[sql] WARN_UNUSED_RESULT on Execute().

chrome/browser/net/sqlite_persistent_cookie_store.cc

 // Copyright (c) 2011 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 "chrome/browser/net/sqlite_persistent_cookie_store.h"
 
 #include <list>
 #include <map>
 #include <set>
 #include <utility>
@@ skipping 276 matching lines @@
                      "expires_utc INTEGER NOT NULL,"
                      "secure INTEGER NOT NULL,"
                      "httponly INTEGER NOT NULL,"
                      "last_access_utc INTEGER NOT NULL, "
                      "has_expires INTEGER NOT NULL DEFAULT 1, "
                      "persistent INTEGER NOT NULL DEFAULT 1)"))
       return false;
   }
 
   // Try to create the index every time. Older versions did not have this index,
-  // so we want those people to get it. Ignore errors, since it may exist.

[wtc, 2011/12/21 01:16:17]

shess: please confirm that you want this function to fail if
the index already exists.

Or do these db->Execute() calls succeed (but do nothing) if
the index already exists?

[Scott Hess - ex-Googler, 2011/12/21 02:41:01]

Yeah, the "CREATE INDEX IF NOT EXISTS" will succeed if the index already exists,
even if it resulted from a different create entirely, but will fail if there is
some other error while creating the index.  Such errors could include a
read-only database, table corruption, running out of disk space, etc.

I'll instrument the code and make sure this is actually happening.  I've run
stuff, everything seems to work, but that could be a false negative...

-  db->Execute("CREATE INDEX IF NOT EXISTS cookie_times ON cookies"
-              " (creation_utc)");
+  // so we want those people to get it.
+  if (!db->Execute("CREATE INDEX IF NOT EXISTS cookie_times ON cookies"
+                   " (creation_utc)"))
+    return false;
 
-  db->Execute("CREATE INDEX IF NOT EXISTS domain ON cookies(host_key)");
+  if (!db->Execute("CREATE INDEX IF NOT EXISTS domain ON cookies(host_key)"))
+    return false;
 
   return true;
 }
 
 }  // namespace
 
 void SQLitePersistentCookieStore::Backend::Load(
     const LoadedCallback& loaded_callback) {
   // This function should be called only once per instance.
   DCHECK(!db_.get());
@@ skipping 352 matching lines @@
   if (cur_version == 3) {
     // The time epoch changed for Mac & Linux in this version to match Windows.
     // This patch came after the main epoch change happened, so some
     // developers have "good" times for cookies added by the more recent
     // versions. So we have to be careful to only update times that are under
     // the old system (which will appear to be from before 1970 in the new
     // system). The magic number used below is 1970 in our time units.
     sql::Transaction transaction(db_.get());
     transaction.Begin();
 #if !defined(OS_WIN)
-    db_->Execute(
+    ignore_result(db_->Execute(
         "UPDATE cookies "
         "SET creation_utc = creation_utc + 11644473600000000 "
         "WHERE rowid IN "
         "(SELECT rowid FROM cookies WHERE "
-          "creation_utc > 0 AND creation_utc < 11644473600000000)");
-    db_->Execute(
+          "creation_utc > 0 AND creation_utc < 11644473600000000)"));
+    ignore_result(db_->Execute(
         "UPDATE cookies "
         "SET expires_utc = expires_utc + 11644473600000000 "
         "WHERE rowid IN "
         "(SELECT rowid FROM cookies WHERE "
-          "expires_utc > 0 AND expires_utc < 11644473600000000)");
-    db_->Execute(
+          "expires_utc > 0 AND expires_utc < 11644473600000000)"));
+    ignore_result(db_->Execute(
         "UPDATE cookies "
         "SET last_access_utc = last_access_utc + 11644473600000000 "
         "WHERE rowid IN "
         "(SELECT rowid FROM cookies WHERE "
-          "last_access_utc > 0 AND last_access_utc < 11644473600000000)");
+          "last_access_utc > 0 AND last_access_utc < 11644473600000000)"));
 #endif
     ++cur_version;
     meta_table_.SetVersionNumber(cur_version);
     transaction.Commit();
   }
 
   if (cur_version == 4) {
     const base::TimeTicks start_time = base::TimeTicks::Now();
     sql::Transaction transaction(db_.get());
     if (!transaction.Begin())
@@ skipping 261 matching lines @@
   if (backend_.get())
     backend_->SetClearLocalStateOnExit(clear_local_state);
 }
 
 void SQLitePersistentCookieStore::Flush(const base::Closure& callback) {
   if (backend_.get())
     backend_->Flush(callback);
   else if (!callback.is_null())
     MessageLoop::current()->PostTask(FROM_HERE, callback);
 }