Initial commit

vendor/github.com/hyperhq/hypercli/api/client/build.go

@@ -0,0 +1,651 @@
+package client
+
+import (
+	"archive/tar"
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"regexp"
+	"runtime"
+	"strings"
+
+	"github.com/docker/engine-api/types"
+	"github.com/docker/go-units"
+	"github.com/hyperhq/hypercli/api"
+	"github.com/hyperhq/hypercli/builder/dockerignore"
+	Cli "github.com/hyperhq/hypercli/cli"
+	"github.com/hyperhq/hypercli/opts"
+	"github.com/hyperhq/hypercli/pkg/archive"
+	"github.com/hyperhq/hypercli/pkg/fileutils"
+	"github.com/hyperhq/hypercli/pkg/gitutils"
+	"github.com/hyperhq/hypercli/pkg/httputils"
+	"github.com/hyperhq/hypercli/pkg/ioutils"
+	"github.com/hyperhq/hypercli/pkg/jsonmessage"
+	flag "github.com/hyperhq/hypercli/pkg/mflag"
+	"github.com/hyperhq/hypercli/pkg/progress"
+	"github.com/hyperhq/hypercli/pkg/streamformatter"
+	"github.com/hyperhq/hypercli/pkg/urlutil"
+	"github.com/hyperhq/hypercli/reference"
+	runconfigopts "github.com/hyperhq/hypercli/runconfig/opts"
+	"golang.org/x/net/context"
+)
+
+type translatorFunc func(context.Context, reference.NamedTagged) (reference.Canonical, error)
+
+// CmdBuild builds a new image from the source code at a given path.
+//
+// If '-' is provided instead of a path or URL, Docker will build an image from either a Dockerfile or tar archive read from STDIN.
+//
+// Usage: docker build [OPTIONS] PATH | URL | -
+func (cli *DockerCli) Build(args ...string) error {
+	cmd := Cli.Subcmd("build", []string{"PATH | URL | -"}, Cli.DockerCommands["build"].Description, true)
+	flTags := opts.NewListOpts(validateTag)
+	cmd.Var(&flTags, []string{"t", "-tag"}, "Name and optionally a tag in the 'name:tag' format")
+	suppressOutput := cmd.Bool([]string{"q", "-quiet"}, false, "Suppress the build output and print image ID on success")
+	noCache := cmd.Bool([]string{"-no-cache"}, false, "Do not use cache when building the image")
+	rm := cmd.Bool([]string{"-rm"}, true, "Remove intermediate containers after a successful build")
+	forceRm := cmd.Bool([]string{"-force-rm"}, false, "Always remove intermediate containers")
+	pull := cmd.Bool([]string{"-pull"}, false, "Always attempt to pull a newer version of the image")
+	dockerfileName := cmd.String([]string{"f", "-file"}, "", "Name of the Dockerfile (Default is 'PATH/Dockerfile')")
+	flMemoryString := cmd.String([]string{"m", "-memory"}, "", "Memory limit")
+	flMemorySwap := cmd.String([]string{"-memory-swap"}, "", "Swap limit equal to memory plus swap: '-1' to enable unlimited swap")
+	flShmSize := cmd.String([]string{"-shm-size"}, "", "Size of /dev/shm, default value is 64MB")
+	flCPUShares := cmd.Int64([]string{"#c", "-cpu-shares"}, 0, "CPU shares (relative weight)")
+	flCPUPeriod := cmd.Int64([]string{"-cpu-period"}, 0, "Limit the CPU CFS (Completely Fair Scheduler) period")
+	flCPUQuota := cmd.Int64([]string{"-cpu-quota"}, 0, "Limit the CPU CFS (Completely Fair Scheduler) quota")
+	flCPUSetCpus := cmd.String([]string{"-cpuset-cpus"}, "", "CPUs in which to allow execution (0-3, 0,1)")
+	flCPUSetMems := cmd.String([]string{"-cpuset-mems"}, "", "MEMs in which to allow execution (0-3, 0,1)")
+	flCgroupParent := cmd.String([]string{"-cgroup-parent"}, "", "Optional parent cgroup for the container")
+	flBuildArg := opts.NewListOpts(runconfigopts.ValidateEnv)
+	cmd.Var(&flBuildArg, []string{"-build-arg"}, "Set build-time variables")
+
+	ulimits := make(map[string]*units.Ulimit)
+	flUlimits := runconfigopts.NewUlimitOpt(&ulimits)
+	cmd.Var(flUlimits, []string{"-ulimit"}, "Ulimit options")
+
+	cmd.Require(flag.Exact, 1)
+
+	// For trusted pull on "FROM <image>" instruction.
