Propagate compression options to the inline cache export

Co-authored-by: Tonis Tiigi <tonistiigi@gmail.com>
Signed-off-by: Kohei Tokunaga <ktokunaga.mail@gmail.com>

cache/manager_test.go

@@ -14,6 +14,7 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -35,6 +36,7 @@ import (
 	"github.com/moby/buildkit/session"
 	"github.com/moby/buildkit/snapshot"
 	containerdsnapshot "github.com/moby/buildkit/snapshot/containerd"
+	"github.com/moby/buildkit/solver"
 	"github.com/moby/buildkit/util/compression"
 	"github.com/moby/buildkit/util/contentutil"
 	"github.com/moby/buildkit/util/leaseutil"
@@ -1125,7 +1127,9 @@ func TestConversion(t *testing.T) {
 	require.NoError(t, eg.Wait())
 }
 
-func TestGetRemote(t *testing.T) {
+type idxToVariants []map[compression.Type]ocispecs.Descriptor
+
+func TestGetRemotes(t *testing.T) {
 	t.Parallel()
 	// windows fails when lazy blob is being extracted with "invalid windows mount type: 'bind'"
 	if runtime.GOOS != "linux" {
@@ -1251,15 +1255,24 @@ func TestGetRemote(t *testing.T) {
 
 	checkNumBlobs(ctx, t, co.cs, 1)
 
-	// Call GetRemote on all the refs
+	variantsMap := make(map[string]idxToVariants)
+	var variantsMapMu sync.Mutex
+
+	// Call GetRemotes on all the refs
 	eg, egctx := errgroup.WithContext(ctx)
 	for _, ir := range refs {
 		ir := ir.(*immutableRef)
 		for _, compressionType := range []compression.Type{compression.Uncompressed, compression.Gzip, compression.EStargz, compression.Zstd} {
 			compressionType := compressionType
+			compressionopt := solver.CompressionOpt{
+				Type:  compressionType,
+				Force: true,
+			}
 			eg.Go(func() error {
-				remote, err := ir.GetRemote(egctx, true, compressionType, true, nil)
+				remotes, err := ir.GetRemotes(egctx, true, compressionopt, false, nil)
 				require.NoError(t, err)
+				require.Equal(t, 1, len(remotes))
+				remote := remotes[0]
 				refChain := ir.parentRefChain()
 				for i, desc := range remote.Descriptors {
 					switch compressionType {
@@ -1278,6 +1291,21 @@ func TestGetRemote(t *testing.T) {
 					require.Contains(t, expectedContent, dgst, "for %v", compressionType)
 					checkDescriptor(ctx, t, co.cs, desc, compressionType)
 
