Move builder cli helper functions to own pkg

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

command/image/build.go

@@ -16,10 +16,10 @@ import (
 	"github.com/docker/docker/api"
 	"github.com/docker/docker/api/types"
 	"github.com/docker/docker/api/types/container"
-	"github.com/docker/docker/builder"
 	"github.com/docker/docker/builder/dockerignore"
 	"github.com/docker/docker/cli"
 	"github.com/docker/docker/cli/command"
+	"github.com/docker/docker/cli/command/image/build"
 	"github.com/docker/docker/opts"
 	"github.com/docker/docker/pkg/archive"
 	"github.com/docker/docker/pkg/fileutils"
@@ -29,7 +29,7 @@ import (
 	"github.com/docker/docker/pkg/urlutil"
 	"github.com/docker/docker/reference"
 	runconfigopts "github.com/docker/docker/runconfig/opts"
-	"github.com/docker/go-units"
+	units "github.com/docker/go-units"
 	"github.com/spf13/cobra"
 )
 
@@ -156,13 +156,13 @@ func runBuild(dockerCli *command.DockerCli, options buildOptions) error {
 
 	switch {
 	case specifiedContext == "-":
-		buildCtx, relDockerfile, err = builder.GetContextFromReader(dockerCli.In(), options.dockerfileName)
+		buildCtx, relDockerfile, err = build.GetContextFromReader(dockerCli.In(), options.dockerfileName)
 	case urlutil.IsGitURL(specifiedContext):
-		tempDir, relDockerfile, err = builder.GetContextFromGitURL(specifiedContext, options.dockerfileName)
+		tempDir, relDockerfile, err = build.GetContextFromGitURL(specifiedContext, options.dockerfileName)
 	case urlutil.IsURL(specifiedContext):
-		buildCtx, relDockerfile, err = builder.GetContextFromURL(progBuff, specifiedContext, options.dockerfileName)
+		buildCtx, relDockerfile, err = build.GetContextFromURL(progBuff, specifiedContext, options.dockerfileName)
 	default:
-		contextDir, relDockerfile, err = builder.GetContextFromLocalDir(specifiedContext, options.dockerfileName)
+		contextDir, relDockerfile, err = build.GetContextFromLocalDir(specifiedContext, options.dockerfileName)
 	}
 
 	if err != nil {
@@ -198,7 +198,7 @@ func runBuild(dockerCli *command.DockerCli, options buildOptions) error {
 			}
 		}
 
-		if err := builder.ValidateContextDirectory(contextDir, excludes); err != nil {
+		if err := build.ValidateContextDirectory(contextDir, excludes); err != nil {
 			return fmt.Errorf("Error checking context: '%s'.", err)
 		}
 

command/image/build/context.go

@@ -0,0 +1,265 @@
+package build
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strings"
+
+	"github.com/docker/docker/pkg/archive"
+	"github.com/docker/docker/pkg/fileutils"
+	"github.com/docker/docker/pkg/gitutils"
+	"github.com/docker/docker/pkg/httputils"
+	"github.com/docker/docker/pkg/ioutils"
+	"github.com/docker/docker/pkg/progress"
+	"github.com/docker/docker/pkg/streamformatter"
+)
+
+const (
+	// DefaultDockerfileName is the Default filename with Docker commands, read by docker build
+	DefaultDockerfileName string = "Dockerfile"
+)
+
+// 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 {
+		if err != nil {
+			if os.IsPermission(err) {
+				return fmt.Errorf("can't stat '%s'", filePath)
+			}
+			if os.IsNotExist(err) {
+				return nil
+			}
+			return err
+		}
+
+		// 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
+		}
+
+		// 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
+	})
+}
+
+// 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, 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
+	}), 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)
+}
+
+// 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 of given context directory %q: %v", givenContextDir, 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, 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(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
+}
+
+// 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, `\\`)
+}

