Unify the error checking of crypto::Encryptor and add WARN_UNUSED_RESULT to prevent misuse.

crypto/encryptor.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 CRYPTO_ENCRYPTOR_H_
 #define CRYPTO_ENCRYPTOR_H_
 #pragma once
 
 #include <string>
 
 #include "base/basictypes.h"
+#include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/string_piece.h"
 #include "build/build_config.h"
 #include "crypto/crypto_export.h"
 
 #if defined(USE_NSS)
 #include "crypto/scoped_nss_types.h"
 #elif defined(OS_WIN)
 #include "crypto/scoped_capi_types.h"
 #endif
@@ skipping 10 matching lines @@
   };
 
   // This class implements a 128-bits counter to be used in AES-CTR encryption.
   // Only 128-bits counter is supported in this class.
   class Counter {
    public:
     explicit Counter(const base::StringPiece& counter);
     ~Counter();
 
     // Increment the counter value.
-    bool Increment();
+    bool Increment() WARN_UNUSED_RESULT;
 
     // Write the content of the counter to |buf|. |buf| should have enough
     // space for |GetLengthInBytes()|.
     void Write(void* buf);
 
     // Return the length of this counter.
     size_t GetLengthInBytes() const;
 
    private:
     union {
       uint32 components32[4];
       uint64 components64[2];
     } counter_;
   };
 
   Encryptor();
   virtual ~Encryptor();
 
   // Initializes the encryptor using |key| and |iv|. Returns false if either the
   // key or the initialization vector cannot be used.
   //
   // When |mode| is CTR then |iv| should be empty.
-  bool Init(SymmetricKey* key, Mode mode, const base::StringPiece& iv);
+  bool Init(SymmetricKey* key, Mode mode,
+            const base::StringPiece& iv) WARN_UNUSED_RESULT;
 
   // Encrypts |plaintext| into |ciphertext|.
-  bool Encrypt(const base::StringPiece& plaintext, std::string* ciphertext);
+  bool Encrypt(const base::StringPiece& plaintext,
+               std::string* ciphertext) WARN_UNUSED_RESULT;
 
   // Decrypts |ciphertext| into |plaintext|.
-  bool Decrypt(const base::StringPiece& ciphertext, std::string* plaintext);
+  bool Decrypt(const base::StringPiece& ciphertext,
+               std::string* plaintext) WARN_UNUSED_RESULT;
 
   // Sets the counter value when in CTR mode. Currently only 128-bits
   // counter value is supported.
   //
   // Returns true only if update was successful.
-  bool SetCounter(const base::StringPiece& counter);
+  bool SetCounter(const base::StringPiece& counter) WARN_UNUSED_RESULT;
 
   // TODO(albertb): Support streaming encryption.
 
  private:
   // Generates a mask using |counter_| to be used for encryption in CTR mode.
   // Resulting mask will be written to |mask| with |mask_len| bytes.
   //
   // Make sure there's enough space in mask when calling this method.
   // Reserve at least |plaintext_len| + 16 bytes for |mask|.
   //
@@ skipping 40 matching lines @@
   std::string iv_;
 #elif defined(OS_WIN)
   ScopedHCRYPTKEY capi_key_;
   DWORD block_size_;
 #endif
 };
 
 }  // namespace crypto
 
 #endif  // CRYPTO_ENCRYPTOR_H_