buildkit/frontend/dockerfile/dockerfile2llb/convert.go

package dockerfile2llb

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"net/url"
	"path"
	"path/filepath"
	"sort"
	"strconv"
	"strings"

	"github.com/containerd/containerd/platforms"
	"github.com/docker/distribution/reference"
	"github.com/docker/docker/pkg/signal"
	"github.com/docker/go-connections/nat"
	"github.com/moby/buildkit/client/llb"
	"github.com/moby/buildkit/client/llb/imagemetaresolver"
	"github.com/moby/buildkit/frontend/dockerfile/instructions"
	"github.com/moby/buildkit/frontend/dockerfile/parser"
	"github.com/moby/buildkit/frontend/dockerfile/shell"
	specs "github.com/opencontainers/image-spec/specs-go/v1"
	"github.com/pkg/errors"
	"golang.org/x/sync/errgroup"
)

const (
	emptyImageName   = "scratch"
	localNameContext = "context"
	historyComment   = "buildkit.dockerfile.v0"

	CopyImage = "tonistiigi/copy:v0.1.3@sha256:e57a3b4d6240f55bac26b655d2cfb751f8b9412d6f7bb1f787e946391fb4b21b"
)

type ConvertOpt struct {
	Target       string
	MetaResolver llb.ImageMetaResolver
	BuildArgs    map[string]string
	Labels       map[string]string
	SessionID    string
	BuildContext *llb.State
	Excludes     []string
	// IgnoreCache contains names of the stages that should not use build cache.
	// Empty slice means ignore cache for all stages. Nil doesn't disable cache.
	IgnoreCache []string
	// CacheIDNamespace scopes the IDs for different cache mounts
	CacheIDNamespace string
	TargetPlatform   *specs.Platform
	BuildPlatforms   []specs.Platform
}

func Dockerfile2LLB(ctx context.Context, dt []byte, opt ConvertOpt) (*llb.State, *Image, error) {
	if len(dt) == 0 {
		return nil, nil, errors.Errorf("the Dockerfile cannot be empty")
	}

	if opt.TargetPlatform != nil && opt.BuildPlatforms == nil {
		opt.BuildPlatforms = []specs.Platform{*opt.TargetPlatform}
	}
	if len(opt.BuildPlatforms) == 0 {
		opt.BuildPlatforms = []specs.Platform{platforms.DefaultSpec()}
	}
	implicitTargetPlatform := false
	if opt.TargetPlatform == nil {
		implicitTargetPlatform = true
		opt.TargetPlatform = &opt.BuildPlatforms[0]
	}

	dockerfile, err := parser.Parse(bytes.NewReader(dt))
	if err != nil {
		return nil, nil, err
	}

	proxyEnv := proxyEnvFromBuildArgs(opt.BuildArgs)

	stages, metaArgs, err := instructions.Parse(dockerfile.AST)
	if err != nil {
		return nil, nil, err
	}

	optMetaArgs := []instructions.KeyValuePairOptional{}
	for _, metaArg := range metaArgs {
		optMetaArgs = append(optMetaArgs, setKVValue(metaArg.KeyValuePairOptional, opt.BuildArgs))
	}

	shlex := shell.NewLex(dockerfile.EscapeToken)

	metaResolver := opt.MetaResolver
	if metaResolver == nil {
		metaResolver = imagemetaresolver.Default()
	}

	allDispatchStates := newDispatchStates()

	// set base state for every image
	for _, st := range stages {
		name, err := shlex.ProcessWordWithMap(st.BaseName, metaArgsToMap(optMetaArgs))
		if err != nil {
			return nil, nil, err
		}
		if name == "" {
			return nil, nil, errors.Errorf("base name (%s) should not be blank", st.BaseName)
		}
		st.BaseName = name

		ds := &dispatchState{
			stage:    st,
			deps:     make(map[*dispatchState]struct{}),
			ctxPaths: make(map[string]struct{}),
		}

		if v := st.Platform; v != "" {
			v, err := shlex.ProcessWordWithMap(v, metaArgsToMap(optMetaArgs))
			if err != nil {
				return nil, nil, errors.Wrapf(err, "failed to process arguments for platform %s", v)
			}