command/image/build/context_test.go

@@ -0,0 +1,383 @@
+package build
+
+import (
+	"archive/tar"
+	"bytes"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+
+	"github.com/docker/docker/pkg/archive"
+)
+
+const dockerfileContents = "FROM busybox"
+
+var prepareEmpty = func(t *testing.T) (string, func()) {
+	return "", func() {}
+}
+
+var prepareNoFiles = func(t *testing.T) (string, func()) {
+	return createTestTempDir(t, "", "builder-context-test")
+}
+
+var prepareOneFile = func(t *testing.T) (string, func()) {
+	contextDir, cleanup := createTestTempDir(t, "", "builder-context-test")
+	createTestTempFile(t, contextDir, DefaultDockerfileName, dockerfileContents, 0777)
+	return contextDir, cleanup
+}
+
+func testValidateContextDirectory(t *testing.T, prepare func(t *testing.T) (string, func()), excludes []string) {
+	contextDir, cleanup := prepare(t)
+	defer cleanup()
+
+	err := ValidateContextDirectory(contextDir, excludes)
+
+	if err != nil {
+		t.Fatalf("Error should be nil, got: %s", err)
+	}
+}
+
+func TestGetContextFromLocalDirNoDockerfile(t *testing.T) {
+	contextDir, cleanup := createTestTempDir(t, "", "builder-context-test")
+	defer cleanup()
+
+	absContextDir, relDockerfile, err := GetContextFromLocalDir(contextDir, "")
+
+	if err == nil {
+		t.Fatalf("Error should not be nil")
+	}
+
+	if absContextDir != "" {
+		t.Fatalf("Absolute directory path should be empty, got: %s", absContextDir)
+	}
+
+	if relDockerfile != "" {
+		t.Fatalf("Relative path to Dockerfile should be empty, got: %s", relDockerfile)
+	}
+}
+
+func TestGetContextFromLocalDirNotExistingDir(t *testing.T) {
+	contextDir, cleanup := createTestTempDir(t, "", "builder-context-test")
+	defer cleanup()
+
+	fakePath := filepath.Join(contextDir, "fake")
+
+	absContextDir, relDockerfile, err := GetContextFromLocalDir(fakePath, "")
+
+	if err == nil {
+		t.Fatalf("Error should not be nil")
+	}
+
+	if absContextDir != "" {
+		t.Fatalf("Absolute directory path should be empty, got: %s", absContextDir)
+	}
+
+	if relDockerfile != "" {
+		t.Fatalf("Relative path to Dockerfile should be empty, got: %s", relDockerfile)
+	}
+}
+
+func TestGetContextFromLocalDirNotExistingDockerfile(t *testing.T) {
+	contextDir, cleanup := createTestTempDir(t, "", "builder-context-test")
+	defer cleanup()
+
+	fakePath := filepath.Join(contextDir, "fake")
+
+	absContextDir, relDockerfile, err := GetContextFromLocalDir(contextDir, fakePath)
+
+	if err == nil {
+		t.Fatalf("Error should not be nil")
+	}
+
+	if absContextDir != "" {
+		t.Fatalf("Absolute directory path should be empty, got: %s", absContextDir)
+	}
+
+	if relDockerfile != "" {
+		t.Fatalf("Relative path to Dockerfile should be empty, got: %s", relDockerfile)
+	}
+}
+
+func TestGetContextFromLocalDirWithNoDirectory(t *testing.T) {
+	contextDir, dirCleanup := createTestTempDir(t, "", "builder-context-test")
+	defer dirCleanup()
+
+	createTestTempFile(t, contextDir, DefaultDockerfileName, dockerfileContents, 0777)
+
+	chdirCleanup := chdir(t, contextDir)
+	defer chdirCleanup()
+
+	absContextDir, relDockerfile, err := GetContextFromLocalDir(contextDir, "")
+
+	if err != nil {
+		t.Fatalf("Error when getting context from local dir: %s", err)
+	}
+
+	if absContextDir != contextDir {
+		t.Fatalf("Absolute directory path should be equal to %s, got: %s", contextDir, absContextDir)
+	}
+
+	if relDockerfile != DefaultDockerfileName {
+		t.Fatalf("Relative path to dockerfile should be equal to %s, got: %s", DefaultDockerfileName, relDockerfile)
+	}
+}
+
+func TestGetContextFromLocalDirWithDockerfile(t *testing.T) {
+	contextDir, cleanup := createTestTempDir(t, "", "builder-context-test")
+	defer cleanup()
+
+	createTestTempFile(t, contextDir, DefaultDockerfileName, dockerfileContents, 0777)
+
+	absContextDir, relDockerfile, err := GetContextFromLocalDir(contextDir, "")
+
+	if err != nil {
+		t.Fatalf("Error when getting context from local dir: %s", err)
+	}
+
+	if absContextDir != contextDir {
