@@ -185,17 +185,6 @@ func sanitizeRepoAndTags(names []string) ([]reference.Named, error) {

 // build runs the Dockerfile builder from a context and a docker object that allows to make calls

 // to Docker.

-//

-// This will (barring errors):

-//

-// * read the dockerfile from context

-// * parse the dockerfile if not already parsed

-// * walk the AST and execute it by dispatching to handlers. If Remove

-//   or ForceRemove is set, additional cleanup around containers happens after

-//   processing.

-// * Tag image, if applicable.

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

-//

 func (b *Builder) build(stdout io.Writer, stderr io.Writer, out io.Writer) (string, error) {

 	defer b.imageContexts.unmount()

@@ -203,7 +192,7 @@ func (b *Builder) build(stdout io.Writer, stderr io.Writer, out io.Writer) (stri

 	b.Stderr = stderr

 	b.Output = out

-	dockerfile, err := b.readDockerfile()

+	dockerfile, err := b.readAndParseDockerfile()

 	if err != nil {

 		return "", err

 	}

@@ -215,14 +204,37 @@ func (b *Builder) build(stdout io.Writer, stderr io.Writer, out io.Writer) (stri

 	addNodesForLabelOption(dockerfile, b.options.Labels)

-	var shortImgID string

-	total := len(dockerfile.Children)

-	for _, n := range dockerfile.Children {

-		if err := b.checkDispatch(n, false); err != nil {

-			return "", errors.Wrapf(err, "Dockerfile parse error line %d", n.StartLine)

+	if err := checkDispatchDockerfile(dockerfile); err != nil {

+		return "", err

+	}

+

+	shortImageID, err := b.dispatchDockerfileWithCancellation(dockerfile)

+	if err != nil {

+		return "", err

+	}

+

+	b.warnOnUnusedBuildArgs()

+

+	if b.image == "" {

+		return "", errors.New("No image was generated. Is your Dockerfile empty?")

+	}

+

+	if b.options.Squash {

+		if err := b.squashBuild(); err != nil {

+			return "", err

 		}

 	}

+	fmt.Fprintf(b.Stdout, "Successfully built %s\n", shortImageID)

+	if err := b.tagImages(repoAndTags); err != nil {

+		return "", err

+	}

+	return b.image, nil

+}

+

+func (b *Builder) dispatchDockerfileWithCancellation(dockerfile *parser.Node) (string, error) {

+	total := len(dockerfile.Children)

+	var shortImgID string

 	for i, n := range dockerfile.Children {

 		select {

 		case <-b.clientCtx.Done():

@@ -255,34 +267,20 @@ func (b *Builder) build(stdout io.Writer, stderr io.Writer, out io.Writer) (stri

 		return "", errors.Errorf("failed to reach build target %s in Dockerfile", b.options.Target)

 	}

-	b.warnOnUnusedBuildArgs()

-

-	if b.image == "" {

-		return "", errors.New("No image was generated. Is your Dockerfile empty?")

-	}

+	return shortImgID, nil

+}

-	if b.options.Squash {

-		var fromID string

-		if b.from != nil {

-			fromID = b.from.ImageID()

-		}

-		b.image, err = b.docker.SquashImage(b.image, fromID)

-		if err != nil {

-			return "", errors.Wrap(err, "error squashing image")

-		}

+func (b *Builder) squashBuild() error {

+	var fromID string

+	var err error

+	if b.from != nil {

+		fromID = b.from.ImageID()

 	}

-

-	fmt.Fprintf(b.Stdout, "Successfully built %s\n", shortImgID)

-

-	imageID := image.ID(b.image)

-	for _, rt := range repoAndTags {

-		if err := b.docker.TagImageWithReference(imageID, rt); err != nil {

-			return "", err

-		}

-		fmt.Fprintf(b.Stdout, "Successfully tagged %s\n", reference.FamiliarString(rt))

+	b.image, err = b.docker.SquashImage(b.image, fromID)

+	if err != nil {

+		return errors.Wrap(err, "error squashing image")

 	}

-

-	return b.image, nil

+	return nil

 }

 func addNodesForLabelOption(dockerfile *parser.Node, labels map[string]string) {

@@ -303,6 +301,17 @@ func (b *Builder) warnOnUnusedBuildArgs() {

 	}

 }

+func (b *Builder) tagImages(repoAndTags []reference.Named) error {

+	imageID := image.ID(b.image)

+	for _, rt := range repoAndTags {

+		if err := b.docker.TagImageWithReference(imageID, rt); err != nil {

+			return err

+		}

+		fmt.Fprintf(b.Stdout, "Successfully tagged %s\n", reference.FamiliarString(rt))

