Refine fallback solution for servers blocking access to http headers

Such server may process partial http requests but do not allow
to read Content-Range header making impossible to parse
multipart response. cernbox is one of such servers.
Partial reading from such servers is possible - but only 1 segmnent per request.
Do not test Accept-Ranges header which not always returned

Author: linev

modules/io.mjs

@@ -2782,16 +2782,14 @@ class TFile {
          }
 
          if (res && first_req) {
-            if (file.fAcceptRanges && !first_req.getResponseHeader('Accept-Ranges')) {
-               file.fAcceptRanges = false;
-               if (res?.byteLength === place[1]) {
-                  // special case with cernbox, let try to get full size content
-                  console.warn(`First block is ${place[1]} bytes but browser does not provides access to header - try to read full file`);
-                  first_block_retry = true;
-                  return send_new_request();
-               }
+            // special workaround for servers like cernbox blocking access to some response headers
+            // as result, it is not possible to parse multipart responses
+            if (file.fAcceptRanges && (first_req.status === 206) && (res?.byteLength === place[1]) && !first_req.getResponseHeader('Content-Range') && (file.fMaxRanges > 1)) {
+               console.warn('Server response with 206 code but browser does not provide access to Content-Range header - setting fMaxRanges = 1, consider to load full file with "filename.root+" argument or adjust server configurations');
+               file.fMaxRanges = 1;
             }
 
+            // workaround for simpleHTTP
             const kind = browser.isFirefox ? first_req.getResponseHeader('Server') : '';
             if (isStr(kind) && kind.indexOf('SimpleHTTP') === 0) {
                file.fMaxRanges = 1;
@@ -2801,7 +2799,6 @@ class TFile {
 
          if (res && first_block && !file.fFileContent) {
             // special case - keep content of first request (could be complete file) in memory
-
             file.fFileContent = new TBuffer(isStr(res) ? res : new DataView(res));
 
             if (!file.fAcceptRanges)