multipart_body.hpp

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/*
 * RESTinio
 */

/*!
 * @file
 * @brief Various tools for working with multipart bodies.
 *
 * @since v.0.6.1
 */

#pragma once

#include <restinio/helpers/string_algo.hpp>
#include <restinio/helpers/easy_parser.hpp>
#include <restinio/helpers/http_field_parsers/basics.hpp>
#include <restinio/helpers/http_field_parsers/content-type.hpp>

#include <restinio/http_headers.hpp>
#include <restinio/request_handler.hpp>
#include <restinio/expected.hpp>

#include <restinio/impl/string_caseless_compare.hpp>

#include <restinio/utils/metaprogramming.hpp>

#include <iostream>

namespace restinio
{

namespace multipart_body
{

//
// split_multipart_body
//
/*!
 * @brief Helper function for spliting a multipart body into a serie of
 * separate parts.
 *
 * @return A list of separate parts. This list will be empty if no parts
 * are found or if there is some error in the body format (for example if
 * some part is opened by @a boundary but is not closed properly).
 *
 * @note
 * A user should extract the value of @a boundary should from Content-Type
 * field and modify it proper way (two leading hypens should be added to the
 * value of "boundary" parameter) by him/herself. Helper function
 * detect_boundary_for_multipart_body() can be used for that purpose.
 *
 * Usage example:
 * @code
 * using namespace restinio::multipart_body;
 *
 * const auto boundary = detect_boundary_for_multipart_body(
 *      req, "multipart", "form-data" );
 * if( boundary )
 * {
 *  const auto parts = split_multipart_body( req.body(), *boundary );
 *  for( restinio::string_view_t one_part : parts )
 *  {
 *      ... // Handling of a part.
 *  }
 * }
 * @endcode
 *
 * @since v.0.6.1
 */
[[nodiscard]]
inline std::vector< string_view_t >
split_multipart_body(
    string_view_t body,
    string_view_t boundary )
{
    using namespace restinio::string_algo;

    std::vector< string_view_t > result;
    std::vector< string_view_t > tmp_result;

    const string_view_t eol{ "\r\n" };
    const string_view_t last_separator{ "--\r\n" };

    // Find the first boundary.
    auto boundary_pos = body.find( boundary );
    if( string_view_t::npos == boundary_pos )
        // There is no initial separator in the body.
        return result;

    // The first body can be at the very begining of the body or
    // there should be CRLF before the initial boundary.
    if( boundary_pos != 0u &&
            (boundary_pos < eol.size() ||
            body.substr( boundary_pos - eol.size(), eol.size() ) != eol) )
        return result;

    auto remaining_body = body.substr( boundary_pos + boundary.size() );
    if( starts_with( remaining_body, last_separator ) )
        // The start boundary is the last boundary.
        return result;

    while( starts_with( remaining_body, eol ) )
    {
        remaining_body = remaining_body.substr( eol.size() );

        boundary_pos = remaining_body.find( boundary );
        if( string_view_t::npos == boundary_pos )
            return result;

        // There should be CRLF before the next boundary.
        if( boundary_pos < eol.size() ||
                remaining_body.substr( boundary_pos - eol.size(), eol.size() ) != eol )
            return result;

        tmp_result.push_back(
                remaining_body.substr( 0u, boundary_pos - eol.size() ) );

        remaining_body = remaining_body.substr( boundary_pos + boundary.size() );
        // Is this boundary the last one?
        if( starts_with( remaining_body, last_separator ) )
        {
            // Yes, our iteration can be stopped and we can return the result.
            swap( tmp_result, result );
            return result;
        }
    }

    // We didn't find the last boundary. Or some error encountered in the format
    // of the body.
    //
    // Empty result should be returned.
    return result;
}

//
// parsed_part_t
//
/*!
 * @brief A description of parsed content of one part of a multipart body.
 *
 * @since v.0.6.1
 */
struct parsed_part_t
{
    //! HTTP-fields local for that part.
    /*!
     * @note
     * It can be empty if no HTTP-fields are found for that part.
     */
    http_header_fields_t fields;
    //! The body of that part.
    string_view_t body;
};

namespace impl
{

namespace parser_details
{

using namespace restinio::http_field_parsers;

namespace easy_parser = restinio::easy_parser;

constexpr char CR = '\r';
constexpr char LF = '\n';

