@@ -16,5 +16,5 @@ type Backend interface {

 	// by the caller.

 	//

 	// TODO: make this return a reference instead of string

-	Build(clientCtx context.Context, config *types.ImageBuildOptions, context builder.Context, stdout io.Writer, stderr io.Writer, out io.Writer, clientGone <-chan bool) (string, error)

+	Build(clientCtx context.Context, config *types.ImageBuildOptions, context builder.Context, stdout io.Writer, stderr io.Writer, out io.Writer) (string, error)

 }

@@ -161,17 +161,12 @@ func (br *buildRouter) postBuild(ctx context.Context, w http.ResponseWriter, r *

 		return progress.NewProgressReader(in, progressOutput, r.ContentLength, "Downloading context", remoteURL)

 	}

-	var (

-		context        builder.ModifiableContext

-		dockerfileName string

-		out            io.Writer

-	)

-	context, dockerfileName, err = builder.DetectContextFromRemoteURL(r.Body, remoteURL, createProgressReader)

+	buildContext, dockerfileName, err := builder.DetectContextFromRemoteURL(r.Body, remoteURL, createProgressReader)

 	if err != nil {

 		return errf(err)

 	}

 	defer func() {

-		if err := context.Close(); err != nil {

+		if err := buildContext.Close(); err != nil {

 			logrus.Debugf("[BUILDER] failed to remove temporary context: %v", err)

 		}

 	}()

@@ -181,7 +176,7 @@ func (br *buildRouter) postBuild(ctx context.Context, w http.ResponseWriter, r *

 	buildOptions.AuthConfigs = authConfigs

-	out = output

+	var out io.Writer = output

 	if buildOptions.SuppressOutput {

 		out = notVerboseBuffer

 	}

@@ -189,15 +184,24 @@ func (br *buildRouter) postBuild(ctx context.Context, w http.ResponseWriter, r *

 	stdout := &streamformatter.StdoutFormatter{Writer: out, StreamFormatter: sf}

 	stderr := &streamformatter.StderrFormatter{Writer: out, StreamFormatter: sf}

-	closeNotifier := make(<-chan bool)

+	finished := make(chan struct{})

+	defer close(finished)

 	if notifier, ok := w.(http.CloseNotifier); ok {

-		closeNotifier = notifier.CloseNotify()

+		notifyContext, cancel := context.WithCancel(ctx)

+		closeNotifier := notifier.CloseNotify()

+		go func() {

+			select {

+			case <-closeNotifier:

+				cancel()

+			case <-finished:

+			}

+		}()

+		ctx = notifyContext

 	}

 	imgID, err := br.backend.Build(ctx, buildOptions,

-		builder.DockerIgnoreContext{ModifiableContext: context},

-		stdout, stderr, out,

-		closeNotifier)

+		builder.DockerIgnoreContext{ModifiableContext: buildContext},

+		stdout, stderr, out)

 	if err != nil {

 		return errf(err)

 	}

@@ -8,7 +8,6 @@ import (

 	"io/ioutil"

 	"os"

 	"strings"

-	"sync"

 	"github.com/Sirupsen/logrus"

 	"github.com/docker/docker/builder"

@@ -56,6 +55,7 @@ type Builder struct {

 	docker    builder.Backend

 	context   builder.Context

 	clientCtx context.Context

+	cancel    context.CancelFunc

 	dockerfile       *parser.Node

 	runConfig        *container.Config // runconfig for cmd, run, entrypoint etc.

@@ -67,8 +67,6 @@ type Builder struct {

 	cmdSet           bool

 	disableCommit    bool

 	cacheBusted      bool

-	cancelled        chan struct{}

-	cancelOnce       sync.Once

 	allowedBuildArgs map[string]bool // list of build-time args that are allowed for expansion/substitution and passing to commands in 'run'.

 	// TODO: remove once docker.Commit can receive a tag

@@ -88,23 +86,24 @@ func NewBuildManager(b builder.Backend) (bm *BuildManager) {

 // NewBuilder creates a new Dockerfile builder from an optional dockerfile and a Config.

 // If dockerfile is nil, the Dockerfile specified by Config.DockerfileName,

 // will be read from the Context passed to Build().

-func NewBuilder(clientCtx context.Context, config *types.ImageBuildOptions, backend builder.Backend, context builder.Context, dockerfile io.ReadCloser) (b *Builder, err error) {

+func NewBuilder(clientCtx context.Context, config *types.ImageBuildOptions, backend builder.Backend, buildContext builder.Context, dockerfile io.ReadCloser) (b *Builder, err error) {

 	if config == nil {

 		config = new(types.ImageBuildOptions)

 	}

 	if config.BuildArgs == nil {

 		config.BuildArgs = make(map[string]string)

 	}

+	ctx, cancel := context.WithCancel(clientCtx)

 	b = &Builder{

-		clientCtx:        clientCtx,

+		clientCtx:        ctx,

+		cancel:           cancel,

 		options:          config,

 		Stdout:           os.Stdout,

 		Stderr:           os.Stderr,

 		docker:           backend,

-		context:          context,

+		context:          buildContext,

 		runConfig:        new(container.Config),

 		tmpContainers:    map[string]struct{}{},

-		cancelled:        make(chan struct{}),

 		id:               stringid.GenerateNonCryptoID(),

 		allowedBuildArgs: make(map[string]bool),

 	}

@@ -161,12 +160,12 @@ func sanitizeRepoAndTags(names []string) ([]reference.Named, error) {

 }

 // Build creates a NewBuilder, which builds the image.