+					variantsMapMu.Lock()
+					if len(variantsMap[ir.ID()]) == 0 {
+						variantsMap[ir.ID()] = make(idxToVariants, len(remote.Descriptors))
+					}
+					variantsMapMu.Unlock()
+
+					require.Equal(t, len(remote.Descriptors), len(variantsMap[ir.ID()]))
+
+					variantsMapMu.Lock()
+					if variantsMap[ir.ID()][i] == nil {
+						variantsMap[ir.ID()][i] = make(map[compression.Type]ocispecs.Descriptor)
+					}
+					variantsMap[ir.ID()][i][compressionType] = desc
+					variantsMapMu.Unlock()
+
 					r := refChain[i]
 					isLazy, err := r.isLazy(egctx)
 					require.NoError(t, err)
@@ -1318,6 +1346,93 @@ func TestGetRemote(t *testing.T) {
 	})
 	require.NoError(t, err)
 	require.Equal(t, map[digest.Digest]struct{}{}, expectedContent)
+
+	// Check if "all" option returns all available blobs
+	for _, ir := range refs {
+		ir := ir.(*immutableRef)
+		variantsMapMu.Lock()
+		variants, ok := variantsMap[ir.ID()]
+		variantsMapMu.Unlock()
+		require.True(t, ok, ir.ID())
+		for _, compressionType := range []compression.Type{compression.Uncompressed, compression.Gzip, compression.EStargz, compression.Zstd} {
+			compressionType := compressionType
+			compressionopt := solver.CompressionOpt{Type: compressionType}
+			eg.Go(func() error {
+				remotes, err := ir.GetRemotes(egctx, false, compressionopt, true, nil)
+				require.NoError(t, err)
+				require.True(t, len(remotes) > 0, "for %s : %d", compressionType, len(remotes))
+				gotMain, gotVariants := remotes[0], remotes[1:]
+
+				// Check the main blob is compatible with all == false
+				mainOnly, err := ir.GetRemotes(egctx, false, compressionopt, false, nil)
+				require.NoError(t, err)
+				require.Equal(t, 1, len(mainOnly))
+				mainRemote := mainOnly[0]
+				require.Equal(t, len(mainRemote.Descriptors), len(gotMain.Descriptors))
+				for i := 0; i < len(mainRemote.Descriptors); i++ {
+					require.Equal(t, mainRemote.Descriptors[i].Digest, gotMain.Descriptors[i].Digest)
+				}
+
+				// Check all variants are covered
+				checkVariantsCoverage(egctx, t, variants, len(remotes[0].Descriptors)-1, gotVariants, &compressionType)
+				return nil
+			})
+		}
+	}
+	require.NoError(t, eg.Wait())
+}
+
+func checkVariantsCoverage(ctx context.Context, t *testing.T, variants idxToVariants, idx int, remotes []*solver.Remote, expectCompression *compression.Type) {
+	if idx < 0 {
+		for _, r := range remotes {
+			require.Equal(t, len(r.Descriptors), 0)
+		}
+		return
+	}
+
+	// check the contents of the topmost blob of each remote
+	got := make(map[digest.Digest][]*solver.Remote)
+	for _, r := range remotes {
+		require.Equal(t, len(r.Descriptors)-1, idx, "idx = %d", idx)
+
+		// record this variant
+		topmost, lower := r.Descriptors[idx], r.Descriptors[:idx]
+		got[topmost.Digest] = append(got[topmost.Digest], &solver.Remote{Descriptors: lower, Provider: r.Provider})
+
+		// check the contents
+		r, err := r.Provider.ReaderAt(ctx, topmost)
+		require.NoError(t, err)
+		dgstr := digest.Canonical.Digester()
+		_, err = io.Copy(dgstr.Hash(), io.NewSectionReader(r, 0, topmost.Size))
+		require.NoError(t, err)
+		require.NoError(t, r.Close())
+		require.Equal(t, dgstr.Digest(), topmost.Digest)
+	}
+
+	// check the lowers as well
+	eg, egctx := errgroup.WithContext(ctx)
+	for _, lowers := range got {
+		lowers := lowers
+		eg.Go(func() error {
+			checkVariantsCoverage(egctx, t, variants, idx-1, lowers, nil) // expect all compression variants
+			return nil
+		})
+	}
+	require.NoError(t, eg.Wait())
+
+	// check the coverage of the variants
+	targets := variants[idx]
+	if expectCompression != nil {
+		c, ok := variants[idx][*expectCompression]
+		require.True(t, ok, "idx = %d, compression = %q, variants = %+v, got = %+v", idx, *expectCompression, variants[idx], got)
+		targets = map[compression.Type]ocispecs.Descriptor{*expectCompression: c}
+	}
+	for c, d := range targets {
+		_, ok := got[d.Digest]
+		require.True(t, ok, "idx = %d, compression = %q, want = %+v, got = %+v", idx, c, d, got)
+		delete(got, d.Digest)
+	}
+	require.Equal(t, 0, len(got))
 }
 
 func checkInfo(ctx context.Context, t *testing.T, cs content.Store, info content.Info) {

cache/refs.go

@@ -42,7 +42,7 @@ type ImmutableRef interface {
 	Clone() ImmutableRef
 
 	Extract(ctx context.Context, s session.Group) error // +progress
-	GetRemote(ctx context.Context, createIfNeeded bool, compressionType compression.Type, forceCompression bool, s session.Group) (*solver.Remote, error)
+	GetRemotes(ctx context.Context, createIfNeeded bool, compressionopt solver.CompressionOpt, all bool, s session.Group) ([]*solver.Remote, error)
 }
 
 type MutableRef interface {
@@ -376,9 +376,29 @@ func compressionVariantDigestLabel(compressionType compression.Type) string {
 	return compressionVariantDigestLabelPrefix + compressionType.String()
 }
 