+		t.Fatalf("Absolute directory path should be equal to %s, got: %s", contextDir, absContextDir)
+	}
+
+	if relDockerfile != DefaultDockerfileName {
+		t.Fatalf("Relative path to dockerfile should be equal to %s, got: %s", DefaultDockerfileName, relDockerfile)
+	}
+}
+
+func TestGetContextFromLocalDirLocalFile(t *testing.T) {
+	contextDir, cleanup := createTestTempDir(t, "", "builder-context-test")
+	defer cleanup()
+
+	createTestTempFile(t, contextDir, DefaultDockerfileName, dockerfileContents, 0777)
+	testFilename := createTestTempFile(t, contextDir, "tmpTest", "test", 0777)
+
+	absContextDir, relDockerfile, err := GetContextFromLocalDir(testFilename, "")
+
+	if err == nil {
+		t.Fatalf("Error should not be nil")
+	}
+
+	if absContextDir != "" {
+		t.Fatalf("Absolute directory path should be empty, got: %s", absContextDir)
+	}
+
+	if relDockerfile != "" {
+		t.Fatalf("Relative path to Dockerfile should be empty, got: %s", relDockerfile)
+	}
+}
+
+func TestGetContextFromLocalDirWithCustomDockerfile(t *testing.T) {
+	contextDir, cleanup := createTestTempDir(t, "", "builder-context-test")
+	defer cleanup()
+
+	chdirCleanup := chdir(t, contextDir)
+	defer chdirCleanup()
+
+	createTestTempFile(t, contextDir, DefaultDockerfileName, dockerfileContents, 0777)
+
+	absContextDir, relDockerfile, err := GetContextFromLocalDir(contextDir, DefaultDockerfileName)
+
+	if err != nil {
+		t.Fatalf("Error when getting context from local dir: %s", err)
+	}
+
+	if absContextDir != contextDir {
+		t.Fatalf("Absolute directory path should be equal to %s, got: %s", contextDir, absContextDir)
+	}
+
+	if relDockerfile != DefaultDockerfileName {
+		t.Fatalf("Relative path to dockerfile should be equal to %s, got: %s", DefaultDockerfileName, relDockerfile)
+	}
+
+}
+
+func TestGetContextFromReaderString(t *testing.T) {
+	tarArchive, relDockerfile, err := GetContextFromReader(ioutil.NopCloser(strings.NewReader(dockerfileContents)), "")
+
+	if err != nil {
+		t.Fatalf("Error when executing GetContextFromReader: %s", err)
+	}
+
+	tarReader := tar.NewReader(tarArchive)
+
+	_, err = tarReader.Next()
+
+	if err != nil {
+		t.Fatalf("Error when reading tar archive: %s", err)
+	}
+
+	buff := new(bytes.Buffer)
+	buff.ReadFrom(tarReader)
+	contents := buff.String()
+
+	_, err = tarReader.Next()
+
+	if err != io.EOF {
+		t.Fatalf("Tar stream too long: %s", err)
+	}
+
+	if err = tarArchive.Close(); err != nil {
+		t.Fatalf("Error when closing tar stream: %s", err)
+	}
+
+	if dockerfileContents != contents {
+		t.Fatalf("Uncompressed tar archive does not equal: %s, got: %s", dockerfileContents, contents)
+	}
+
+	if relDockerfile != DefaultDockerfileName {
+		t.Fatalf("Relative path not equals %s, got: %s", DefaultDockerfileName, relDockerfile)
+	}
+}
+
+func TestGetContextFromReaderTar(t *testing.T) {
+	contextDir, cleanup := createTestTempDir(t, "", "builder-context-test")
+	defer cleanup()
+
+	createTestTempFile(t, contextDir, DefaultDockerfileName, dockerfileContents, 0777)
+
+	tarStream, err := archive.Tar(contextDir, archive.Uncompressed)
+
+	if err != nil {
+		t.Fatalf("Error when creating tar: %s", err)
+	}
+
+	tarArchive, relDockerfile, err := GetContextFromReader(tarStream, DefaultDockerfileName)
+
+	if err != nil {
+		t.Fatalf("Error when executing GetContextFromReader: %s", err)
+	}
+
+	tarReader := tar.NewReader(tarArchive)
+
+	header, err := tarReader.Next()
+
+	if err != nil {
+		t.Fatalf("Error when reading tar archive: %s", err)
+	}
+
+	if header.Name != DefaultDockerfileName {
+		t.Fatalf("Dockerfile name should be: %s, got: %s", DefaultDockerfileName, header.Name)
+	}
+
+	buff := new(bytes.Buffer)
+	buff.ReadFrom(tarReader)
+	contents := buff.String()
+
+	_, err = tarReader.Next()
+
+	if err != io.EOF {
+		t.Fatalf("Tar stream too long: %s", err)
+	}
+
+	if err = tarArchive.Close(); err != nil {
+		t.Fatalf("Error when closing tar stream: %s", err)
+	}
+
+	if dockerfileContents != contents {
+		t.Fatalf("Uncompressed tar archive does not equal: %s, got: %s", dockerfileContents, contents)
+	}
+