//
// body_producer_t
//
/*!
 * @brief A special producer that consumes the whole remaining
 * content from the input stream.
 *
 * @attention
 * This producer can be seen as a hack. It can't be used safely
 * outside the context for that this producer was created. It's because
 * body_producer_t doesn't shift the current position in the input
 * stream.
 *
 * @since v.0.6.1
 */
struct body_producer_t
    :   public easy_parser::impl::producer_tag< string_view_t >
{
    [[nodiscard]]
    expected_t< string_view_t, easy_parser::parse_error_t >
    try_parse( easy_parser::impl::source_t & from ) const noexcept
    {
        // Return the whole content from the current position.
        return from.fragment( from.current_position() );
    }
};

//
// field_value_producer_t
//
/*!
 * @brief A special producer that consumes the rest of the current
 * line in the input stream until CR/LF will be found.
 *
 * @note
 * CR and LF symbols are not consumed from the input stream.
 *
 * @since v.0.6.1
 */
struct field_value_producer_t
    :   public easy_parser::impl::producer_tag< std::string >
{
    [[nodiscard]]
    expected_t< std::string, easy_parser::parse_error_t >
    try_parse( easy_parser::impl::source_t & from ) const
    {
        std::string accumulator;
        auto ch = from.getch();
        while( !ch.m_eof && ch.m_ch != CR && ch.m_ch != LF )
        {
            accumulator += ch.m_ch;
            ch = from.getch();
        }

        if( ch.m_eof )
            return make_unexpected( easy_parser::parse_error_t{
                    from.current_position(),
                    easy_parser::error_reason_t::unexpected_eof
            } );

        // CR or LF symbol should be returned back.
        from.putback();

        return { std::move(accumulator) };
    }
};

} /* namespace parser_details */

//
// make_parser
//
/*!
 * @brief A factory function for a parser of a part of multipart message.
 *
 * Handles the following rule:
@verbatim
part := *( token ':' OWS field-value CR LF ) CR LF body
@endverbatim
 *
 * Produces parsed_part_t instance.
 *
 * @since v.0.6.1
 */
[[nodiscard]]
auto
make_parser()
{
    using namespace parser_details;

    return produce< parsed_part_t >(
            produce< http_header_fields_t >(
                repeat( 0, N,
                    produce< http_header_field_t >(
                        token_p() >> to_lower() >> custom_consumer(
                                [](auto & f, std::string && v) {
                                    f.name(std::move(v));
                                } ),
                        symbol(':'),
                        ows(),
                        field_value_producer_t{} >> custom_consumer(
                                [](auto & f, std::string && v) {
                                    f.value(std::move(v));
                                } ),
                        symbol(CR), symbol(LF)
                    ) >> custom_consumer(
                            [](auto & to, http_header_field_t && v) {
                                to.add_field( std::move(v) );
                            } )
                )
            ) >> &parsed_part_t::fields,
            symbol(CR), symbol(LF),
            body_producer_t{} >> &parsed_part_t::body );
}

} /* namespace impl */

//
// try_parse_part
//
/*!
 * @brief Helper function for parsing content of one part of a multipart body.
 *
 * This function is intended to be used with split_multipart_body():
 * @code
 * using namespace restinio::multipart_body;
 *
 * const auto boundary = detect_boundary_for_multipart_body(
 *      req, "multipart", "form-data" );
 * if( boundary )
 * {
 *  const auto parts = split_multipart_body( req.body(), *boundary );
 *  for( restinio::string_view_t one_part : parts )
 *  {
 *      const auto parsed_part = try_parse_part( one_part );
 *      if( parsed_part )
 *      {
 *          ... // Handle the content of the parsed part.
 *      }
 *  }
 * }
 * @endcode
 *
 * @since v.0.6.1
 */
[[nodiscard]]
expected_t< parsed_part_t, restinio::easy_parser::parse_error_t >
try_parse_part( string_view_t part )
{
    namespace easy_parser = restinio::easy_parser;

    easy_parser::impl::source_t source{ part };

    auto actual_producer = impl::make_parser();

    return easy_parser::impl::top_level_clause_t< decltype(actual_producer) >{
                std::move(actual_producer)
            }.try_process( source );
}

