SimpleCache: open with fewer seeks.

net/disk_cache/simple/simple_synchronous_entry.h

Index: net/disk_cache/simple/simple_synchronous_entry.h
diff --git a/net/disk_cache/simple/simple_synchronous_entry.h b/net/disk_cache/simple/simple_synchronous_entry.h
index 629be76e1cfaf0ea79cf30eb7c76a7fabcb8ad54..613acbec4ff51dc916bcd4c3edd4fa50f5378a54 100644
--- a/net/disk_cache/simple/simple_synchronous_entry.h
+++ b/net/disk_cache/simple/simple_synchronous_entry.h
@@ -41,12 +41,10 @@ class NET_EXPORT_PRIVATE SimpleEntryStat {
                   const int32_t data_size[],
                   const int32_t sparse_data_size);
 
-  int GetOffsetInFile(const std::string& key,
-                      int offset,
-                      int stream_index) const;
-  int GetEOFOffsetInFile(const std::string& key, int stream_index) const;
-  int GetLastEOFOffsetInFile(const std::string& key, int file_index) const;
-  int64_t GetFileSize(const std::string& key, int file_index) const;
+  int GetOffsetInFile(size_t key_length, int offset, int stream_index) const;
+  int GetEOFOffsetInFile(size_t key_length, int stream_index) const;
+  int GetLastEOFOffsetInFile(size_t key_length, int file_index) const;
+  int64_t GetFileSize(size_t key_length, int file_index) const;
 
   base::Time last_used() const { return last_used_; }
   base::Time last_modified() const { return last_modified_; }
@@ -114,8 +112,12 @@ class SimpleSynchronousEntry {
     bool doomed;
   };
 
+  // Opens a disk cache entry on disk. The |key| parameter is optional, if empty
+  // the operation may be slower. The |entry_hash| parameter is required.
+  // |had_index| is provided only for histograms.
   static void OpenEntry(net::CacheType cache_type,
                         const base::FilePath& path,
+                        const std::string& key,
                         uint64_t entry_hash,
                         bool had_index,
                         SimpleEntryCreationResults* out_results);
@@ -150,7 +152,7 @@ class SimpleSynchronousEntry {
                 net::IOBuffer* out_buf,
                 uint32_t* out_crc32,
                 SimpleEntryStat* entry_stat,
-                int* out_result) const;
+                int* out_result);
   void WriteData(const EntryOperationData& in_entry_op,
                  net::IOBuffer* in_buf,
                  SimpleEntryStat* out_entry_stat,
@@ -210,7 +212,8 @@ class SimpleSynchronousEntry {
   SimpleSynchronousEntry(net::CacheType cache_type,
                          const base::FilePath& path,
                          const std::string& key,
-                         uint64_t entry_hash);
+                         uint64_t entry_hash,
+                         bool had_index);
 
   // Like Entry, the SimpleSynchronousEntry self releases when Close() is
   // called.
@@ -227,18 +230,19 @@ class SimpleSynchronousEntry {
   bool MaybeCreateFile(int file_index,
                        FileRequired file_required,
                        base::File::Error* out_error);
-  bool OpenFiles(bool had_index,
-                 SimpleEntryStat* out_entry_stat);
-  bool CreateFiles(bool had_index,
-                   SimpleEntryStat* out_entry_stat);
+  bool OpenFiles(SimpleEntryStat* out_entry_stat);
+  bool CreateFiles(SimpleEntryStat* out_entry_stat);
   void CloseFile(int index);
   void CloseFiles();
 
-  // Returns a net error, i.e. net::OK on success. |had_index| is passed
-  // from the main entry for metrics purposes, and is true if the index was
-  // initialized when the open operation began.
-  int InitializeForOpen(bool had_index,
-                        SimpleEntryStat* out_entry_stat,
+  // Read the header and key at the beginning of the file, and validate that
+  // they are correct. If this entry was opened with a key, the key is checked
+  // for a match. If not, then the |key_| member is set based on the value in
+  // this header. Records histograms if any check is failed.
+  bool CheckHeaderAndKeyForOpen(int file_index);
+
+  // Returns a net error, i.e. net::OK on success.
+  int InitializeForOpen(SimpleEntryStat* out_entry_stat,
                         scoped_refptr<net::GrowableIOBuffer>* stream_0_data,
                         uint32_t* out_stream_0_crc32);
 
@@ -248,10 +252,8 @@ class SimpleSynchronousEntry {
   bool InitializeCreatedFile(int index, CreateEntryResult* out_result);
 
   // Returns a net error, including net::OK on success and net::FILE_EXISTS
-  // when the entry already exists. |had_index| is passed from the main entry
-  // for metrics purposes, and is true if the index was initialized when the
-  // create operation began.
-  int InitializeForCreate(bool had_index, SimpleEntryStat* out_entry_stat);
+  // when the entry already exists.
+  int InitializeForCreate(SimpleEntryStat* out_entry_stat);
 
   // Allocates and fills a buffer with stream 0 data in |stream_0_data|, then
   // checks its crc32.
@@ -320,11 +322,17 @@ class SimpleSynchronousEntry {
   const net::CacheType cache_type_;
   const base::FilePath path_;
   const uint64_t entry_hash_;
+  const bool had_index_;
   std::string key_;
 
   bool have_open_files_;
   bool initialized_;
 
+  // Initially false, this is set to true when an entry is opened and the
+  // headers have not yet been checked. Any subsequent Read of data should
+  // validate them before completing.
+  bool header_and_key_check_needed_;
+
   base::File files_[kSimpleEntryFileCount];
 
   // True if the corresponding stream is empty and therefore no on-disk file