Support delta-compressed variations server responses.

chrome/browser/metrics/variations/variations_seed_store.h

Index: chrome/browser/metrics/variations/variations_seed_store.h
diff --git a/chrome/browser/metrics/variations/variations_seed_store.h b/chrome/browser/metrics/variations/variations_seed_store.h
index 2de275f7a4fdf141a30bba3315ec251254772310..edda22fa0b715adb7de159b4778c140335640b37 100644
--- a/chrome/browser/metrics/variations/variations_seed_store.h
+++ b/chrome/browser/metrics/variations/variations_seed_store.h
@@ -32,15 +32,19 @@ class VariationsSeedStore {
   // successful, |seed| will contain the loaded data and true is returned.
   bool LoadSeed(variations::VariationsSeed* seed);
 
-  // Stores the given seed data (serialized protobuf data) to local state, along
+  // Stores the given seed data (serialized protobuf) to local state, along

[rkaplow, 2015/08/04 22:37:05]

nit, would change to |data| too then

[Alexei Svitkine (slow), 2015/08/05 15:46:15]

Done.

   // with a base64-encoded digital signature for seed and the date when it was
-  // fetched. The |seed_data| will be base64 encoded for storage. If the string
-  // is invalid, the existing prefs are left as is and false is returned. On
+  // fetched. If |is_delta_compressed| is true, treats |data| as being delta
+  // compressed and attempts to decode it first using the store seed data.

[rkaplow, 2015/08/04 22:37:05]

did you mean stored btw?

[Alexei Svitkine (slow), 2015/08/05 15:46:15]

No meant, store's - i.e. refererring to this class which is a
VariationsSeedStore. Added an apostrophe - let me know if it's better now or
whether you prefer that I rephrase it more.

[rkaplow, 2015/08/05 18:01:56]

it's fine - wasn't sure which way you meant it.

+  // The actual seed data will be base64 encoded for storage. If the string
+  // is invalid, the existing prefs are untouched and false is returned. On
   // success and if |parsed_seed| is not NULL, |parsed_seed| will be filled
-  // with the de-serialized protobuf decoded from |seed_data|.
-  bool StoreSeedData(const std::string& seed_data,
+  // with the de-serialized decoded protobuf.
+  bool StoreSeedData(const std::string& data,
                      const std::string& base64_seed_signature,
+                     const std::string& country_code,

[rkaplow, 2015/08/04 22:37:05]

might be worth to add a line in the comment on how country_code interacts.

[Alexei Svitkine (slow), 2015/08/05 15:46:15]

Done.

                      const base::Time& date_fetched,
+                     bool is_delta_compressed,
                      variations::VariationsSeed* parsed_seed);
 
   // Updates |kVariationsSeedDate| and logs when previous date was from a
@@ -52,13 +56,18 @@ class VariationsSeedStore {
     return variations_serial_number_;
   }
 
-  // Registers Local State prefs used by this class.
-  static void RegisterPrefs(PrefRegistrySimple* registry);
+  // Returns whether the last loaded or stored seed has the country field set.
+  bool seed_has_country_code() const {
+    return seed_has_country_code_;
+  }
 
   // Returns the invalid signature in base64 format, or an empty string if the
   // signature was valid, missing, or if signature verification is disabled.
   std::string GetInvalidSignature() const;
 
+  // Registers Local State prefs used by this class.
+  static void RegisterPrefs(PrefRegistrySimple* registry);
+
  protected:
   // Note: UMA histogram enum - don't re-order or remove entries.
   enum VerifySignatureResult {
@@ -82,6 +91,7 @@ class VariationsSeedStore {
 
  private:
   FRIEND_TEST_ALL_PREFIXES(VariationsSeedStoreTest, VerifySeedSignature);
+  FRIEND_TEST_ALL_PREFIXES(VariationsSeedStoreTest, ApplyDeltaPatch);
 
   // Clears all prefs related to variations seed storage.
   void ClearPrefs();
@@ -89,12 +99,31 @@ class VariationsSeedStore {
   // Reads the variations seed data from prefs; returns true on success.
   bool ReadSeedData(std::string* seed_data);
 
+  // Internal version of |StoreSeedData()| that assumes |seed_data| is not delta
+  // compressed.
+  bool StoreSeedDataNoDelta(
+      const std::string& seed_data,
+      const std::string& base64_seed_signature,
+      const std::string& country_code,
+      const base::Time& date_fetched,
+      variations::VariationsSeed* parsed_seed);
+
+  // Applies a delta-compressed |patch| to |existing_data|, producing the result
+  // in |output|. Returns whether the operation was successful.
+  static bool ApplyDeltaPatch(const std::string& existing_data,
+                              const std::string& patch,
+                              std::string* output);
+
   // The pref service used to persist the variations seed.
   PrefService* local_state_;
 
   // Cached serial number from the most recently fetched variations seed.
   std::string variations_serial_number_;
 
+  // Whether the most recently fetched variations seed has the country code
+  // field set.
+  bool seed_has_country_code_;
+
   // Keeps track of an invalid signature.
   std::string invalid_base64_signature_;