mstore/pkg/repocli/imager.go

/*
 * Copyright 2026 Oleg Borodin <onborodin@gmail.com>
 *
 * This work is published and licensed under a Creative Commons
 * Attribution-NonCommercial-NoDerivatives 4.0 International License.
 *
 * Distribution of this work is permitted, but commercial use and
 * modifications are strictly prohibited.
 */

package repocli

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"

	ocidigest "github.com/opencontainers/go-digest"
	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
)

type Imager struct {
	index ocispec.Index
	place string
}

func NewEmptyImager(place string) *Imager {
	imager := &Imager{
		index: ocispec.Index{
			MediaType: MediaTypeOIIv1,
			Manifests: make([]ocispec.Descriptor, 0),
		},
		place: place,
	}
	imager.index.SchemaVersion = 2
	return imager
}

func NewImagerFromPlace(place string) (*Imager, error) {
	var err error
	imager := &Imager{
		index: ocispec.Index{
			MediaType: MediaTypeOIIv1,
			Manifests: make([]ocispec.Descriptor, 0),
		},
		place: place,
	}
	imager.index.SchemaVersion = 2

	// Read and check layout version
	lpath := filepath.Join(imager.place, ocispec.ImageLayoutFile)
	lfile, err := os.OpenFile(lpath, os.O_RDONLY, 0)
	if err != nil {
		return imager, err
	}
	defer lfile.Close()
	buffer := bytes.NewBuffer(nil)
	if err != nil {
		return imager, err
	}
	_, err = io.Copy(buffer, lfile)
	if err != nil {
		return imager, err
	}
	layout := ocispec.ImageLayout{}
	err = json.Unmarshal(buffer.Bytes(), &layout)
	if err != nil {
		return imager, err
	}
	if layout.Version != ocispec.ImageLayoutVersion {
		err = fmt.Errorf("Unknown layout version: %s", layout.Version)
		return imager, err
	}
	// Read image
	ipath := filepath.Join(imager.place, ocispec.ImageIndexFile)
	ifile, err := os.OpenFile(ipath, os.O_RDONLY, 0)
	if err != nil {
		return imager, err
	}
	defer ifile.Close()
	buffer = bytes.NewBuffer(nil)
	_, err = io.Copy(buffer, ifile)
	if err != nil {
		return imager, err
	}
	err = json.Unmarshal(buffer.Bytes(), &imager.index)
	if err != nil {
		return imager, err
	}
	return imager, err
}

func (ima *Imager) Index() *ocispec.Index {
	return &ima.index
}

func (ima *Imager) ReadManifest(ctx context.Context, digstr string) (bool, string, []byte, error) {
	var exist bool
	var mime string
	var man []byte
	var err error

	digobj, err := ocidigest.Parse(digstr)
	if err != nil {
		return exist, mime, man, err
	}
	for _, descr := range ima.index.Manifests {
		if digstr == descr.Digest.String() {
			mime = descr.MediaType
			exist = true
		}
	}
	if !exist {
		err = errors.New("Manifest not found in index")
		return exist, mime, man, err
	}
	subdir := string(digobj.Algorithm())
	mpath := filepath.Join(ima.place, ocispec.ImageBlobsDir, subdir, digobj.Encoded())
	mfile, err := os.OpenFile(mpath, os.O_RDONLY, 0)
	if err != nil {
		return exist, mime, man, err
	}
	defer mfile.Close()

	buffer := bytes.NewBuffer(nil)
	verifier := digobj.Verifier()
	mwriter := io.MultiWriter(verifier, buffer)
	_, err = io.Copy(mwriter, mfile)
	man = buffer.Bytes()
	if !verifier.Verified() {
		err = errors.New("Mismatch manifest digests")
		return exist, mime, man, err
	}
	return exist, mime, man, err
}

func (ima *Imager) WriteManifest(ctx context.Context, digest, mime string, payload []byte) error {
	err := ima.writeManifest(ctx, digest, mime, payload)
	if err != nil {
		return err
	}
	err = ima.writeIndex(ctx)
	if err != nil {
		return err
	}
	return err
}

func (ima *Imager) writeManifest(ctx context.Context, digest, mime string, payload []byte) error {
	var err error
	digobj, err := ocidigest.Parse(digest)
	if err != nil {
		return err
	}
	subdir := string(digobj.Algorithm())
	blobdir := filepath.Join(ima.place, ocispec.ImageBlobsDir, subdir)
	err = os.MkdirAll(blobdir, 0750)
	if err != nil {
		return err
	}
	mpath := filepath.Join(blobdir, digobj.Encoded())
	mfile, err := os.OpenFile(mpath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0640)
	if err != nil {
		return err
	}
	defer mfile.Close()
	reader := bytes.NewReader(payload)
	verifier := digobj.Verifier()
	mwriter := io.MultiWriter(verifier, mfile)
	recsize, err := io.Copy(mwriter, reader)
	size := int64(len(payload))
	if size != recsize {
		err = errors.New("Mismatch manigest sizes")
		return err
	}
	if !verifier.Verified() {
		err = errors.New("Mismatch manifest digests")
		return err
	}
	descr := ocispec.Descriptor{
		MediaType: mime,
		Digest:    digobj,
		Size:      size,
	}
	ima.index.Manifests = append(ima.index.Manifests, descr)
	return err
}