			p, err := platforms.Parse(v)
			if err != nil {
				return nil, nil, errors.Wrapf(err, "failed to parse platform %s", v)
			}
			ds.platform = &p
		}

		allDispatchStates.addState(ds)
		if opt.IgnoreCache != nil {
			if len(opt.IgnoreCache) == 0 {
				ds.ignoreCache = true
			} else if st.Name != "" {
				for _, n := range opt.IgnoreCache {
					if strings.EqualFold(n, st.Name) {
						ds.ignoreCache = true
					}
				}
			}
		}
	}

	var target *dispatchState
	if opt.Target == "" {
		target = allDispatchStates.lastTarget()
	} else {
		var ok bool
		target, ok = allDispatchStates.findStateByName(opt.Target)
		if !ok {
			return nil, nil, errors.Errorf("target stage %s could not be found", opt.Target)
		}
	}

	// fill dependencies to stages so unreachable ones can avoid loading image configs
	for _, d := range allDispatchStates.states {
		d.commands = make([]command, len(d.stage.Commands))
		for i, cmd := range d.stage.Commands {
			newCmd, err := toCommand(cmd, allDispatchStates)
			if err != nil {
				return nil, nil, err
			}
			d.commands[i] = newCmd
			for _, src := range newCmd.sources {
				if src != nil {
					d.deps[src] = struct{}{}
					if src.unregistered {
						allDispatchStates.addState(src)
					}
				}
			}
		}
	}

	eg, ctx := errgroup.WithContext(ctx)
	for i, d := range allDispatchStates.states {
		reachable := isReachable(target, d)
		// resolve image config for every stage
		if d.base == nil {
			if d.stage.BaseName == emptyImageName {
				d.state = llb.Scratch()
				d.image = emptyImage(*opt.TargetPlatform)
				continue
			}
			func(i int, d *dispatchState) {
				eg.Go(func() error {
					ref, err := reference.ParseNormalizedNamed(d.stage.BaseName)
					if err != nil {
						return err
					}
					platform := d.platform
					if platform == nil {
						platform = opt.TargetPlatform
					}
					d.stage.BaseName = reference.TagNameOnly(ref).String()
					var isScratch bool
					if metaResolver != nil && reachable {
						dgst, dt, err := metaResolver.ResolveImageConfig(ctx, d.stage.BaseName, platform)
						if err == nil { // handle the error while builder is actually running
							var img Image
							if err := json.Unmarshal(dt, &img); err != nil {
								return err
							}
							img.Created = nil
							// if there is no explicit target platform, try to match based on image config
							if d.platform == nil && implicitTargetPlatform {
								p := autoDetectPlatform(img, *platform, opt.BuildPlatforms)
								platform = &p
							}
							d.image = img
							if dgst != "" {
								ref, err = reference.WithDigest(ref, dgst)
								if err != nil {
									return err
								}
							}
							d.stage.BaseName = ref.String()
							_ = ref
							if len(img.RootFS.DiffIDs) == 0 {
								isScratch = true
							}
						}
					}
					if isScratch {
						d.state = llb.Scratch()
					} else {
						d.state = llb.Image(d.stage.BaseName, dfCmd(d.stage.SourceCode), llb.Platform(*platform))
					}
					return nil
				})
			}(i, d)
		}
	}

	if err := eg.Wait(); err != nil {
		return nil, nil, err
	}

	buildContext := &mutableOutput{}
	ctxPaths := map[string]struct{}{}

	for _, d := range allDispatchStates.states {
		if !isReachable(target, d) {
			continue
		}
		if d.base != nil {
			d.state = d.base.state
			d.image = clone(d.base.image)
		}

		// initialize base metadata from image conf
		for _, env := range d.image.Config.Env {
			k, v := parseKeyValue(env)
			d.state = d.state.AddEnv(k, v)
		}
		if d.image.Config.WorkingDir != "" {
			if err = dispatchWorkdir(d, &instructions.WorkdirCommand{Path: d.image.Config.WorkingDir}, false); err != nil {
				return nil, nil, err
			}
		}
		if d.image.Config.User != "" {
			if err = dispatchUser(d, &instructions.UserCommand{User: d.image.Config.User}, false); err != nil {
				return nil, nil, err
			}
		}

