Add support to sha256 hash the downloaded file....

chrome/browser/download/base_file.h

 // Copyright (c) 2010 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.
 
 #ifndef CHROME_BROWSER_DOWNLOAD_BASE_FILE_H_
 #define CHROME_BROWSER_DOWNLOAD_BASE_FILE_H_
 #pragma once
 
 #include <string>
 
 #include "base/file_path.h"
 #include "base/linked_ptr.h"
+#include "base/scoped_ptr.h"
 #include "chrome/browser/power_save_blocker.h"
 #include "googleurl/src/gurl.h"
 
 namespace net {
 class FileStream;
 }
 
+struct SHA256ContextStr;
+typedef struct SHA256ContextStr SHA256Context;
+
 // File being downloaded and saved to disk. This is a base class
 // for DownloadFile and SaveFile, which keep more state information.
 class BaseFile {
  public:
   BaseFile(const FilePath& full_path,
            const GURL& source_url,
            const GURL& referrer_url,
            int64 received_bytes,
-           const linked_ptr<net::FileStream>& file_stream);
+           const linked_ptr<net::FileStream>& file_stream,
+           bool calculate_hash);

[Scott Hess - ex-Googler, 2011/01/10 23:12:07]

Is there any real advantage to making the hash calculation optional?  AFAICT, it
will kick in for all of the expensive cases, and not for the inexpensive cases,
so maybe it would be reasonable (and simpler) to always calculate it and only
use the results when necessary.

Alternately, WDYT about making the relevant methods virtual so that DownloadFile
can override them to calculate the digest and SaveFile can ignore?

[lzheng, 2011/01/11 01:06:44]

I made the "GetSha256Hash" virtual. 

I am still hesitate to let all downloads calculate the sha256 hash -- the hash
does not come free, if the hash is not needed, we should avoid it. Plus, the
"calculate_hash" flag does not make the code too complicated. Unless you have
other thoughts? 

On 2011/01/10 23:12:07, shess wrote:

   ~BaseFile();
 
   bool Initialize();
 
   // Write a new chunk of data to the file. Returns true on success (all bytes
   // written to the file).
   bool AppendDataToFile(const char* data, size_t data_len);
 
   // Rename the download file. Returns true on success.
   // |path_renamed_| is set to true only if |is_final_rename| is true.
   // Marked virtual for testing.
   virtual bool Rename(const FilePath& full_path, bool is_final_rename);
 
   // Abort the download and automatically close the file.
   void Cancel();
 
   // Indicate that the download has finished. No new data will be received.
   void Finish();
 
   // Informs the OS that this file came from the internet.
   void AnnotateWithSourceInformation();
 
   FilePath full_path() const { return full_path_; }
   bool path_renamed() const { return path_renamed_; }
   bool in_progress() const { return file_stream_ != NULL; }
   int64 bytes_so_far() const { return bytes_so_far_; }
 
+  // Set |hash| with sha256 digest for the file. The |hash| would be a
+  // lower-case hex string. Returns false if the digest is not calcuated.
+  bool GetSha256Hash(std::string* hash);
+
   virtual std::string DebugString() const;
 
  protected:
   bool Open();
   void Close();
 
   // Full path to the file including the file name.
   FilePath full_path_;
 
   // Whether the download is still using its initial temporary path.
   bool path_renamed_;
 
  private:
+  static const size_t kSha256HashLen_ = 32;
+
   // Source URL for the file being downloaded.
   GURL source_url_;
 
   // The URL where the download was initiated.
   GURL referrer_url_;
 
   // OS file stream for writing
   linked_ptr<net::FileStream> file_stream_;
 
   // Amount of data received up so far, in bytes.
   int64 bytes_so_far_;
 
   // RAII handle to keep the system from sleeping while we're downloading.
   PowerSaveBlocker power_save_blocker_;
 
+  // Indicates if sha256 hash should be calculated for the downloaded file.
+  bool calculate_hash_;
+
+  scoped_ptr<SHA256Context> sha_context_;
+
+  unsigned char sha256_hash_[kSha256HashLen_];
+
   DISALLOW_COPY_AND_ASSIGN(BaseFile);
 };
 
 #endif  // CHROME_BROWSER_DOWNLOAD_BASE_FILE_H_