util: simplify progress syncronization

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

util/progress/multiwriter.go

@@ -1,101 +1,32 @@
 package progress
 
 import (
-	"context"
 	"strings"
-	"sync"
 
 	"github.com/moby/buildkit/client"
-	"golang.org/x/sync/errgroup"
 )
 
-type MultiWriter struct {
-	w     Writer
-	eg    *errgroup.Group
-	once  sync.Once
-	ready chan struct{}
-}
-
-func (mw *MultiWriter) WithPrefix(pfx string, force bool) Writer {
-	in := make(chan *client.SolveStatus)
-	out := mw.w.Status()
-	p := &prefixed{
-		main: mw.w,
-		in:   in,
+func WithPrefix(w Writer, pfx string, force bool) Writer {
+	return &prefixed{
+		main:  w,
+		pfx:   pfx,
+		force: force,
 	}
-	mw.eg.Go(func() error {
-		mw.once.Do(func() {
-			close(mw.ready)
-		})
-		for {
-			select {
-			case v, ok := <-in:
-				if ok {
-					if force {
-						for _, v := range v.Vertexes {
-							v.Name = addPrefix(pfx, v.Name)
-						}
-					}
-					out <- v
-				} else {
-					return nil
-				}
-			case <-mw.Done():
-				return mw.Err()
-			}
-		}
-	})
-	return p
-}
-
-func (mw *MultiWriter) Done() <-chan struct{} {
-	return mw.w.Done()
-}
-
-func (mw *MultiWriter) Err() error {
-	return mw.w.Err()
-}
-
-func (mw *MultiWriter) Status() chan *client.SolveStatus {
-	return nil
 }
 
 type prefixed struct {
-	main Writer
-	in   chan *client.SolveStatus
+	main  Writer
+	pfx   string
+	force bool
 }
 
-func (p *prefixed) Done() <-chan struct{} {
-	return p.main.Done()
-}
-
-func (p *prefixed) Err() error {
-	return p.main.Err()
-}
-
-func (p *prefixed) Status() chan *client.SolveStatus {
-	return p.in
-}
-
-func NewMultiWriter(pw Writer) *MultiWriter {
-	if pw == nil {
-		return nil
-	}
-	eg, _ := errgroup.WithContext(context.TODO())
-
-	ready := make(chan struct{})
-
-	go func() {
-		<-ready
-		eg.Wait()
-		close(pw.Status())
-	}()
-
-	return &MultiWriter{
-		w:     pw,
-		eg:    eg,
-		ready: ready,
+func (p *prefixed) Write(v *client.SolveStatus) {
+	if p.force {
+		for _, v := range v.Vertexes {
+			v.Name = addPrefix(p.pfx, v.Name)
+		}
 	}
+	p.main.Write(v)
 }
 
 func addPrefix(pfx, name string) string {