assimp/code/StreamReader.h

/*
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Open Asset Import Library (assimp)
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Copyright (c) 2006-2012, assimp team

All rights reserved.

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  following disclaimer.

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*/

/** @file Defines the StreamReader class which reads data from
 *  a binary stream with a well-defined endianess. */

#ifndef AI_STREAMREADER_H_INCLUDED
#define AI_STREAMREADER_H_INCLUDED

#include "ByteSwap.h"

namespace Assimp {

// --------------------------------------------------------------------------------------------
/** Wrapper class around IOStream to allow for consistent reading of binary data in both 
 *  little and big endian format. Don't attempt to instance the template directly. Use 
 *  StreamReaderLE to read from a little-endian stream and StreamReaderBE to read from a 
 *  BE stream. The class expects that the endianess of any input data is known at 
 *  compile-time, which should usually be true (#BaseImporter::ConvertToUTF8 implements
 *  runtime endianess conversions for text files). 
 *
 *  XXX switch from unsigned int for size types to size_t? or ptrdiff_t?*/
// --------------------------------------------------------------------------------------------
template <bool SwapEndianess = false, bool RuntimeSwitch = false>
class StreamReader
{

public:

	// FIXME: use these data types throughout the whole library,
	// then change them to 64 bit values :-)
	
	typedef int diff;
	typedef unsigned int pos;

public:


	// ---------------------------------------------------------------------
	/** Construction from a given stream with a well-defined endianess.
	 * 
	 *  The StreamReader holds a permanent strong reference to the
	 *  stream, which is released upon destruction.
	 *  @param stream Input stream. The stream is not restarted if
	 *    its file pointer is not at 0. Instead, the stream reader
	 *    reads from the current position to the end of the stream.
	 *  @param le If @c RuntimeSwitch is true: specifies whether the
	 *    stream is in little endian byte order. Otherwise the
	 *    endianess information is contained in the @c SwapEndianess
	 *    template parameter and this parameter is meaningless.  */
	StreamReader(boost::shared_ptr<IOStream> stream, bool le = false)
		: stream(stream)
		, le(le)
	{
		ai_assert(stream); 
		InternBegin();
	}

	// ---------------------------------------------------------------------
	StreamReader(IOStream* stream, bool le = false)
		: stream(boost::shared_ptr<IOStream>(stream))
		, le(le)
	{
		ai_assert(stream);
		InternBegin();
	}

	// ---------------------------------------------------------------------
	~StreamReader() {
		delete[] buffer;
	}

public:

	// deprecated, use overloaded operator>> instead

	// ---------------------------------------------------------------------
	/** Read a float from the stream  */
	float GetF4()
	{
		return Get<float>();
	}

	// ---------------------------------------------------------------------
	/** Read a double from the stream  */
	double GetF8()	{
		return Get<double>();
	}

	// ---------------------------------------------------------------------
	/** Read a signed 16 bit integer from the stream */
	int16_t GetI2()	{
		return Get<int16_t>();
	}

	// ---------------------------------------------------------------------
	/** Read a signed 8 bit integer from the stream */
	int8_t GetI1()	{
		return Get<int8_t>();
	}

	// ---------------------------------------------------------------------
	/** Read an signed 32 bit integer from the stream */
	int32_t GetI4()	{
		return Get<int32_t>();
	}

	// ---------------------------------------------------------------------
	/** Read a signed 64 bit integer from the stream */
	int64_t GetI8()	{
		return Get<int64_t>();
	}

	// ---------------------------------------------------------------------
	/** Read a unsigned 16 bit integer from the stream */
	uint16_t GetU2()	{
		return Get<uint16_t>();
	}

	// ---------------------------------------------------------------------
	/** Read a unsigned 8 bit integer from the stream */
	uint8_t GetU1()	{
		return Get<uint8_t>();
	}

	// ---------------------------------------------------------------------
	/** Read an unsigned 32 bit integer from the stream */
	uint32_t GetU4()	{
		return Get<uint32_t>();
	}

	// ---------------------------------------------------------------------
	/** Read a unsigned 64 bit integer from the stream */
	uint64_t GetU8()	{
		return Get<uint64_t>();
	}

public:

	// ---------------------------------------------------------------------
	/** Get the remaining stream size (to the end of the srream) */
	unsigned int GetRemainingSize() const {
		return (unsigned int)(end - current);
	}


	// ---------------------------------------------------------------------
	/** Get the remaining stream size (to the current read limit). The
	 *  return value is the remaining size of the stream if no custom
	 *  read limit has been set. */
	unsigned int GetRemainingSizeToLimit() const {
		return (unsigned int)(limit - current);
	}


