Fix issues and feature polishing for parallel download.

content/browser/download/parallel_download_utils.cc

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/download/parallel_download_utils.h"
 
 #include "base/metrics/field_trial_params.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/time/time.h"
 #include "content/public/browser/download_save_info.h"
@@ skipping 45 matching lines @@
       !create_info.etag.empty() || !create_info.last_modified.empty();
 
   return has_strong_validator && create_info.accept_range &&
          create_info.total_bytes >= GetMinSliceSizeConfig() &&
          create_info.connection_info ==
              net::HttpResponseInfo::CONNECTION_INFO_HTTP1_1 &&
          base::FeatureList::IsEnabled(features::kParallelDownloading);
 }
 
 std::vector<DownloadItem::ReceivedSlice> FindSlicesForRemainingContent(
-    int64_t bytes_received,
-    int64_t content_length,
-    int request_count) {
-  std::vector<DownloadItem::ReceivedSlice> slices_to_download;
-  if (request_count <= 0)
-    return slices_to_download;
+    int64_t current_offset,
+    int64_t total_length,
+    int request_count,
+    int64_t min_slice_size) {
+  std::vector<DownloadItem::ReceivedSlice> new_slices;
 
-  // TODO(xingliu): Consider to use minimum size of a slice.
-  int64_t slice_size = content_length / request_count;
-  slice_size = slice_size > 0 ? slice_size : 1;
-  int64_t current_offset = bytes_received;
-  for (int i = 0, num_requests = content_length / slice_size;
-       i < num_requests - 1; ++i) {
-    slices_to_download.emplace_back(current_offset, slice_size);
-    current_offset += slice_size;
+  if (request_count > 0) {
+    int64_t slice_size =
+        std::max<int64_t>(total_length / request_count, min_slice_size);
+    slice_size = slice_size > 0 ? slice_size : 1;
+    for (int i = 0, num_requests = total_length / slice_size;
+         i < num_requests - 1; ++i) {
+      new_slices.emplace_back(current_offset, slice_size);
+      current_offset += slice_size;
+    }
   }
 
   // Last slice is a half open slice, which results in sending range request
   // like "Range:50-" to fetch from 50 bytes to the end of the file.
-  slices_to_download.emplace_back(current_offset,
-                                  DownloadSaveInfo::kLengthFullContent);
-  return slices_to_download;
+  new_slices.emplace_back(current_offset, DownloadSaveInfo::kLengthFullContent);
+  return new_slices;
 }
 
 std::vector<DownloadItem::ReceivedSlice> FindSlicesToDownload(
     const std::vector<DownloadItem::ReceivedSlice>& received_slices) {
   std::vector<DownloadItem::ReceivedSlice> result;
   if (received_slices.empty()) {
     result.emplace_back(0, DownloadSaveInfo::kLengthFullContent);
     return result;
   }
 
@@ skipping 66 matching lines @@
 
 void DebugSlicesInfo(const DownloadItem::ReceivedSlices& slices) {
   DVLOG(1) << "Received slices size : " << slices.size();
   for (const auto& it : slices) {
     DVLOG(1) << "Slice offset = " << it.offset
              << " , received_bytes = " << it.received_bytes;
   }
 }
 
 }  // namespace content