werkdock/internal/cli/build.go

package cli

import (
	"errors"
	"flag"
	"fmt"
	"io"
	"os"
	"path/filepath"

	"werkdock/internal/build"
	"werkdock/internal/registry"
	"werkdock/internal/store"
)

// buildOptions is the parsed form of `werkdock build` flags,
// separated from execution so the parsing is testable (as parseRun is).
type buildOptions struct {
	Dockerfile string
	Context    string
	Tag        string
	Quiet      bool
	NoCache    bool
}

// buildCmd is `docker build`: an image from a Dockerfile, built on this
// host (RFC 0006). `werkdock build [-f Dockerfile] -t IMAGE CONTEXT`.
func buildCmd(args []string) int {
	opts, err := parseBuild(args)
	if err != nil {
		return fail(err)
	}
	st, err := store.Default()
	if err != nil {
		return fail(err)
	}
	backend, how := build.Select()
	log := io.Writer(os.Stdout)
	if opts.Quiet {
		log = io.Discard
	}
	fmt.Fprintf(log, "werkdock: %s\n", how)
	if opts.NoCache && !backend.CachesSteps() {
		fmt.Fprintf(log, "werkdock: --no-cache is a no-op here; this backend caches no steps\n")
	}
	result, err := build.Run(st, build.Options{
		Dockerfile: opts.Dockerfile,
		Context:    opts.Context,
		Tag:        opts.Tag,
		Backend:    backend,
		Resolve:    resolveBase(st),
		Stdout:     log,
		Stderr:     os.Stderr,
	})
	if err != nil {
		return fail(err)
	}
	if opts.Quiet {
		fmt.Println(result.ID)
	}
	return 0
}

// parseBuild parses the docker-shaped build flags. Docker flags whose
// promise werkdock cannot keep are registered and refused with a
// reason — never silently ignored (RFC 0002).
func parseBuild(args []string) (*buildOptions, error) {
	fs := flag.NewFlagSet("build", flag.ContinueOnError)
	fs.SetOutput(io.Discard)
	var tags stringList
	dockerfile := fs.String("f", "", "Dockerfile to read (default CONTEXT/Dockerfile)")
	fs.StringVar(dockerfile, "file", "", "Dockerfile to read (default CONTEXT/Dockerfile)")
	fs.Var(&tags, "t", "reference for the built image, REPOSITORY[:TAG]")
	fs.Var(&tags, "tag", "reference for the built image, REPOSITORY[:TAG]")
	quiet := fs.Bool("q", false, "print the image id only")
	fs.BoolVar(quiet, "quiet", false, "print the image id only")
	// docker's --no-cache asks for what the copy backend does anyway.
	noCache := fs.Bool("no-cache", false, "do not use a build cache (the copy backend has none)")
	refuse(fs, "build-arg", "ARG and --build-arg are stage 2 of RFC 0006")
	refuse(fs, "target", "--target needs multi-stage builds, which are stage 3 of RFC 0006")
	refuse(fs, "platform", "werkdock builds for the host's platform; there is no emulation")
	refuse(fs, "pull", "the base image is pulled when the store does not have it; werkdock rmi it to force a refetch")
	refuse(fs, "squash", "a werkdock image is one flat tree already; there is nothing to squash")
	refuse(fs, "cache-from", "there is no layer cache to import from (RFC 0006, What \"no layers\" means)")
	refuse(fs, "cache-to", "there is no layer cache to export (RFC 0006, What \"no layers\" means)")
	refuse(fs, "secret", "build secrets are BuildKit's; a RUN step cannot mount anything (CapEff is 0 in the sandbox)")
	refuse(fs, "ssh", "SSH agent forwarding into a build is BuildKit's")
	refuse(fs, "network", "the sandbox shares the host's network by contract; there is no build network to choose")
	refuse(fs, "output", "--output is BuildKit's exporter; the result is a store image, and save writes an archive")
	refuse(fs, "load", "--load is buildx's; the image is in the store when the build succeeded")
	refuse(fs, "push", "--push is buildx's; werkdock has no push verb")
	refuse(fs, "progress", "werkdock prints the steps and the commands' own output, nothing else")
	if err := fs.Parse(args); err != nil {
		return nil, err
	}
	rest := fs.Args()
	if len(rest) == 0 {
		return nil, errors.New("build needs a CONTEXT directory (werkdock build [-f Dockerfile] -t IMAGE CONTEXT)")
	}
	if len(rest) > 1 {
		return nil, fmt.Errorf("unexpected argument %q", rest[1])
	}
	if rest[0] == "-" {
		return nil, errors.New("a Dockerfile on stdin needs no context and is not supported; pass a context directory")
	}
	if len(tags) == 0 {
		return nil, errors.New("build needs -t REPOSITORY[:TAG]: a werkdock image is named, there is no untagged image")
	}
	if len(tags) > 1 {
		return nil, errors.New("one -t per build: a second reference for the same image needs a tag verb, which werkdock does not have yet")
	}
	if _, err := store.ParseReference(tags[0]); err != nil {
		return nil, err
	}
	opts := &buildOptions{Context: rest[0], Tag: tags[0], Quiet: *quiet, NoCache: *noCache, Dockerfile: *dockerfile}
	if opts.Dockerfile == "" {
		opts.Dockerfile = filepath.Join(opts.Context, "Dockerfile")
	}
	return opts, nil
}

// resolveBase is FROM's lookup: the store first, then a pull, as
// `docker build` pulls a base it does not have. Without a registry
// client the error names the two verbs that would put the image there.
func resolveBase(st store.Store) func(string) (string, store.ImageMeta, error) {
	return func(reference string) (string, store.ImageMeta, error) {
		rootfs, err := st.RootFS(reference)
		if err == nil {
			meta, metaErr := st.Meta(reference)
			return rootfs, meta, metaErr
		}
		fmt.Fprintf(os.Stderr, "werkdock: %s is not in the store, pulling it\n", reference)
		if _, pullErr := registry.Pull(st, reference, registry.DefaultPlatform(), os.Stderr); pullErr != nil {
			return "", store.ImageMeta{}, fmt.Errorf("FROM %s: not in the store and could not be pulled: %w\n"+
				"\tput it there with: werkdock pull %s — or werkdock load -i ARCHIVE", reference, pullErr, reference)
		}
		rootfs, err = st.RootFS(reference)
		if err != nil {
			return "", store.ImageMeta{}, err
		}
		meta, err := st.Meta(reference)
		return rootfs, meta, err
	}
}