//
// handling_result_t
//
/*!
 * @brief The result to be returned from user-provided handler of
 * parts of multipart body.
 *
 * @since v.0.6.1
 */
enum class handling_result_t
{
    //! Enumeration of parts should be continued.
    //! If there is another part the user-provided handler will
    //! be called for it.
    continue_enumeration,
    //! Enumeration of parts should be stopped.
    //! All remaining parts of multipart body will be skipped.
    //! But the result of the enumeration will be successful.
    stop_enumeration,
    //! Enumeration of parts should be ignored.
    //! All remaining parts of multipart body will be skipped and
    //! the result of the enumeration will be a failure.
    terminate_enumeration
};

//
// enumeration_error_t
//
/*!
 * @brief The result of an attempt to enumerate parts of a multipart body.
 *
 * @since v.0.6.1
 */
enum class enumeration_error_t
{
    //! Content-Type field is not found.
    //! If Content-Type is absent there is no way to detect 'boundary'
    //! parameter.
    content_type_field_not_found,
    //! Unable to parse Content-Type field value.
    content_type_field_parse_error,
    //! Content-Type field value parsed but doesn't contain an appropriate
    //! value. For example there can be media-type different from 'multipart'
    //! or 'boundary' parameter can be absent.
    content_type_field_inappropriate_value,
    //! Value of 'boundary' parameter is invalid (for example it contains
    //! some illegal characters).
    illegal_boundary_value,
    //! No parts of a multipart body actually found.
    no_parts_found,
    //! Enumeration of parts was aborted by user-provided handler.
    //! This code is returned when user-provided handler returns
    //! handling_result_t::terminate_enumeration.
    terminated_by_handler,
    //! Some unexpected error encountered during the enumeration.
    unexpected_error
};

namespace impl
{

namespace boundary_value_checkers
{

// From https://tools.ietf.org/html/rfc1521:
//
// boundary := 0*69<bchars> bcharsnospace
//
// bchars := bcharsnospace / " "
//
// bcharsnospace :=  DIGIT / ALPHA / "'" / "(" / ")" / "+" /"_"
//                 / "," / "-" / "." / "/" / ":" / "=" / "?"
//
[[nodiscard]]
constexpr bool
is_bcharnospace( char ch )
{
    return (ch >= '0' && ch <= '9') // DIGIT
        || ((ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z')) // ALPHA
        || ch == '\''
        || ch == '('
        || ch == ')'
        || ch == '+'
        || ch == '_'
        || ch == ','
        || ch == '-'
        || ch == '.'
        || ch == '/'
        || ch == ':'
        || ch == '='
        || ch == '?';
}

[[nodiscard]]
constexpr bool
is_bchar( char ch )
{
    return is_bcharnospace(ch) || ch == ' ';
}

} /* namespace boundary_value_checkers */

} /* namespace impl */

//
// check_boundary_value
//
/*!
 * @brief A helper function for checking the validity of 'boundary' value.
 *
 * The allowed format for 'boundary' value is defined here:
 * https://tools.ietf.org/html/rfc2046
@verbatim
     boundary := 0*69<bchars> bcharsnospace

     bchars := bcharsnospace / " "

     bcharsnospace := DIGIT / ALPHA / "'" / "(" / ")" /
                      "+" / "_" / "," / "-" / "." /
                      "/" / ":" / "=" / "?"
@endverbatim
 *
 * @return enumeration_error_t::illegal_boundary_value if @a value has
 * illegal value or an empty optional if there is no errros detected.
 *
 * @since v.0.6.1
 */
[[nodiscard]]
inline std::optional< enumeration_error_t >
check_boundary_value( string_view_t value )
{
    using namespace impl::boundary_value_checkers;

    if( value.size() >= 1u && value.size() <= 70u )
    {
        const std::size_t last_index = value.size() - 1u;
        for( std::size_t i = 0u; i != last_index; ++i )
            if( !is_bchar( value[i] ) )
                return enumeration_error_t::illegal_boundary_value;