+	if relDockerfile != DefaultDockerfileName {
+		t.Fatalf("Relative path not equals %s, got: %s", DefaultDockerfileName, relDockerfile)
+	}
+}
+
+func TestValidateContextDirectoryEmptyContext(t *testing.T) {
+	// This isn't a valid test on Windows. See https://play.golang.org/p/RR6z6jxR81.
+	// The test will ultimately end up calling filepath.Abs(""). On Windows,
+	// golang will error. On Linux, golang will return /. Due to there being
+	// drive letters on Windows, this is probably the correct behaviour for
+	// Windows.
+	if runtime.GOOS == "windows" {
+		t.Skip("Invalid test on Windows")
+	}
+	testValidateContextDirectory(t, prepareEmpty, []string{})
+}
+
+func TestValidateContextDirectoryContextWithNoFiles(t *testing.T) {
+	testValidateContextDirectory(t, prepareNoFiles, []string{})
+}
+
+func TestValidateContextDirectoryWithOneFile(t *testing.T) {
+	testValidateContextDirectory(t, prepareOneFile, []string{})
+}
+
+func TestValidateContextDirectoryWithOneFileExcludes(t *testing.T) {
+	testValidateContextDirectory(t, prepareOneFile, []string{DefaultDockerfileName})
+}
+
+// createTestTempDir creates a temporary directory for testing.
+// It returns the created path and a cleanup function which is meant to be used as deferred call.
+// When an error occurs, it terminates the test.
+func createTestTempDir(t *testing.T, dir, prefix string) (string, func()) {
+	path, err := ioutil.TempDir(dir, prefix)
+
+	if err != nil {
+		t.Fatalf("Error when creating directory %s with prefix %s: %s", dir, prefix, err)
+	}
+
+	return path, func() {
+		err = os.RemoveAll(path)
+
+		if err != nil {
+			t.Fatalf("Error when removing directory %s: %s", path, err)
+		}
+	}
+}
+
+// createTestTempSubdir creates a temporary directory for testing.
+// It returns the created path but doesn't provide a cleanup function,
+// so createTestTempSubdir should be used only for creating temporary subdirectories
+// whose parent directories are properly cleaned up.
+// When an error occurs, it terminates the test.
+func createTestTempSubdir(t *testing.T, dir, prefix string) string {
+	path, err := ioutil.TempDir(dir, prefix)
+
+	if err != nil {
+		t.Fatalf("Error when creating directory %s with prefix %s: %s", dir, prefix, err)
+	}
+
+	return path
+}
+
+// createTestTempFile creates a temporary file within dir with specific contents and permissions.
+// When an error occurs, it terminates the test
+func createTestTempFile(t *testing.T, dir, filename, contents string, perm os.FileMode) string {
+	filePath := filepath.Join(dir, filename)
+	err := ioutil.WriteFile(filePath, []byte(contents), perm)
+
+	if err != nil {
+		t.Fatalf("Error when creating %s file: %s", filename, err)
+	}
+
+	return filePath
+}
+
+// chdir changes current working directory to dir.
+// It returns a function which changes working directory back to the previous one.
+// This function is meant to be executed as a deferred call.
+// When an error occurs, it terminates the test.
+func chdir(t *testing.T, dir string) func() {
+	workingDirectory, err := os.Getwd()
+
+	if err != nil {
+		t.Fatalf("Error when retrieving working directory: %s", err)
+	}
+
+	err = os.Chdir(dir)
+
+	if err != nil {
+		t.Fatalf("Error when changing directory to %s: %s", dir, err)
+	}
+
+	return func() {
+		err = os.Chdir(workingDirectory)
+
+		if err != nil {
+			t.Fatalf("Error when changing back to working directory (%s): %s", workingDirectory, err)
+		}
+	}
+}

command/image/build/context_unix.go

@@ -0,0 +1,11 @@
+// +build !windows
+
+package build
+
+import (
+	"path/filepath"
+)
+
+func getContextRoot(srcPath string) (string, error) {
+	return filepath.Join(srcPath, "."), nil
+}

command/image/build/context_windows.go

@@ -0,0 +1,17 @@
+// +build windows
+
+package build
+
+import (
+	"path/filepath"
+
+	"github.com/docker/docker/pkg/longpath"
+)
+
+func getContextRoot(srcPath string) (string, error) {
+	cr, err := filepath.Abs(srcPath)
+	if err != nil {
+		return "", err
+	}
+	return longpath.AddPrefix(cr), nil
+}