mesh-controller/internal/builder/template.go

package builder

import (
	"archive/tar"
	"bytes"
	"compress/gzip"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"path/filepath"

	"github.com/novox/mesh-controller/internal/catalogue"
)

// withTemplateTexts is what was built with each template's text, for a module whose files name templates
// (novox/hq ADR 0349 §2): its templates archive gains the text of every file in it, read back from the packed
// bytes, by its path inside the archive. Resolve reads them into the files' content.
//
// **Read from the archive, proven by its digest.** The module's files/ is packed again, as the build packs it,
// and the bytes are read only when they hash to the digest the build made or took: a fresh build's own archive,
// or a check's build a walk copied by digest without building (novox/hq ADR 0350 §2). Packing is deterministic,
// so one source packs to one digest; a tree that packs to another is not the archive, and its text is refused.
func withTemplateTexts(manifest catalogue.Manifest, within string, built []catalogue.Built) ([]catalogue.Built, error) {
	if !manifest.Templated() {
		return built, nil
	}
	name := catalogue.TemplatesArtifact(manifest)
	at := -1
	for i, b := range built {
		if b.Name == name {
			at = i
		}
	}
	if name == "" || at < 0 {
		return nil, fmt.Errorf("%s names templates and built no archive of %s/ to read them from",
			manifest.Module, catalogue.TemplatesDir)
	}
	body, err := pack(filepath.Join(within, catalogue.TemplatesDir))
	if err != nil {
		return nil, fmt.Errorf("%s: packing %s/ to read its templates back failed: %w", manifest.Module,
			catalogue.TemplatesDir, err)
	}
	sum := sha256.Sum256(body)
	digest := "sha256:" + hex.EncodeToString(sum[:])
	if built[at].Digest != digest {
		return nil, fmt.Errorf("%s: %s/ packs to the digest %s, and the archive %q built or taken is %s: the "+
			"templates are read only from the archive the mesh records", manifest.Module, catalogue.TemplatesDir,
			digest, name, orNone(built[at].Digest))
	}
	texts, err := unpackTexts(body)
	if err != nil {
		return nil, fmt.Errorf("%s: reading the archive %q back failed: %w", manifest.Module, name, err)
	}
	out := append([]catalogue.Built(nil), built...)
	out[at].Texts = texts
	return out, nil
}

// unpackTexts is every file of a packed archive (pack), by its path inside it.
func unpackTexts(body []byte) (map[string]string, error) {
	zipped, err := gzip.NewReader(bytes.NewReader(body))
	if err != nil {
		return nil, err
	}
	defer zipped.Close()
	reader := tar.NewReader(zipped)
	texts := map[string]string{}
	for {
		header, err := reader.Next()
		if errors.Is(err, io.EOF) {
			return texts, nil
		}
		if err != nil {
			return nil, err
		}
		if header.Typeflag != tar.TypeReg {
			continue
		}
		text, err := io.ReadAll(reader)
		if err != nil {
			return nil, err
		}
		texts[header.Name] = string(text)
	}
}

func orNone(digest string) string {
	if digest == "" {
		return "no digest"
	}
	return digest
}