Make USE_OPENSSL and USE_NSS mutually exclusive

base/openssl_util.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 BASE_OPENNSSL_UTIL_H_
+#define BASE_OPENNSSL_UTIL_H_
+#pragma once
+
+#include "base/basictypes.h"
+
+namespace base {
+
+// Provides a buffer of at least MIN_SIZE bytes, for use when calling OpenSSL's
+// SHA256, HMAC, etc functions, adapting the buffer sizing rules to meet those
+// of the our base wrapper APIs.
+// This allows the library to write directly to the caller's buffer if it is of
+// sufficient size, but if not it will write to temporary |min_sized_buffer_|
+// of required size and then its content is automatically copied out on
+// destruction, with truncation as appropriate.
+template<int MIN_SIZE>
+class ScopedOpenSSLSafeSizeBuffer {
+ public:
+  ScopedOpenSSLSafeSizeBuffer(unsigned char* output, size_t output_len)
+      : output_(output),
+        output_len_(output_len) {
+  }
+
+  ~ScopedOpenSSLSafeSizeBuffer() {
+    if (output_len_ < MIN_SIZE) {
+      // Copy the temporary buffer out, truncating as needed.
+      memcpy(output_, min_sized_buffer_, output_len_);
+    }
+    // else... any writing already happened directly into |output_|.
+  }
+
+  unsigned char* safe_buffer() {
+    return output_len_ < MIN_SIZE ? min_sized_buffer_ : output_;
+  }
+
+ private:
+  // Pointer to the caller's data area and it's associated size, where data
+  // written via safe_buffer() will [eventually] end up.
+  unsigned char* output_;
+  size_t output_len_;
+
+  // Temporary buffer writen into in the case where the caller's
+  // buffer is not of sufficient size.
+  unsigned char min_sized_buffer_[MIN_SIZE];
+};
+
+}  // namespace base
+
+#endif  // BASE_NSS_UTIL_H_