buildkit: introduce initial support

This patch adds a new `Builder` entry to the RFC2822 image manifest
files, allowing individual image components to opt into buildkit
support, using docker buildx.

Additionally, docker build is changed to explicitly set
DOCKER_BUILDKIT=0 to force a non-buildkit build in preparation for
the switching default in any upcoming docker versions.

Signed-off-by: Justin Chadwell <[email protected]>

Author: jedevc

cmd/bashbrew/cmd-build.go

@@ -95,16 +95,27 @@ func cmdBuild(c *cli.Context) error {
 
 					// TODO use "meta.StageNames" to do "docker build --target" so we can tag intermediate stages too for cache (streaming "git archive" directly to "docker build" makes that a little hard to accomplish without re-streaming)
 
-					var extraEnv []string = nil
-					if fromScratch {
-						// https://github.com/docker/cli/blob/v20.10.7/cli/command/image/build.go#L163
-						extraEnv = []string{"DOCKER_DEFAULT_PLATFORM=" + ociArch.String()}
-						// ideally, we would set this via an explicit "--platform" flag on "docker build", but it's not supported without buildkit until 20.10+ and this is a trivial way to get Docker to do the right thing in both cases without explicitly trying to detect whether we're on 20.10+
-					}
-
-					err = dockerBuild(cacheTag, entry.ArchFile(arch), archive, extraEnv)
-					if err != nil {
-						return cli.NewMultiError(fmt.Errorf(`failed building %q (tags %q)`, r.RepoName, entry.TagsString()), err)
+					switch builder := entry.ArchBuilder(arch); builder {
+					case "classic", "":
+						var platform string
+						if fromScratch {
+							platform = ociArch.String()
+						}
+						err = dockerBuild(cacheTag, entry.ArchFile(arch), archive, platform)
+						if err != nil {
+							return cli.NewMultiError(fmt.Errorf(`failed building %q (tags %q)`, r.RepoName, entry.TagsString()), err)
+						}
+					case "buildkit":
+						var platform string
+						if fromScratch {
+							platform = ociArch.String()
+						}
+						err = dockerBuildxBuild(cacheTag, entry.ArchFile(arch), archive, platform)
+						if err != nil {
+							return cli.NewMultiError(fmt.Errorf(`failed building %q (tags %q)`, r.RepoName, entry.TagsString()), err)
+						}
+					default:
+						return cli.NewMultiError(fmt.Errorf(`unknown builder %q`, builder))
 					}
 					archive.Close() // be sure this happens sooner rather than later (defer might take a while, and we want to reap zombies more aggressively)
 				}

cmd/bashbrew/docker.go

@@ -13,8 +13,8 @@ import (
 	"strconv"
 	"strings"
 
-	"github.com/urfave/cli"
 	"github.com/docker-library/bashbrew/manifest"
+	"github.com/urfave/cli"
 )
 
 type dockerfileMetadata struct {
@@ -218,6 +218,11 @@ func (r Repo) dockerBuildUniqueBits(entry *manifest.Manifest2822Entry) ([]string
 		entry.ArchDirectory(arch),
 		entry.ArchFile(arch),
 	}
+	if builder := entry.ArchBuilder(arch); builder != "" {
+		// NOTE: preserve long-term unique id by only attaching builder if
+		// explicitly specified
+		uniqueBits = append(uniqueBits, entry.ArchBuilder(arch))
+	}
 	meta, err := r.dockerfileMetadata(entry)
 	if err != nil {
 		return nil, err
@@ -237,14 +242,20 @@ func (r Repo) dockerBuildUniqueBits(entry *manifest.Manifest2822Entry) ([]string
 	return uniqueBits, nil
 }
 
-func dockerBuild(tag string, file string, context io.Reader, extraEnv []string) error {
+func dockerBuild(tag string, file string, context io.Reader, platform string) error {
 	args := []string{"build", "--tag", tag, "--file", file, "--rm", "--force-rm"}
 	args = append(args, "-")
 	cmd := exec.Command("docker", args...)
-	if extraEnv != nil {
-		cmd.Env = append(os.Environ(), extraEnv...)
+	cmd.Env = append(os.Environ(), "DOCKER_BUILDKIT=0")
+	if debugFlag {
+		fmt.Println("$ export DOCKER_BUILDKIT=0")
+	}
+	if platform != "" {
+		// ideally, we would set this via an explicit "--platform" flag on "docker build", but it's not supported without buildkit until 20.10+ and this is a trivial way to get Docker to do the right thing in both cases without explicitly trying to detect whether we're on 20.10+
+		// https://github.com/docker/cli/blob/v20.10.7/cli/command/image/build.go#L163
+		cmd.Env = append(cmd.Env, "DOCKER_DEFAULT_PLATFORM="+platform)
 		if debugFlag {
-			fmt.Printf("$ export %q\n", extraEnv)
+			fmt.Printf("$ export DOCKER_DEFAULT_PLATFORM=%q\n", platform)
 		}
 	}
 	cmd.Stdin = context
@@ -265,6 +276,41 @@ func dockerBuild(tag string, file string, context io.Reader, extraEnv []string)
 	}
 }
 
