Fix Cache with ONBUILD

Signed-off-by: Daniel Nephin <dnephin@docker.com>

integration-cli/docker_api_build_test.go

@@ -3,6 +3,7 @@ package main
 import (
 	"archive/tar"
 	"bytes"
+	"encoding/json"
 	"io/ioutil"
 	"net/http"
 	"regexp"
@@ -15,6 +16,9 @@ import (
 	"github.com/docker/docker/integration-cli/request"
 	"github.com/docker/docker/pkg/testutil"
 	"github.com/go-check/check"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/net/context"
 )
 
 func (s *DockerSuite) TestBuildAPIDockerFileRemote(c *check.C) {
@@ -274,3 +278,68 @@ func (s *DockerSuite) TestBuildOnBuildWithCopy(c *check.C) {
 	c.Assert(err, checker.IsNil)
 	c.Assert(string(out), checker.Contains, "Successfully built")
 }
+
+func (s *DockerSuite) TestBuildOnBuildCache(c *check.C) {
+	build := func(dockerfile string) []byte {
+		ctx := fakecontext.New(c, "",
+			fakecontext.WithDockerfile(dockerfile),
+		)
+		defer ctx.Close()
+
+		res, body, err := request.Post(
+			"/build",
+			request.RawContent(ctx.AsTarReader(c)),
+			request.ContentType("application/x-tar"))
+		require.NoError(c, err)
+		assert.Equal(c, http.StatusOK, res.StatusCode)
+
+		out, err := testutil.ReadBody(body)
+		require.NoError(c, err)
+		assert.Contains(c, string(out), "Successfully built")
+		return out
+	}
+
+	dockerfile := `
+		FROM ` + minimalBaseImage() + ` as onbuildbase
+		ENV something=bar
+		ONBUILD ENV foo=bar
+	`
+	build(dockerfile)
+
+	dockerfile += "FROM onbuildbase"
+	out := build(dockerfile)
+
+	imageIDs := getImageIDsFromBuild(c, out)
+	assert.Len(c, imageIDs, 2)
+	parentID, childID := imageIDs[0], imageIDs[1]
+
+	client, err := request.NewClient()
+	require.NoError(c, err)
+
+	// check parentID is correct
+	image, _, err := client.ImageInspectWithRaw(context.Background(), childID)
+	require.NoError(c, err)
+	assert.Equal(c, parentID, image.Parent)
+}
+
+type buildLine struct {
+	Stream string
+	Aux    struct {
+		ID string
+	}
+}
+
+func getImageIDsFromBuild(c *check.C, output []byte) []string {
+	ids := []string{}
+	for _, line := range bytes.Split(output, []byte("\n")) {
+		if len(line) == 0 {
+			continue
+		}
+		entry := buildLine{}
+		require.NoError(c, json.Unmarshal(line, &entry))
+		if entry.Aux.ID != "" {
+			ids = append(ids, entry.Aux.ID)
+		}
+	}
+	return ids
+}