		opt := dispatchOpt{
			allDispatchStates: allDispatchStates,
			metaArgs:          optMetaArgs,
			buildArgValues:    opt.BuildArgs,
			shlex:             shlex,
			sessionID:         opt.SessionID,
			buildContext:      llb.NewState(buildContext),
			proxyEnv:          proxyEnv,
			cacheIDNamespace:  opt.CacheIDNamespace,
			buildPlatforms:    opt.BuildPlatforms,
			targetPlatform:    *opt.TargetPlatform,
		}

		if err = dispatchOnBuild(d, d.image.Config.OnBuild, opt); err != nil {
			return nil, nil, err
		}

		for _, cmd := range d.commands {
			if err := dispatch(d, cmd, opt); err != nil {
				return nil, nil, err
			}
		}

		for p := range d.ctxPaths {
			ctxPaths[p] = struct{}{}
		}
	}

	if len(opt.Labels) != 0 && target.image.Config.Labels == nil {
		target.image.Config.Labels = make(map[string]string, len(opt.Labels))
	}
	for k, v := range opt.Labels {
		target.image.Config.Labels[k] = v
	}

	opts := []llb.LocalOption{
		llb.SessionID(opt.SessionID),
		llb.ExcludePatterns(opt.Excludes),
		llb.SharedKeyHint(localNameContext),
	}
	if includePatterns := normalizeContextPaths(ctxPaths); includePatterns != nil {
		opts = append(opts, llb.FollowPaths(includePatterns))
	}
	bc := llb.Local(localNameContext, opts...)
	if opt.BuildContext != nil {
		bc = *opt.BuildContext
	}
	buildContext.Output = bc.Output()

	st := target.state.SetMarhalDefaults(llb.Platform(*opt.TargetPlatform))

	if !implicitTargetPlatform {
		target.image.OS = opt.TargetPlatform.OS
		target.image.Architecture = opt.TargetPlatform.Architecture
	}

	return &st, &target.image, nil
}

func metaArgsToMap(metaArgs []instructions.KeyValuePairOptional) map[string]string {
	m := map[string]string{}

	for _, arg := range metaArgs {
		m[arg.Key] = arg.ValueString()
	}

	return m
}

func toCommand(ic instructions.Command, allDispatchStates *dispatchStates) (command, error) {
	cmd := command{Command: ic}
	if c, ok := ic.(*instructions.CopyCommand); ok {
		if c.From != "" {
			var stn *dispatchState
			index, err := strconv.Atoi(c.From)
			if err != nil {
				stn, ok = allDispatchStates.findStateByName(c.From)
				if !ok {
					stn = &dispatchState{
						stage:        instructions.Stage{BaseName: c.From},
						deps:         make(map[*dispatchState]struct{}),
						unregistered: true,
					}
				}
			} else {
				stn, err = allDispatchStates.findStateByIndex(index)
				if err != nil {
					return command{}, err
				}
			}
			cmd.sources = []*dispatchState{stn}
		}
	}

	if ok := detectRunMount(&cmd, allDispatchStates); ok {
		return cmd, nil
	}

	return cmd, nil
}

type dispatchOpt struct {
	allDispatchStates *dispatchStates
	metaArgs          []instructions.KeyValuePairOptional
	buildArgValues    map[string]string
	shlex             *shell.Lex
	sessionID         string
	buildContext      llb.State
	proxyEnv          *llb.ProxyEnv
	cacheIDNamespace  string
	targetPlatform    specs.Platform
	buildPlatforms    []specs.Platform
}

func dispatch(d *dispatchState, cmd command, opt dispatchOpt) error {
	if ex, ok := cmd.Command.(instructions.SupportsSingleWordExpansion); ok {
		err := ex.Expand(func(word string) (string, error) {
			return opt.shlex.ProcessWordWithMap(word, toEnvMap(d.buildArgs, d.image.Config.Env))
		})
		if err != nil {
			return err
		}
	}

