DockerCLI/vendor/github.com/moby/buildkit/util/progress/progresswriter/multiwriter.go

package progresswriter

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,
	}
	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
}

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 addPrefix(pfx, name string) string {
	if strings.HasPrefix(name, "[") {
		return "[" + pfx + " " + name[1:]
	}
	return "[" + pfx + "] " + name
}