#!/bin/bash

# Copyright Broadcom, Inc. All Rights Reserved.
# SPDX-License-Identifier: APACHE-2.0

# Copyright 2020 The Kubernetes Authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# This is a variant of the original Kubernetes iptables-wrapper below:
# https://github.com/kubernetes-sigs/iptables-wrappers/blob/v2/iptables-wrapper-installer.sh
# Adapted to use bash interpreter and make it compatible with read-only
# root filesystems.

# shellcheck disable=SC2126

set -o errexit
set -o nounset

# In kubernetes 1.17 and later, kubelet will have created at least
# one chain in the "mangle" table (either "KUBE-IPTABLES-HINT" or
# "KUBE-KUBELET-CANARY"), so check that first, against
# iptables-nft, because we can check that more efficiently and
# it's more common these days.
nft_kubelet_rules=$( (iptables-nft-save -t mangle || true; ip6tables-nft-save -t mangle || true) 2>/dev/null | grep -E '^:(KUBE-IPTABLES-HINT|KUBE-KUBELET-CANARY)' | wc -l)
if [ "${nft_kubelet_rules}" -ne 0 ]; then
    mode=nft
else
    # Check for kubernetes 1.17-or-later with iptables-legacy. We
    # can't pass "-t mangle" to iptables-legacy-save because it would
    # cause the kernel to create that table if it didn't already
    # exist, which we don't want. So we have to grab all the rules
    legacy_kubelet_rules=$( (iptables-legacy-save || true; ip6tables-legacy-save || true) 2>/dev/null | grep -E '^:(KUBE-IPTABLES-HINT|KUBE-KUBELET-CANARY)' | wc -l)
    if [ "${legacy_kubelet_rules}" -ne 0 ]; then
        mode=legacy
    else
        # With older kubernetes releases there may not be any _specific_
        # rules we can look for, but we assume that some non-containerized process
        # (possibly kubelet) will have created _some_ iptables rules.
        num_legacy_lines=$( (iptables-legacy-save || true; ip6tables-legacy-save || true) 2>/dev/null | grep '^-' | wc -l)
        num_nft_lines=$( (iptables-nft-save || true; ip6tables-nft-save || true) 2>/dev/null | grep '^-' | wc -l)
        if [ "${num_legacy_lines}" -gt "${num_nft_lines}" ]; then
            mode=legacy
        else
            mode=nft
        fi
    fi
fi

original_command="$(basename "$0")"
# Update links to point to the selected binaries
if [ -x /usr/sbin/alternatives ]; then
    # Fedora/SUSE style alternatives
    alternatives --set iptables "/usr/sbin/iptables-${mode}" > /dev/null || failed=1
    if [ "${failed:-0}" = 1 ]; then
        # Try the multi-binary if alternatives failed
        exec "/usr/sbin/xtables-${mode}-multi" "$original_command" "$@"
    fi
elif [ -x /usr/sbin/update-alternatives ] || [ -x /usr/bin/update-alternatives ]; then
    # Debian style alternatives
    update-alternatives --set iptables "/usr/sbin/iptables-${mode}" > /dev/null || failed=1
    update-alternatives --set ip6tables "/usr/sbin/ip6tables-${mode}" > /dev/null || failed=1
    if [ "${failed:-0}" = 1 ]; then
        # Try the multi-binary if update-alternatives failed
        exec "/usr/sbin/xtables-${mode}-multi" "$original_command" "$@"
    fi
else
    # Try the multi-binary
    exec "/usr/sbin/xtables-${mode}-multi" "$original_command" "$@"
fi

# Now re-exec the original command with the newly-selected alternative
exec "$original_command" "$@"