Kea dhcp server sanitize hostname hook

compile.sh

#!/bin/bash
#debian trixie:
apt update && apt -y install kea-dev libboost-dev g++
g++ -fPIC -shared -o libkea_sanitize_hostname.so sanitize_hostname.cc \
    -I/usr/include/kea -lkea-dhcp++ -lkea-hooks
cp libkea_sanitize_hostname.so /usr/local/lib/libkea_sanitize_hostname.so

kea-dhcp4.conf

{
"Dhcp4": {
"control-socket": {
"socket-type": "unix",
"socket-name": "kea4-ctrl-socket"
},

"hooks-libraries": [
{
"library": "/usr/lib/-ARCH-/kea/hooks/libdhcp_lease_cmds.so"
},
{
"library": "/usr/local/lib/libkea_sanitize_hostname.so"
}
],

...

sanitize_hostname.cc

#include <hooks/hooks.h>
#include <dhcp/pkt4.h>
#include <dhcp/option_string.h>
#include <boost/algorithm/string.hpp>
#include <iostream>
#include <chrono>
#include <iomanip>
#include <sstream>
#include <thread>
#include <unistd.h>

using namespace isc::hooks;
using namespace isc::dhcp;
using namespace std;

// Timestamp
static std::string kea_timestamp() {
    using namespace std::chrono;

    auto now = system_clock::now();
    auto t = system_clock::to_time_t(now);
    auto ms = duration_cast<milliseconds>(now.time_since_epoch()) % 1000;

    std::tm tm{};
    localtime_r(&t, &tm);

    std::ostringstream oss;
    oss << std::put_time(&tm, "%Y-%m-%d %H:%M:%S")
        << "." << std::setw(3) << std::setfill('0') << ms.count();
    return oss.str();
}

// Thread ID
static std::string thread_id() {
    std::ostringstream oss;
    oss << std::this_thread::get_id();
    return oss.str();
}

// Logger Kea-like
static void kea_log(const std::string& msg) {
    std::cerr
        << kea_timestamp()
        << " INFO  [kea-dhcp4.hook_sanitize_hostname/"
        << getpid() << "." << thread_id()
        << "] MESSAGE "
        << msg
        << std::endl;
}

extern "C" {

int version() {
    return KEA_HOOKS_VERSION;
}

bool multi_threading_compatible() {
    return true;
}

int load(LibraryHandle&) {
    kea_log("hook loaded");
    return 0;
}

int unload() {
    kea_log("hook unloaded");
    return 0;
}

int lease4_select(CalloutHandle& handle) {
    Pkt4Ptr query;
    handle.getArgument("query4", query);
    if (!query) {
        return 0;
    }

    OptionPtr opt = query->getOption(DHO_HOST_NAME);
    if (!opt) {
        return 0;
    }

    auto hostname_opt = dynamic_pointer_cast<OptionString>(opt);
    if (!hostname_opt) {
        return 0;
    }

    std::string hostname = hostname_opt->getValue();
    kea_log("original hostname: " + hostname);

    boost::replace_all(hostname, "_", "-");
    boost::algorithm::to_lower(hostname);

    hostname_opt->setValue(hostname);

    kea_log("rewritten hostname: " + hostname);

    return 0;
}

}