	var err error
	switch c := cmd.Command.(type) {
	case *instructions.MaintainerCommand:
		err = dispatchMaintainer(d, c)
	case *instructions.EnvCommand:
		err = dispatchEnv(d, c)
	case *instructions.RunCommand:
		err = dispatchRun(d, c, opt.proxyEnv, cmd.sources, opt)
	case *instructions.WorkdirCommand:
		err = dispatchWorkdir(d, c, true)
	case *instructions.AddCommand:
		err = dispatchCopy(d, c.SourcesAndDest, opt.buildContext, true, c, "", opt)
		if err == nil {
			for _, src := range c.Sources() {
				d.ctxPaths[path.Join("/", filepath.ToSlash(src))] = struct{}{}
			}
		}
	case *instructions.LabelCommand:
		err = dispatchLabel(d, c)
	case *instructions.OnbuildCommand:
		err = dispatchOnbuild(d, c)
	case *instructions.CmdCommand:
		err = dispatchCmd(d, c)
	case *instructions.EntrypointCommand:
		err = dispatchEntrypoint(d, c)
	case *instructions.HealthCheckCommand:
		err = dispatchHealthcheck(d, c)
	case *instructions.ExposeCommand:
		err = dispatchExpose(d, c, opt.shlex)
	case *instructions.UserCommand:
		err = dispatchUser(d, c, true)
	case *instructions.VolumeCommand:
		err = dispatchVolume(d, c)
	case *instructions.StopSignalCommand:
		err = dispatchStopSignal(d, c)
	case *instructions.ShellCommand:
		err = dispatchShell(d, c)
	case *instructions.ArgCommand:
		err = dispatchArg(d, c, opt.metaArgs, opt.buildArgValues)
	case *instructions.CopyCommand:
		l := opt.buildContext
		if len(cmd.sources) != 0 {
			l = cmd.sources[0].state
		}
		err = dispatchCopy(d, c.SourcesAndDest, l, false, c, c.Chown, opt)
		if err == nil && len(cmd.sources) == 0 {
			for _, src := range c.Sources() {
				d.ctxPaths[path.Join("/", filepath.ToSlash(src))] = struct{}{}
			}
		}
	default:
	}
	return err
}

type dispatchState struct {
	state        llb.State
	image        Image
	platform     *specs.Platform
	stage        instructions.Stage
	base         *dispatchState
	deps         map[*dispatchState]struct{}
	buildArgs    []instructions.KeyValuePairOptional
	commands     []command
	ctxPaths     map[string]struct{}
	ignoreCache  bool
	cmdSet       bool
	unregistered bool
}

type dispatchStates struct {
	states       []*dispatchState
	statesByName map[string]*dispatchState
}

func newDispatchStates() *dispatchStates {
	return &dispatchStates{statesByName: map[string]*dispatchState{}}
}

func (dss *dispatchStates) addState(ds *dispatchState) {
	dss.states = append(dss.states, ds)

	if d, ok := dss.statesByName[ds.stage.BaseName]; ok {
		ds.base = d
	}
	if ds.stage.Name != "" {
		dss.statesByName[strings.ToLower(ds.stage.Name)] = ds
	}
}

func (dss *dispatchStates) findStateByName(name string) (*dispatchState, bool) {
	ds, ok := dss.statesByName[strings.ToLower(name)]
	return ds, ok
}

func (dss *dispatchStates) findStateByIndex(index int) (*dispatchState, error) {
	if index < 0 || index >= len(dss.states) {
		return nil, errors.Errorf("invalid stage index %d", index)
	}

	return dss.states[index], nil
}

func (dss *dispatchStates) lastTarget() *dispatchState {
	return dss.states[len(dss.states)-1]
}

type command struct {
	instructions.Command
	sources []*dispatchState
}

func dispatchOnBuild(d *dispatchState, triggers []string, opt dispatchOpt) error {
	for _, trigger := range triggers {
		ast, err := parser.Parse(strings.NewReader(trigger))
		if err != nil {
			return err
		}
		if len(ast.AST.Children) != 1 {
			return errors.New("onbuild trigger should be a single expression")
		}
		ic, err := instructions.ParseCommand(ast.AST.Children[0])
		if err != nil {
			return err
		}
		cmd, err := toCommand(ic, opt.allDispatchStates)
		if err != nil {
			return err
		}
		if err := dispatch(d, cmd, opt); err != nil {
			return err
		}
	}
	return nil
}

