Download driver for components/download.

content/browser/download/download_item_impl.cc

 // Copyright (c) 2012 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.
 
 // File method ordering: Methods in this file are in the same order as
 // in download_item_impl.h, with the following exception: The public
 // interface Start is placed in chronological order with the other
 // (private) routines that together define a DownloadItem's state
 // transitions as the download progresses.  See "Download progression
 // cascade" later in this file.
@@ skipping 185 matching lines @@
          state_ == CANCELLED_INTERNAL);
   DCHECK(base::IsValidGUID(guid_));
   Init(false /* not actively downloading */, SRC_HISTORY_IMPORT);
 }
 
 // Constructing for a regular download:
 DownloadItemImpl::DownloadItemImpl(DownloadItemImplDelegate* delegate,
                                    uint32_t download_id,
                                    const DownloadCreateInfo& info,
                                    const net::NetLogWithSource& net_log)
-    : guid_(base::ToUpperASCII(base::GenerateGUID())),
+    : guid_(info.guid.empty() ? base::ToUpperASCII(base::GenerateGUID())

[qinmin, 2017/05/23 04:21:24]

will this download item be written to the history db? if so, why the GUID
generation logic is here instead of in the history db?

[xingliu, 2017/05/23 16:56:13]

I think this logic happens before writing to history db. Also previously we
generated the uuid here.

I guess the reason to generate uuid here is, the in-memory object still needs a
uuid before db persists.

[qinmin, 2017/05/23 18:12:17]

Sorry, what I am saying is that why not let DownloadItemImpl create the GUID,
and pass it back to the caller of DownloadDriver in onDownloadStarted()?  

+                              : info.guid),
       download_id_(download_id),
       target_disposition_((info.save_info->prompt_for_save_location)
                               ? TARGET_DISPOSITION_PROMPT
                               : TARGET_DISPOSITION_OVERWRITE),
       url_chain_(info.url_chain),
       referrer_url_(info.referrer_url),
       site_url_(info.site_url),
       tab_url_(info.tab_url),
       tab_referrer_url_(info.tab_referrer_url),
       suggested_filename_(base::UTF16ToUTF8(info.save_info->suggested_name)),
@@ skipping 2084 matching lines @@
     case RESUME_MODE_USER_CONTINUE:
       return "USER_CONTINUE";
     case RESUME_MODE_USER_RESTART:
       return "USER_RESTART";
   }
   NOTREACHED() << "Unknown resume mode " << mode;
   return "unknown";
 }
 
 }  // namespace content