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memstreams.h

/*
 * Copyright (c) 2000-2004 Apple Computer, Inc. All Rights Reserved.
 * 
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 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
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//
// memstreams - primitive memory block streaming support
//
#ifndef _H_MEMSTREAMS
#define _H_MEMSTREAMS

#include <security_utilities/memutils.h>
#include <security_utilities/endian.h>


namespace Security
{

//
// Encapsulate these very sharp tools in a separate namespace
//
namespace LowLevelMemoryUtilities
{


//
// A simple utility for incremental creation of a contiguous memory block.
//
// Note that Writer and Writer::Counter go together. They use the same alignment
// and padding rules, so Writer::Counter will correctly calculate total buffer
// size for Writer, *presuming* that they are called in the same order.
//
// This layer allocates no memory; that's up to the caller (you).
//
// WARNING: There is no check for overflow. If you write too much, you will die.
// Writer::Counter can tell you how much you need.
//
class Writer {
private:
      void *advance(size_t size)
      {
            void *here = alignUp(writePos);
            writePos = increment(here, size);
            return here;
      }
    
public:    
      Writer() { }
      Writer(void *base) : writePos(base) { }
      void operator = (void *base) { writePos = base; }

      template <class T>
      T *operator () (const T &obj)
      { T *here = (T *)advance(sizeof(T)); *here = obj; return here; }

      void *operator () (const void *addr, size_t size)
      { void *here = advance(size); return memcpy(here, addr, size); }

      char *operator () (const char *s)
      { return (char *)(*this)(s, strlen(s) + 1); }
      
      void countedData(const void *data, UInt32 length)
      { Endian<UInt32> temp = length; (*this)(temp); (*this)(data, length); }
      
      template <class Data>
      void countedData(const Data &data)
      { countedData(data.data(), data.length()); }

      class Counter;

private:
      void *writePos;               // next byte address
};

class Writer::Counter {
private:
      void align() { totalSoFar = alignUp(totalSoFar); }

public:
      Counter() : totalSoFar(0) { }
      operator size_t () { return totalSoFar; }

      template <class T> size_t operator () (const T &) { align(); return totalSoFar += sizeof(T); }
      size_t insert(size_t size) { align(); return totalSoFar += size; }
      size_t operator () (const char *s) { align(); return totalSoFar += strlen(s) + 1; }
      
      void countedData(const void *, UInt32 length)
      { insert(sizeof(UInt32)); insert(length); }
      
      template <class Data>
      void countedData(const Data &data)
      { countedData(data.data(), data.length()); }

private:
      size_t totalSoFar;      // total size counted so far
};


//
// The Reader counter-part for a Writer.
// Again, Reader and Writer share alignment and representation rules, so what was
// Written shall be Read again, just fine.
//
class Reader {
private:
    const void *advance(size_t size = 0)
    {
        const void *here = alignUp(readPos);
        readPos = increment(here, size);
        return here;
    }

public:
    Reader() { }
    Reader(const void *base) : readPos(base) { }
    void operator = (const void *base) { readPos = base; }
    
    template <class T>
    void operator () (T &obj) {     obj = *reinterpret_cast<const T *>(advance(sizeof(T))); }
    void operator () (void *addr, size_t size)  { memcpy(addr, advance(size), size); }
    void operator () (const char * &s)
    { s = reinterpret_cast<const char *>(advance()); advance(strlen(s) + 1); }
    template <class T>
    const T *get(size_t size)
      { return reinterpret_cast<const T *>(advance(size)); }
      
      void countedData(const void * &data, UInt32 &length)
      { Endian<UInt32> temp; (*this)(temp); length = temp; data = advance(length); }

private:
      // Explicitly forbid some invocations that are likely to be wrong.
      void operator () (char * &s); // can't get writable string in-place
    
private:
    const void *readPos;      // next byte address
};


} // end namespace LowLevelMemoryUtilities

} // end namespace Security

#endif //_H_MEMUTILS

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