xbot/driver/web.cpp

#include "web.hpp"

#include <boost/beast.hpp>
#include <boost/json.hpp>
#include <boost/log/trivial.hpp>
#include <boost/system/system_error.hpp>

#include <openssl/hmac.h>

#include <chrono>
#include <fstream>
#include <sstream>
#include <vector>

namespace beast = boost::beast; // from <boost/beast.hpp>
namespace http = beast::http; // from <boost/beast/http.hpp>
namespace net = boost::asio; // from <boost/asio.hpp>
namespace websocket = beast::websocket;
using tcp = net::ip::tcp; // from <boost/asio/ip/tcp.hpp>

using namespace std::literals;

namespace {

auto report_error(std::exception_ptr eptr) -> void
{
    if (eptr)
    {
        try
        {
            std::rethrow_exception(eptr);
        }
        catch (const std::exception &e)
        {
            BOOST_LOG_TRIVIAL(error) << "An error occurred: " << e.what();
        }
    }
}

static auto simple_response(http::status status, unsigned version, bool keep_alive) -> http::message_generator
{
    http::response<http::string_body> res{status, version};
    res.set(http::field::server, BOOST_BEAST_VERSION_STRING);
    res.keep_alive(keep_alive);
    res.content_length(0);
    return res;
}

static auto compute_signature(const std::string_view secret, const std::string_view body) -> std::string
{
    unsigned int digest_length = EVP_MAX_MD_SIZE;
    unsigned char digest[EVP_MAX_MD_SIZE];

    HMAC(EVP_sha256(), secret.data(), secret.size(), reinterpret_cast<const unsigned char *>(body.data()), body.size(), digest, &digest_length);

    std::stringstream ss;
    ss << "sha256=";
    ss << std::hex << std::setfill('0');
    for (unsigned int i = 0; i < digest_length; i++)
    {
        ss << std::setw(2) << static_cast<int>(digest[i]);
    }
    return ss.str();
}

static auto process_event(
    std::shared_ptr<GithubWebhook> self,
    const std::string_view notify_user,
    const std::string_view event,
    const boost::json::value &json
) -> void
{
    auto &project = json.as_object();

    std::string full_name;
    if (project.contains("repository"))
    {
        full_name = std::string{project.at("repository").as_object().at("full_name").as_string()};
    }
    else if (project.contains("organization"))
    {
        full_name = std::string{project.at("organization").as_object().at("login").as_string()};
    }
    else
    {
        BOOST_LOG_TRIVIAL(warning) << "No repository or organization detected";
        return;
    }

    const auto &settings = self->settings_.projects.at(full_name);

    // Ensure that this sender is authorized to send for this project
    if (settings.credential_name != notify_user)
    {
        BOOST_LOG_TRIVIAL(warning) << "Credential mismatch for " << full_name << " wanted: " << settings.credential_name << " got: " << notify_user;
        return;
    }

    if (not settings.enabled)
    {
        return;
    }

    const auto message = std::string{event} + " on " + full_name;
    self->add_event({settings.channel, message});
}

template <class Body, class Allocator>
static auto handle_request(
    std::shared_ptr<GithubWebhook> self,
    http::request<Body, http::basic_fields<Allocator>> &&req
) -> http::message_generator
{
    BOOST_LOG_TRIVIAL(info) << "HTTP request " << req.method_string() << " " << req.target();

    if (not req.target().starts_with("/notify/"))
    {
        BOOST_LOG_TRIVIAL(warning) << "HTTP Bad target: " << req.target();
        return simple_response(http::status::not_found, req.version(), req.keep_alive());
    }
    std::string notify_user = req.target().substr(8);

    if (req.method() != http::verb::post)
    {
        BOOST_LOG_TRIVIAL(warning) << "HTTP Bad method: " << req.method_string();
        return simple_response(http::status::method_not_allowed, req.version(), req.keep_alive());
    }

    const auto event = req["x-github-event"];
    const auto signature = req["x-hub-signature-256"];
    if (event.empty() || signature.empty())
    {
        BOOST_LOG_TRIVIAL(warning) << "HTTP Missing headers";
        return simple_response(http::status::bad_request, req.version(), req.keep_alive());
    }

    const auto credential_cursor = self->settings_.credentials.find(notify_user);
    if (credential_cursor == self->settings_.credentials.end())
    {
        BOOST_LOG_TRIVIAL(warning) << "HTTP Unknown user: " << notify_user;
        return simple_response(http::status::unauthorized, req.version(), req.keep_alive());
    }
    const auto &secret = credential_cursor->second;

    const auto expected_signature = compute_signature(secret, req.body());
    if (signature != expected_signature)
    {
        BOOST_LOG_TRIVIAL(warning) << "HTTP Bad signature: " << signature << " expected: " << expected_signature;
        return simple_response(http::status::unauthorized, req.version(), req.keep_alive());
    }

    try
    {
        process_event(self, notify_user, event, boost::json::parse(req.body()));
    }
    catch (const boost::system::system_error &e)
    {
        BOOST_LOG_TRIVIAL(error) << "HTTP Failed to process event: " << e.what();
        return simple_response(http::status::internal_server_error, req.version(), req.keep_alive());
    }

    return simple_response(http::status::ok, req.version(), req.keep_alive());
}

auto read_loop(tcp::socket socket, std::shared_ptr<GithubWebhook> self) -> boost::asio::awaitable<void>
{
    beast::tcp_stream stream{std::move(socket)};
    beast::flat_buffer buffer;
    http::request<http::string_body> req;

    for (;;)
    {
        req.clear();
        stream.expires_after(30s);

