pystreambuf.h

/*
Based on https://gist.github.com/asford/544323a5da7dddad2c9174490eb5ed06
but was heavily modified.

Original license text
---------------------

This component utilizes components derived from cctbx, available at
http://cci.lbl.gov/cctbx_sources/boost_adaptbx/python_streambuf.h

*** License agreement ***

cctbx Copyright (c) 2006, The Regents of the University of
California, through Lawrence Berkeley National Laboratory (subject to
receipt of any required approvals from the U.S. Dept. of Energy).  All
rights reserved.

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) Neither the name of the University of California, Lawrence Berkeley
National Laboratory, U.S. Dept. of Energy nor the names of its
contributors may be used to endorse or promote products derived from
this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT OWNER
OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

You are under no obligation whatsoever to provide any bug fixes,
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to install, use, modify, prepare derivative works, incorporate into
other computer software, distribute, and sublicense such enhancements or
derivative works thereof, in binary and source code form.

*/

#pragma once

#include <pybind11/pybind11.h>

#include <iostream>
#include <sstream>

namespace py = pybind11;


namespace pybind11::detail {
    template <> struct type_caster<std::istream> {

        bool load(handle src, bool) {

            auto read_method = getattr(src, "read", py::none());

            if (read_method.is_none()){
              return false;
            }

            value = std::make_unique<std::istringstream>(py::reinterpret_borrow<py::bytes>(read_method()));

            return true;
        }

        static handle cast(std::istream &src, return_value_policy policy, handle parent) {
            return none().release();
        }

        static constexpr auto name = const_name("io.BytesIO");
        operator std::istream*() { return value.get(); }
        operator std::istream&() { return *value; }
        template <typename _T> using cast_op_type = pybind11::detail::cast_op_type<_T>;

        std::unique_ptr<std::istringstream> value;

    };

    template <> struct type_caster<std::ostream> {

        // std::ostringstream subclass writing back to python upon destruction
        struct pyostringstream : std::ostringstream {

            py::object write_method;

            pyostringstream(py::object write_method_) : std::ostringstream{}, write_method{write_method_} {};

            // Write back to the python object
            ~pyostringstream(){ this->write_method(py::bytes(this->str()));}

        };

        bool load(handle src, bool) {

            auto write_method = getattr(src, "write", py::none()); 

            if (write_method.is_none()){
              return false;
            }

            value = std::make_unique<pyostringstream>(write_method);

            return true;
        }

        static handle cast(std::ostream &src, return_value_policy policy, handle parent) {
            return none().release();
        }

        static constexpr auto name = const_name("io.BytesIO");
        operator std::ostream*() { return value.get(); }
        operator std::ostream&() { return *value; }
        template <typename _T> using cast_op_type = pybind11::detail::cast_op_type<_T>;

        std::unique_ptr<pyostringstream> value;

    };
} // namespace pybind11::detail