base::MD5IntermediateFinal() generates digest non-destructively.

base/md5.h

 // Copyright (c) 2011 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 BASE_MD5_H_
 #define BASE_MD5_H_
 
 #include "base/base_export.h"
 #include "base/strings/string_piece.h"
 
@@ skipping 40 matching lines @@
 BASE_EXPORT void MD5Init(MD5Context* context);
 
 // For the given buffer of |data| as a StringPiece, updates the given MD5
 // context with the sum of the data. You can call this any number of times
 // during the computation, except that MD5Init() must have been called first.
 BASE_EXPORT void MD5Update(MD5Context* context, const StringPiece& data);
 
 // Finalizes the MD5 operation and fills the buffer with the digest.
 BASE_EXPORT void MD5Final(MD5Digest* digest, MD5Context* context);
 
+// MD5IntermediateFinal() generates a digest without finalizing the MD5
+// operation.  Can be used to generate digests for the input seen thus far,
+// without affecting the digest generated for the entire input.
+BASE_EXPORT void MD5IntermediateFinal(MD5Digest* digest,
+                                      const MD5Context* context);
+
 // Converts a digest into human-readable hexadecimal.
 BASE_EXPORT std::string MD5DigestToBase16(const MD5Digest& digest);
 
 // Returns the MD5 (in hexadecimal) of a string.
 BASE_EXPORT std::string MD5String(const StringPiece& str);
 
 }  // namespace base
 
 #endif  // BASE_MD5_H_