+	addTrustedFlags(cmd, true)
+
+	cmd.ParseFlags(args, true)
+
+	var (
+		buildCtx io.ReadCloser
+		err      error
+	)
+
+	specifiedContext := cmd.Arg(0)
+
+	var (
+		contextDir    string
+		tempDir       string
+		relDockerfile string
+		progBuff      io.Writer
+		buildBuff     io.Writer
+	)
+
+	progBuff = cli.out
+	buildBuff = cli.out
+	if *suppressOutput {
+		progBuff = bytes.NewBuffer(nil)
+		buildBuff = bytes.NewBuffer(nil)
+	}
+
+	switch {
+	case specifiedContext == "-":
+		buildCtx, relDockerfile, err = getContextFromReader(cli.in, *dockerfileName)
+	case urlutil.IsGitURL(specifiedContext):
+		tempDir, relDockerfile, err = getContextFromGitURL(specifiedContext, *dockerfileName)
+	case urlutil.IsURL(specifiedContext):
+		buildCtx, relDockerfile, err = getContextFromURL(progBuff, specifiedContext, *dockerfileName)
+	default:
+		contextDir, relDockerfile, err = getContextFromLocalDir(specifiedContext, *dockerfileName)
+	}
+
+	if err != nil {
+		if *suppressOutput && urlutil.IsURL(specifiedContext) {
+			fmt.Fprintln(cli.err, progBuff)
+		}
+		return fmt.Errorf("unable to prepare context: %s", err)
+	}
+
+	if tempDir != "" {
+		defer os.RemoveAll(tempDir)
+		contextDir = tempDir
+	}
+
+	if buildCtx == nil {
+		// And canonicalize dockerfile name to a platform-independent one
+		relDockerfile, err = archive.CanonicalTarNameForPath(relDockerfile)
+		if err != nil {
+			return fmt.Errorf("cannot canonicalize dockerfile path %s: %v", relDockerfile, err)
+		}
+
+		f, err := os.Open(filepath.Join(contextDir, ".dockerignore"))
+		if err != nil && !os.IsNotExist(err) {
+			return err
+		}
+
+		var excludes []string
+		if err == nil {
+			excludes, err = dockerignore.ReadAll(f)
+			if err != nil {
+				return err
+			}
+		}
+
+		if err := validateContextDirectory(contextDir, excludes); err != nil {
+			return fmt.Errorf("Error checking context: '%s'.", err)
+		}
+
+		// If .dockerignore mentions .dockerignore or the Dockerfile
+		// then make sure we send both files over to the daemon
+		// because Dockerfile is, obviously, needed no matter what, and
+		// .dockerignore is needed to know if either one needs to be
+		// removed. The daemon will remove them for us, if needed, after it
+		// parses the Dockerfile. Ignore errors here, as they will have been
+		// caught by validateContextDirectory above.
+		var includes = []string{"."}
+		keepThem1, _ := fileutils.Matches(".dockerignore", excludes)
+		keepThem2, _ := fileutils.Matches(relDockerfile, excludes)
+		if keepThem1 || keepThem2 {
+			includes = append(includes, ".dockerignore", relDockerfile)
+		}
+
+		buildCtx, err = archive.TarWithOptions(contextDir, &archive.TarOptions{
+			Compression:     archive.Uncompressed,
+			ExcludePatterns: excludes,
+			IncludeFiles:    includes,
+		})
+		if err != nil {
+			return err
+		}
+	}
+
+	ctx := context.Background()
+
+	var resolvedTags []*resolvedTag
+	if isTrusted() {
+		// Wrap the tar archive to replace the Dockerfile entry with the rewritten
+		// Dockerfile which uses trusted pulls.
