mandoline filesystem: add a sqlite3 vfs to proxy filesystem usage.

sql/connection.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 "sql/connection.h"
 
 #include <string.h>
 
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
@@ skipping 589 matching lines @@
 
   RollbackAllTransactions();
   CloseInternal(true);
 
   // Mark the database so that future API calls fail appropriately,
   // but don't DCHECK (because after calling this function they are
   // expected to fail).
   poisoned_ = true;
 }
 
+std::string AsUTF8ForSQL(const base::FilePath& path) {
+#if defined(OS_WIN)
+  return base::WideToUTF8(path.value());
+#elif defined(OS_POSIX)
+  return path.value();
+#endif
+}
+
 // TODO(shess): To the extent possible, figure out the optimal
 // ordering for these deletes which will prevent other connections
 // from seeing odd behavior.  For instance, it may be necessary to
 // manually lock the main database file in a SQLite-compatible fashion
 // (to prevent other processes from opening it), then delete the
 // journal files, then delete the main database file.  Another option
 // might be to lock the main database file and poison the header with
 // junk to prevent other processes from opening it successfully (like
 // Gears "SQLite poison 3" trick).
 //
 // static
 bool Connection::Delete(const base::FilePath& path) {
   base::ThreadRestrictions::AssertIOAllowed();
 
   base::FilePath journal_path(path.value() + FILE_PATH_LITERAL("-journal"));
   base::FilePath wal_path(path.value() + FILE_PATH_LITERAL("-wal"));
 
-  base::DeleteFile(journal_path, false);
-  base::DeleteFile(wal_path, false);
-  base::DeleteFile(path, false);
+  std::string journal_str = AsUTF8ForSQL(journal_path);
+  std::string wal_str = AsUTF8ForSQL(wal_path);
+  std::string path_str = AsUTF8ForSQL(path);
 
-  return !base::PathExists(journal_path) &&
-      !base::PathExists(wal_path) &&
-      !base::PathExists(path);
+  sqlite3_vfs* vfs = sqlite3_vfs_find(NULL);

[Scott Hess - ex-Googler, 2015/06/10 22:35:45]

I don't think it's appropriate to change this code from depending on our code to
depending on SQLite depending on our code.  It should depend more directly.

[I see _why_ you did it, so I'll try to circle back with other thoughts as I
process the review.]

[[I didn't think of anything.  I still dislike it.]]

[Elliot Glaysher, 2015/06/12 22:36:43]

Per our conversation yesterday, I added a check on the name of the vfs to make
sure its one of the win32, unix or mojo vfses.

[Scott Hess - ex-Googler, 2015/06/17 19:32:58]

I'm happier with it, though not ecstatic.  At least we're saving some poor
client from having to know about it :-).

+  CHECK(vfs);
+  CHECK(vfs->xDelete);
+  CHECK(vfs->xAccess);
+
+  vfs->xDelete(vfs, journal_str.c_str(), 0);
+  vfs->xDelete(vfs, wal_str.c_str(), 0);
+  vfs->xDelete(vfs, path_str.c_str(), 0);
+
+  int journal_exists = 0;
+  vfs->xAccess(vfs, journal_str.c_str(), SQLITE_ACCESS_EXISTS,
+               &journal_exists);
+
+  int wal_exists = 0;
+  vfs->xAccess(vfs, wal_str.c_str(), SQLITE_ACCESS_EXISTS,
+               &wal_exists);
+
+  int path_exists = 0;
+  vfs->xAccess(vfs, path_str.c_str(), SQLITE_ACCESS_EXISTS,
+               &path_exists);
+
+  return !journal_exists && !wal_exists && !path_exists;
 }
 
 bool Connection::BeginTransaction() {
   if (needs_rollback_) {
     DCHECK_GT(transaction_nesting_, 0);
 
     // When we're going to rollback, fail on this begin and don't actually
     // mark us as entering the nested transaction.
     return false;
   }
@@ skipping 663 matching lines @@
   ignore_result(Execute(kNoWritableSchema));
 
   return ret;
 }
 
 base::TimeTicks TimeSource::Now() {
   return base::TimeTicks::Now();
 }
 
 }  // namespace sql