blasphem/pkg/storage/filesystem.go

package storage

import (
	"encoding/json"
	"fmt"
	"io/fs"
	"os"
	"path"
	"strings"
	"sync"

	"github.com/rs/zerolog/log"
)

var (
	IndentStr = strings.Repeat(" ", 2)
)

const (
	SecretMode  fs.FileMode = 0600
	DefaultMode fs.FileMode = 0644
)

type item struct {
	sync.Mutex   `json:"-"`
	Version      int         `json:"version"`
	MinorVersion *int        `json:"minor_version,omitempty"`
	Key          string      `json:"key"`
	Data         interface{} `json:"data"`

	fmode fs.FileMode
	dirty bool
}

func (i *item) Dirty()                { i.Lock(); defer i.Unlock(); i.dirty = true }
func (i *item) IsDirty() bool         { i.Lock(); defer i.Unlock(); return i.dirty }
func (i *item) GetData() interface{}  { i.Lock(); defer i.Unlock(); return i.Data }
func (i *item) SetData(d interface{}) { i.Lock(); defer i.Unlock(); i.Data = d; i.dirty = true }
func (i *item) ItemKey() string       { return i.Key /* key is immutable */ }

func (it *item) mode() fs.FileMode {
	if it.fmode != 0 {
		return it.fmode
	}

	return SecretMode
}

type fsStore struct {
	sync.RWMutex
	fs        fs.FS
	storeRoot string
	s         map[string]*item
}

func (s *fsStore) get(key string) *item {
	s.RLock()
	defer s.RUnlock()

	i, ok := s.s[key]
	if !ok {
		return nil
	}

	return i
}

func (s *fsStore) put(key string, it *item) {
	s.Lock()
	defer s.Unlock()

	s.s[key] = it
}

func (s *fsStore) persist(it *item) error {
	it.Lock()
	defer it.Unlock()

	f, err := os.OpenFile(path.Join(s.storeRoot, it.Key), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, it.mode())
	if err != nil {
		return err
	}

	defer f.Close()

	enc := json.NewEncoder(f)
	enc.SetIndent("", IndentStr)

	err = enc.Encode(it)
	if err == nil {
		it.dirty = false
	}

	return err
}

func (s *fsStore) Dirty(key string) error {
	it := s.get(key)
	if it == nil {
		return ErrNoSuchKey
	}

	it.Dirty()

	return nil
}

func (s *fsStore) Flush(key string) error {
	it := s.get(key)
	if it == nil {
		return ErrNoSuchKey
	}

	return s.persist(it)
}

func (s *fsStore) FlushAll() []error {
	s.RLock()
	defer s.RUnlock()

	var errs []error
	for _, it := range s.s {
		err := s.persist(it)
		if err != nil {
			errs = append(errs, fmt.Errorf("store key %s: %w", it.Key, err))
		}
	}

	return errs
}

func (s *fsStore) ShutdownStore() {
	errs := s.FlushAll()
	if errs != nil {
		log.Error().Errs("errors", errs).Msg("errors persisting store")
	}
}

// Put puts an item into the store.
// NB: Any user of a previous item with this key will now have a dangling reference that will not be persisted.
// It is up to consumers to coordinate against this case!
func (s *fsStore) Put(key string, version, minorVersion int, secretMode bool, data interface{}) (Item, error) {
	var mv *int
	if minorVersion != 0 {
		mv = &minorVersion
	}

	mode := DefaultMode

	if secretMode {
		mode = SecretMode
	}

	it := &item{
		Version:      version,
		MinorVersion: mv,
		Key:          key,
		Data:         data,

		fmode: mode,
		dirty: true,
	}

	s.s[key] = it
	return it, s.persist(it)
}

func (s *fsStore) Get(key string, data interface{}) error {
	_, err := s.GetItem(key, data)

	return err
}

func (s *fsStore) GetItem(key string, data interface{}) (Item, error) {
	exists := s.get(key)
	if exists != nil {
		return exists, ErrKeyExists
	}

	f, err := s.fs.Open(key)
	if err != nil {
		return nil, err
	}

	defer f.Close()

	fi, err := f.Stat()
	if err != nil {
		return nil, err
	}

	item := &item{
		Data:  data,
		fmode: fi.Mode(),
	}
	d := json.NewDecoder(f)
	err = d.Decode(item)
	if err != nil {
		return nil, err
	}

	if item.Key != key {
		return nil, fmt.Errorf("key mismatch '%s' != '%s'", item.Key, key)
	}

	s.put(key, item)

	return item, nil
}

func OpenFileStore(configRoot string) (*fsStore, error) {
	storeRoot := path.Join(configRoot, ".storage")
	stor := os.DirFS(storeRoot)

	return &fsStore{
		fs:        stor,
		storeRoot: storeRoot,
		s:         make(map[string]*item),
	}, nil
}