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store.go (9840 bytes)

 package main
 
 import (
 	"crypto/rand"
 	"crypto/sha256"
 	"encoding/hex"
 	"encoding/json"
 	"errors"
 	"io/fs"
 	"net/mail"
 	"os"
 	"path/filepath"
 	"regexp"
 	"sort"
 	"strings"
 	"sync"
 	"time"
 
 	"golang.org/x/crypto/bcrypt"
 )
 
 const (
 	maxTokens   = 20 // sign-ins kept per account; the oldest goes first
 	maxVersions = 50 // versions of the bookmark file kept per account
 )
 
 var (
 	errTaken    = errors.New("an account with this email exists already")
 	errEmail    = errors.New("this is not an email address")
 	errPassword = errors.New("the password must have 8 to 72 characters")
 	errWrong    = errors.New("wrong email or password")
 	errGone     = errors.New("the account does not exist")
 	hashName    = regexp.MustCompile(`^[0-9a-f]{64}$`)
 )
 
 // Account is one user. The file of the user is in files/<ID>.
 type Account struct {
 	ID       string    `json:"id"`
 	Email    string    `json:"email"`
 	Hash     string    `json:"hash"` // bcrypt hash of the password
 	Created  time.Time `json:"created"`
 	Tokens   []string  `json:"tokens"` // SHA-256 of each sign-in token
 	Customer string    `json:"customer,omitempty"`
 	Status   string    `json:"status,omitempty"`    // of the Stripe subscription
 	StatusAt int64     `json:"status_at,omitempty"` // time of the Stripe event that set Status
 }
 
 // Store keeps the accounts in one JSON file, accounts.json, and the versions
 // of each bookmark file in files/<account ID>/<SHA-256 of the text>. The file
 // HEAD beside the versions names the current one.
 type Store struct {
 	dir      string
 	mu       sync.Mutex // for the maps, the accounts and accounts.json
 	accounts map[string]*Account
 	byEmail  map[string]*Account
 	byToken  map[string]*Account
 	locks    map[string]*sync.Mutex // one for the files of each account
 }
 
 func openStore(dir string) (*Store, error) {
 	if err := os.MkdirAll(filepath.Join(dir, "files"), 0o700); err != nil {
 		return nil, err
 	}
 	s := &Store{
 		dir:      dir,
 		accounts: map[string]*Account{},
 		byEmail:  map[string]*Account{},
 		byToken:  map[string]*Account{},
 		locks:    map[string]*sync.Mutex{},
 	}
 	b, err := os.ReadFile(filepath.Join(dir, "accounts.json"))
 	if errors.Is(err, fs.ErrNotExist) {
 		return s, nil
 	} else if err != nil {
 		return nil, err
 	}
 	var list []*Account
 	if err := json.Unmarshal(b, &list); err != nil {
 		return nil, err
 	}
 	for _, a := range list {
 		s.index(a)
 	}
 	return s, nil
 }
 
 func (s *Store) index(a *Account) {
 	s.accounts[a.ID] = a
 	s.byEmail[a.Email] = a
 	for _, t := range a.Tokens {
 		s.byToken[t] = a
 	}
 }
 
 // save writes accounts.json. The caller holds s.mu.
 func (s *Store) save() error {
 	list := make([]*Account, 0, len(s.accounts))
 	for _, a := range s.accounts {
 		list = append(list, a)
 	}
 	sort.Slice(list, func(i, j int) bool { return list[i].Created.Before(list[j].Created) })
 	b, err := json.MarshalIndent(list, "", "\t")
 	if err != nil {
 		return err
 	}
 	return writeFile(filepath.Join(s.dir, "accounts.json"), b)
 }
 