func (ima *Imager) readIndex(ctx context.Context) (*ocispec.Index, error) {
	// Read index
	var err error
	res := &ocispec.Index{}
	ipath := filepath.Join(ima.place, ocispec.ImageIndexFile)
	ifile, err := os.OpenFile(ipath, os.O_RDONLY, 0)
	if err != nil {
		return res, err
	}
	defer ifile.Close()
	buffer := bytes.NewBuffer(nil)
	_, err = io.Copy(buffer, buffer)
	if err != nil {
		return res, err
	}
	err = json.Unmarshal(buffer.Bytes(), res)
	if err != nil {
		return res, err
	}
	return res, err
}

func (ima *Imager) writeIndex(ctx context.Context) error {
	indexdat, err := json.Marshal(ima.index)
	if err != nil {
		return err
	}
	// Flush index
	ipath := filepath.Join(ima.place, ocispec.ImageIndexFile)
	ifile, err := os.OpenFile(ipath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0640)
	if err != nil {
		return err
	}
	defer ifile.Close()
	reader := bytes.NewReader(indexdat)
	recsize, err := io.Copy(ifile, reader)
	if err != nil {
		return err
	}
	if recsize != int64(len(indexdat)) {
		err = errors.New("Mismatch index sizes")
		return err
	}
	// Flush layout
	lpath := filepath.Join(ima.place, ocispec.ImageLayoutFile)
	lfile, err := os.OpenFile(lpath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0640)
	if err != nil {
		return err
	}
	defer lfile.Close()
	layout := ocispec.ImageLayout{
		Version: ocispec.ImageLayoutVersion,
	}
	layoutdat, err := json.Marshal(layout)
	reader = bytes.NewReader(layoutdat)
	if err != nil {
		return err
	}
	recsize, err = io.Copy(lfile, reader)
	if err != nil {
		return err
	}
	if recsize != int64(len(layoutdat)) {
		err = errors.New("Mismatch layout sizes")
		return err
	}
	return err
}

func (ima *Imager) WriteLayer(ctx context.Context, digest string, size int64, reader io.Reader) error {
	var err error
	digobj, err := ocidigest.Parse(digest)
	if err != nil {
		return err
	}
	subdir := string(digobj.Algorithm())
	blobdir := filepath.Join(ima.place, ocispec.ImageBlobsDir, subdir)
	err = os.MkdirAll(blobdir, 0750)
	if err != nil {
		return err
	}
	fpath := filepath.Join(blobdir, digobj.Encoded())
	file, err := os.OpenFile(fpath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0640)
	if err != nil {
		return err
	}
	verifier := digobj.Verifier()
	mwriter := io.MultiWriter(verifier, file)
	recsize, err := io.Copy(mwriter, reader)
	if size != recsize {
		err = errors.New("Mismatch sizes")
		return err
	}
	if !verifier.Verified() {
		err = errors.New("Mismatch digests")
		return err
	}
	return err
}

func (ima *Imager) ReadLayer(ctx context.Context, digstr string, writer io.Writer) (bool, error) {
	var exist bool
	var err error
	digobj, err := ocidigest.Parse(digstr)
	if err != nil {
		return exist, err
	}
	subdir := string(digobj.Algorithm())
	mpath := filepath.Join(ima.place, ocispec.ImageBlobsDir, subdir, digobj.Encoded())
	stat, err := os.Stat(mpath)
	if err != nil {
		return exist, err
	}
	size := stat.Size()
	mfile, err := os.OpenFile(mpath, os.O_RDONLY, 0)
	if err != nil {
		return exist, err
	}
	defer mfile.Close()

	verifier := digobj.Verifier()
	mwriter := io.MultiWriter(verifier, writer)
	readsize, err := io.Copy(mwriter, mfile)
	if size != readsize {
		err = errors.New("Mismatch layer sizes")
		return exist, err
	}
	if !verifier.Verified() {
		err = errors.New("Mismatch layer digests")
		return exist, err
	}
	exist = true
	return exist, err
}

func (ima *Imager) LayerReader(ctx context.Context, digstr string) (int64, io.ReadCloser, error) {
	var reader io.ReadCloser
	var err error
	var size int64
	digobj, err := ocidigest.Parse(digstr)
	if err != nil {
		return size, reader, err
	}
	subdir := string(digobj.Algorithm())
	mpath := filepath.Join(ima.place, ocispec.ImageBlobsDir, subdir, digobj.Encoded())
	stat, err := os.Stat(mpath)
	if err != nil {
		return size, reader, err
	}
	size = stat.Size()
	mfile, err := os.OpenFile(mpath, os.O_RDONLY, 0)
	if err != nil {
		return size, reader, err
	}
	reader = mfile
	return size, reader, err
}