build: Add support for using context from stdin with buildkit

Signed-off-by: Tibor Vass <tibor@docker.com>

cli/command/image/build/context.go

@@ -81,59 +81,81 @@ func ValidateContextDirectory(srcPath string, excludes []string) error {
 	})
 }
 
-// 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)
+// DetectArchiveReader detects whether the input stream is an archive or a
+// Dockerfile and returns a buffered version of input, safe to consume in lieu
+// of input. If an archive is detected, isArchive is set to true, and to false
+// otherwise, in which case it is safe to assume input represents the contents
+// of a Dockerfile.
+func DetectArchiveReader(input io.ReadCloser) (rc io.ReadCloser, isArchive bool, err error) {
+	buf := bufio.NewReader(input)
 
 	magic, err := buf.Peek(archiveHeaderSize)
 	if err != nil && err != io.EOF {
-		return nil, "", errors.Errorf("failed to peek context header from STDIN: %v", err)
+		return nil, false, errors.Errorf("failed to peek context header from STDIN: %v", err)
 	}
 
-	if IsArchive(magic) {
-		return ioutils.NewReadCloserWrapper(buf, func() error { return r.Close() }), dockerfileName, nil
+	return ioutils.NewReadCloserWrapper(buf, func() error { return input.Close() }), IsArchive(magic), nil
+}
+
+
+// WriteTempDockerfile writes a Dockerfile stream to a temporary file with a
+// name specified by DefaultDockerfileName and returns the path to the
+// temporary directory containing the Dockerfile.
+func WriteTempDockerfile(rc io.ReadCloser) (string, error) {
+	dockerfileDir, err := ioutil.TempDir("", "docker-build-tempdockerfile-")
+	if err != nil {
+		return "", errors.Errorf("unable to create temporary context directory: %v", err)
 	}
 
+	f, err := os.Create(filepath.Join(dockerfileDir, DefaultDockerfileName))
+	if err != nil {
+		return "", err
+	}
+	_, err = io.Copy(f, rc)
+	if err != nil {
+		f.Close()
+		return "", err
+	}
+	if err := f.Close(); err != nil {
+		return "", err
+	}
+	return dockerfileDir, rc.Close()
+}
+
+// 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(rc io.ReadCloser, dockerfileName string) (out io.ReadCloser, relDockerfile string, err error) {
+	rc, isArchive, err := DetectArchiveReader(rc)
+	if err != nil {
+		return nil, "", err
+	}
+
+	if isArchive {
+		return rc, dockerfileName, nil
+	}
+
+	// Input should be read as a Dockerfile.
+
 	if dockerfileName == "-" {
 		return nil, "", errors.New("build context is not an archive")
 	}
 
-	// Input should be read as a Dockerfile.
-	tmpDir, err := ioutil.TempDir("", "docker-build-context-")
-	if err != nil {
-		return nil, "", errors.Errorf("unable to create temporary context directory: %v", err)
-	}
-
-	f, err := os.Create(filepath.Join(tmpDir, DefaultDockerfileName))
+	dockerfileDir, err := WriteTempDockerfile(rc)
 	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)
+	tar, err := archive.Tar(dockerfileDir, archive.Uncompressed)
 	if err != nil {
 		return nil, "", err
 	}
 
 	return ioutils.NewReadCloserWrapper(tar, func() error {
 		err := tar.Close()
-		os.RemoveAll(tmpDir)
+		os.RemoveAll(dockerfileDir)
 		return err
 	}), DefaultDockerfileName, nil
-
 }
 
 // IsArchive checks for the magic bytes of a tar or any supported compression

cli/command/image/build_buildkit.go

@@ -4,12 +4,14 @@ import (
 	"context"
 	"encoding/json"
 	"io"
+	"io/ioutil"
 	"os"
 	"path/filepath"
 
 	"github.com/containerd/console"
 	"github.com/docker/cli/cli"
 	"github.com/docker/cli/cli/command"
+	"github.com/docker/cli/cli/command/image/build"
 	"github.com/docker/cli/opts"
 	"github.com/docker/docker/api/types"
 	"github.com/docker/docker/api/types/container"
@@ -46,9 +48,45 @@ func runBuildBuildKit(dockerCli command.Cli, options buildOptions) error {
 	var body io.Reader
 	switch {
 	case options.contextFromStdin():
-		body = os.Stdin
-		remote = uploadRequestRemote
+		rc, isArchive, err := build.DetectArchiveReader(os.Stdin)
+		if err != nil {
+			return err
+		}
+		if isArchive {
+			body = rc
+			remote = uploadRequestRemote
+		} else {
+			dockerfileDir, err := build.WriteTempDockerfile(rc)
+			if err != nil {
+				return err
+			}
+			defer os.RemoveAll(dockerfileDir)
+			emptyDir, _ := ioutil.TempDir("", "stupid-empty-dir")
+			defer os.RemoveAll(emptyDir)
+			s.Allow(filesync.NewFSSyncProvider([]filesync.SyncedDir{
+				{
+					Name: "context",
+					Dir: emptyDir,
+				},
+				{
+					Name: "dockerfile",
+					Dir:  string(dockerfileDir),
+				},
+			}))
+			remote = clientSessionRemote
+		}
 	case isLocalDir(options.context):
+		s.Allow(filesync.NewFSSyncProvider([]filesync.SyncedDir{
+			{
+				Name: "context",
+				Dir:  options.context,
+				Map:  resetUIDAndGID,
+			},
+			{
+				Name: "dockerfile",
+				Dir:  filepath.Dir(options.dockerfileName),
+			},
+		}))
 		remote = clientSessionRemote
 	case urlutil.IsGitURL(options.context):
 		remote = options.context
@@ -65,20 +103,6 @@ func runBuildBuildKit(dockerCli command.Cli, options buildOptions) error {
 	// 	statusContext = opentracing.ContextWithSpan(statusContext, span)
 	// }
 
-	if remote == clientSessionRemote {
-		s.Allow(filesync.NewFSSyncProvider([]filesync.SyncedDir{
-			{
-				Name: "context",
-				Dir:  options.context,
-				Map:  resetUIDAndGID,
-			},
-			{
-				Name: "dockerfile",
-				Dir:  filepath.Dir(options.dockerfileName),
-			},
-		}))
-	}
-
 	s.Allow(authprovider.NewDockerAuthProvider())
 
 	eg, ctx := errgroup.WithContext(ctx)