func dispatchEnv(d *dispatchState, c *instructions.EnvCommand) error {
	commitMessage := bytes.NewBufferString("ENV")
	for _, e := range c.Env {
		commitMessage.WriteString(" " + e.String())
		d.state = d.state.AddEnv(e.Key, e.Value)
		d.image.Config.Env = addEnv(d.image.Config.Env, e.Key, e.Value)
	}
	return commitToHistory(&d.image, commitMessage.String(), false, nil)
}

func dispatchRun(d *dispatchState, c *instructions.RunCommand, proxy *llb.ProxyEnv, sources []*dispatchState, dopt dispatchOpt) error {
	var args []string = c.CmdLine
	if c.PrependShell {
		args = withShell(d.image, args)
	} else if d.image.Config.Entrypoint != nil {
		args = append(d.image.Config.Entrypoint, args...)
	}
	opt := []llb.RunOption{llb.Args(args)}
	for _, arg := range d.buildArgs {
		opt = append(opt, llb.AddEnv(arg.Key, arg.ValueString()))
	}
	opt = append(opt, dfCmd(c))
	if d.ignoreCache {
		opt = append(opt, llb.IgnoreCache)
	}
	if proxy != nil {
		opt = append(opt, llb.WithProxy(*proxy))
	}

	runMounts, err := dispatchRunMounts(d, c, sources, dopt)
	if err != nil {
		return err
	}
	opt = append(opt, runMounts...)

	d.state = d.state.Run(opt...).Root()
	return commitToHistory(&d.image, "RUN "+runCommandString(args, d.buildArgs), true, &d.state)
}

func dispatchWorkdir(d *dispatchState, c *instructions.WorkdirCommand, commit bool) error {
	d.state = d.state.Dir(c.Path)
	wd := c.Path
	if !path.IsAbs(c.Path) {
		wd = path.Join("/", d.image.Config.WorkingDir, wd)
	}
	d.image.Config.WorkingDir = wd
	if commit {
		return commitToHistory(&d.image, "WORKDIR "+wd, false, nil)
	}
	return nil
}

func dispatchCopy(d *dispatchState, c instructions.SourcesAndDest, sourceState llb.State, isAddCommand bool, cmdToPrint interface{}, chown string, opt dispatchOpt) error {
	// TODO: this should use CopyOp instead. Current implementation is inefficient
	img := llb.Image(CopyImage, llb.Platform(opt.buildPlatforms[0]))

	dest := path.Join(".", pathRelativeToWorkingDir(d.state, c.Dest()))
	if c.Dest() == "." || c.Dest()[len(c.Dest())-1] == filepath.Separator {
		dest += string(filepath.Separator)
	}
	args := []string{"copy"}
	unpack := isAddCommand

	mounts := make([]llb.RunOption, 0, len(c.Sources()))
	if chown != "" {
		args = append(args, fmt.Sprintf("--chown=%s", chown))
		_, _, err := parseUser(chown)
		if err != nil {
			mounts = append(mounts, llb.AddMount("/etc/passwd", d.state, llb.SourcePath("/etc/passwd"), llb.Readonly))
			mounts = append(mounts, llb.AddMount("/etc/group", d.state, llb.SourcePath("/etc/group"), llb.Readonly))
		}
	}

	commitMessage := bytes.NewBufferString("")
	if isAddCommand {
		commitMessage.WriteString("ADD")
	} else {
		commitMessage.WriteString("COPY")
	}

	for i, src := range c.Sources() {
		commitMessage.WriteString(" " + src)
		if strings.HasPrefix(src, "http://") || strings.HasPrefix(src, "https://") {
			if !isAddCommand {
				return errors.New("source can't be a URL for COPY")
			}

			// Resources from remote URLs are not decompressed.
			// https://docs.docker.com/engine/reference/builder/#add
			//
			// Note: mixing up remote archives and local archives in a single ADD instruction
			// would result in undefined behavior: https://github.com/moby/buildkit/pull/387#discussion_r189494717
			unpack = false
			u, err := url.Parse(src)
			f := "__unnamed__"
			if err == nil {
				if base := path.Base(u.Path); base != "." && base != "/" {
					f = base
				}
			}
			target := path.Join(fmt.Sprintf("/src-%d", i), f)
			args = append(args, target)
			mounts = append(mounts, llb.AddMount(path.Dir(target), llb.HTTP(src, llb.Filename(f), dfCmd(c)), llb.Readonly))
		} else {
			d, f := splitWildcards(src)
			targetCmd := fmt.Sprintf("/src-%d", i)
			targetMount := targetCmd
			if f == "" {
				f = path.Base(src)
				targetMount = path.Join(targetMount, f)
			}
			targetCmd = path.Join(targetCmd, f)
			args = append(args, targetCmd)
			mounts = append(mounts, llb.AddMount(targetMount, sourceState, llb.SourcePath(d), llb.Readonly))
		}
	}

