$this->page->set_pagelayout('base'); //TODO: MDL-20676 blocks on error pages are weird, unfortunately it somehow detect the pagelayout from URL :-(

lib/setuplib.php

@@ -1547,12 +1547,9 @@ width: 80%; -moz-border-radius: 20px; padding: 15px">
         }
 
         // In the name of protocol correctness, monitoring and performance
-        // profiling, set the appropriate error headers for machine consumption
-        if (isset($_SERVER['SERVER_PROTOCOL'])) {
-            // Avoid it with cron.php. Note that we assume it's HTTP/1.x
-            // The 503 ode here means our Moodle does not work at all, the error happened too early
-            @header($_SERVER['SERVER_PROTOCOL'] . ' 503 Service Unavailable');
-        }
+        // profiling, set the appropriate error headers for machine consumption.
+        $protocol = (isset($_SERVER['SERVER_PROTOCOL']) ? $_SERVER['SERVER_PROTOCOL'] : 'HTTP/1.0');
+        @header($protocol . ' 503 Service Unavailable');
 
         // better disable any caching
         @header('Content-Type: text/html; charset=utf-8');