[webcrypto] Match the error handling defined by the spec.

public/platform/WebCrypto.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 26 matching lines @@
 
 namespace WebCore { class CryptoResult; }
 
 #if BLINK_IMPLEMENTATION
 namespace WTF { template <typename T> class PassRefPtr; }
 #endif
 
 namespace blink {
 
 class WebArrayBuffer;
+class WebString;
 
 class WebCryptoResult {
 public:
     WebCryptoResult(const WebCryptoResult& o)
     {
         assign(o);
     }
 
     ~WebCryptoResult()
     {
         reset();
     }
 
     WebCryptoResult& operator=(const WebCryptoResult& o)
     {
         assign(o);
         return *this;
     }
 
     BLINK_EXPORT void completeWithError();
+
+    // Note that WebString is NOT safe to pass across threads.
+    //
+    // Error details are intended to be displayed to developers for debugging.
+    // They MUST NEVER reveal any secret information such as bytes of the key
+    // or plain text. An appropriate error would be something like:
+    //   "iv must be 16 bytes long".
+    BLINK_EXPORT void completeWithError(const WebString&);
+
     // Note that WebArrayBuffer is NOT safe to create from another thread.
     BLINK_EXPORT void completeWithBuffer(const WebArrayBuffer&);
     // Makes a copy of the input data given as a pointer and byte length.
     BLINK_EXPORT void completeWithBuffer(const void*, unsigned);
     BLINK_EXPORT void completeWithBoolean(bool);
     BLINK_EXPORT void completeWithKey(const WebCryptoKey&);
     BLINK_EXPORT void completeWithKeyPair(const WebCryptoKey& publicKey, const WebCryptoKey& privateKey);
 
 #if BLINK_IMPLEMENTATION
     explicit WebCryptoResult(const WTF::PassRefPtr<WebCore::CryptoResult>&);
 #endif
 
 private:
     BLINK_EXPORT void reset();
     BLINK_EXPORT void assign(const WebCryptoResult&);
 
     WebPrivatePtr<WebCore::CryptoResult> m_impl;
 };
 
 class WebCrypto {
 public:
-    // WebCrypto is the interface for starting one-shot cryptographic operations.
+    // WebCrypto is the interface for starting one-shot cryptographic
+    // operations.
     //
     // -----------------------
     // Completing the request
     // -----------------------
     //
     // Implementations signal completion by calling one of the methods on
     // "result". Only a single result/error should be set for the request.
     // Different operations expect different result types based on the
     // algorithm parameters; see the Web Crypto standard for details.
     //
@@ skipping 68 matching lines @@
     // It is possible that unwrappedKeyAlgorithm.isNull()
     virtual void unwrapKey(WebCryptoKeyFormat, const unsigned char* wrappedKey, unsigned wrappedKeySize, const WebCryptoKey&, const WebCryptoAlgorithm& unwrapAlgorithm, const WebCryptoAlgorithm& unwrappedKeyAlgorithm, bool extractable, WebCryptoKeyUsageMask, WebCryptoResult result) { result.completeWithError(); }
 
 protected:
     virtual ~WebCrypto() { }
 };
 
 } // namespace blink
 
 #endif