+		buildCtx = replaceDockerfileTarWrapper(ctx, buildCtx, relDockerfile, cli.trustedReference, &resolvedTags)
+	}
+
+	// Setup an upload progress bar
+	progressOutput := streamformatter.NewStreamFormatter().NewProgressOutput(progBuff, true)
+
+	var body io.Reader = progress.NewProgressReader(buildCtx, progressOutput, 0, "", "Sending build context to Docker daemon")
+
+	var memory int64
+	if *flMemoryString != "" {
+		parsedMemory, err := units.RAMInBytes(*flMemoryString)
+		if err != nil {
+			return err
+		}
+		memory = parsedMemory
+	}
+
+	var memorySwap int64
+	if *flMemorySwap != "" {
+		if *flMemorySwap == "-1" {
+			memorySwap = -1
+		} else {
+			parsedMemorySwap, err := units.RAMInBytes(*flMemorySwap)
+			if err != nil {
+				return err
+			}
+			memorySwap = parsedMemorySwap
+		}
+	}
+
+	var shmSize int64
+	if *flShmSize != "" {
+		shmSize, err = units.RAMInBytes(*flShmSize)
+		if err != nil {
+			return err
+		}
+	}
+
+	options := types.ImageBuildOptions{
+		Memory:         memory,
+		MemorySwap:     memorySwap,
+		Tags:           flTags.GetAll(),
+		SuppressOutput: *suppressOutput,
+		NoCache:        *noCache,
+		Remove:         *rm,
+		ForceRemove:    *forceRm,
+		PullParent:     *pull,
+		CPUSetCPUs:     *flCPUSetCpus,
+		CPUSetMems:     *flCPUSetMems,
+		CPUShares:      *flCPUShares,
+		CPUQuota:       *flCPUQuota,
+		CPUPeriod:      *flCPUPeriod,
+		CgroupParent:   *flCgroupParent,
+		Dockerfile:     relDockerfile,
+		ShmSize:        shmSize,
+		Ulimits:        flUlimits.GetList(),
+		BuildArgs:      runconfigopts.ConvertKVStringsToMap(flBuildArg.GetAll()),
+		AuthConfigs:    cli.configFile.AuthConfigs,
+	}
+
+	response, err := cli.client.ImageBuild(ctx, body, options)
+	if err != nil {
+		return err
+	}
+
+	err = jsonmessage.DisplayJSONMessagesStream(response.Body, buildBuff, cli.outFd, cli.isTerminalOut, nil)
+	if err != nil {
+		if jerr, ok := err.(*jsonmessage.JSONError); ok {
+			// If no error code is set, default to 1
+			if jerr.Code == 0 {
+				jerr.Code = 1
+			}
+			if *suppressOutput {
+				fmt.Fprintf(cli.err, "%s%s", progBuff, buildBuff)
+			}
+			return Cli.StatusError{Status: jerr.Message, StatusCode: jerr.Code}
+		}
+	}
+
+	// Windows: show error message about modified file permissions if the
+	// daemon isn't running Windows.
+	if response.OSType != "windows" && runtime.GOOS == "windows" {
+		fmt.Fprintln(cli.err, `SECURITY WARNING: You are building a Docker image from Windows against a non-Windows Docker host. All files and directories added to build context will have '-rwxr-xr-x' permissions. It is recommended to double check and reset permissions for sensitive files and directories.`)
+	}
+
+	// Everything worked so if -q was provided the output from the daemon
+	// should be just the image ID and we'll print that to stdout.
+	if *suppressOutput {
+		fmt.Fprintf(cli.out, "%s", buildBuff)
+	}
+
+	if isTrusted() {
+		// Since the build was successful, now we must tag any of the resolved
+		// images from the above Dockerfile rewrite.
+		for _, resolved := range resolvedTags {
+			if err := cli.tagTrusted(ctx, resolved.digestRef, resolved.tagRef); err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
+
+// validateContextDirectory checks if all the contents of the directory
+// can be read and returns an error if some files can't be read
+// symlinks which point to non-existing files don't trigger an error
+func validateContextDirectory(srcPath string, excludes []string) error {
+	contextRoot, err := getContextRoot(srcPath)
+	if err != nil {
+		return err
+	}
+	return filepath.Walk(contextRoot, func(filePath string, f os.FileInfo, err error) error {
+		// skip this directory/file if it's not in the path, it won't get added to the context
+		if relFilePath, err := filepath.Rel(contextRoot, filePath); err != nil {
+			return err
+		} else if skip, err := fileutils.Matches(relFilePath, excludes); err != nil {
+			return err
+		} else if skip {
+			if f.IsDir() {
+				return filepath.SkipDir
+			}
+			return nil
+		}
+
+		if err != nil {
+			if os.IsPermission(err) {
+				return fmt.Errorf("can't stat '%s'", filePath)
+			}
+			if os.IsNotExist(err) {
+				return nil
+			}
+			return err
+		}
+
+		// skip checking if symlinks point to non-existing files, such symlinks can be useful
+		// also skip named pipes, because they hanging on open
+		if f.Mode()&(os.ModeSymlink|os.ModeNamedPipe) != 0 {
+			return nil
+		}
+
+		if !f.IsDir() {
+			currentFile, err := os.Open(filePath)
+			if err != nil && os.IsPermission(err) {
+				return fmt.Errorf("no permission to read from '%s'", filePath)
+			}
+			currentFile.Close()
+		}
+		return nil
+	})
+}
+
+// validateTag checks if the given image name can be resolved.
