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

crypto/encryptor_win.cc

Index: crypto/encryptor_win.cc
diff --git a/crypto/encryptor_win.cc b/crypto/encryptor_win.cc
index fae1f8220b73035252e91751bfcb8877f5d7d781..e4f108f03bbf7dc40810547c1ef5d48107c4f25b 100644
--- a/crypto/encryptor_win.cc
+++ b/crypto/encryptor_win.cc
@@ -41,8 +41,8 @@ Encryptor::~Encryptor() {
 bool Encryptor::Init(SymmetricKey* key,
                      Mode mode,
                      const base::StringPiece& iv) {
-  DCHECK(key);
-  DCHECK_EQ(CBC, mode) << "Unsupported mode of operation";
+  if (!key || mode != CBC)
+    return false;
 
   // In CryptoAPI, the IV, padding mode, and feedback register (for a chaining
   // mode) are properties of a key, so we have to create a copy of the key for
@@ -82,44 +82,50 @@ bool Encryptor::Init(SymmetricKey* key,
 
 bool Encryptor::Encrypt(const base::StringPiece& plaintext,
                         std::string* ciphertext) {
+  ciphertext->clear();
+  if (plaintext.empty() && mode_ != CBC)
+    return false;
+
   DWORD data_len = plaintext.size();
   DWORD total_len = data_len + block_size_;
-  CHECK_GT(total_len, data_len);
+  if (total_len == 0 || total_len + 1 < data_len)
+    return false;
 
   // CryptoAPI encrypts/decrypts in place.
-  char* ciphertext_data = WriteInto(ciphertext, total_len + 1);
-  memcpy(ciphertext_data, plaintext.data(), data_len);
+  std::string result;
+  char* result_data = WriteInto(&result, total_len + 1);
+  memcpy(result_data, plaintext.data(), data_len);
 
   BOOL ok = CryptEncrypt(capi_key_.get(), NULL, TRUE, 0,
-                         reinterpret_cast<BYTE*>(ciphertext_data), &data_len,
+                         reinterpret_cast<BYTE*>(result_data), &data_len,
                          total_len);
-  if (!ok) {
-    ciphertext->clear();
+  if (!ok)
     return false;
-  }
 
-  ciphertext->resize(data_len);
+  result.resize(data_len);
+  ciphertext->swap(result);
   return true;
 }
 
 bool Encryptor::Decrypt(const base::StringPiece& ciphertext,
                         std::string* plaintext) {
+  plaintext->clear();
   DWORD data_len = ciphertext.size();
-  if (data_len == 0 || (data_len + 1) < data_len)
+  if (data_len == 0 || data_len + 1 < data_len)
     return false;
 
   // CryptoAPI encrypts/decrypts in place.
-  char* plaintext_data = WriteInto(plaintext, data_len + 1);
-  memcpy(plaintext_data, ciphertext.data(), data_len);
+  std::string result;
+  char* result_data = WriteInto(&result, data_len + 1);
+  memcpy(result_data, ciphertext.data(), data_len);
 
   BOOL ok = CryptDecrypt(capi_key_.get(), NULL, TRUE, 0,
-                         reinterpret_cast<BYTE*>(plaintext_data), &data_len);
-  if (!ok) {
-    plaintext->clear();
+                         reinterpret_cast<BYTE*>(result_data), &data_len);
+  if (!ok)
     return false;
-  }
 
-  plaintext->resize(data_len);
+  result.resize(data_len);
+  plaintext->swap(result);
   return true;
 }