-func (bm *BuildManager) Build(clientCtx context.Context, config *types.ImageBuildOptions, context builder.Context, stdout io.Writer, stderr io.Writer, out io.Writer, clientGone <-chan bool) (string, error) {

+func (bm *BuildManager) Build(clientCtx context.Context, config *types.ImageBuildOptions, context builder.Context, stdout io.Writer, stderr io.Writer, out io.Writer) (string, error) {

 	b, err := NewBuilder(clientCtx, config, bm.backend, context, nil)

 	if err != nil {

 		return "", err

 	}

-	img, err := b.build(config, context, stdout, stderr, out, clientGone)

+	img, err := b.build(config, context, stdout, stderr, out)

 	return img, err

 }

@@ -184,7 +183,7 @@ func (bm *BuildManager) Build(clientCtx context.Context, config *types.ImageBuil

 // * Tag image, if applicable.

 // * Print a happy message and return the image ID.

 //

-func (b *Builder) build(config *types.ImageBuildOptions, context builder.Context, stdout io.Writer, stderr io.Writer, out io.Writer, clientGone <-chan bool) (string, error) {

+func (b *Builder) build(config *types.ImageBuildOptions, context builder.Context, stdout io.Writer, stderr io.Writer, out io.Writer) (string, error) {

 	b.options = config

 	b.context = context

 	b.Stdout = stdout

@@ -198,19 +197,6 @@ func (b *Builder) build(config *types.ImageBuildOptions, context builder.Context

 		}

 	}

-	finished := make(chan struct{})

-	defer close(finished)

-	go func() {

-		select {

-		case <-finished:

-		case <-clientGone:

-			b.cancelOnce.Do(func() {

-				close(b.cancelled)

-			})

-		}

-

-	}()

-

 	repoAndTags, err := sanitizeRepoAndTags(config.Tags)

 	if err != nil {

 		return "", err

@@ -223,7 +209,7 @@ func (b *Builder) build(config *types.ImageBuildOptions, context builder.Context

 			b.addLabels()

 		}

 		select {

-		case <-b.cancelled:

+		case <-b.clientCtx.Done():

 			logrus.Debug("Builder: build cancelled!")

 			fmt.Fprintf(b.Stdout, "Build cancelled")

 			return "", fmt.Errorf("Build cancelled")

@@ -271,9 +257,7 @@ func (b *Builder) build(config *types.ImageBuildOptions, context builder.Context

 // Cancel cancels an ongoing Dockerfile build.

 func (b *Builder) Cancel() {

-	b.cancelOnce.Do(func() {

-		close(b.cancelled)

-	})

+	b.cancel()

 }

 // BuildFromConfig builds directly from `changes`, treating it as if it were the contents of a Dockerfile

@@ -6,6 +6,7 @@ package dockerfile

 import (

 	"crypto/sha256"

 	"encoding/hex"

+	"errors"

 	"fmt"

 	"io"

 	"io/ioutil"

@@ -16,6 +17,7 @@ import (

 	"runtime"

 	"sort"

 	"strings"

+	"sync"

 	"time"

 	"github.com/Sirupsen/logrus"

@@ -553,6 +555,8 @@ func (b *Builder) create() (string, error) {

 	return c.ID, nil

 }

+var errCancelled = errors.New("build cancelled")

+

 func (b *Builder) run(cID string) (err error) {

 	errCh := make(chan error)

 	go func() {

@@ -560,14 +564,19 @@ func (b *Builder) run(cID string) (err error) {

 	}()

 	finished := make(chan struct{})

-	defer close(finished)

+	var once sync.Once

+	finish := func() { close(finished) }

+	cancelErrCh := make(chan error, 1)

+	defer once.Do(finish)

 	go func() {

 		select {

-		case <-b.cancelled:

+		case <-b.clientCtx.Done():

 			logrus.Debugln("Build cancelled, killing and removing container:", cID)

 			b.docker.ContainerKill(cID, 0)

 			b.removeContainer(cID)

+			cancelErrCh <- errCancelled

 		case <-finished:

+			cancelErrCh <- nil

 		}

 	}()

@@ -587,8 +596,8 @@ func (b *Builder) run(cID string) (err error) {

 			Code:    ret,

 		}

 	}

-

-	return nil

+	once.Do(finish)

+	return <-cancelErrCh

 }

 func (b *Builder) removeContainer(c string) error {