Implement cache for networks

utils/cache.go

@@ -0,0 +1,86 @@
+package utils
+
+import (
+	"errors"
+	"os"
+	"path"
+	"time"
+)
+
+type Cache interface {
+	Get(key string, maxAge time.Duration) ([]byte, error)
+
+	Set(key string, value []byte) error
+}
+
+func CachePrefix(c Cache, prefix string) Cache {
+	if c == nil {
+		return nil
+	}
+	return prefixCache{
+		c:      c,
+		prefix: prefix,
+	}
+}
+
+func CacheDirectory(directory string) (Cache, error) {
+	if stat, err := os.Stat(directory); err != nil {
+		return nil, err
+	} else if !stat.IsDir() {
+		return nil, errors.New("not a directory")
+	}
+	return dirCache(directory), nil
+}
+
+type prefixCache struct {
+	c      Cache
+	prefix string
+}
+
+func (c prefixCache) Get(key string, maxAge time.Duration) ([]byte, error) {
+	return c.c.Get(c.prefix+key, maxAge)
+}
+
+func (c prefixCache) Set(key string, value []byte) error {
+	return c.c.Set(c.prefix+key, value)
+}
+
+type dirCache string
+
+var ErrExpired = errors.New("key expired")
+
+func (d dirCache) Get(key string, maxAge time.Duration) ([]byte, error) {
+	fname := path.Join(string(d), key)
+	stat, err := os.Stat(fname)
+	if err != nil {
+		return nil, err
+	}
+	if stat.IsDir() {
+		return nil, errors.New("key is directory")
+	}
+	data, err := os.ReadFile(fname)
+	if err != nil {
+		return nil, err
+	}
+
+	if stat.ModTime().Before(time.Now().Add(-maxAge)) {
+		return data, ErrExpired
+	} else {
+		return data, nil
+	}
+}
+
+func (d dirCache) Set(key string, value []byte) error {
+	fname := path.Join(string(d), key)
+	fs, err := os.Create(fname)
+	if err != nil {
+		return err
+	}
+	defer fs.Close()
+	_, err = fs.Write(value)
+	fs.Sync()
+	fs.Close()
+
+	_ = os.Chtimes(fname, time.Time{}, time.Now())
+	return err
+}