emit a "tag" event when building image with "-t" parameter

This is useful for cluster systems such as swarm to sync the image
state when new images are successfully built.

Signed-off-by: Shijiang Wei <mountkin@gmail.com>
Upstream-commit: 2968fa44eb2a53c121ad2b27c519ae47ca7653c3
Component: engine

components/engine/integration-cli/docker_cli_build_test.go

@@ -7,6 +7,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
+	"net/http"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -6223,3 +6224,37 @@ func (s *DockerSuite) TestBuildNoNamedVolume(c *check.C) {
 	_, err := buildImage("test", dockerFile, false)
 	c.Assert(err, check.NotNil, check.Commentf("image build should have failed"))
 }
+
+func (s *DockerSuite) TestBuildTagEvent(c *check.C) {
+	testRequires(c, DaemonIsLinux)
+	resp, rc, err := sockRequestRaw("GET", `/events?filters={"event":["tag"]}`, nil, "application/json")
+	c.Assert(err, check.IsNil)
+	defer rc.Close()
+	c.Assert(resp.StatusCode, check.Equals, http.StatusOK)
+
+	type event struct {
+		Status string `json:"status"`
+		ID     string `json:"id"`
+	}
+	ch := make(chan event)
+	go func() {
+		ev := event{}
+		if err := json.NewDecoder(rc).Decode(&ev); err == nil {
+			ch <- ev
+		}
+	}()
+
+	dockerFile := `FROM busybox
+	RUN echo events
+	`
+	_, err = buildImage("test", dockerFile, false)
+	c.Assert(err, check.IsNil)
+
+	select {
+	case ev := <-ch:
+		c.Assert(ev.Status, check.Equals, "tag")
+		c.Assert(ev.ID, check.Equals, "test:")
+	case <-time.After(time.Second):
+		c.Fatal("The 'tag' event not heard from the server")
+	}
+}