HttpCache::Transaction layer allowing parallel validation

net/http/http_cache_transaction.h

Index: net/http/http_cache_transaction.h
diff --git a/net/http/http_cache_transaction.h b/net/http/http_cache_transaction.h
index 51c0db70256cbd31505ca20ffba6486ab4c36aad..6061f0c82e0ec9af4937b9134866bb6ea1f16ecb 100644
--- a/net/http/http_cache_transaction.h
+++ b/net/http/http_cache_transaction.h
@@ -80,6 +80,8 @@ class HttpCache::Transaction : public HttpTransaction {
 
   Mode mode() const { return mode_; }
 
+  std::string& method() { return method_; }
+
   const std::string& key() const { return cache_key_; }
 
   // Writes |buf_len| bytes of meta-data from the provided buffer |buf|. to the
@@ -164,6 +166,10 @@ class HttpCache::Transaction : public HttpTransaction {
   int ResumeNetworkStart() override;
   void GetConnectionAttempts(ConnectionAttempts* out) const override;
 
+  // Invoked when parallel validation cannot proceed due to response failure
+  // and this transaction needs to be restarted.
+  void SetValidatingCannotProceed();
+
   // Returns the estimate of dynamically allocated memory in bytes.
   size_t EstimateMemoryUsage() const;
 
@@ -178,6 +184,13 @@ class HttpCache::Transaction : public HttpTransaction {
     bool initialized;
   };
 
+  // Used when restarting the transaction.

[jkarlin, 2017/05/30 14:42:38]

The comment could be more clear about where this data is coming from, for
example: 

"A snapshot of pieces of the transaction before entering the state machine so
that the state can be restored when restarting the state machine."

[shivanisha, 2017/05/31 17:32:12]

Done

+  struct RestartInfo {
+    Mode mode = NONE;
+    HttpResponseInfo::CacheEntryStatus cache_entry_status =
+        HttpResponseInfo::CacheEntryStatus::ENTRY_UNDEFINED;
+  };
+
   enum State {
     STATE_UNSET,
 
@@ -220,6 +233,9 @@ class HttpCache::Transaction : public HttpTransaction {
     STATE_PARTIAL_HEADERS_RECEIVED,
     STATE_CACHE_READ_METADATA,
     STATE_CACHE_READ_METADATA_COMPLETE,
+    STATE_HEADERS_PHASE_CANNOT_PROCEED,
+    STATE_FINISH_HEADERS,
+    STATE_FINISH_HEADERS_COMPLETE,
 
     // These states are entered from Read/AddTruncatedFlag.
     STATE_NETWORK_READ,
@@ -288,6 +304,9 @@ class HttpCache::Transaction : public HttpTransaction {
   int DoPartialHeadersReceived();
   int DoCacheReadMetadata();
   int DoCacheReadMetadataComplete(int result);
+  int DoHeadersPhaseCannotProceed();
+  int DoFinishHeaders(int result);
+  int DoFinishHeadersComplete(int result);
   int DoNetworkRead();
   int DoNetworkReadComplete(int result);
   int DoCacheReadData();
@@ -430,7 +449,12 @@ class HttpCache::Transaction : public HttpTransaction {
   void SyncCacheEntryStatusToResponse();
   void RecordHistograms();
 
-  // Called to signal completion of asynchronous IO.
+  // Called to signal completion of asynchronous IO. Note that this callback is
+  // used in the conventional sense where one layer calls the callback of the
+  // layer above it e.g. this callback gets called from the network transaction
+  // layer. In addition, it is also used for HttpCache layer to let this
+  // transaction know when it is out of a queued state in ActiveEntry and can
+  // continue its processing.
   void OnIOComplete(int result);
 
   // When in a DoLoop, use this to set the next state as it verifies that the
@@ -439,6 +463,7 @@ class HttpCache::Transaction : public HttpTransaction {
 
   State next_state_;
   const HttpRequestInfo* request_;
+  std::string method_;
   RequestPriority priority_;
   NetLogWithSource net_log_;
   std::unique_ptr<HttpRequestInfo> custom_request_;
@@ -514,6 +539,8 @@ class HttpCache::Transaction : public HttpTransaction {
   // True if the Transaction is currently processing the DoLoop.
   bool in_do_loop_;
 
+  RestartInfo restart_info_;

[jkarlin, 2017/05/30 14:42:38]

Please add a comment to this.

[shivanisha, 2017/05/31 17:32:12]

done

+
   base::WeakPtrFactory<Transaction> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(Transaction);