github.com/containerd/nerdctl/v2@v2.0.0-beta.5.0.20240520001846-b5758f54fa28/pkg/dnsutil/hostsstore/hostsstore.go

/*
   Copyright The containerd 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 hostsstore provides the interface for /var/lib/nerdctl/<ADDRHASH>/etchosts .
// Prioritize simplicity over scalability.
package hostsstore

import (
	"encoding/json"
	"errors"
	"os"
	"path/filepath"

	"github.com/containerd/containerd/errdefs"
	"github.com/containerd/nerdctl/v2/pkg/lockutil"
	types100 "github.com/containernetworking/cni/pkg/types/100"
)

const (
	// hostsDirBasename is the base name of /var/lib/nerdctl/<ADDRHASH>/etchosts
	hostsDirBasename = "etchosts"
	// metaJSON is stored as /var/lib/nerdctl/<ADDRHASH>/etchosts/<NS>/<ID>/meta.json
	metaJSON = "meta.json"
)

// HostsPath returns "/var/lib/nerdctl/<ADDRHASH>/etchosts/<NS>/<ID>/hosts"
func HostsPath(dataStore, ns, id string) string {
	if dataStore == "" || ns == "" || id == "" {
		panic(errdefs.ErrInvalidArgument)
	}
	return filepath.Join(dataStore, hostsDirBasename, ns, id, "hosts")
}

// ensureFile ensures a file with permission 0644.
// The file is initialized with no content.
// The dir (if not exists) is created with permission 0700.
func ensureFile(path string) error {
	if path == "" {
		return errdefs.ErrInvalidArgument
	}
	dir := filepath.Dir(path)
	if err := os.MkdirAll(dir, 0700); err != nil {
		return err
	}
	return os.WriteFile(path, []byte{}, 0644)
}

// AllocHostsFile is used for creating mount-bindable /etc/hosts file.
// The file is initialized with no content.
func AllocHostsFile(dataStore, ns, id string) (string, error) {
	lockDir := filepath.Join(dataStore, hostsDirBasename)
	if err := os.MkdirAll(lockDir, 0700); err != nil {
		return "", err
	}
	path := HostsPath(dataStore, ns, id)
	fn := func() error {
		return ensureFile(path)
	}
	err := lockutil.WithDirLock(lockDir, fn)
	return path, err
}

func DeallocHostsFile(dataStore, ns, id string) error {
	lockDir := filepath.Join(dataStore, hostsDirBasename)
	if err := os.MkdirAll(lockDir, 0700); err != nil {
		return err
	}
	dirToBeRemoved := filepath.Dir(HostsPath(dataStore, ns, id))
	fn := func() error {
		return os.RemoveAll(dirToBeRemoved)
	}
	return lockutil.WithDirLock(lockDir, fn)
}

func NewStore(dataStore string) (Store, error) {
	store := &store{
		dataStore: dataStore,
		hostsD:    filepath.Join(dataStore, hostsDirBasename),
	}
	return store, os.MkdirAll(store.hostsD, 0700)
}

type Meta struct {
	Namespace  string
	ID         string
	Networks   map[string]*types100.Result
	Hostname   string
	ExtraHosts map[string]string // host:ip
	Name       string
}

type Store interface {
	Acquire(Meta) error
	Release(ns, id string) error
	Update(ns, id, newName string) error
}

type store struct {
	// dataStore is /var/lib/nerdctl/<ADDRHASH>
	dataStore string
	// hostsD is /var/lib/nerdctl/<ADDRHASH>/etchosts
	hostsD string
}

func (x *store) Acquire(meta Meta) error {
	fn := func() error {
		hostsPath := HostsPath(x.dataStore, meta.Namespace, meta.ID)
		if err := ensureFile(hostsPath); err != nil {
			return err
		}
		metaB, err := json.Marshal(meta)
		if err != nil {
			return err
		}
		metaPath := filepath.Join(x.hostsD, meta.Namespace, meta.ID, metaJSON)
		if err := os.WriteFile(metaPath, metaB, 0644); err != nil {
			return err
		}
		return newUpdater(meta.ID, x.hostsD).update()
	}
	return lockutil.WithDirLock(x.hostsD, fn)
}

// Release is triggered by Poststop hooks.
// It is called after the containerd task is deleted but before the delete operation returns.
func (x *store) Release(ns, id string) error {
	fn := func() error {
		metaPath := filepath.Join(x.hostsD, ns, id, metaJSON)
		if _, err := os.Stat(metaPath); errors.Is(err, os.ErrNotExist) {
			return nil
		}
		// We remove "meta.json" but we still retain the "hosts" file
		// because it is needed for restarting. The "hosts" is removed on
		// `nerdctl rm`.
		// https://github.com/rootless-containers/rootlesskit/issues/220#issuecomment-783224610
		if err := os.RemoveAll(metaPath); err != nil {
			return err
		}
		return newUpdater(id, x.hostsD).update()
	}
	return lockutil.WithDirLock(x.hostsD, fn)
}

func (x *store) Update(ns, id, newName string) error {
	fn := func() error {
		metaPath := filepath.Join(x.hostsD, ns, id, metaJSON)
		metaB, err := os.ReadFile(metaPath)
		if err != nil {
			return err
		}
		meta := &Meta{}
		if err := json.Unmarshal(metaB, meta); err != nil {
			return err
		}
		meta.Name = newName
		metaB, err = json.Marshal(meta)
		if err != nil {
			return err
		}
		if err := os.WriteFile(metaPath, metaB, 0644); err != nil {
			return err
		}
		return newUpdater(meta.ID, x.hostsD).update()
	}
	return lockutil.WithDirLock(x.hostsD, fn)
}