mesh-controller/cmd/mesh-builder/once.go

package main

import (
	"context"
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"os"
	"strings"

	"github.com/novox/mesh-control/internal/builder"
)

// buildOnce is the builder doing one build and stopping, with no broker and no mesh.
//
// **This is how a mesh is raised** (novox/hq ADR 0073). The installer carries this program and runs
// it once, before anything else exists, to produce the control plane from the same repository and
// path that every later rebuild of it will use. What raises the mesh is therefore the same thing
// that maintains it — not a second mechanism that has to be kept in step with the first and is
// exercised once per new mesh, which is how often enough to rot.
//
// It takes no work from a queue and answers nobody: there is no broker yet, and the only thing
// waiting for the answer is the installer that started it. So the result goes to standard output as
// JSON, which is what the installer reads.
//
// With no --registry it publishes nowhere and the image stays in this machine's container runtime,
// named by the digest of its own configuration (see builder.Local). That is the genesis case. With
// one, it publishes as it always does — the same command is how an operator builds a module by hand
// on a mesh that already exists.
func buildOnce(ctx context.Context, args []string) error {
	set := flag.NewFlagSet("build", flag.ContinueOnError)
	path := set.String("path", "", "the module's directory inside the repository (default: its root)")
	ref := set.String("ref", "", "the commit to build; a branch is a moving target somebody else controls")
	registry := set.String("registry", "",
		"host:port to publish to. Without it the artifacts stay in this machine's container runtime, which is the genesis case")
	workspace := set.String("workspace", "", "where to clone and build (default: a temporary directory)")
	on := multiple(set, "on",
		"a base this build stands on, as <module>/<artifact>=<reference>. Repeatable")
	positionals, err := parseAround(set, args)
	if err != nil {
		return err
	}
	if len(positionals) != 1 {
		return errors.New("mesh-builder build <repository> [--path P] [--ref COMMIT] [--registry HOST:PORT]")
	}
	repository := positionals[0]

	where := *workspace
	if where == "" {
		where = os.TempDir() + "/mesh-builder-once"
	}

	// What this build may stand on, said on the command line because there is no mesh to ask.
	//
	// **This is the genesis case and it is meant to be awkward.** On a running mesh the control
	// plane answers this, because only it knows what this mesh holds. Here nothing has been built
	// yet, so whoever runs this says what to use — and for the control plane, which is the one
	// module raised before anything else exists, the answer is ordinarily nothing at all.
	bases := map[string]string{}
	for _, pair := range *on {
		key, reference, found := strings.Cut(pair, "=")
		if !found || key == "" || reference == "" {
			return fmt.Errorf(
				"--on takes <module>/<artifact>=<reference>, and %q is not that", pair)
		}
		bases[key] = reference
	}

	// Local unless told otherwise, because the moment this exists for has nowhere to publish. A
	// default pointing at a registry would mean genesis failing at a push to something that is not
	// there yet, one step away from the thing that could explain it.
	var publisher builder.Publisher = builder.Local{Run: builder.Command}
	if *registry != "" {
		publisher = builder.Registry{Address: *registry, Run: builder.Command}
	}

	fmt.Fprintf(os.Stderr, "building %s", repository)
	if *path != "" {
		fmt.Fprintf(os.Stderr, " at %s", *path)
	}
	if *ref != "" {
		fmt.Fprintf(os.Stderr, " at %s", *ref)
	}
	fmt.Fprintln(os.Stderr)

	built, buildErr := builder.Build(ctx, builder.Command, publisher, repository, *path, *ref, where, bases)
	if buildErr != nil {
		return buildErr
	}

	// To standard output, and everything else to standard error, so the caller can read this
	// without having to separate it from progress.
	out := onceResult{
		Module:     built.Manifest.Module,
		Commit:     built.Commit,
		Repository: repository,
		Path:       *path,
		Ref:        *ref,
		Manifest:   built.Manifest,
		Against:    built.Against,
	}
	for _, made := range built.Built {
		out.Made = append(out.Made, madeArtifact{Name: made.Name, Kind: made.Kind, Reference: made.Reference})
	}
	body, err := json.MarshalIndent(out, "", "  ")
	if err != nil {
		return err
	}
	fmt.Println(string(body))
	fmt.Fprintf(os.Stderr, "  built %s from %s\n", built.Manifest.Module, short(built.Commit))
	return nil
}

// onceResult is what one build reports to whoever started it.
//
// The same fields the mesh records for a build, so a reader comparing a genesis build against an
// ordinary one is comparing the same thing said the same way.
type onceResult struct {
	Module     string         `json:"module"`
	Commit     string         `json:"commit"`
	Repository string         `json:"repository"`
	Path       string         `json:"path,omitempty"`
	Ref        string         `json:"ref,omitempty"`
	Manifest   any            `json:"manifest"`
	Made       []madeArtifact `json:"made"`
	Against    []string       `json:"against,omitempty"`
}

type madeArtifact struct {
	Name      string `json:"name"`
	Kind      string `json:"kind"`
	Reference string `json:"reference"`
}

// parseAround lets flags appear on either side of the repository, because a person writing this by
// hand will put them wherever reads best and the standard parser stops at the first thing that is
// not a flag. The same helper the control plane's commands use, for the same reason.
func parseAround(set *flag.FlagSet, args []string) ([]string, error) {
	var positionals []string
	rest := args
	for {
		if err := set.Parse(rest); err != nil {
			return nil, err
		}
		rest = set.Args()
		if len(rest) == 0 {
			return positionals, nil
		}
		positionals = append(positionals, rest[0])
		rest = rest[1:]
	}
}

// multiple is a flag that may be given more than once.
type repeated []string

func (r *repeated) String() string     { return strings.Join(*r, ", ") }
func (r *repeated) Set(v string) error { *r = append(*r, v); return nil }

func multiple(set *flag.FlagSet, name, usage string) *[]string {
	var values repeated
	set.Var(&values, name, usage)
	return (*[]string)(&values)
}