+func validateTag(rawRepo string) (string, error) {
+	_, err := reference.ParseNamed(rawRepo)
+	if err != nil {
+		return "", err
+	}
+
+	return rawRepo, nil
+}
+
+// isUNC returns true if the path is UNC (one starting \\). It always returns
+// false on Linux.
+func isUNC(path string) bool {
+	return runtime.GOOS == "windows" && strings.HasPrefix(path, `\\`)
+}
+
+// getDockerfileRelPath uses the given context directory for a `docker build`
+// and returns the absolute path to the context directory, the relative path of
+// the dockerfile in that context directory, and a non-nil error on success.
+func getDockerfileRelPath(givenContextDir, givenDockerfile string) (absContextDir, relDockerfile string, err error) {
+	if absContextDir, err = filepath.Abs(givenContextDir); err != nil {
+		return "", "", fmt.Errorf("unable to get absolute context directory: %v", err)
+	}
+
+	// The context dir might be a symbolic link, so follow it to the actual
+	// target directory.
+	//
+	// FIXME. We use isUNC (always false on non-Windows platforms) to workaround
+	// an issue in golang. On Windows, EvalSymLinks does not work on UNC file
+	// paths (those starting with \\). This hack means that when using links
+	// on UNC paths, they will not be followed.
+	if !isUNC(absContextDir) {
+		absContextDir, err = filepath.EvalSymlinks(absContextDir)
+		if err != nil {
+			return "", "", fmt.Errorf("unable to evaluate symlinks in context path: %v", err)
+		}
+	}
+
+	stat, err := os.Lstat(absContextDir)
+	if err != nil {
+		return "", "", fmt.Errorf("unable to stat context directory %q: %v", absContextDir, err)
+	}
+
+	if !stat.IsDir() {
+		return "", "", fmt.Errorf("context must be a directory: %s", absContextDir)
+	}
+
+	absDockerfile := givenDockerfile
+	if absDockerfile == "" {
+		// No -f/--file was specified so use the default relative to the
+		// context directory.
+		absDockerfile = filepath.Join(absContextDir, api.DefaultDockerfileName)
+
+		// Just to be nice ;-) look for 'dockerfile' too but only
+		// use it if we found it, otherwise ignore this check
+		if _, err = os.Lstat(absDockerfile); os.IsNotExist(err) {
+			altPath := filepath.Join(absContextDir, strings.ToLower(api.DefaultDockerfileName))
+			if _, err = os.Lstat(altPath); err == nil {
+				absDockerfile = altPath
+			}
+		}
+	}
+
+	// If not already an absolute path, the Dockerfile path should be joined to
+	// the base directory.
+	if !filepath.IsAbs(absDockerfile) {
+		absDockerfile = filepath.Join(absContextDir, absDockerfile)
+	}
+
+	// Evaluate symlinks in the path to the Dockerfile too.
+	//
+	// FIXME. We use isUNC (always false on non-Windows platforms) to workaround
+	// an issue in golang. On Windows, EvalSymLinks does not work on UNC file
+	// paths (those starting with \\). This hack means that when using links
+	// on UNC paths, they will not be followed.
+	if !isUNC(absDockerfile) {
+		absDockerfile, err = filepath.EvalSymlinks(absDockerfile)
+		if err != nil {
+			return "", "", fmt.Errorf("unable to evaluate symlinks in Dockerfile path: %v", err)
+		}
+	}
+
+	if _, err := os.Lstat(absDockerfile); err != nil {
+		if os.IsNotExist(err) {
+			return "", "", fmt.Errorf("Cannot locate Dockerfile: %q", absDockerfile)
+		}
+		return "", "", fmt.Errorf("unable to stat Dockerfile: %v", err)
+	}
+
+	if relDockerfile, err = filepath.Rel(absContextDir, absDockerfile); err != nil {
+		return "", "", fmt.Errorf("unable to get relative Dockerfile path: %v", err)
+	}
+
+	if strings.HasPrefix(relDockerfile, ".."+string(filepath.Separator)) {
+		return "", "", fmt.Errorf("The Dockerfile (%s) must be within the build context (%s)", givenDockerfile, givenContextDir)
+	}
+
+	return absContextDir, relDockerfile, nil
+}
+
+// writeToFile copies from the given reader and writes it to a file with the
+// given filename.