+	}

+	return nil

+}

+

 // hasFromImage returns true if the builder has processed a `FROM <image>` line

 func (b *Builder) hasFromImage() bool {

 	return b.image != "" || b.noBaseImage

@@ -345,18 +354,31 @@ func BuildFromConfig(config *container.Config, changes []string) (*container.Con

 	b.Stderr = ioutil.Discard

 	b.disableCommit = true

-	total := len(ast.Children)

-	for _, n := range ast.Children {

-		if err := b.checkDispatch(n, false); err != nil {

-			return nil, err

+	if err := checkDispatchDockerfile(ast); err != nil {

+		return nil, err

+	}

+

+	if err := dispatchFromDockerfile(b, ast); err != nil {

+		return nil, err

+	}

+	return b.runConfig, nil

+}

+

+func checkDispatchDockerfile(dockerfile *parser.Node) error {

+	for _, n := range dockerfile.Children {

+		if err := checkDispatch(n); err != nil {

+			return errors.Wrapf(err, "Dockerfile parse error line %d", n.StartLine)

 		}

 	}

+	return nil

+}

+func dispatchFromDockerfile(b *Builder, ast *parser.Node) error {

+	total := len(ast.Children)

 	for i, n := range ast.Children {

 		if err := b.dispatch(i, total, n); err != nil {

-			return nil, err

+			return err

 		}

 	}

-

-	return b.runConfig, nil

+	return nil

 }

@@ -206,8 +206,7 @@ func (b *Builder) runConfigEnvMapping() map[string]string {

 // arg, env, etc., this syntax check will not be complete and could not replace

 // the runtime check. Instead, this function is only a helper that allows

 // user to find out the obvious error in Dockerfile earlier on.

-// onbuild bool: indicate if instruction XXX is part of `ONBUILD XXX` trigger

-func (b *Builder) checkDispatch(ast *parser.Node, onbuild bool) error {

+func checkDispatch(ast *parser.Node) error {

 	cmd := ast.Value

 	upperCasedCmd := strings.ToUpper(cmd)

@@ -225,16 +224,6 @@ func (b *Builder) checkDispatch(ast *parser.Node, onbuild bool) error {

 		}

 	}

-	// The instruction is part of ONBUILD trigger (not the instruction itself)

-	if onbuild {

-		switch upperCasedCmd {

-		case "ONBUILD":

-			return errors.New("Chaining ONBUILD via `ONBUILD ONBUILD` isn't allowed")

-		case "MAINTAINER", "FROM":

-			return fmt.Errorf("%s isn't allowed as an ONBUILD trigger", upperCasedCmd)

-		}

-	}

-

 	if _, ok := evaluateTable[cmd]; ok {

 		return nil

 	}

@@ -467,19 +467,24 @@ func (b *Builder) processImageFrom(img builder.Image) error {

 			return err

 		}

-		total := len(ast.Children)

 		for _, n := range ast.Children {

-			if err := b.checkDispatch(n, true); err != nil {

+			if err := checkDispatch(n); err != nil {

 				return err

 			}

-		}

-		for i, n := range ast.Children {

-			if err := b.dispatch(i, total, n); err != nil {

-				return err

+

+			upperCasedCmd := strings.ToUpper(n.Value)

+			switch upperCasedCmd {

+			case "ONBUILD":

+				return errors.New("Chaining ONBUILD via `ONBUILD ONBUILD` isn't allowed")

+			case "MAINTAINER", "FROM":

+				return errors.Errorf("%s isn't allowed as an ONBUILD trigger", upperCasedCmd)

 			}

 		}

-	}

+		if err := dispatchFromDockerfile(b, ast); err != nil {

+			return err

+		}

+	}

 	return nil

 }

@@ -644,8 +649,8 @@ func (b *Builder) clearTmp() {

 	}

 }

-// readDockerfile reads a Dockerfile from the current context.

-func (b *Builder) readDockerfile() (*parser.Node, error) {

+// readAndParseDockerfile reads a Dockerfile from the current context.

+func (b *Builder) readAndParseDockerfile() (*parser.Node, error) {

 	// If no -f was specified then look for 'Dockerfile'. If we can't find

 	// that then look for 'dockerfile'.  If neither are found then default

 	// back to 'Dockerfile' and use that in the error message.

@@ -77,6 +77,6 @@ func readAndCheckDockerfile(t *testing.T, testName, contextDir, dockerfilePath,

 	b := &Builder{options: options, context: context}

-	_, err = b.readDockerfile()

+	_, err = b.readAndParseDockerfile()

 	assert.Error(t, err, expectedError)

 }