SafeBrowising: Read and write V4Store from/to disk

components/safe_browsing_db/v4_store.h

Index: components/safe_browsing_db/v4_store.h
diff --git a/components/safe_browsing_db/v4_store.h b/components/safe_browsing_db/v4_store.h
index d3fdaea7fa23289a519d2b5b4bb053c68464e121..97aeb63c3cef8fcf264b079c24d94030f2dd9beb 100644
--- a/components/safe_browsing_db/v4_store.h
+++ b/components/safe_browsing_db/v4_store.h
@@ -18,6 +18,43 @@ class V4Store;
 typedef base::Callback<void(std::unique_ptr<V4Store>)>
     UpdatedStoreReadyCallback;
 
+// Enumerate different failure events while parsing the file read from disk for
+// histogramming purposes.  DO NOT CHANGE THE ORDERING OF THESE VALUES.
+enum StoreReadFailureType {
+  // Reserved for errors in parsing this enum.

[Nathan Parker, 2016/06/16 00:07:50]

(if this isn't stored in a proto, it probably won't have a parse error, but this
is a good general practice imho)

[vakh (use Gerrit instead), 2016/06/16 08:25:18]

Acknowledged.

+  UNEXPECTED_FAILURE = 0,
+
+  // No errors.
+  SUCCESS = 1,
+
+  // The contents of the file could not be read.
+  FILE_UNREADABLE_FAILURE = 2,
+
+  // The file was found to be empty.
+  FILE_EMPTY_FAILURE = 3,
+
+  // The contents of the file could not be interpreted as a valid
+  // V4StoreFileFormat proto.
+  PROTO_PARSING_FAILURE = 4,
+
+  // The magic number didn't match. We're most likely trying to read a file
+  // that doesn't contain hash-prefixes.
+  UNEXPECTED_MAGIC_NUMBER_FAILURE = 5,
+
+  // The version of the file is lower than expected and Chromium doesn't know
+  // how to interpret this file anymore.
+  FILE_VERSION_TOO_LOW_FAILURE = 6,
+
+  // The rest of the file could not be parsed as a ListUpdateResponse protobuf.
+  // The only case when this can happen is if the machine crashed before the
+  // file was fully written to disk.

[Nathan Parker, 2016/06/16 00:07:50]

Or any general corruption on disk, ya?

[vakh (use Gerrit instead), 2016/06/16 08:25:18]

Done.

+  HASH_PREFIX_INFO_MISSING_FAILURE = 7,
+
+  // Memory space for histograms is determined by the max.  ALWAYS
+  // ADD NEW VALUES BEFORE THIS ONE.
+  FORMAT_FAILURE_MAX
+};
+
 // Factory for creating V4Store. Tests implement this factory to create fake
 // stores for testing.
 class V4StoreFactory {
@@ -41,6 +78,8 @@ class V4Store {
 
   const std::string& state() const { return state_; }
 
+  void Initialize();
+
   void ApplyUpdate(const ListUpdateResponse&,
                    const scoped_refptr<base::SingleThreadTaskRunner>&,
                    UpdatedStoreReadyCallback);
@@ -56,9 +95,29 @@ class V4Store {
   std::string state_;
 
  private:
+  // Creates a new store from an existing one when processing an update.
   V4Store(const V4Store& other);
 
+  // Reads the state of the store from the file on disk and returns the reason
+  // for the failure or reports success.
+  StoreReadFailureType ReadFromDisk();
+
+  // Writes the FULL_UPDATE |response| to disk as a V4StoreFileFormat proto.
+  // Returns false if the write fails.
+  bool WriteToDisk(const ListUpdateResponse& response) const;
+
   std::string GetHumanReadableState() const;
+
+  FRIEND_TEST_ALL_PREFIXES(V4StoreTest, TestReadFromEmptyFile);
+  FRIEND_TEST_ALL_PREFIXES(V4StoreTest, TestReadFromAbsentFile);
+  FRIEND_TEST_ALL_PREFIXES(V4StoreTest, TestReadFromInvalidContentsFile);
+  FRIEND_TEST_ALL_PREFIXES(V4StoreTest, TestReadFromUnexpectedMagicFile);
+  FRIEND_TEST_ALL_PREFIXES(V4StoreTest, TestReadFromLowVersionFile);
+  FRIEND_TEST_ALL_PREFIXES(V4StoreTest, TestReadFromNoHashPrefixInfoFile);
+  FRIEND_TEST_ALL_PREFIXES(V4StoreTest, TestReadFromNoHashPrefixesFile);
+  FRIEND_TEST_ALL_PREFIXES(V4StoreTest, TestWriteNoResponseType);
+  FRIEND_TEST_ALL_PREFIXES(V4StoreTest, TestWritePartialResponseType);
+  FRIEND_TEST_ALL_PREFIXES(V4StoreTest, TestWriteFullResponseType);
 };
 
 inline std::ostream& operator<<(std::ostream& os, const V4Store& store) {