File as an std::istream

I needed to use an Urho3D::File (for resource cache support) as an std::istream (for a 3rd party library). This seems to work (though I’ve not thoroughly tested it)
FileStream.hpp

[code] #pragma once

//based on http://www.mr-edd.co.uk/blog/beginners_guide_streambuf

#include
#include
#include
#include

#include <IO/Deserializer.h>

class FileStream : public std::streambuf
{
public:
explicit FileStream(Urho3D::Deserializer &src, std::size_t buff_sz = 256, std::size_t put_back = 8);
virtual ~FileStream() {};
private:
// overrides base class underflow()
int_type underflow();

    // copy ctor and assignment not implemented;
    // copying not allowed
    FileStream(const FileStream &);
    FileStream &operator= (const FileStream &);

private:
    Urho3D::Deserializer& src_;
    const std::size_t put_back_;
    std::vector<char> buffer_;

};
[/code]

FileStream.cpp

[code] #include “FileStream.hpp”

#include
#include

using std::size_t;

FileStream::FileStream(Urho3D::Deserializer &src, size_t buff_sz, size_t put_back) :
src_(src),
put_back_(std::max(put_back, size_t(1))),
buffer_(std::max(buff_sz, put_back_) + put_back_)
{
char *end = &buffer_.front() + buffer_.size();
setg(end, end, end);
}

std::streambuf::int_type FileStream::underflow()
{
if (gptr() < egptr()) // buffer not exhausted
return traits_type::to_int_type(*gptr());

char *base = &buffer_.front();
char *start = base;

if (eback() == base) // true when this isn't the first fill
{
    // Make arrangements for putback characters
    std::memmove(base, egptr() - put_back_, put_back_);
    start += put_back_;
}

// start is now the start of the buffer, proper.
// Read from fptr_ in to the provided buffer

// size_t n = std::fread(start, 1, buffer_.size() - (start - base), fptr_);
unsigned n = src_.Read(start,buffer_.size() - (start - base));
if (n == 0)
return traits_type::eof();

// Set buffer pointers
setg(base, start, start + n);

return traits_type::to_int_type(*gptr());

}
[/code].
You can then create an istream like:

File f(context_,filename,FILE_READ); FileStream fs(f); std::istream is(&fs);