+func writeToFile(r io.Reader, filename string) error {
+	file, err := os.OpenFile(filename, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, os.FileMode(0600))
+	if err != nil {
+		return fmt.Errorf("unable to create file: %v", err)
+	}
+	defer file.Close()
+
+	if _, err := io.Copy(file, r); err != nil {
+		return fmt.Errorf("unable to write file: %v", err)
+	}
+
+	return nil
+}
+
+// getContextFromReader will read the contents of the given reader as either a
+// Dockerfile or tar archive. Returns a tar archive used as a context and a
+// path to the Dockerfile inside the tar.
+func getContextFromReader(r io.ReadCloser, dockerfileName string) (out io.ReadCloser, relDockerfile string, err error) {
+	buf := bufio.NewReader(r)
+
+	magic, err := buf.Peek(archive.HeaderSize)
+	if err != nil && err != io.EOF {
+		return nil, "", fmt.Errorf("failed to peek context header from STDIN: %v", err)
+	}
+
+	if archive.IsArchive(magic) {
+		return ioutils.NewReadCloserWrapper(buf, func() error { return r.Close() }), dockerfileName, nil
+	}
+
+	// Input should be read as a Dockerfile.
+	tmpDir, err := ioutil.TempDir("", "docker-build-context-")
+	if err != nil {
+		return nil, "", fmt.Errorf("unbale to create temporary context directory: %v", err)
+	}
+
+	f, err := os.Create(filepath.Join(tmpDir, api.DefaultDockerfileName))
+	if err != nil {
+		return nil, "", err
+	}
+	_, err = io.Copy(f, buf)
+	if err != nil {
+		f.Close()
+		return nil, "", err
+	}
+
+	if err := f.Close(); err != nil {
+		return nil, "", err
+	}
+	if err := r.Close(); err != nil {
+		return nil, "", err
+	}
+
+	tar, err := archive.Tar(tmpDir, archive.Uncompressed)
+	if err != nil {
+		return nil, "", err
+	}
+
+	return ioutils.NewReadCloserWrapper(tar, func() error {
+		err := tar.Close()
+		os.RemoveAll(tmpDir)
+		return err
+	}), api.DefaultDockerfileName, nil
+
+}
+
+// getContextFromGitURL uses a Git URL as context for a `docker build`. The
+// git repo is cloned into a temporary directory used as the context directory.
+// Returns the absolute path to the temporary context directory, the relative
+// path of the dockerfile in that context directory, and a non-nil error on
+// success.
+func getContextFromGitURL(gitURL, dockerfileName string) (absContextDir, relDockerfile string, err error) {
+	if _, err := exec.LookPath("git"); err != nil {
+		return "", "", fmt.Errorf("unable to find 'git': %v", err)
+	}
+	if absContextDir, err = gitutils.Clone(gitURL); err != nil {
+		return "", "", fmt.Errorf("unable to 'git clone' to temporary context directory: %v", err)
+	}
+
+	return getDockerfileRelPath(absContextDir, dockerfileName)
+}
+
+// getContextFromURL uses a remote URL as context for a `docker build`. The
+// remote resource is downloaded as either a Dockerfile or a tar archive.
+// Returns the tar archive used for the context and a path of the
+// dockerfile inside the tar.
+func getContextFromURL(out io.Writer, remoteURL, dockerfileName string) (io.ReadCloser, string, error) {
+	response, err := httputils.Download(remoteURL)
+	if err != nil {
+		return nil, "", fmt.Errorf("unable to download remote context %s: %v", remoteURL, err)
+	}
+	progressOutput := streamformatter.NewStreamFormatter().NewProgressOutput(out, true)
+
+	// Pass the response body through a progress reader.
+	progReader := progress.NewProgressReader(response.Body, progressOutput, response.ContentLength, "", fmt.Sprintf("Downloading build context from remote url: %s", remoteURL))
+
+	return getContextFromReader(ioutils.NewReadCloserWrapper(progReader, func() error { return response.Body.Close() }), dockerfileName)
+}
+
+// getContextFromLocalDir uses the given local directory as context for a
+// `docker build`. Returns the absolute path to the local context directory,
+// the relative path of the dockerfile in that context directory, and a non-nil
+// error on success.
