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 2d249c1eda028c6329ed2edc603bfc2f4064a082..5d74ad2acb3925a0e3629d94f43da8c7091147d9 100644
--- a/net/http/http_cache_transaction.h
+++ b/net/http/http_cache_transaction.h
@@ -163,6 +163,7 @@ class HttpCache::Transaction : public HttpTransaction {
       const BeforeHeadersSentCallback& callback) override;
   int ResumeNetworkStart() override;
   void GetConnectionAttempts(ConnectionAttempts* out) const override;
+  void SetValidatingCannotProceed();
 
   // Returns the estimate of dynamically allocated memory in bytes.
   size_t EstimateMemoryUsage() const;
@@ -218,6 +219,8 @@ class HttpCache::Transaction : public HttpTransaction {
     STATE_PARTIAL_HEADERS_RECEIVED,
     STATE_CACHE_READ_METADATA,
     STATE_CACHE_READ_METADATA_COMPLETE,
+    STATE_WAIT_BEFORE_READ,
+    STATE_WAIT_BEFORE_READ_COMPLETE,
 
     // These states are entered from Read/AddTruncatedFlag.
     STATE_NETWORK_READ,
@@ -245,6 +248,7 @@ class HttpCache::Transaction : public HttpTransaction {
   // Runs the state transition loop. Resets and calls |callback_| on exit,
   // unless the return value is ERR_IO_PENDING.
   int DoLoop(int result);
+  int DoLoopImpl(int result);
 
   // Each of these methods corresponds to a State value.  If there is an
   // argument, the value corresponds to the return of the previous state or
@@ -284,6 +288,8 @@ class HttpCache::Transaction : public HttpTransaction {
   int DoTruncateCachedMetadata();
   int DoTruncateCachedMetadataComplete(int result);
   int DoPartialHeadersReceived();
+  int DoWaitBeforeRead();
+  int DoWaitBeforeReadComplete(int result);
   int DoCacheReadMetadata();
   int DoCacheReadMetadataComplete(int result);
   int DoNetworkRead();
@@ -412,6 +418,13 @@ class HttpCache::Transaction : public HttpTransaction {
   // |old_network_trans_load_timing_|, which must be NULL when this is called.
   void ResetNetworkTransaction();
 
+  // Since a transaction could be doing validation of request headers in
+  // parallel with another request writing response data to the entry, failure
+  // to write the data might lead to restarting this request. This function
+  // resets all the required variables to be able to restart the transaction's
+  // state machine.
+  void RestartAfterValidationStarted();
+
   // Returns true if we should bother attempting to resume this request if it is
   // aborted while in progress. If |has_data| is true, the size of the stored
   // data is considered for the result.
@@ -451,6 +464,7 @@ class HttpCache::Transaction : public HttpTransaction {
   const HttpResponseInfo* new_response_;
   std::string cache_key_;
   Mode mode_;
+  Mode original_mode_;  // Used when restarting the transaction.
   bool reading_;  // We are already reading. Never reverts to false once set.
   bool invalid_range_;  // We may bypass the cache for this request.
   bool truncated_;  // We don't have all the response data.
@@ -463,6 +477,7 @@ class HttpCache::Transaction : public HttpTransaction {
   bool couldnt_conditionalize_request_;
   bool bypass_lock_for_test_;  // A test is exercising the cache lock.
   bool fail_conditionalization_for_test_;  // Fail ConditionalizeRequest.
+  bool validating_cannot_proceed_;
   scoped_refptr<IOBuffer> read_buf_;
   int io_buf_len_;
   int read_offset_;