We build too many walls and not enough bridges

internal/store/cache.go

@@ -0,0 +1,114 @@
+// Copyright (c) 2020 Proton Technologies AG
+//
+// This file is part of ProtonMail Bridge.
+//
+// ProtonMail Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// ProtonMail Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with ProtonMail Bridge.  If not, see <https://www.gnu.org/licenses/>.
+
+package store
+
+import (
+	"encoding/json"
+	"os"
+	"sync"
+
+	"github.com/pkg/errors"
+)
+
+// Cache caches the last event IDs for all accounts (there should be only one instance).
+type Cache struct {
+	// cache is map from userID => key (such as last event) => value (such as event ID).
+	cache map[string]map[string]string
+	path  string
+	lock  *sync.RWMutex
+}
+
+// NewCache constructs a new cache at the given path.
+func NewCache(path string) *Cache {
+	return &Cache{
+		path: path,
+		lock: &sync.RWMutex{},
+	}
+}
+
+func (c *Cache) getEventID(userID string) string {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	_ = c.loadCache()
+
+	if c.cache == nil {
+		c.cache = map[string]map[string]string{}
+	}
+	if c.cache[userID] == nil {
+		c.cache[userID] = map[string]string{}
+	}
+
+	return c.cache[userID]["events"]
+}
+
+func (c *Cache) setEventID(userID, eventID string) error {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	if c.cache[userID] == nil {
+		c.cache[userID] = map[string]string{}
+	}
+	c.cache[userID]["events"] = eventID
+
+	return c.saveCache()
+}
+
+func (c *Cache) loadCache() error {
+	if c.cache != nil {
+		return nil
+	}
+
+	f, err := os.Open(c.path)
+	if err != nil {
+		return err
+	}
+	defer f.Close() //nolint[errcheck]
+
+	return json.NewDecoder(f).Decode(&c.cache)
+}
+
+func (c *Cache) saveCache() error {
+	if c.cache == nil {
+		return errors.New("events: cannot save cache: cache is nil")
+	}
+
+	f, err := os.Create(c.path)
+	if err != nil {
+		return err
+	}
+	defer f.Close() //nolint[errcheck]
+
+	return json.NewEncoder(f).Encode(c.cache)
+}
+
+func (c *Cache) clearCacheUser(userID string) error {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	if c.cache == nil {
+		log.WithField("user", userID).Warning("Cannot clear user from cache: cache is nil")
+		return nil
+	}
+
+	log.WithField("user", userID).Trace("Removing user from event loop cache")
+
+	delete(c.cache, userID)
+
+	return c.saveCache()
+}