Make SQL in DownloadDatabase SQLite pre 3.8.3 compatible

components/history/core/browser/download_database.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.
 
 #include "components/history/core/browser/download_database.h"
 
 #include <limits>
 #include <string>
 #include <vector>
 
@@ skipping 221 matching lines @@
   // assumes that the likelihood of a collision with a GUID generated via
   // base::GenerateGUID() will be vanishingly small.
   //
   // A previous version of this code generated GUIDs that used random bits for
   // all but the first 32-bits. I.e. the scheme didn't respect the 6 fixed bits
   // as prescribed for type 4 GUIDs. The resulting GUIDs are not believed to
   // have an elevated risk of collision with GUIDs generated via
   // base::GenerateGUID() and are considered valid by all known consumers. Hence
   // no additional migration logic is being introduced to fix those GUIDs.
   const char kMigrateGuidsQuery[] =
-      "UPDATE downloads SET guid = printf"
-      "(\"%08X-%s-4%s-%01X%s-%s\","
-      " id,"
-      " hex(randomblob(2)),"
-      " substr(hex(randomblob(2)),2),"
-      " (8 | (random() & 3)),"
-      " substr(hex(randomblob(2)),2),"
-      " hex(randomblob(6)))";
+      "UPDATE downloads SET guid = "
+      "substr(hex(char( id>>28)    ),2) || substr(hex(char((id>>24)&15)),2) || "

[Scott Hess - ex-Googler, 2016/04/21 02:32:55]

Since SQLite integers are 64-bit, I'd throw in the &15 just for the heck of it.

+      "substr(hex(char((id>>20)&15)),2) || substr(hex(char((id>>16)&15)),2) || "
+      "substr(hex(char((id>>12)&15)),2) || substr(hex(char((id>> 8)&15)),2) || "
+      "substr(hex(char((id>> 4)&15)),2) || substr(hex(char( id     &15)),2) || "
+      "'-' || hex(randomblob(2)) || "
+      "'-4' || substr(hex(randomblob(2)),2) || "
+      "'-' || substr('89AB',1+(random()&3),1) || "
+      "       substr(hex(randomblob(2)),2) || "
+      "'-' || hex(randomblob(6))";

[Scott Hess - ex-Googler, 2016/04/21 02:32:55]

Wow.  I assume you have golden tests for this so you'd notice it breaking?

Since generally the majority of the real work is in reading and writing the file
itself, not the processing, and this is a migration anyhow, I wonder if this
wouldn't be more easily done with something like:
  sql::Statement s(GetCached("SELECT id FROM downloads"));
  sql::Statement u(GetCached("UPDATE downloads SET guid = ? WHERE id = ?"));
  while (s.Step()) {
    u.BindBlob(0, MakeGuid(s.ColumnInt(0)));
    u.BindInteger(1, s.ColumnInt(0));
  }

   return GetDB().Execute(kMigrateGuidsQuery);
 }
 
 bool DownloadDatabase::MigrateDownloadTabUrl() {
   return EnsureColumnExists("tab_url", "VARCHAR NOT NULL DEFAULT ''") &&
          EnsureColumnExists("tab_referrer_url", "VARCHAR NOT NULL DEFAULT ''");
 }
 
 bool DownloadDatabase::InitDownloadTable() {
   const char kSchema[] =
@@ skipping 400 matching lines @@
 size_t DownloadDatabase::CountDownloads() {
   EnsureInProgressEntriesCleanedUp();
 
   sql::Statement statement(GetDB().GetCachedStatement(SQL_FROM_HERE,
       "SELECT count(*) from downloads"));
   statement.Step();
   return statement.ColumnInt(0);
 }
 
 }  // namespace history