add git.iim.gay/grufwub/go-store for storage backend, replacing blob.Storage

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

vendor/git.iim.gay/grufwub/go-errors/once.go

@@ -0,0 +1,45 @@
+package errors
+
+import (
+	"sync/atomic"
+	"unsafe"
+)
+
+// OnceError is an error structure that supports safe multi-threaded
+// usage and setting only once (until reset)
+type OnceError struct {
+	err unsafe.Pointer
+}
+
+// NewOnce returns a new OnceError instance
+func NewOnce() OnceError {
+	return OnceError{
+		err: nil,
+	}
+}
+
+func (e *OnceError) Store(err error) {
+	// Nothing to do
+	if err == nil {
+		return
+	}
+
+	// Only set if not already
+	atomic.CompareAndSwapPointer(
+		&e.err,
+		nil,
+		unsafe.Pointer(&err),
+	)
+}
+
+func (e *OnceError) Load() error {
+	return *(*error)(atomic.LoadPointer(&e.err))
+}
+
+func (e *OnceError) IsSet() bool {
+	return (atomic.LoadPointer(&e.err) != nil)
+}
+
+func (e *OnceError) Reset() {
+	atomic.StorePointer(&e.err, nil)
+}