	commitMessage.WriteString(" " + c.Dest())

	args = append(args, dest)
	if unpack {
		args = append(args[:1], append([]string{"--unpack"}, args[1:]...)...)
	}

	runOpt := []llb.RunOption{llb.Args(args), llb.Dir("/dest"), llb.ReadonlyRootFS(), dfCmd(cmdToPrint)}
	if d.ignoreCache {
		runOpt = append(runOpt, llb.IgnoreCache)
	}
	run := img.Run(append(runOpt, mounts...)...)
	d.state = run.AddMount("/dest", d.state).Platform(opt.targetPlatform)

	return commitToHistory(&d.image, commitMessage.String(), true, &d.state)
}

func dispatchMaintainer(d *dispatchState, c *instructions.MaintainerCommand) error {
	d.image.Author = c.Maintainer
	return commitToHistory(&d.image, fmt.Sprintf("MAINTAINER %v", c.Maintainer), false, nil)
}

func dispatchLabel(d *dispatchState, c *instructions.LabelCommand) error {
	commitMessage := bytes.NewBufferString("LABEL")
	if d.image.Config.Labels == nil {
		d.image.Config.Labels = make(map[string]string, len(c.Labels))
	}
	for _, v := range c.Labels {
		d.image.Config.Labels[v.Key] = v.Value
		commitMessage.WriteString(" " + v.String())
	}
	return commitToHistory(&d.image, commitMessage.String(), false, nil)
}

func dispatchOnbuild(d *dispatchState, c *instructions.OnbuildCommand) error {
	d.image.Config.OnBuild = append(d.image.Config.OnBuild, c.Expression)
	return nil
}

func dispatchCmd(d *dispatchState, c *instructions.CmdCommand) error {
	var args []string = c.CmdLine
	if c.PrependShell {
		args = withShell(d.image, args)
	}
	d.image.Config.Cmd = args
	d.image.Config.ArgsEscaped = true
	d.cmdSet = true
	return commitToHistory(&d.image, fmt.Sprintf("CMD %q", args), false, nil)
}

func dispatchEntrypoint(d *dispatchState, c *instructions.EntrypointCommand) error {
	var args []string = c.CmdLine
	if c.PrependShell {
		args = withShell(d.image, args)
	}
	d.image.Config.Entrypoint = args
	if !d.cmdSet {
		d.image.Config.Cmd = nil
	}
	return commitToHistory(&d.image, fmt.Sprintf("ENTRYPOINT %q", args), false, nil)
}

func dispatchHealthcheck(d *dispatchState, c *instructions.HealthCheckCommand) error {
	d.image.Config.Healthcheck = &HealthConfig{
		Test:        c.Health.Test,
		Interval:    c.Health.Interval,
		Timeout:     c.Health.Timeout,
		StartPeriod: c.Health.StartPeriod,
		Retries:     c.Health.Retries,
	}
	return commitToHistory(&d.image, fmt.Sprintf("HEALTHCHECK %q", d.image.Config.Healthcheck), false, nil)
}

func dispatchExpose(d *dispatchState, c *instructions.ExposeCommand, shlex *shell.Lex) error {
	ports := []string{}
	for _, p := range c.Ports {
		ps, err := shlex.ProcessWordsWithMap(p, toEnvMap(d.buildArgs, d.image.Config.Env))
		if err != nil {
			return err
		}
		ports = append(ports, ps...)
	}
	c.Ports = ports

	ps, _, err := nat.ParsePortSpecs(c.Ports)
	if err != nil {
		return err
	}

	if d.image.Config.ExposedPorts == nil {
		d.image.Config.ExposedPorts = make(map[string]struct{})
	}
	for p := range ps {
		d.image.Config.ExposedPorts[string(p)] = struct{}{}
	}

