Add docker build --iidfile=FILE

This is synonymous with `docker run --cidfile=FILE` and writes the digest of
the newly built image to the named file. This is intended to be used by build
systems which want to avoid tagging (perhaps because they are in CI or
otherwise want to avoid fixed names which can clash) by enabling e.g. Makefile
constructs like:

    image.id: Dockerfile
    	docker build --iidfile=image.id .

    do-some-more-stuff: image.id
    	do-stuff-with <image.id

Currently the only way to achieve this is to use `docker build -q` and capture
the stdout, but at the expense of losing the build output.

In non-silent mode (without `-q`) with API >= v1.29 the caller will now see a
`JSONMessage` with the `Aux` field containing a `types.BuildResult` in the
output stream for each image/layer produced during the build, with the final
one being the end product.  Having all of the intermediate images might be
interesting in some cases.

In silent mode (with `-q`) there is no change, on success the only output will
be the resulting image digest as it was previosuly.

There was no wrapper to just output an Aux section without enclosing it in a
Progress, so add one here.

Added some tests to integration cli tests.

Signed-off-by: Ian Campbell <ian.campbell@docker.com>
Upstream-commit: c3648a9c94
Component: cli

components/cli/cli/command/image/build.go

@@ -4,8 +4,10 @@ import (
 	"archive/tar"
 	"bufio"
 	"bytes"
+	"encoding/json"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"os"
 	"regexp"
 	"runtime"
@@ -59,6 +61,7 @@ type buildOptions struct {
 	networkMode    string
 	squash         bool
 	target         string
+	imageIDFile    string
 }
 
 // dockerfileFromStdin returns true when the user specified that the Dockerfile
@@ -123,6 +126,7 @@ func NewBuildCommand(dockerCli *command.DockerCli) *cobra.Command {
 	flags.SetAnnotation("network", "version", []string{"1.25"})
 	flags.Var(&options.extraHosts, "add-host", "Add a custom host-to-IP mapping (host:ip)")
 	flags.StringVar(&options.target, "target", "", "Set the target build stage to build.")
+	flags.StringVar(&options.imageIDFile, "iidfile", "", "Write the image ID to the file")
 
 	command.AddTrustVerificationFlags(flags)
 
@@ -176,6 +180,12 @@ func runBuild(dockerCli *command.DockerCli, options buildOptions) error {
 		progBuff = bytes.NewBuffer(nil)
 		buildBuff = bytes.NewBuffer(nil)
 	}
+	if options.imageIDFile != "" {
+		// Avoid leaving a stale file if we eventually fail
+		if err := os.Remove(options.imageIDFile); err != nil && !os.IsNotExist(err) {
+			return errors.Wrap(err, "Removing image ID file")
+		}
+	}
 
 	switch {
 	case options.contextFromStdin():
@@ -301,7 +311,17 @@ func runBuild(dockerCli *command.DockerCli, options buildOptions) error {
 	}
 	defer response.Body.Close()
 
-	err = jsonmessage.DisplayJSONMessagesStream(response.Body, buildBuff, dockerCli.Out().FD(), dockerCli.Out().IsTerminal(), nil)
+	imageID := ""
+	aux := func(auxJSON *json.RawMessage) {
+		var result types.BuildResult
+		if err := json.Unmarshal(*auxJSON, &result); err != nil {
+			fmt.Fprintf(dockerCli.Err(), "Failed to parse aux message: %s", err)
+		} else {
+			imageID = result.ID
+		}
+	}
+
+	err = jsonmessage.DisplayJSONMessagesStream(response.Body, buildBuff, dockerCli.Out().FD(), dockerCli.Out().IsTerminal(), aux)
 	if err != nil {
 		if jerr, ok := err.(*jsonmessage.JSONError); ok {
 			// If no error code is set, default to 1
@@ -329,9 +349,18 @@ func runBuild(dockerCli *command.DockerCli, options buildOptions) error {
 	// Everything worked so if -q was provided the output from the daemon
 	// should be just the image ID and we'll print that to stdout.
 	if options.quiet {
-		fmt.Fprintf(dockerCli.Out(), "%s", buildBuff)
+		imageID = fmt.Sprintf("%s", buildBuff)
+		fmt.Fprintf(dockerCli.Out(), imageID)
 	}
 
+	if options.imageIDFile != "" {
+		if imageID == "" {
+			return errors.Errorf("Server did not provide an image ID. Cannot write %s", options.imageIDFile)
+		}
+		if err := ioutil.WriteFile(options.imageIDFile, []byte(imageID), 0666); err != nil {
+			return err
+		}
+	}
 	if command.IsTrusted() {
 		// Since the build was successful, now we must tag any of the resolved
 		// images from the above Dockerfile rewrite.