pcre_regex_engine.hpp

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/*
    restinio
*/

/*!
    Regex engine for using std::regex.
*/

#pragma once

#include <pcre.h>

#include <fmt/format.h>

#include <restinio/exception.hpp>

namespace restinio
{

namespace router
{

namespace pcre_details
{


//
// match_results_t
//

//! A wrapper class for working with pcre match results.
template < typename Traits >
struct match_results_t final
{
    struct matched_item_descriptor_t final
    {
        matched_item_descriptor_t(
            int begin,
            int end )
            :   m_begin{ begin }
            ,   m_end{ end }
        {}

        int m_begin;
        int m_end;
    };

    matched_item_descriptor_t
    operator [] ( std::size_t i ) const
    {
        if( m_submatches[ 2 * i ] >= 0 )
        {
            // Submatch has non-empty value.
            return matched_item_descriptor_t{
                    m_submatches[ 2 * i ],
                    m_submatches[ 1 + 2 * i ] };
        }

        // This submatch group is empty.
        return matched_item_descriptor_t{ 0, 0 };
    }

    std::size_t size() const { return m_size; }

    std::size_t m_size{ 0 };
    std::array< int, 3 * Traits::max_capture_groups > m_submatches;
};

//
// regex_t
//

//! A wrapper for using pcre regexes in express_router.
class regex_t final
{
    public:
        regex_t() = default;
        regex_t( string_view_t r, int options )
        {
            compile( r, options );
        }

        regex_t( const regex_t & ) = delete;
        regex_t & operator = ( const regex_t & ) = delete;

        regex_t( regex_t && rw )
        {
            (*this) = std::move( rw );
        }

        regex_t & operator = ( regex_t && rw )
        {
            if( this != &rw )
            {
                m_route_regex = rw.m_route_regex;
                rw.m_route_regex = nullptr;
            }

            return *this;
        }

        ~regex_t()
        {
            if( nullptr != m_route_regex )
            {
                pcre_free( m_route_regex );
            }
        }

        const pcre *
        pcre_regex() const
        {
            return m_route_regex;
        }

    private:
        pcre * m_route_regex{ nullptr };

        void
        compile( string_view_t r, int options )
        {
            const char* compile_error;
            int eoffset;

            // We need zero-terminated string.
            const std::string route{ r.data(), r.size() };

            m_route_regex = pcre_compile( route.c_str(), options, &compile_error, &eoffset, nullptr );

            if( nullptr == m_route_regex )
            {
                throw exception_t{
                        fmt::format(
                            "unable to compile regex \"{}\": {}",
                            route,
                            compile_error ) };
            }
        }
};

} /* namespace pcre_details */

//
// pcre_traits_t
//

//! PCRE traits.
template < std::size_t Max_Capture_Groups = 20, int Compile_Options = 0, int Match_Options = 0 >
struct pcre_traits_t
{
    static constexpr std::size_t max_capture_groups = Max_Capture_Groups;
    static constexpr int compile_options = Compile_Options;
    static constexpr int match_options = Match_Options;
};

//
// pcre_regex_engine_t
//

//! Regex engine implementation for PCRE.
template < typename Traits = pcre_traits_t<> >
struct pcre_regex_engine_t
{
    using compiled_regex_t = pcre_details::regex_t;
    using match_results_t = pcre_details::match_results_t< Traits >;
    using matched_item_descriptor_t = typename match_results_t::matched_item_descriptor_t;

    // Max itemes that can be captured be pcre engine.
    static constexpr std::size_t
    max_capture_groups()
    {
        return Traits::max_capture_groups;
    }

    //! Create compiled regex object for a given route.
    static auto
    compile_regex(
        //! Regular expression (the pattern).
        string_view_t r,
        //! Option for case sensativity.
        bool is_case_sensative )
    {
        int options = Traits::compile_options;

        if( !is_case_sensative )
        {
            options |= PCRE_CASELESS;
        }

        return compiled_regex_t{ r, options };
    }

    //! Wrapper function for matching logic invokation.
    static auto
    try_match(
        string_view_t target_path,
        const compiled_regex_t & r,
        match_results_t & match_results )
    {
        const int rc =
            pcre_exec(
                r.pcre_regex(),
                nullptr,
                target_path.data(),
                static_cast< int >( target_path.size() ),
                0, // startoffset
                Traits::match_options,
                match_results.m_submatches.data(),
                static_cast< int >( match_results.m_submatches.size() ) );

        if( rc > 0 )
        {
            match_results.m_size = static_cast<std::size_t>(rc);
            return true;
        }
        else if( rc == 0 )
        {
            // This should not happen,
            // because the number of groups is checked when creating route matcher.
            throw exception_t{ "unexpected: not enough submatch vector size" };
        }
        if( PCRE_ERROR_NOMATCH != rc )
        {
            throw exception_t{ fmt::format("pcre error: {}", rc ) };
        }
        // else PCRE_ERROR_NOMATCH -- no match for this route

        return false;
    }

    //! Get the beginning of a submatch.
    static auto
    submatch_begin_pos( const matched_item_descriptor_t & m )
    {
        return static_cast< std::size_t >( m.m_begin );
    }

    //! Get the end of a submatch.
    static auto
    submatch_end_pos( const matched_item_descriptor_t & m )
    {
        return static_cast< std::size_t >( m.m_end );
    }
};

} /* namespace router */

} /* namespace restinio */