dockerfile: move image frontend to this repo until api stabilizes

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

frontend/dockerfile/cmd/dockerfile-frontend/Dockerfile

@@ -0,0 +1,7 @@
+FROM golang:1.8-alpine AS builder
+COPY . /go/src/github.com/moby/buildkit
+RUN CGO_ENABLED=0 go build -o /dockerfile-frontend --ldflags '-extldflags "-static"' github.com/moby/buildkit/frontend/dockerfile/cmd/dockerfile-frontend
+
+FROM scratch
+COPY --from=builder /dockerfile-frontend /bin/dockerfile-frontend
+ENTRYPOINT ["/bin/dockerfile-frontend"]

frontend/dockerfile/cmd/dockerfile-frontend/main.go

@@ -0,0 +1,107 @@
+package main
+
+import (
+	"encoding/json"
+	"path"
+	"strings"
+
+	"github.com/moby/buildkit/client/llb"
+	"github.com/moby/buildkit/frontend/dockerfile/dockerfile2llb"
+	"github.com/moby/buildkit/frontend/gateway/client"
+	"github.com/moby/buildkit/util/appcontext"
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+)
+
+const (
+	keyTarget             = "target"
+	keyFilename           = "filename"
+	exporterImageConfig   = "containerimage.config"
+	defaultDockerfileName = "Dockerfile"
+	localNameDockerfile   = "dockerfile"
+	buildArgPrefix        = "build-arg:"
+)
+
+func main() {
+	if err := run(); err != nil {
+		logrus.Errorf("fatal error: %+v", err)
+		panic(err)
+	}
+}
+
+func run() error {
+	c, err := client.Current()
+	if err != nil {
+		return errors.Wrap(err, "failed to create client")
+	}
+
+	ctx := appcontext.Context()
+
+	opts := c.Opts()
+
+	filename := opts[keyFilename]
+	if filename == "" {
+		filename = defaultDockerfileName
+	}
+	if path.Base(filename) != filename {
+		return errors.Errorf("invalid filename: %s", filename)
+	}
+
+	src := llb.Local(localNameDockerfile,
+		llb.IncludePatterns([]string{filename}),
+		llb.SessionID(c.SessionID()),
+	)
+	def, err := src.Marshal()
+	if err != nil {
+		return err
+	}
+
+	ref, err := c.Solve(ctx, def.ToPB(), "", nil, false)
+	if err != nil {
+		return err
+	}
+
+	dtDockerfile, err := ref.ReadFile(ctx, filename)
+	if err != nil {
+		return err
+	}
+
+	st, img, err := dockerfile2llb.Dockerfile2LLB(ctx, dtDockerfile, dockerfile2llb.ConvertOpt{
+		Target:       opts[keyTarget],
+		MetaResolver: c,
+		BuildArgs:    filterBuildArgs(opts),
+		SessionID:    c.SessionID(),
+	})
+
+	if err != nil {
+		return err
+	}
+
+	def, err = st.Marshal()
+	if err != nil {
+		return err
+	}
+
+	config, err := json.Marshal(img)
+	if err != nil {
+		return err
+	}
+
+	_, err = c.Solve(ctx, def.ToPB(), "", map[string][]byte{
+		exporterImageConfig: config,
+	}, true)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func filterBuildArgs(opt map[string]string) map[string]string {
+	m := map[string]string{}
+	for k, v := range opt {
+		if strings.HasPrefix(k, buildArgPrefix) {
+			m[strings.TrimPrefix(k, buildArgPrefix)] = v
+		}
+	}
+	return m
+}