talk/base/sec_buffer.h

/*
 * libjingle
 * Copyright 2004--2005, Google Inc.
 *
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions are met:
 *
 *  1. Redistributions of source code must retain the above copyright notice, 
 *     this list of conditions and the following disclaimer.
 *  2. Redistributions in binary form must reproduce the above copyright notice,
 *     this list of conditions and the following disclaimer in the documentation
 *     and/or other materials provided with the distribution.
 *  3. The name of the author may not be used to endorse or promote products 
 *     derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
 * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 
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 */

// @file Contains utility classes that make it easier to use SecBuffers

#ifndef TALK_BASE_SEC_BUFFER_H__
#define TALK_BASE_SEC_BUFFER_H__

namespace talk_base {

// A base class for CSecBuffer<T>. Contains
// all implementation that does not require
// template arguments.
class CSecBufferBase : public SecBuffer {
 public:
  CSecBufferBase() {
    Clear();
  }

  // Uses the SSPI to free a pointer, must be
  // used for buffers returned from SSPI APIs.
  static void FreeSSPI(void *ptr) {
    if ( ptr ) {
      SECURITY_STATUS status;
      status = ::FreeContextBuffer(ptr);
      ASSERT(SEC_E_OK == status); // "Freeing context buffer"
    }
  }

  // Deletes a buffer with operator delete
  static void FreeDelete(void *ptr) {
    delete [] reinterpret_cast<char*>(ptr);
  }

  // A noop delete, for buffers over other
  // people's memory
  static void FreeNone(void *ptr) {
  }

 protected:
  // Clears the buffer to EMPTY & NULL
  void Clear() {
    this->BufferType = SECBUFFER_EMPTY;
    this->cbBuffer = 0;
    this->pvBuffer = NULL;
  }
};

// Wrapper class for SecBuffer to take care
// of initialization and destruction.
template <void (*pfnFreeBuffer)(void *ptr)>
class CSecBuffer: public CSecBufferBase {
 public:
  // Initializes buffer to empty & NULL
  CSecBuffer() {
  }

  // Frees any allocated memory
  ~CSecBuffer() {
    Release();
  }

  // Frees the buffer appropriately, and re-nulls
  void Release() {
    pfnFreeBuffer(this->pvBuffer);
    Clear();
  }

 private:
  // A placeholder function for compile-time asserts on the class
  void CompileAsserts() {
    // never invoked...
    assert(false); // _T("Notreached")

    // This class must not extend the size of SecBuffer, since
    // we use arrays of CSecBuffer in CSecBufferBundle below
    cassert(sizeof(CSecBuffer<SSPIFree> == sizeof(SecBuffer)));
  }
};

// Contains all generic implementation for the
// SecBufferBundle class
class SecBufferBundleBase {
 public:
};

// A template class that bundles a SecBufferDesc with
// one or more SecBuffers for convenience. Can take
// care of deallocating buffers appropriately, as indicated
// by pfnFreeBuffer function.
// By default does no deallocation.
template <int num_buffers,
          void (*pfnFreeBuffer)(void *ptr) = CSecBufferBase::FreeNone>
class CSecBufferBundle : public SecBufferBundleBase {
 public:
  // Constructs a security buffer bundle with num_buffers
  // buffers, all of which are empty and nulled.
  CSecBufferBundle() {
    desc_.ulVersion = SECBUFFER_VERSION;
    desc_.cBuffers = num_buffers;
    desc_.pBuffers = buffers_;
  }

  // Frees all currently used buffers.
  ~CSecBufferBundle() {
    Release();
  }

  // Accessor for the descriptor
  PSecBufferDesc desc() {
    return &desc_;
  }

  // Accessor for the descriptor
  const PSecBufferDesc desc() const {
    return &desc_;
  }

  // returns the i-th security buffer
  SecBuffer &operator[] (size_t num) {
    ASSERT(num < num_buffers); // "Buffer index out of bounds"
    return buffers_[num];
  }

  // returns the i-th security buffer
  const SecBuffer &operator[] (size_t num) const {
    ASSERT(num < num_buffers); // "Buffer index out of bounds"
    return buffers_[num];
  }

  // Frees all non-NULL security buffers,
  // using the deallocation function
  void Release() {
    for ( size_t i = 0; i < num_buffers; ++i ) {
      buffers_[i].Release();
    }
  }

 private:
  // Our descriptor
  SecBufferDesc               desc_;
  // Our bundled buffers, each takes care of its own
  // initialization and destruction
  CSecBuffer<pfnFreeBuffer>   buffers_[num_buffers];
};

} // namespace talk_base

#endif  // TALK_BASE_SEC_BUFFER_H__