+func getContextFromLocalDir(localDir, dockerfileName string) (absContextDir, relDockerfile string, err error) {
+	// When using a local context directory, when the Dockerfile is specified
+	// with the `-f/--file` option then it is considered relative to the
+	// current directory and not the context directory.
+	if dockerfileName != "" {
+		if dockerfileName, err = filepath.Abs(dockerfileName); err != nil {
+			return "", "", fmt.Errorf("unable to get absolute path to Dockerfile: %v", err)
+		}
+	}
+
+	return getDockerfileRelPath(localDir, dockerfileName)
+}
+
+var dockerfileFromLinePattern = regexp.MustCompile(`(?i)^[\s]*FROM[ \f\r\t\v]+(?P<image>[^ \f\r\t\v\n#]+)`)
+
+// resolvedTag records the repository, tag, and resolved digest reference
+// from a Dockerfile rewrite.
+type resolvedTag struct {
+	digestRef reference.Canonical
+	tagRef    reference.NamedTagged
+}
+
+// rewriteDockerfileFrom rewrites the given Dockerfile by resolving images in
+// "FROM <image>" instructions to a digest reference. `translator` is a
+// function that takes a repository name and tag reference and returns a
+// trusted digest reference.
+func rewriteDockerfileFrom(ctx context.Context, dockerfile io.Reader, translator translatorFunc) (newDockerfile []byte, resolvedTags []*resolvedTag, err error) {
+	scanner := bufio.NewScanner(dockerfile)
+	buf := bytes.NewBuffer(nil)
+
+	// Scan the lines of the Dockerfile, looking for a "FROM" line.
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		matches := dockerfileFromLinePattern.FindStringSubmatch(line)
+		if matches != nil && matches[1] != api.NoBaseImageSpecifier {
+			// Replace the line with a resolved "FROM repo@digest"
+			ref, err := reference.ParseNamed(matches[1])
+			if err != nil {
+				return nil, nil, err
+			}
+			ref = reference.WithDefaultTag(ref)
+			if ref, ok := ref.(reference.NamedTagged); ok && isTrusted() {
+				trustedRef, err := translator(ctx, ref)
+				if err != nil {
+					return nil, nil, err
+				}
+
+				line = dockerfileFromLinePattern.ReplaceAllLiteralString(line, fmt.Sprintf("FROM %s", trustedRef.String()))
+				resolvedTags = append(resolvedTags, &resolvedTag{
+					digestRef: trustedRef,
+					tagRef:    ref,
+				})
+			}
+		}
+
+		_, err := fmt.Fprintln(buf, line)
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+
+	return buf.Bytes(), resolvedTags, scanner.Err()
+}
+
+// replaceDockerfileTarWrapper wraps the given input tar archive stream and
+// replaces the entry with the given Dockerfile name with the contents of the
+// new Dockerfile. Returns a new tar archive stream with the replaced
+// Dockerfile.
+func replaceDockerfileTarWrapper(ctx context.Context, inputTarStream io.ReadCloser, dockerfileName string, translator translatorFunc, resolvedTags *[]*resolvedTag) io.ReadCloser {
+	pipeReader, pipeWriter := io.Pipe()
+	go func() {
+		tarReader := tar.NewReader(inputTarStream)
+		tarWriter := tar.NewWriter(pipeWriter)
+
+		defer inputTarStream.Close()
+
+		for {
+			hdr, err := tarReader.Next()
+			if err == io.EOF {
+				// Signals end of archive.
+				tarWriter.Close()
+				pipeWriter.Close()
+				return
+			}
+			if err != nil {
+				pipeWriter.CloseWithError(err)
+				return
+			}
+
+			var content io.Reader = tarReader
+			if hdr.Name == dockerfileName {
+				// This entry is the Dockerfile. Since the tar archive was
+				// generated from a directory on the local filesystem, the
+				// Dockerfile will only appear once in the archive.
+				var newDockerfile []byte
+				newDockerfile, *resolvedTags, err = rewriteDockerfileFrom(ctx, content, translator)
+				if err != nil {
+					pipeWriter.CloseWithError(err)
+					return
+				}
+				hdr.Size = int64(len(newDockerfile))
+				content = bytes.NewBuffer(newDockerfile)
+			}
+
+			if err := tarWriter.WriteHeader(hdr); err != nil {
+				pipeWriter.CloseWithError(err)
+				return
+			}
+
+			if _, err := io.Copy(tarWriter, content); err != nil {
+				pipeWriter.CloseWithError(err)
+				return
+			}
+		}
+	}()
+
+	return pipeReader
+}