kilo/pkg/iptables/rulecache.go

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// Copyright 2021 the Kilo 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.
package iptables
import (
"fmt"
"strings"
)
type ruleCacheFlag byte
const (
exists ruleCacheFlag = 1 << iota
populated
)
type isNotExistError interface {
error
IsNotExist() bool
}
// ruleCache is a lazy cache that can be used to
// check if a given rule or chain exists in an iptables
// table.
type ruleCache [2]map[string]ruleCacheFlag
func (rc *ruleCache) populateTable(c Client, proto Protocol, table string) error {
// If the table already exists in the destination map,
// exit early since it has already been populated.
if rc[proto][table]&populated != 0 {
return nil
}
cs, err := c.ListChains(table)
if err != nil {
return fmt.Errorf("failed to populate chains for table %q: %v", table, err)
}
rc[proto][table] = exists | populated
for i := range cs {
rc[proto][chainToString(table, cs[i])] |= exists
}
return nil
}
func (rc *ruleCache) populateChain(c Client, proto Protocol, table, chain string) error {
// If the destination chain true, then it has already been populated.
if rc[proto][chainToString(table, chain)]&populated != 0 {
return nil
}
rs, err := c.List(table, chain)
if err != nil {
if existsErr, ok := err.(isNotExistError); ok && existsErr.IsNotExist() {
rc[proto][chainToString(table, chain)] = populated
return nil
}
return fmt.Errorf("failed to populate rules in chain %q for table %q: %v", chain, table, err)
}
for i := range rs {
rc[proto][strings.Join([]string{table, rs[i]}, " ")] = exists
}
// If there are rules on the chain, then the chain exists too.
if len(rs) > 0 {
rc[proto][chainToString(table, chain)] = exists
}
rc[proto][chainToString(table, chain)] |= populated
return nil
}
func (rc *ruleCache) populateRules(c Client, r Rule) error {
// Ensure a map for the proto exists.
if rc[r.Proto()] == nil {
rc[r.Proto()] = make(map[string]ruleCacheFlag)
}
if ch, ok := r.(*chain); ok {
return rc.populateTable(c, r.Proto(), ch.table)
}
ru := r.(*rule)
return rc.populateChain(c, r.Proto(), ru.table, ru.chain)
}
func (rc *ruleCache) exists(c Client, r Rule) (bool, error) {
// Exit early if the exact rule exists by name.
if rc[r.Proto()][r.String()]&exists != 0 {
return true, nil
}
// Otherwise, populate the respective rules.
if err := rc.populateRules(c, r); err != nil {
return false, err
}
return rc[r.Proto()][r.String()]&exists != 0, nil
}