HttpCache::Transaction layer allowing parallel validation

net/http/http_cache_transaction.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file declares HttpCache::Transaction, a private class of HttpCache so
 // it should only be included by http_cache.cc
 
 #ifndef NET_HTTP_HTTP_CACHE_TRANSACTION_H_
 #define NET_HTTP_HTTP_CACHE_TRANSACTION_H_
 
@@ skipping 62 matching lines @@
     READ_WRITE      = READ | WRITE,
     UPDATE          = READ_META | WRITE,  // READ_WRITE & ~READ_DATA
   };
 
   Transaction(RequestPriority priority,
               HttpCache* cache);
   ~Transaction() override;
 
   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
   // HTTP cache entry that backs this transaction (if any).
   // Returns the number of bytes actually written, or a net error code. If the
   // operation cannot complete immediately, returns ERR_IO_PENDING, grabs a
   // reference to the buffer (until completion), and notifies the caller using
   // the provided |callback| when the operation finishes.
   //
   // The first time this method is called for a given transaction, previous
   // meta-data will be overwritten with the provided data, and subsequent
   // invocations will keep appending to the cached entry.
   //
   // In order to guarantee that the metadata is set to the correct entry, the
   // response (or response info) must be evaluated by the caller, for instance
   // to make sure that the response_time is as expected, before calling this
   // method.
   int WriteMetadata(IOBuffer* buf,
                     int buf_len,
                     const CompletionCallback& callback);
 
   // 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, |*is_truncated| will be set if it was actually

[jkarlin, 2017/06/08 16:14:10]

It'd be cleaner if is_truncated were assigned a value regardless.

[shivanisha, 2017/06/08 18:26:02]

Done

+  // truncated.
+  bool AddTruncatedFlag(bool* is_truncated);

[jkarlin, 2017/06/08 16:14:09]

optional nit: rename is_truncated to did_truncate

[shivanisha, 2017/06/08 18:26:02]

done

 
   HttpCache::ActiveEntry* entry() { return entry_; }
 
   // Returns the LoadState of the writer transaction of a given ActiveEntry. In
   // other words, returns the LoadState of this transaction without asking the
   // http cache, because this transaction should be the one currently writing
   // to the cache entry.
   LoadState GetWriterLoadState() const;
 
   const CompletionCallback& io_callback() { return io_callback_; }
@@ skipping 38 matching lines @@
   void SetPriority(RequestPriority priority) override;
   void SetWebSocketHandshakeStreamCreateHelper(
       WebSocketHandshakeStreamBase::CreateHelper* create_helper) override;
   void SetBeforeNetworkStartCallback(
       const BeforeNetworkStartCallback& callback) override;
   void SetBeforeHeadersSentCallback(
       const BeforeHeadersSentCallback& callback) override;
   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;
 
  private:
   static const size_t kNumValidationHeaders = 2;
   // Helper struct to pair a header name with its value, for
   // headers used to validate cache entries.
   struct ValidationHeaders {
     ValidationHeaders() : initialized(false) {}
 
     std::string values[kNumValidationHeaders];
     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,
 
     // Normally, states are traversed in approximately this order.
     STATE_NONE,
     STATE_GET_BACKEND,
     STATE_GET_BACKEND_COMPLETE,
     STATE_INIT_ENTRY,
     STATE_OPEN_ENTRY,
     STATE_OPEN_ENTRY_COMPLETE,
@@ skipping 22 matching lines @@
     STATE_OVERWRITE_CACHED_RESPONSE,
     STATE_CACHE_WRITE_RESPONSE,
     STATE_CACHE_WRITE_RESPONSE_COMPLETE,
     STATE_TRUNCATE_CACHED_DATA,
     STATE_TRUNCATE_CACHED_DATA_COMPLETE,
     STATE_TRUNCATE_CACHED_METADATA,
     STATE_TRUNCATE_CACHED_METADATA_COMPLETE,
     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,
     STATE_NETWORK_READ_COMPLETE,
     STATE_CACHE_READ_DATA,
     STATE_CACHE_READ_DATA_COMPLETE,
     STATE_CACHE_WRITE_DATA,
     STATE_CACHE_WRITE_DATA_COMPLETE,
     STATE_CACHE_WRITE_TRUNCATED_RESPONSE,
     STATE_CACHE_WRITE_TRUNCATED_RESPONSE_COMPLETE
@@ skipping 48 matching lines @@
   int DoOverwriteCachedResponse();
   int DoCacheWriteResponse();
   int DoCacheWriteResponseComplete(int result);
   int DoTruncateCachedData();
   int DoTruncateCachedDataComplete(int result);
   int DoTruncateCachedMetadata();
   int DoTruncateCachedMetadataComplete(int result);
   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();
   int DoCacheReadDataComplete(int result);
   int DoCacheWriteData(int num_bytes);
   int DoCacheWriteDataComplete(int result);
   int DoCacheWriteTruncatedResponse();
   int DoCacheWriteTruncatedResponseComplete(int result);
 
   // Sets request_ and fields derived from it.
@@ skipping 122 matching lines @@
   void SetResponse(const HttpResponseInfo& new_response);
   void SetAuthResponse(const HttpResponseInfo& new_response);
 
   void UpdateCacheEntryStatus(
       HttpResponseInfo::CacheEntryStatus new_cache_entry_status);
 
   // Sets the response.cache_entry_status to the current cache_entry_status_.
   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
   // state isn't set twice.
   void TransitionToState(State state);
 
   State next_state_;
   const HttpRequestInfo* request_;
+  std::string method_;
   RequestPriority priority_;
   NetLogWithSource net_log_;
   std::unique_ptr<HttpRequestInfo> custom_request_;
   HttpRequestHeaders request_headers_copy_;
   // If extra_headers specified a "if-modified-since" or "if-none-match",
   // |external_validation_| contains the value of those headers.
   ValidationHeaders external_validation_;
   base::WeakPtr<HttpCache> cache_;
   HttpCache::ActiveEntry* entry_;
   HttpCache::ActiveEntry* new_entry_;
@@ skipping 55 matching lines @@
   // case the transaction does not exist yet.
   WebSocketHandshakeStreamBase::CreateHelper*
       websocket_handshake_stream_base_create_helper_;
 
   BeforeNetworkStartCallback before_network_start_callback_;
   BeforeHeadersSentCallback before_headers_sent_callback_;
 
   // 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);
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_CACHE_TRANSACTION_H_