build: multi-node build support

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

util/progress/writer.go

@@ -1,7 +1,11 @@
 package progress
 
 import (
+	"time"
+
 	"github.com/moby/buildkit/client"
+	"github.com/moby/buildkit/identity"
+	"github.com/opencontainers/go-digest"
 )
 
 type Writer interface {
@@ -9,3 +13,31 @@ type Writer interface {
 	Err() error
 	Status() chan *client.SolveStatus
 }
+
+func Write(w Writer, name string, f func() error) {
+	status := w.Status()
+	dgst := digest.FromBytes([]byte(identity.NewID()))
+	tm := time.Now()
+
+	vtx := client.Vertex{
+		Digest:  dgst,
+		Name:    name,
+		Started: &tm,
+	}
+
+	status <- &client.SolveStatus{
+		Vertexes: []*client.Vertex{&vtx},
+	}
+
+	err := f()
+
+	tm2 := time.Now()
+	vtx2 := vtx
+	vtx2.Completed = &tm2
+	if err != nil {
+		vtx2.Error = err.Error()
+	}
+	status <- &client.SolveStatus{
+		Vertexes: []*client.Vertex{&vtx2},
+	}
+}