assimp/code/StreamReader.h

/*
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Open Asset Import Library (assimp)
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Copyright (c) 2006-2017, assimp team


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*/

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

#ifndef AI_STREAMREADER_H_INCLUDED
#define AI_STREAMREADER_H_INCLUDED

#include "ByteSwapper.h"
#include "Exceptional.h"
#include <memory>
#include <assimp/IOStream.hpp>
#include <assimp/Defines.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 endianness of any input data is known at
 *  compile-time, which should usually be true (#BaseImporter::ConvertToUTF8 implements
 *  runtime endianness 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 endianness.
     *
     *  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
     *    endianness information is contained in the @c SwapEndianess
     *    template parameter and this parameter is meaningless.  */
    StreamReader(std::shared_ptr<IOStream> stream, bool le = false)
        : stream(stream)
        , le(le)
    {
        ai_assert(stream);
        InternBegin();
    }

    // ---------------------------------------------------------------------
    StreamReader(IOStream* stream, bool le = false)
        : stream(std::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 stream) */
    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(size_t 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.
     *  Returns the previously set limit. */
    unsigned int SetReadLimit(unsigned int _limit)  {
        unsigned int prev = GetReadLimit();
        if (UINT_MAX == _limit) {
            limit = end;
            return prev;
        }

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

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

    // ---------------------------------------------------------------------
    /** Skip to the read limit in bytes. Reading over this limit
     *  accidentally 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;
        ::memcpy (&f, current, sizeof(T));
        Intern::Getter<SwapEndianess,T,RuntimeSwitch>() (&f,le);
        current += sizeof(T);

        return f;
    }

    // ---------------------------------------------------------------------
    void InternBegin() {
        if (!stream) {
            // in case 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:
    std::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