        if( !is_bcharnospace( value[ last_index ] ) )
            return enumeration_error_t::illegal_boundary_value;
    }
    else
        return enumeration_error_t::illegal_boundary_value;

    return std::nullopt;
}

//
// detect_boundary_for_multipart_body
//
/*!
 * @brief Helper function for parsing Content-Type field and extracting
 * the value of 'boundary' parameter.
 *
 * It finds Content-Type field, then parses it, then checks the value
 * of media-type, then finds 'boundary' parameter, the checks the validity
 * of 'boundary' value and then adds two leading hypens to the value of
 * 'boundary' parameter.
 *
 * The returned value (if there is no error) can be used for spliting
 * a multipart body to separate parts.
 *
 * @since v.0.6.1
 */
template< typename Extra_Data >
[[nodiscard]]
expected_t< std::string, enumeration_error_t >
detect_boundary_for_multipart_body(
    const generic_request_t< Extra_Data > & req,
    string_view_t expected_media_type,
    std::optional< string_view_t > expected_media_subtype )
{
    namespace hfp = restinio::http_field_parsers;
    using restinio::impl::is_equal_caseless;

    // Content-Type header file should be present.
    const auto content_type = req.header().opt_value_of(
            restinio::http_field::content_type );
    if( !content_type )
        return make_unexpected(
                enumeration_error_t::content_type_field_not_found );

    // Content-Type field should successfuly parsed and should
    // contain value that correspond to expected media-type.
    const auto parse_result = hfp::content_type_value_t::try_parse(
            *content_type );
    if( !parse_result )
        return make_unexpected(
                enumeration_error_t::content_type_field_parse_error );

    const auto & media_type = parse_result->media_type;
    if( !is_equal_caseless( expected_media_type, media_type.type ) )
    {
        return make_unexpected(
                enumeration_error_t::content_type_field_inappropriate_value );
    }
    if( expected_media_subtype &&
            !is_equal_caseless( *expected_media_subtype, media_type.subtype ) )
    {
        return make_unexpected(
                enumeration_error_t::content_type_field_inappropriate_value );
    }

    // `boundary` param should be present in parsed Content-Type value.
    const auto boundary = hfp::find_first(
            parse_result->media_type.parameters,
            "boundary" );
    if( !boundary )
        return make_unexpected(
                enumeration_error_t::content_type_field_inappropriate_value );

    // `boundary` should have valid value.
    const auto boundary_check_result = check_boundary_value( *boundary );
    if( boundary_check_result )
        return make_unexpected( *boundary_check_result );

    // Actual value of boundary mark can be created.
    std::string actual_boundary_mark;
    actual_boundary_mark.reserve( 2 + boundary->size() );
    actual_boundary_mark.append( "--" );
    actual_boundary_mark.append( boundary->data(), boundary->size() );

    return { std::move(actual_boundary_mark) };
}

namespace impl
{

/*!
 * @brief A function that parses every part of a multipart body and
 * calls a user-provided handler for every parsed part.
 *
 * @return the count of parts successfuly handled by @a handler or
 * error code in the case if some error is detected.
 *
 * @since v.0.6.1
 */
template< typename Handler >
[[nodiscard]]
expected_t< std::size_t, enumeration_error_t >
enumerate_parts_of_request_body(
    const std::vector< string_view_t > & parts,
    Handler && handler )
{
    std::size_t parts_processed{ 0u };
    std::optional< enumeration_error_t > error;

    for( auto current_part : parts )
    {
        // The current part should be parsed to headers and the body.
        auto part_parse_result = try_parse_part( current_part );
        if( !part_parse_result )
            return make_unexpected( enumeration_error_t::unexpected_error );