+func getCompressionVariants(ctx context.Context, cs content.Store, dgst digest.Digest) (res []compression.Type, _ error) {
+	info, err := cs.Info(ctx, dgst)
+	if errors.Is(err, errdefs.ErrNotFound) {
+		return nil, nil
+	} else if err != nil {
+		return nil, err
+	}
+	for k := range info.Labels {
+		if strings.HasPrefix(k, compressionVariantDigestLabelPrefix) {
+			if t := compression.Parse(strings.TrimPrefix(k, compressionVariantDigestLabelPrefix)); t != compression.UnknownCompression {
+				res = append(res, t)
+			}
+		}
+	}
+	return
+}
+
 func (sr *immutableRef) getCompressionBlob(ctx context.Context, compressionType compression.Type) (ocispecs.Descriptor, error) {
-	cs := sr.cm.ContentStore
+	return getCompressionVariantBlob(ctx, sr.cm.ContentStore, sr.getBlob(), compressionType)
-	info, err := cs.Info(ctx, sr.getBlob())
+}
+
+func getCompressionVariantBlob(ctx context.Context, cs content.Store, dgst digest.Digest, compressionType compression.Type) (ocispecs.Descriptor, error) {
+	info, err := cs.Info(ctx, dgst)
 	if err != nil {
 		return ocispecs.Descriptor{}, err
 	}

cache/remote.go

@@ -25,16 +25,122 @@ type Unlazier interface {
 	Unlazy(ctx context.Context) error
 }
 
-// GetRemote gets a *solver.Remote from content store for this ref (potentially pulling lazily).
+// GetRemotes gets []*solver.Remote from content store for this ref (potentially pulling lazily).
-// Note: Use WorkerRef.GetRemote instead as moby integration requires custom GetRemote implementation.
+// Compressionopt can be used to specify the compression type of blobs. If Force is true, the compression
-func (sr *immutableRef) GetRemote(ctx context.Context, createIfNeeded bool, compressionType compression.Type, forceCompression bool, s session.Group) (*solver.Remote, error) {
+// type is applied to all blobs in the chain. If Force is false, it's applied only to the newly created
+// layers. If all is true, all available chains that has the specified compression type of topmost blob are
+// appended to the result.
+// Note: Use WorkerRef.GetRemotes instead as moby integration requires custom GetRemotes implementation.
+func (sr *immutableRef) GetRemotes(ctx context.Context, createIfNeeded bool, compressionopt solver.CompressionOpt, all bool, s session.Group) ([]*solver.Remote, error) {
 	ctx, done, err := leaseutil.WithLease(ctx, sr.cm.LeaseManager, leaseutil.MakeTemporary)
 	if err != nil {
 		return nil, err
 	}
 	defer done(ctx)
 
-	err = sr.computeBlobChain(ctx, createIfNeeded, compressionType, forceCompression, s)
+	// fast path if compression variants aren't required
+	// NOTE: compressionopt is applied only to *newly created layers* if Force != true.
+	remote, err := sr.getRemote(ctx, createIfNeeded, compressionopt, s)
+	if err != nil {
+		return nil, err
+	}
+	if !all || compressionopt.Force || len(remote.Descriptors) == 0 {
+		return []*solver.Remote{remote}, nil // early return if compression variants aren't required
+	}
+
+	// Search all available remotes that has the topmost blob with the specified
+	// compression with all combination of copmressions
+	res := []*solver.Remote{remote}
+	topmost, parentChain := remote.Descriptors[len(remote.Descriptors)-1], remote.Descriptors[:len(remote.Descriptors)-1]
+	vDesc, err := getCompressionVariantBlob(ctx, sr.cm.ContentStore, topmost.Digest, compressionopt.Type)
+	if err != nil {
+		return res, nil // compression variant doesn't exist. return the main blob only.
+	}
+
+	var variants []*solver.Remote
+	if len(parentChain) == 0 {
+		variants = append(variants, &solver.Remote{
+			Descriptors: []ocispecs.Descriptor{vDesc},
+			Provider:    sr.cm.ContentStore,
+		})
+	} else {
+		// get parents with all combination of all available compressions.
+		parents, err := getAvailableBlobs(ctx, sr.cm.ContentStore, &solver.Remote{
+			Descriptors: parentChain,
+			Provider:    remote.Provider,
+		})
+		if err != nil {
+			return nil, err
+		}
+		variants = appendRemote(parents, vDesc, sr.cm.ContentStore)
+	}
+
+	// Return the main remote and all its compression variants.
+	// NOTE: Because compressionopt is applied only to *newly created layers* in the main remote (i.e. res[0]),
+	//       it's possible that the main remote doesn't contain any blobs of the compressionopt.Type.
+	//       The topmost blob of the variants (res[1:]) is guaranteed to be the compressionopt.Type.
+	res = append(res, variants...)
+	return res, nil
+}
+
+func appendRemote(parents []*solver.Remote, desc ocispecs.Descriptor, p content.Provider) (res []*solver.Remote) {
+	for _, pRemote := range parents {
+		provider := contentutil.NewMultiProvider(pRemote.Provider)
+		provider.Add(desc.Digest, p)
+		res = append(res, &solver.Remote{
+			Descriptors: append(pRemote.Descriptors, desc),
+			Provider:    provider,
+		})
+	}
+	return
+}
+
+func getAvailableBlobs(ctx context.Context, cs content.Store, chain *solver.Remote) ([]*solver.Remote, error) {
+	if len(chain.Descriptors) == 0 {
+		return nil, nil
+	}
+	target, parentChain := chain.Descriptors[len(chain.Descriptors)-1], chain.Descriptors[:len(chain.Descriptors)-1]
+	parents, err := getAvailableBlobs(ctx, cs, &solver.Remote{
+		Descriptors: parentChain,
+		Provider:    chain.Provider,
+	})
+	if err != nil {
+		return nil, err
+	}
+	compressions, err := getCompressionVariants(ctx, cs, target.Digest)
+	if err != nil {
+		return nil, err
+	}
+	var res []*solver.Remote
+	for _, c := range compressions {
+		desc, err := getCompressionVariantBlob(ctx, cs, target.Digest, c)
+		if err != nil {
+			return nil, err
+		}
+		if len(parents) == 0 { // bottommost ref
+			res = append(res, &solver.Remote{
+				Descriptors: []ocispecs.Descriptor{desc},
+				Provider:    cs,
+			})
+			continue
+		}
+		res = append(res, appendRemote(parents, desc, cs)...)
+	}
+	if len(res) == 0 {
+		// no available compression blobs for this blob. return the original blob.
+		if len(parents) == 0 { // bottommost ref
+			return []*solver.Remote{chain}, nil
+		}
+		return appendRemote(parents, target, chain.Provider), nil
+	}
+	return res, nil
+}
+
+func (sr *immutableRef) getRemote(ctx context.Context, createIfNeeded bool, compressionopt solver.CompressionOpt, s session.Group) (*solver.Remote, error) {
+	compressionType := compressionopt.Type
+	forceCompression := compressionopt.Force
+
+	err := sr.computeBlobChain(ctx, createIfNeeded, compressionType, forceCompression, s)
 	if err != nil {
 		return nil, err
 	}