        boost::system::error_code ec;
        co_await http::async_read(stream, buffer, req, net::redirect_error(net::use_awaitable, ec));
        if (ec == http::error::end_of_stream)
        {
            stream.socket().shutdown(tcp::socket::shutdown_send, ec);
            co_return;
        }
        else if (ec)
        {
            throw boost::system::system_error{ec};
        }

        const auto keep_alive = req.keep_alive();
        auto msg = handle_request(self, std::move(req));

        co_await beast::async_write(stream, std::move(msg), net::use_awaitable);

        if (!keep_alive)
        {
            stream.socket().shutdown(tcp::socket::shutdown_send, ec);
            co_return;
        }
    }
}

auto accept_loop(
    tcp::acceptor acceptor,
    std::shared_ptr<GithubWebhook> self
) -> boost::asio::awaitable<void>
{
    for (;;)
    {
        auto socket = co_await acceptor.async_accept(net::use_awaitable);
        boost::asio::co_spawn(
            acceptor.get_executor(),
            read_loop(std::move(socket), self),
            report_error
        );
    }
}

auto spawn_webhook(
    boost::asio::io_context &io,
    const std::shared_ptr<GithubWebhook> webhook
) -> boost::asio::awaitable<void>
{
    tcp::resolver resolver{io};
    auto results = co_await resolver.async_resolve(webhook->settings_.host, webhook->settings_.service, tcp::resolver::passive, boost::asio::use_awaitable);

    for (auto &&result : results)
    {
        const auto endpoint = result.endpoint();
        BOOST_LOG_TRIVIAL(info) << "HTTP: Listening on " << endpoint;
        tcp::acceptor acceptor{io};
        acceptor.open(endpoint.protocol());
        acceptor.set_option(net::socket_base::reuse_address(true));
        acceptor.bind(endpoint);
        acceptor.listen(net::socket_base::max_listen_connections);
        boost::asio::co_spawn(io, accept_loop(std::move(acceptor), webhook), report_error);
    }
}

} // namespace

auto start_webhook(
    boost::asio::io_context &io,
    const char *webhook_settings_filename
) -> std::shared_ptr<GithubWebhook>
{
    std::ifstream webhook_settings_file{webhook_settings_filename};
    if (!webhook_settings_file)
    {
        BOOST_LOG_TRIVIAL(error) << "Unable to open webhook settings file";
        std::exit(1);
    }

    auto webhook_settings = toml::parse(webhook_settings_file);
    WebhookSettings settings = WebhookSettings::from_toml(webhook_settings);
    BOOST_LOG_TRIVIAL(info) << "Webhook settings: " << settings.to_toml();
    auto webhook = std::make_shared<GithubWebhook>(std::move(settings));
    boost::asio::co_spawn(io, spawn_webhook(io, webhook), report_error);
    return webhook;
}

auto GithubWebhook::write_event(WebhookEvent event) -> void
{
    connection_->send_notice("glguy", event.channel + ": " + event.message);
}

auto ProjectSettings::from_toml(const toml::table &v) -> ProjectSettings
{
    ProjectSettings result;
    result.channel = v["channel"].value_or(""s);
    result.credential_name = v["credential_name"].value_or(""s);
    result.enabled = v["enabled"].value_or(false);

    if (const auto events = v["events"].as_array())
    {
        for (const auto &event : *events)
        {
            result.events.insert(event.value_or(""s));
        }
    }

    if (const auto accounts = v["authorized_accounts"].as_array())
    {
        for (const auto &account : *accounts)
        {
            result.authorized_accounts.insert(account.value_or(""s));
        }
    }

    return result;
}

auto ProjectSettings::to_toml() const -> toml::table
{
    toml::array events_array;
    for (const auto &event : events)
    {
        events_array.emplace_back(event);
    }

    toml::array authorized_accounts_array;
    for (const auto &account : authorized_accounts)
    {
        authorized_accounts_array.emplace_back(account);
    }

    return toml::table{
        {"channel", channel},
        {"credential_name", credential_name},
        {"enabled", enabled},
        {"events", std::move(events_array)},
        {"authorized_accounts", std::move(authorized_accounts_array)}
    };
}

auto WebhookSettings::from_toml(const toml::table &v) -> WebhookSettings
{
    WebhookSettings result;
    result.host = v["host"].value_or(""s);
    result.service = v["service"].value_or("http"s);

    if (const auto credentials = v["credentials"].as_array())
    {
        for (const auto &credential : *credentials)
        {
            if (auto credential_table = credential.as_table())
            {
                result.credentials.emplace(
                    (*credential_table)["name"].value_or(""s),
                    (*credential_table)["key"].value_or(""s)
                );
            }
        }
    }

    if (const auto projects = v["projects"].as_array())
    {
        for (const auto &project : *projects)
        {
            if (auto project_table = project.as_table())
            {
                result.projects.emplace(
                    (*project_table)["name"].value_or(""s),
                    ProjectSettings::from_toml(*project_table)
                );
            }
        }
    }

    return result;
}

auto WebhookSettings::to_toml() const -> toml::table
{
    toml::array credential_tables;
    for (const auto &[name, key] : credentials)
    {
        credential_tables.emplace_back(toml::table{
            {"name", name},
            {"key", key}
        });
    }

    toml::array project_tables;
    for (const auto &[name, project] : projects)
    {
        auto tab = project.to_toml();
        tab.emplace("name", name);
        project_tables.emplace_back(std::move(tab));
    }

    return toml::table{
        {"host", host},
        {"service", service},
        {"credentials", std::move(credential_tables)},
        {"projects", std::move(project_tables)}
    };
}