        // NOTE: parsed_part is passed as rvalue reference!
        const handling_result_t handler_ret_code = handler(
                std::move(*part_parse_result) );

        if( handling_result_t::terminate_enumeration != handler_ret_code )
            ++parts_processed;
        else
            error = enumeration_error_t::terminated_by_handler;

        if( handling_result_t::continue_enumeration != handler_ret_code )
            break;
    }

    if( error )
        return make_unexpected( *error );

    return parts_processed;
}

//
// valid_handler_type
//
template< typename, typename = restinio::utils::metaprogramming::void_t<> >
struct valid_handler_type : public std::false_type {};

template< typename T >
struct valid_handler_type<
        T,
        restinio::utils::metaprogramming::void_t<
            std::enable_if_t<
                std::is_same<
                    handling_result_t,
                    decltype(std::declval<T>()(std::declval<parsed_part_t>()))
                >::value,
                bool
            >
        >
    > : public std::true_type
{};

} /* namespace impl */

//
// enumerate_parts
//
/*!
 * @brief A helper function for enumeration of parts of a multipart body.
 *
 * This function:
 *
 * - finds Content-Type field for @a req;
 * - parses Content-Type field, checks the media-type and extracts
 *   the value of 'boundary' parameter. The extracted 'boundary'
 *   parameter is checked for validity;
 * - splits the body of @a req using value of 'boundary' parameter;
 * - enumerates every part of body, parses every part and calls
 *   @handler for every parsed part.
 *
 * Enumeration stops if @a handler returns handling_result_t::stop_enumeration
 * or handling_result_t::terminate_enumeration. If @a handler returns
 * handling_result_t::terminate_enumeration the enumerate_parts() returns
 * enumeration_error_t::terminated_by_handler error code.
 *
 * A handler passed as @a handler argument should be a function or
 * lambda/functor with one of the following formats:
 * @code
 * handling_result_t(parsed_part_t part);
 * handling_result_t(parsed_part_t && part);
 * handling_result_t(const parsed_part_t & part);
 * @endcode
 * Note that enumerate_part() passes parsed_part_t instance to
 * @a handler as rvalue reference. And this reference will be invalidaded
 * after the return from @a handler.
 *
 * Usage example:
 * @code
 * auto on_post(const restinio::request_handle_t & req) {
 *  using namespace restinio::multipart_body;
 *  const auto result = enumerate_parts( *req,
 *      [](parsed_part_t part) {
 *          ... // Some actions with the current part.
 *          return handling_result_t::continue_enumeration;
 *      },
 *      "multipart", "form-data" );
 *  if(result) {
 *      ... // Producing positive response.
 *  }
 *  else {
 *      ... // Producing negative response.
 *  }
 *  return restinio::request_accepted();
 * }
 * @endcode
 *
 * @return the count of parts successfuly handled by @a handler or
 * error code in the case if some error is detected.
 *
 * @since v.0.6.1
 */
template< typename User_Type, typename Handler >
[[nodiscard]]
expected_t< std::size_t, enumeration_error_t >
enumerate_parts(
    //! The request to be handled.
    const generic_request_t< User_Type > & req,
    //! The handler to be called for every parsed part.
    Handler && handler,
    //! The expected value of 'type' part of 'media-type' from Content-Type.
    //! If 'type' part is not equal to @a expected_media_type then
    //! enumeration won't be performed.
    //!
    //! @note
    //! The special value '*' is not handled here.
    string_view_t expected_media_type = string_view_t{ "multipart" },
    //! The optional expected value of 'subtype' part of 'media-type'
    //! from Content-Type. If @a expected_media_subtype is specified and
    //! missmatch with 'subtype' part then enumeration won't be performed.
    //!
    //! @note
    //! The special value '*' is not handled here.
    std::optional< string_view_t > expected_media_subtype = std::nullopt )
{
    static_assert(
            impl::valid_handler_type< std::decay_t<Handler> >::value,
            "Handler should be callable object, "
            "should accept parsed_part_t by value, const or rvalue reference, "
            "and should return handling_result_t" );

    const auto boundary = detect_boundary_for_multipart_body(
            req,
            expected_media_type,
            expected_media_subtype );
    if( boundary )
    {
        const auto parts = split_multipart_body( req.body(), *boundary );

        if( parts.empty() )
            return make_unexpected(
                    enumeration_error_t::no_parts_found );

        return impl::enumerate_parts_of_request_body(
                parts,
                std::forward<Handler>(handler) );
    }

    return make_unexpected( boundary.error() );
}

} /* namespace multipart_body */

} /* namespace restinio */