vendor: add buildkit

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/moby/buildkit/frontend/gateway/client/result.go

@@ -0,0 +1,54 @@
+package client
+
+import (
+	"context"
+	"sync"
+
+	"github.com/pkg/errors"
+)
+
+type BuildFunc func(context.Context, Client) (*Result, error)
+
+type Result struct {
+	mu       sync.Mutex
+	Ref      Reference
+	Refs     map[string]Reference
+	Metadata map[string][]byte
+}
+
+func NewResult() *Result {
+	return &Result{}
+}
+
+func (r *Result) AddMeta(k string, v []byte) {
+	r.mu.Lock()
+	if r.Metadata == nil {
+		r.Metadata = map[string][]byte{}
+	}
+	r.Metadata[k] = v
+	r.mu.Unlock()
+}
+
+func (r *Result) AddRef(k string, ref Reference) {
+	r.mu.Lock()
+	if r.Refs == nil {
+		r.Refs = map[string]Reference{}
+	}
+	r.Refs[k] = ref
+	r.mu.Unlock()
+}
+
+func (r *Result) SetRef(ref Reference) {
+	r.Ref = ref
+}
+
+func (r *Result) SingleRef() (Reference, error) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	if r.Refs != nil && r.Ref == nil {
+		return nil, errors.Errorf("invalid map result")
+	}
+
+	return r.Ref, nil
+}