This is very confusing as seen in #12974 or #12906. My suggestion would be "legacy."
total: Math.max(loaded, fullRequest.contentLength || 0),
              });
            }
            if (newPdfManager) {
              newPdfManager.sendProgressiveData(value);
            } else {
              cachedChunks.push(value);
            }
            fullRequest.read().then(readChunk, reject);
          } catch (e) {
            reject(e);
          }
        };
        fullRequest.read().then(readChunk, reject);
      });
      readPromise.catch(function (e) {
        pdfManagerCapability.reject(e);
        cancelXHRs = null;
      });
      cancelXHRs = function (reason) {
        pdfStream.cancelAllRequests(reason);
      };
      return pdfManagerCapability.promise;
    }
    function setupDoc(data) {
      function onSuccess(doc) {
        ensureNotTerminated();
        handler.send("GetDoc", { pdfInfo: doc });
      }
      function onFailure(ex) {