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..080d8b923bffea7c40e20dfaf7ddbe10c608f234 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
@@ -104,8 +106,10 @@ class HttpCache::Transaction : public HttpTransaction {
   // This transaction is being deleted and we are not done writing to the cache.
   // We need to indicate that the response data was truncated.  Returns true on
   // success. Keep in mind that this operation may have side effects, such as
-  // deleting the active entry.
-  bool AddTruncatedFlag();
+  // deleting the active entry. This also returns success if the response was
+  // completely written, |*did_truncate| will be set to true if it was actually
+  // truncated.
+  bool AddTruncatedFlag(bool* did_truncate);
 
   HttpCache::ActiveEntry* entry() { return entry_; }
 
@@ -164,6 +168,10 @@ 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 +186,14 @@ class HttpCache::Transaction : public HttpTransaction {
     bool initialized;
   };
 
+  // A snapshot of pieces of the transaction before entering the state machine
+  // so that the state can be restored when restarting the state machine.
+  struct RestartInfo {
+    Mode mode = NONE;
+    HttpResponseInfo::CacheEntryStatus cache_entry_status =
+        HttpResponseInfo::CacheEntryStatus::ENTRY_UNDEFINED;
+  };
+
   enum State {
     STATE_UNSET,
 
@@ -220,6 +236,9 @@ 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 +307,9 @@ 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 +452,12 @@ 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 +466,7 @@ 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 +542,12 @@ class HttpCache::Transaction : public HttpTransaction {
   // True if the Transaction is currently processing the DoLoop.
   bool in_do_loop_;
 
+  // Used to restore some members when the state machine is restarted after it
+  // has already been added to an entry e.g after |this| has completed
+  // validation and the writer transaction fails to completely write the
+  // response to the cache.
+  RestartInfo restart_info_;
+
   base::WeakPtrFactory<Transaction> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(Transaction);