	return commitToHistory(&d.image, fmt.Sprintf("EXPOSE %v", ps), false, nil)
}

func dispatchUser(d *dispatchState, c *instructions.UserCommand, commit bool) error {
	d.state = d.state.User(c.User)
	d.image.Config.User = c.User
	if commit {
		return commitToHistory(&d.image, fmt.Sprintf("USER %v", c.User), false, nil)
	}
	return nil
}

func dispatchVolume(d *dispatchState, c *instructions.VolumeCommand) error {
	if d.image.Config.Volumes == nil {
		d.image.Config.Volumes = map[string]struct{}{}
	}
	for _, v := range c.Volumes {
		if v == "" {
			return errors.New("VOLUME specified can not be an empty string")
		}
		d.image.Config.Volumes[v] = struct{}{}
	}
	return commitToHistory(&d.image, fmt.Sprintf("VOLUME %v", c.Volumes), false, nil)
}

func dispatchStopSignal(d *dispatchState, c *instructions.StopSignalCommand) error {
	if _, err := signal.ParseSignal(c.Signal); err != nil {
		return err
	}
	d.image.Config.StopSignal = c.Signal
	return commitToHistory(&d.image, fmt.Sprintf("STOPSIGNAL %v", c.Signal), false, nil)
}

func dispatchShell(d *dispatchState, c *instructions.ShellCommand) error {
	d.image.Config.Shell = c.Shell
	return commitToHistory(&d.image, fmt.Sprintf("SHELL %v", c.Shell), false, nil)
}

func dispatchArg(d *dispatchState, c *instructions.ArgCommand, metaArgs []instructions.KeyValuePairOptional, buildArgValues map[string]string) error {
	commitStr := "ARG " + c.Key
	buildArg := setKVValue(c.KeyValuePairOptional, buildArgValues)

	if c.Value != nil {
		commitStr += "=" + *c.Value
	}
	if buildArg.Value == nil {
		for _, ma := range metaArgs {
			if ma.Key == buildArg.Key {
				buildArg.Value = ma.Value
			}
		}
	}

	d.buildArgs = append(d.buildArgs, buildArg)
	return commitToHistory(&d.image, commitStr, false, nil)
}

func pathRelativeToWorkingDir(s llb.State, p string) string {
	if path.IsAbs(p) {
		return p
	}
	return path.Join(s.GetDir(), p)
}

func splitWildcards(name string) (string, string) {
	i := 0
	for ; i < len(name); i++ {
		ch := name[i]
		if ch == '\\' {
			i++
		} else if ch == '*' || ch == '?' || ch == '[' {
			break
		}
	}
	if i == len(name) {
		return name, ""
	}

	base := path.Base(name[:i])
	if name[:i] == "" || strings.HasSuffix(name[:i], string(filepath.Separator)) {
		base = ""
	}
	return path.Dir(name[:i]), base + name[i:]
}

func addEnv(env []string, k, v string) []string {
	gotOne := false
	for i, envVar := range env {
		key, _ := parseKeyValue(envVar)
		if shell.EqualEnvKeys(key, k) {
			env[i] = k + "=" + v
			gotOne = true
			break
		}
	}
	if !gotOne {
		env = append(env, k+"="+v)
	}
	return env
}

func parseKeyValue(env string) (string, string) {
	parts := strings.SplitN(env, "=", 2)
	v := ""
	if len(parts) > 1 {
		v = parts[1]
	}

	return parts[0], v
}

func setKVValue(kvpo instructions.KeyValuePairOptional, values map[string]string) instructions.KeyValuePairOptional {
	if v, ok := values[kvpo.Key]; ok {
		kvpo.Value = &v
	}
	return kvpo
}

func toEnvMap(args []instructions.KeyValuePairOptional, env []string) map[string]string {
	m := shell.BuildEnvs(env)

	for _, arg := range args {
		// If key already exists, keep previous value.
		if _, ok := m[arg.Key]; ok {
			continue
		}
		m[arg.Key] = arg.ValueString()
	}
	return m
}

func dfCmd(cmd interface{}) llb.ConstraintsOpt {
	// TODO: add fmt.Stringer to instructions.Command to remove interface{}
	var cmdStr string
	if cmd, ok := cmd.(fmt.Stringer); ok {
		cmdStr = cmd.String()
	}
	if cmd, ok := cmd.(string); ok {
		cmdStr = cmd
	}
	return llb.WithDescription(map[string]string{
		"com.docker.dockerfile.v1.command": cmdStr,
	})
}

