malcontent/nss/helpers.cc

// SPDX-FileCopyrightText: Matteo Settenvini <matteo.settenvini@montecristosoftware.eu>
// SPDX-License-Identifier: GPL-3.0-or-later

#include "helpers.hh"

#include <new>
#include <nss.h>
#include <netdb.h>

#include <cstring>
#include <memory>

auto malcontent::copy_hostent(const hostent& src, hostent& dst, void *buffer, size_t buflen) -> void {
    dst.h_addrtype = src.h_addrtype;
    dst.h_length = src.h_length;

    // copy name
    {
        auto name_len = std::strlen(src.h_name) + 1;
        buffer = std::align(alignof(char), name_len, buffer, buflen);
        if (buffer == nullptr) {
            throw std::bad_alloc{};
        }

        dst.h_name = static_cast<char *>(std::memcpy(buffer, src.h_name, name_len));
        reinterpret_cast<char *&>(buffer) += name_len;
        buflen -= name_len;
    }

    // copy addresses
    {
        auto begin_it = src.h_addr_list;
        auto end_it = begin_it;
        for (; *end_it != nullptr; ++end_it);
        auto n = std::distance(begin_it, end_it);

        auto needs_bytes = (n + 1) * sizeof(char *);
        buffer = std::align(alignof(char *), needs_bytes, buffer, buflen);
        if (buffer == nullptr) {
            throw std::bad_alloc {};
        }
        dst.h_addr_list = static_cast<char **>(buffer);
        reinterpret_cast<char **&>(buffer) += n + 1;

        for (auto i = 0; i < n; ++i) {
            buffer = std::align(alignof(char), src.h_length, buffer, buflen);
            if (buffer == nullptr) {
                throw std::bad_alloc {};
            }

            dst.h_addr_list[i] = static_cast<char *>(
                std::memcpy(buffer, src.h_addr_list[i], src.h_length));
            reinterpret_cast<char *&>(buffer) += src.h_length;
            buflen -= src.h_length;
        }
        dst.h_addr_list[n] = nullptr;
    }

    // copy aliases
    {
        auto begin_it = src.h_aliases;
        auto end_it = begin_it;
        for (; *end_it != nullptr; ++end_it);

        auto n = std::distance(begin_it, end_it);
        auto needs_bytes = (n + 1) * sizeof(char *);
        buffer = std::align(alignof(char *), needs_bytes, buffer, buflen);
        if (buffer == nullptr) {
            throw std::bad_alloc {};
        }

        dst.h_aliases = static_cast<char **>(buffer);
        reinterpret_cast<char **&>(buffer) += n + 1;
        buflen -= needs_bytes;

        for (int i = 0; i < n; ++i) {
            auto alias_len = strlen(*begin_it) + 1;
            buffer = std::align(alignof(char), alias_len, buffer, buflen);
            if (buffer == nullptr) {
                throw std::bad_alloc{};
            }

            dst.h_addr_list[i] = static_cast<char *>(
                std::memcpy(buffer, src.h_aliases[i], n));

            reinterpret_cast<char *&>(buffer) += alias_len;
            buflen -= alias_len;
        }
        dst.h_aliases[n] = nullptr;
    }
}

auto malcontent::copy_hostent_to_gaih_addrtuple(const hostent& src, gaih_addrtuple *head, void *& buffer, size_t& buflen) -> gaih_addrtuple * {
    auto name_len = std::strlen(src.h_name) + 1;
    buffer = std::align(alignof(char), name_len, buffer, buflen);
    if (buffer == nullptr) {
        throw std::bad_alloc{};
    }
    auto namep = static_cast<char *>(std::memcpy(buffer, src.h_name, name_len));
    reinterpret_cast<char *&>(buffer) += name_len;
    buflen -= name_len;

    for (auto addr = src.h_addr_list; *addr != nullptr; ++addr) {
        buffer = std::align(alignof(gaih_addrtuple), sizeof(gaih_addrtuple), buffer, buflen);
        if (buffer == nullptr) {
            throw std::bad_alloc{};
        }

        auto tuple = static_cast<gaih_addrtuple *>(buffer);

        tuple->family = src.h_addrtype;
        tuple->name = namep;
        std::memcpy(tuple->addr, *addr, src.h_length);
        tuple->next = head; // <-- We are reversing result order here, but it shouldn't be a problem, right?
        tuple->scopeid = 0; // FIXME: I have no clue how to determine this
        head = tuple;

        buflen -= sizeof(gaih_addrtuple);
    }

    return head;
}