SimpleCache: try to recover on CreateEntry on missing cache dir

net/disk_cache/simple/simple_synchronous_entry.cc

 // Copyright (c) 2013 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 "net/disk_cache/simple/simple_synchronous_entry.h"
 
 #include <algorithm>
 #include <cstring>
 #include <functional>
 #include <limits>
@@ skipping 850 matching lines @@
 
   if (CanOmitEmptyFile(file_index) && file_required == FILE_NOT_REQUIRED) {
     empty_file_omitted_[file_index] = true;
     return true;
   }
 
   FilePath filename = GetFilenameFromFileIndex(file_index);
   int flags = File::FLAG_CREATE | File::FLAG_READ | File::FLAG_WRITE |
               File::FLAG_SHARE_DELETE;
   files_[file_index].Initialize(filename, flags);
+
+  // It's possible that the creation failed because someone deleted the
+  // directory (e.g. because someone pressed "clear cache" on Android).
+  // If so, we would keep failing for a while until periodic index snapshot
+  // re-creates the cache dir, so try to recover from it quickly here.
+  if (!files_[file_index].IsValid() &&
+      files_[file_index].error_details() == File::FILE_ERROR_NOT_FOUND &&
+      !base::DirectoryExists(path_) && base::CreateDirectory(path_)) {
+    files_[file_index].Initialize(filename, flags);

[jkarlin, 2017/05/05 17:16:21]

I worry a bit about the state of the cache being strange here. E.g., we write
some entry but don't have an index. How about instead we simply write the empty
index out to disk after the user clears the cache?

[pasko, 2017/05/05 17:24:15]

Writing index here would probably fix the issue, but it looks a bit too tightly
coupled this way IMO. The philosophy of the index is that its existence is not
necessary for correct functioning of the backend (modulo eviction - adding more
states beyond eviction would complicate things like interpreting UMA metrics).
Also index file lifecycle depends a lot on OS/environment behavior, better to
keep these platform differences small. So I am more with morlovich@ here.

[jkarlin, 2017/05/05 17:42:18]

Okay, works with me.

+  }
+
   *out_error = files_[file_index].error_details();
-
   empty_file_omitted_[file_index] = false;
 
   return files_[file_index].IsValid();
 }
 
 bool SimpleSynchronousEntry::OpenFiles(SimpleEntryStat* out_entry_stat) {
   for (int i = 0; i < kSimpleEntryFileCount; ++i) {
     File::Error error;
     if (!MaybeOpenFile(i, &error)) {
       // TODO(juliatuttle,gavinp): Remove one each of these triplets of
@@ skipping 751 matching lines @@
   range.offset = offset;
   range.length = len;
   range.data_crc32 = data_crc32;
   range.file_offset = data_file_offset;
   sparse_ranges_.insert(std::make_pair(offset, range));
 
   return true;
 }
 
 }  // namespace disk_cache