+const dockerfileSyntax = "docker/dockerfile:1"
+
+func dockerBuildxBuild(tag string, file string, context io.Reader, platform string) error {
+	args := []string{
+		"buildx",
+		"build",
+		"--progress", "plain",
+		"--build-arg", "BUILDKIT_SYNTAX=" + dockerfileSyntax,
+		"--tag", tag,
+		"--file", file,
+	}
+	if platform != "" {
+		args = append(args, "--platform", platform)
+	}
+	args = append(args, "-")
+
+	cmd := exec.Command("docker", args...)
+	cmd.Stdin = context
+	if debugFlag {
+		cmd.Stdout = os.Stdout
+		cmd.Stderr = os.Stderr
+		fmt.Printf("$ docker %q\n", args)
+		return cmd.Run()
+	} else {
+		buf := &bytes.Buffer{}
+		cmd.Stdout = buf
+		cmd.Stderr = buf
+		err := cmd.Run()
+		if err != nil {
+			err = cli.NewMultiError(err, fmt.Errorf(`docker %q output:%s`, args, "\n"+buf.String()))
+		}
+		return err
+	}
+}
+
 func dockerTag(tag1 string, tag2 string) error {
 	if debugFlag {
 		fmt.Printf("$ docker tag %q %q\n", tag1, tag2)

manifest/rfc2822.go

@@ -43,6 +43,7 @@ type Manifest2822Entry struct {
 	GitCommit string
 	Directory string
 	File      string
+	Builder   string
 
 	// architecture-specific versions of the above fields
 	ArchValues map[string]string
@@ -93,7 +94,7 @@ func (entry Manifest2822Entry) Clone() Manifest2822Entry {
 
 func (entry *Manifest2822Entry) SeedArchValues() {
 	for field, val := range entry.Paragraph.Values {
-		if strings.HasSuffix(field, "-GitRepo") || strings.HasSuffix(field, "-GitFetch") || strings.HasSuffix(field, "-GitCommit") || strings.HasSuffix(field, "-Directory") || strings.HasSuffix(field, "-File") {
+		if strings.HasSuffix(field, "-GitRepo") || strings.HasSuffix(field, "-GitFetch") || strings.HasSuffix(field, "-GitCommit") || strings.HasSuffix(field, "-Directory") || strings.HasSuffix(field, "-File") || strings.HasSuffix(field, "-Builder") {
 			entry.ArchValues[field] = val
 		}
 	}
@@ -142,7 +143,7 @@ func (a Manifest2822Entry) SameBuildArtifacts(b Manifest2822Entry) bool {
 		}
 	}
 
-	return a.ArchitecturesString() == b.ArchitecturesString() && a.GitRepo == b.GitRepo && a.GitFetch == b.GitFetch && a.GitCommit == b.GitCommit && a.Directory == b.Directory && a.File == b.File && a.ConstraintsString() == b.ConstraintsString()
+	return a.ArchitecturesString() == b.ArchitecturesString() && a.GitRepo == b.GitRepo && a.GitFetch == b.GitFetch && a.GitCommit == b.GitCommit && a.Directory == b.Directory && a.File == b.File && a.Builder == b.Builder && a.ConstraintsString() == b.ConstraintsString()
 }
 
 // returns a list of architecture-specific fields in an Entry
@@ -187,6 +188,9 @@ func (entry Manifest2822Entry) ClearDefaults(defaults Manifest2822Entry) Manifes
 	if entry.File == defaults.File {
 		entry.File = ""
 	}
+	if entry.Builder == defaults.Builder {
+		entry.Builder = ""
+	}
 	for _, key := range defaults.archFields() {
 		if defaults.ArchValues[key] == entry.ArchValues[key] {
 			delete(entry.ArchValues, key)
@@ -227,6 +231,9 @@ func (entry Manifest2822Entry) String() string {
 	if str := entry.File; str != "" {
 		ret = append(ret, "File: "+str)
 	}
+	if str := entry.Builder; str != "" {
+		ret = append(ret, "Builder: "+str)
+	}
 	for _, key := range entry.archFields() {
 		ret = append(ret, key+": "+entry.ArchValues[key])
 	}
@@ -300,6 +307,13 @@ func (entry Manifest2822Entry) ArchFile(arch string) string {
 	return entry.File
 }
 
+func (entry Manifest2822Entry) ArchBuilder(arch string) string {
+	if val, ok := entry.ArchValues[arch+"-Builder"]; ok && val != "" {
+		return val
+	}
+	return entry.Builder
+}
+
 func (entry Manifest2822Entry) HasTag(tag string) bool {
 	for _, existingTag := range entry.Tags {
 		if tag == existingTag {