	// ---------------------------------------------------------------------
	/** Increase the file pointer (relative seeking)  */
	void IncPtr(int plus)	{
		current += plus;
		if (current > limit) {
			throw DeadlyImportError("End of file or read limit was reached");
		}
	}

	// ---------------------------------------------------------------------
	/** Get the current file pointer */
	int8_t* GetPtr() const	{
		return current;
	}


	// ---------------------------------------------------------------------
	/** Set current file pointer (Get it from #GetPtr). This is if you
	 *  prefer to do pointer arithmetics on your own or want to copy 
	 *  large chunks of data at once. 
	 *  @param p The new pointer, which is validated against the size
	 *    limit and buffer boundaries. */
	void SetPtr(int8_t* p)	{

		current = p;
		if (current > limit || current < buffer) {
			throw DeadlyImportError("End of file or read limit was reached");
		}
	}

	// ---------------------------------------------------------------------
	/** Copy n bytes to an external buffer
	 *  @param out Destination for copying
	 *  @param bytes Number of bytes to copy */
	void CopyAndAdvance(void* out, size_t bytes)	{

		int8_t* ur = GetPtr();
		SetPtr(ur+bytes); // fire exception if eof

		memcpy(out,ur,bytes);
	}


	// ---------------------------------------------------------------------
	/** Get the current offset from the beginning of the file */
	int GetCurrentPos() const	{
		return (unsigned int)(current - buffer);
	}

	void SetCurrentPos(size_t pos) {
		SetPtr(buffer + pos);
	}

	// ---------------------------------------------------------------------
	/** Setup a temporary read limit
	 * 
	 *  @param limit Maximum number of bytes to be read from
	 *    the beginning of the file. Specifying UINT_MAX
	 *    resets the limit to the original end of the stream. */
	void SetReadLimit(unsigned int _limit)	{

		if (UINT_MAX == _limit) {
			limit = end;
			return;
		}

		limit = buffer + _limit;
		if (limit > end) {
			throw DeadlyImportError("StreamReader: Invalid read limit");
		}
	}

	// ---------------------------------------------------------------------
	/** Get the current read limit in bytes. Reading over this limit
	 *  accidentially raises an exception.  */
	int GetReadLimit() const	{
		return (unsigned int)(limit - buffer);
	}

	// ---------------------------------------------------------------------
	/** Skip to the read limit in bytes. Reading over this limit
	 *  accidentially raises an exception. */
	void SkipToReadLimit()	{
		current = limit;
	}

	// ---------------------------------------------------------------------
	/** overload operator>> and allow chaining of >> ops. */
	template <typename T>
	StreamReader& operator >> (T& f) {
		f = Get<T>(); 
		return *this;
	}

private:

	// ---------------------------------------------------------------------
	/** Generic read method. ByteSwap::Swap(T*) *must* be defined */
	template <typename T>
	T Get()	{
		if (current + sizeof(T) > limit) {
			throw DeadlyImportError("End of file or stream limit was reached");
		}

		T f = *((const T*)current);
		Intern :: Getter<SwapEndianess,T,RuntimeSwitch>() (&f,le);

		current += sizeof(T);
		return f;
	}

	// ---------------------------------------------------------------------
	void InternBegin() {
		if (!stream) {
			// incase someone wonders: StreamReader is frequently invoked with
			// no prior validation whether the input stream is valid. Since
			// no one bothers changing the error message, this message here
			// is passed down to the caller and 'unable to open file'
			// simply describes best what happened.
			throw DeadlyImportError("StreamReader: Unable to open file");
		}

		const size_t s = stream->FileSize() - stream->Tell();
		if (!s) {
			throw DeadlyImportError("StreamReader: File is empty or EOF is already reached");
		}

		current = buffer = new int8_t[s];
		const size_t read = stream->Read(current,1,s);
		// (read < s) can only happen if the stream was opened in text mode, in which case FileSize() is not reliable
		ai_assert(read <= s);
		end = limit = &buffer[read];
	}

private:


	boost::shared_ptr<IOStream> stream;
	int8_t *buffer, *current, *end, *limit;
	bool le;
};


// --------------------------------------------------------------------------------------------
// `static` StreamReaders. Their byte order is fixed and they might be a little bit faster.
#ifdef AI_BUILD_BIG_ENDIAN
	typedef StreamReader<true>  StreamReaderLE;
	typedef StreamReader<false> StreamReaderBE;
#else
	typedef StreamReader<true>  StreamReaderBE;
	typedef StreamReader<false> StreamReaderLE;
#endif

// `dynamic` StreamReader. The byte order of the input data is specified in the
// c'tor. This involves runtime branching and might be a little bit slower.
typedef StreamReader<true,true> StreamReaderAny;

} // end namespace Assimp

#endif // !! AI_STREAMREADER_H_INCLUDED