func runCommandString(args []string, buildArgs []instructions.KeyValuePairOptional) string {
	var tmpBuildEnv []string
	for _, arg := range buildArgs {
		tmpBuildEnv = append(tmpBuildEnv, arg.Key+"="+arg.ValueString())
	}
	if len(tmpBuildEnv) > 0 {
		tmpBuildEnv = append([]string{fmt.Sprintf("|%d", len(tmpBuildEnv))}, tmpBuildEnv...)
	}

	return strings.Join(append(tmpBuildEnv, args...), " ")
}

func commitToHistory(img *Image, msg string, withLayer bool, st *llb.State) error {
	if st != nil {
		msg += " # buildkit"
	}

	img.History = append(img.History, specs.History{
		CreatedBy:  msg,
		Comment:    historyComment,
		EmptyLayer: !withLayer,
	})
	return nil
}

func isReachable(from, to *dispatchState) (ret bool) {
	if from == nil {
		return false
	}
	if from == to || isReachable(from.base, to) {
		return true
	}
	for d := range from.deps {
		if isReachable(d, to) {
			return true
		}
	}
	return false
}

func parseUser(str string) (uid uint32, gid uint32, err error) {
	if str == "" {
		return 0, 0, nil
	}
	parts := strings.SplitN(str, ":", 2)
	for i, v := range parts {
		switch i {
		case 0:
			uid, err = parseUID(v)
			if err != nil {
				return 0, 0, err
			}
			if len(parts) == 1 {
				gid = uid
			}
		case 1:
			gid, err = parseUID(v)
			if err != nil {
				return 0, 0, err
			}
		}
	}
	return
}

func parseUID(str string) (uint32, error) {
	if str == "root" {
		return 0, nil
	}
	uid, err := strconv.ParseUint(str, 10, 32)
	if err != nil {
		return 0, err
	}
	return uint32(uid), nil
}

func normalizeContextPaths(paths map[string]struct{}) []string {
	pathSlice := make([]string, 0, len(paths))
	for p := range paths {
		if p == "/" {
			return nil
		}
		pathSlice = append(pathSlice, p)
	}

	toDelete := map[string]struct{}{}
	for i := range pathSlice {
		for j := range pathSlice {
			if i == j {
				continue
			}
			if strings.HasPrefix(pathSlice[j], pathSlice[i]+"/") {
				delete(paths, pathSlice[j])
			}
		}
	}

	toSort := make([]string, 0, len(paths))
	for p := range paths {
		if _, ok := toDelete[p]; !ok {
			toSort = append(toSort, path.Join(".", p))
		}
	}
	sort.Slice(toSort, func(i, j int) bool {
		return toSort[i] < toSort[j]
	})
	return toSort
}

func proxyEnvFromBuildArgs(args map[string]string) *llb.ProxyEnv {
	pe := &llb.ProxyEnv{}
	isNil := true
	for k, v := range args {
		if strings.EqualFold(k, "http_proxy") {
			pe.HttpProxy = v
			isNil = false
		}
		if strings.EqualFold(k, "https_proxy") {
			pe.HttpsProxy = v
			isNil = false
		}
		if strings.EqualFold(k, "ftp_proxy") {
			pe.FtpProxy = v
			isNil = false
		}
		if strings.EqualFold(k, "no_proxy") {
			pe.NoProxy = v
			isNil = false
		}
	}
	if isNil {
		return nil
	}
	return pe
}

type mutableOutput struct {
	llb.Output
}

func withShell(img Image, args []string) []string {
	var shell []string
	if len(img.Config.Shell) > 0 {
		shell = append([]string{}, img.Config.Shell...)
	} else {
		shell = defaultShell()
	}
	return append(shell, strings.Join(args, " "))
}

func autoDetectPlatform(img Image, target specs.Platform, supported []specs.Platform) specs.Platform {
	os := img.OS
	arch := img.Architecture
	if target.OS == os && target.Architecture == arch {
		return target
	}
	for _, p := range supported {
		if p.OS == os && p.Architecture == arch {
			return p
		}
	}
	return target
}