 // writeFile replaces a file in one step: a crash leaves the old file or the
 // new one, never a part of one.
 func writeFile(name string, data []byte) error {
 	tmp := name + ".tmp"
 	f, err := os.OpenFile(tmp, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o600)
 	if err != nil {
 		return err
 	}
 	_, err = f.Write(data)
 	if err == nil {
 		err = f.Sync()
 	}
 	if cerr := f.Close(); err == nil {
 		err = cerr
 	}
 	if err != nil {
 		os.Remove(tmp)
 		return err
 	}
 	return os.Rename(tmp, name)
 }
 
 func random(n int) string {
 	b := make([]byte, n)
 	if _, err := rand.Read(b); err != nil {
 		panic(err) // crypto/rand does not fail on supported systems
 	}
 	return hex.EncodeToString(b)
 }
 
 func digest(s string) string {
 	sum := sha256.Sum256([]byte(s))
 	return hex.EncodeToString(sum[:])
 }
 
 // cleanEmail gives the email address in the form that the store keeps.
 func cleanEmail(email string) (string, error) {
 	email = strings.ToLower(strings.TrimSpace(email))
 	a, err := mail.ParseAddress(email)
 	if err != nil || a.Name != "" || a.Address != email || len(email) > 254 {
 		return "", errEmail
 	}
 	return email, nil
 }
 
 func (s *Store) signup(email, password string) (*Account, error) {
 	email, err := cleanEmail(email)
 	if err != nil {
 		return nil, err
 	}
 	if len(password) < 8 || len(password) > 72 {
 		return nil, errPassword
 	}
 	hash, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
 	if err != nil {
 		return nil, err
 	}
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	if s.byEmail[email] != nil {
 		return nil, errTaken
 	}
 	a := &Account{ID: random(16), Email: email, Hash: string(hash), Created: time.Now().UTC()}
 	s.index(a)
 	if err := s.save(); err != nil {
 		delete(s.accounts, a.ID)
 		delete(s.byEmail, a.Email)
 		return nil, err
 	}
 	return a, nil
 }
 
 // dummy is compared when the email is unknown, so that a wrong email takes
 // as long as a wrong password.
 var dummy, _ = bcrypt.GenerateFromPassword([]byte("sbm-sync dummy password"), bcrypt.DefaultCost)
 
 func (s *Store) check(email, password string) (*Account, error) {
 	email = strings.ToLower(strings.TrimSpace(email))
 	s.mu.Lock()
 	a := s.byEmail[email]
 	hash := dummy
 	if a != nil {
 		hash = []byte(a.Hash)
 	}
 	s.mu.Unlock()
 	if bcrypt.CompareHashAndPassword(hash, []byte(password)) != nil || a == nil {
 		return nil, errWrong
 	}
 	return a, nil
 }
 
 // signIn gives a new token for the account. Only its hash is kept.
 func (s *Store) signIn(a *Account) (string, error) {
 	token := random(32)
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	if s.accounts[a.ID] == nil {
 		return "", errGone
 	}
 	a.Tokens = append(a.Tokens, digest(token))
 	s.byToken[digest(token)] = a
 	for len(a.Tokens) > maxTokens {
 		delete(s.byToken, a.Tokens[0])
 		a.Tokens = a.Tokens[1:]
 	}
 	return token, s.save()
 }
 
 func (s *Store) signOut(token string) error {
 	h := digest(token)
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	a := s.byToken[h]
 	if a == nil {
 		return nil
 	}
 	delete(s.byToken, h)
 	for i, t := range a.Tokens {
 		if t == h {
 			a.Tokens = append(a.Tokens[:i], a.Tokens[i+1:]...)
 			break
 		}
 	}
 	return s.save()
 }
 
 func (s *Store) byTok(token string) *Account {
 	if token == "" {
 		return nil
 	}
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	return s.byToken[digest(token)]
 }
 
 func (s *Store) byID(id string) *Account {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	return s.accounts[id]
 }
 
 func (s *Store) byCustomer(customer string) *Account {
 	if customer == "" {
 		return nil
 	}
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	for _, a := range s.accounts {
 		if a.Customer == customer {
 			return a
 		}
 	}
 	return nil
 }
 
