feat(session): add web storage API based session storage

session/storage_js.go

@@ -0,0 +1,85 @@
+// +build js,wasm
+
+package session
+
+import (
+	"context"
+	"syscall/js"
+
+	"golang.org/x/xerrors"
+)
+
+// WebLocalStorage is a Web Storage API based session storage.
+type WebLocalStorage struct {
+	Key string
+}
+
+func getStorage() (js.Value, bool) {
+	localStorage := js.Global().Get("localStorage")
+
+	if localStorage.IsUndefined() || localStorage.IsNull() {
+		return js.Value{}, false
+	}
+
+	const testValue = "__test__"
+	localStorage.Set(testValue, testValue)
+	value := localStorage.Get(testValue)
+	if value.IsUndefined() || value.IsNull() {
+		return js.Value{}, false
+	}
+	localStorage.Delete(testValue)
+
+	return localStorage, true
+}
+
+// ErrLocalStorageIsNotAvailable is returned if localStorage is not available and Storage can't use it.
+var ErrLocalStorageIsNotAvailable = xerrors.New("localStorage is not available")
+
+func catch(err *error)  { // nolint:gocritic
+	if r := recover(); r != nil {
+		rErr, ok := r.(error)
+		if !ok {
+			*err = xerrors.Errorf("catch: %v", r)
+		} else {
+			*err = xerrors.Errorf("catch: %w", rErr)
+		}
+	}
+}
+
+// LoadSession loads session using Web Storage API.
+func (w WebLocalStorage) LoadSession(_ context.Context) (_ []byte, rerr error) {
+	defer catch(&rerr)
+
+	if w.Key == "" {
+		return nil, xerrors.Errorf("invalid key %q", w.Key)
+	}
+
+	store, ok := getStorage()
+	if !ok {
+		return nil, ErrLocalStorageIsNotAvailable
+	}
+
+	value := store.Call("getItem", w.Key)
+	if value.IsNull() || value.IsUndefined() {
+		return nil, ErrNotFound
+	}
+
+	return []byte(value.String()), nil
+}
+
+// StoreSession saves session using Web Storage API.
+func (w WebLocalStorage) StoreSession(_ context.Context, data []byte) (rerr error) {
+	defer catch(&rerr)
+
+	if w.Key == "" {
+		return xerrors.Errorf("invalid key %q", w.Key)
+	}
+
+	store, ok := getStorage()
+	if !ok {
+		return ErrLocalStorageIsNotAvailable
+	}
+
+	store.Call("setItem", w.Key, string(data))
+	return nil
+}