backend/src/cgi.cpp

/*  This file is part of FediBlock-backend.
 *  Copyright © 2020, 2021 tastytea <tastytea@tastytea.de>
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Affero General Public License as published by
 *  the Free Software Foundation, version 3.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Affero General Public License for more details.
 *
 *  You should have received a copy of the GNU Affero General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "cgi.hpp"

#include "files.hpp"
#include "fs-compat.hpp"
#include "git.hpp"
#include "time.hpp"

#include <cgicc/Cgicc.h>
#include <curl/curl.h>
#include <fmt/format.h>
#include <unicode/unistr.h>

#include <algorithm>
#include <array>
#include <chrono>
#include <cstdint>
#include <fstream>
#include <ios>
#include <iostream>
#include <iterator>
#include <map>
#include <regex>
#include <sstream>
#include <stdexcept>
#include <string>
#include <string_view>
#include <vector>

namespace FediBlock::cgi
{

using fmt::format;
using std::getline;
using std::ios;
using std::map;
using std::ofstream;
using std::runtime_error;
using std::string;
using std::string_view;
using std::stringstream;
using std::transform;
using std::vector;
using std::chrono::system_clock;

entry_type parse_formdata()
{
    entry_type entry;

    cgicc::Cgicc cgi;

    // Catch non-targeted spam.
    if (!cgi("url").empty())
    {
        throw SpamException{};
    }

    if (!captcha_valid(static_cast<std::uint8_t>(std::stoul(cgi("captcha_id"))),
                       cgi("captcha_answer")))
    {
        throw CaptchaException{};
    }

    entry.instance = cgi("instance");

    if (!cgi("tags").empty()) // Old form.
    {
        entry.tags = string_to_vector(cgi("tags"));
    }
    else
    {
        entry.tags = get_array("tags[]");
    }
    transform(entry.tags.begin(), entry.tags.end(), entry.tags.begin(),
              [](const auto &tag) { return tolower(tag); });
    add_tags(entry);

    if (!cgi("receipts").empty()) // Old form.
    {
        entry.receipts = string_to_vector(cgi("receipts"));
    }
    else
    {
        entry.receipts = get_array("receipts[]");
    }

    entry.description = cgi("description");
    entry.report_time = time::to_string(system_clock::now());

    if (is_spam(entry))
    {
        throw SpamException{};
    }

    std::uint8_t screenshot_counter{1};
    for (const auto &screenshot : cgi.getFiles())
    {
        constexpr size_t size_limit{1024 * 1024};
        if (screenshot.getDataLength() > size_limit)
        {
            throw runtime_error{format("The screenshot “{0:s}” is too big. "
                                       "The limit is {1:.1f} kilobyte (KiB).",
                                       screenshot.getFilename(),
                                       size_limit / 1024.0)};
        }

        const string filepath{
            files::get_tmpdir()
            / format("{:s}-{:d}{:s}", git::get_branch_name(),
                     screenshot_counter,
                     fs::path(screenshot.getFilename()).extension().string())};
        ofstream file{filepath, ios::binary};
        if (!file.good())
        {
            throw runtime_error{"Could not open temporary file: " + filepath};
        }
        screenshot.writeToStream(file);
        entry.screenshot_filepaths.push_back(filepath);
        ++screenshot_counter;
    }

    return entry;
}

vector<string> string_to_vector(const string_view str)
{
    vector<string> vec;

    stringstream input{str.data()};
    string element;

    while (getline(input, element, ','))
    {
        if (!element.empty())
        {
            const size_t startpos{element.find_first_not_of(' ')};
            if (element[startpos] == *element.end())
            {
                continue;
            }
            const size_t length{element.find_last_not_of(' ') - startpos + 1};
            vec.push_back(element.substr(startpos, length));
        }
    }

    return vec;
}

vector<string> get_array(const string &name)
{
    cgicc::Cgicc cgi;
    vector<cgicc::FormEntry> form;
    vector<string> values;

    cgi.getElement(name, form);
    for (const auto &element : form)
    {
        const string value{element.getValue()};
        if (!value.empty())
        {
            const auto new_values{string_to_vector(tolower(value))};
            values.insert(values.end(),
                          std::make_move_iterator(new_values.begin()),
                          std::make_move_iterator(new_values.end()));
        }
    }

    return values;
}

string tolower(const string_view str)
{
    string result;

    const auto unistr{icu::UnicodeString(str.data(), "UTF-8").toLower()};
    unistr.toUTF8String(result);

    return result;
}

string text2html(string text)
{
    static const map<string_view, string_view> entities{{"<", "&lt;"},
                                                        {">", "&gt;"}};
    static const map<string_view, string_view> html{{"\r\n", "<br>"}};

    for (const auto &replacementmap : {entities, html})
    {
        for (const auto &repl : replacementmap)
        {
            size_t pos{0};
            while ((pos = text.find(repl.first, pos)) != string::npos)
            {
                text.replace(pos, repl.first.size(), repl.second);
                pos += repl.second.size();
            }
        }
    }

    return text;
}

bool captcha_valid(std::uint8_t id, const string_view answer)
{
    std::array<string, 6> answers{"2", "6", "17", "12", "4", "1"};
    return answers.at(id) == answer;
}

bool is_spam(const entry_type &entry)
{
    using std::regex;
    using std::regex_search;

    std::ifstream file(files::get_datadir() / "spamfilter.lst");
    if (file.good())
    {
        string line;
        while (getline(file, line))
        {
            if (!line.empty() && regex_search(entry.description, regex{line}))
            {
                return true;
            }
        }
    }
    return false;
}

void add_tags(entry_type &entry)
{
    for (const auto &tag : entry.tags)
    {
        if (tag == "nazism")
        {
            entry.tags.emplace_back("fascism");
        }
    }
}

} // namespace FediBlock::cgi

const char *SpamException::what() const noexcept
{
    return "Spam detected.";
}

const char *CaptchaException::what() const noexcept
{
    return "The solution to the captcha is not correct.";
}