 // view gives a copy of the account, safe to read without the lock.
 func (s *Store) view(a *Account) Account {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	c := *a
 	c.Tokens = nil
 	return c
 }
 
 func (s *Store) setCustomer(a *Account, customer string) error {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	a.Customer = customer
 	return s.save()
 }
 
 // setStatus records the state of the subscription, unless the store has a
 // newer event already: Stripe does not send events in order.
 func (s *Store) setStatus(a *Account, status string, at int64) error {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	if at < a.StatusAt {
 		return nil
 	}
 	a.Status, a.StatusAt = status, at
 	return s.save()
 }
 
 func (s *Store) lock(id string) *sync.Mutex {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	m := s.locks[id]
 	if m == nil {
 		m = &sync.Mutex{}
 		s.locks[id] = m
 	}
 	return m
 }
 
 // remove deletes the account and all versions of its file.
 func (s *Store) remove(a *Account) error {
 	m := s.lock(a.ID)
 	m.Lock()
 	defer m.Unlock()
 	s.mu.Lock()
 	delete(s.accounts, a.ID)
 	delete(s.byEmail, a.Email)
 	for _, t := range a.Tokens {
 		delete(s.byToken, t)
 	}
 	err := s.save()
 	s.mu.Unlock()
 	if err != nil {
 		return err
 	}
 	return os.RemoveAll(filepath.Join(s.dir, "files", a.ID))
 }
 
 // sync merges the file that a device sends into the current version, keeps
 // the result as the new current version and gives it with its name. base
 // names the version that the device got last time, or is "" for none.
 func (s *Store) sync(a *Account, base, local string) (string, string, error) {
 	m := s.lock(a.ID)
 	m.Lock()
 	defer m.Unlock()
 	if s.byID(a.ID) == nil {
 		return "", "", errGone
 	}
 	dir := filepath.Join(s.dir, "files", a.ID)
 	if err := os.MkdirAll(dir, 0o700); err != nil {
 		return "", "", err
 	}
 	remote := ""
 	head, err := os.ReadFile(filepath.Join(dir, "HEAD"))
 	if err == nil {
 		b, err := os.ReadFile(filepath.Join(dir, strings.TrimSpace(string(head))))
 		if err != nil {
 			return "", "", err
 		}
 		remote = string(b)
 	} else if !errors.Is(err, fs.ErrNotExist) {
 		return "", "", err
 	}
 	old := ""
 	if hashName.MatchString(base) {
 		if b, err := os.ReadFile(filepath.Join(dir, base)); err == nil {
 			old = string(b)
 		}
 	}
 	merged := merge(old, local, remote)
 	name := digest(merged)
 	path := filepath.Join(dir, name)
 	if _, err := os.Stat(path); err == nil {
 		now := time.Now()
 		err = os.Chtimes(path, now, now) // the newest versions are kept
 		if err != nil {
 			return "", "", err
 		}
 	} else if err := writeFile(path, []byte(merged)); err != nil {
 		return "", "", err
 	}
 	if err := writeFile(filepath.Join(dir, "HEAD"), []byte(name+"\n")); err != nil {
 		return "", "", err
 	}
 	return merged, name, prune(dir, name)
 }
 
 // prune deletes all but the newest versions in dir, and never keep.
 func prune(dir, keep string) error {
 	entries, err := os.ReadDir(dir)
 	if err != nil {
 		return err
 	}
 	type version struct {
 		name string
 		time time.Time
 	}
 	var vs []version
 	for _, e := range entries {
 		if !hashName.MatchString(e.Name()) || e.Name() == keep {
 			continue
 		}
 		info, err := e.Info()
 		if err != nil {
 			return err
 		}
 		vs = append(vs, version{e.Name(), info.ModTime()})
 	}
 	sort.Slice(vs, func(i, j int) bool { return vs[i].time.After(vs[j].time) })
 	for i := maxVersions - 1; i < len(vs); i++ {
 		if err := os.Remove(filepath.Join(dir, vs[i].name)); err != nil {
 			return err
 		}
 	}
 	return nil
 }