cache/remotecache/v1/cachestorage.go

@@ -267,9 +267,25 @@ func (cs *cacheResultStorage) Load(ctx context.Context, res solver.CacheResult)
 	return worker.NewWorkerRefResult(ref, cs.w), nil
 }
 
-func (cs *cacheResultStorage) LoadRemote(ctx context.Context, res solver.CacheResult, _ session.Group) (*solver.Remote, error) {
+func (cs *cacheResultStorage) LoadRemotes(ctx context.Context, res solver.CacheResult, compressionopts *solver.CompressionOpt, _ session.Group) ([]*solver.Remote, error) {
 	if r := cs.byResultID(res.ID); r != nil && r.result != nil {
-		return r.result, nil
+		if compressionopts == nil {
+			return []*solver.Remote{r.result}, nil
+		}
+		// Any of blobs in the remote must meet the specified compression option.
+		match := false
+		for _, desc := range r.result.Descriptors {
+			m := compressionopts.Type.IsMediaType(desc.MediaType)
+			match = match || m
+			if compressionopts.Force && !m {
+				match = false
+				break
+			}
+		}
+		if match {
+			return []*solver.Remote{r.result}, nil
+		}
+		return nil, nil // return nil as it's best effort.
 	}
 	return nil, errors.WithStack(solver.ErrNotFound)
 }

client/client_test.go

@@ -2231,6 +2231,12 @@ func testBuildExportZstd(t *testing.T, sb integration.Sandbox) {
 				},
 			},
 		},
+		// compression option should work even with inline cache exports
+		CacheExports: []CacheOptionsEntry{
+			{
+				Type: "inline",
+			},
+		},
 	}, nil)
 	require.NoError(t, err)
 
@@ -3034,6 +3040,50 @@ func testBasicInlineCacheImportExport(t *testing.T, sb integration.Sandbox) {
 
 	checkAllRemoved(t, c, sb)
 
+	// Export the cache again with compression
+	resp, err = c.Solve(sb.Context(), def, SolveOpt{
+		// specifying inline cache exporter is needed for reproducing containerimage.digest
+		// (not needed for reproducing rootfs/unique)
+		Exports: []ExportEntry{
+			{
+				Type: ExporterImage,
+				Attrs: map[string]string{
+					"name":              target,
+					"push":              "true",
+					"compression":       "uncompressed", // inline cache should work with compression
+					"force-compression": "true",
+				},
+			},
+		},
+		CacheExports: []CacheOptionsEntry{
+			{
+				Type: "inline",
+			},
+		},
+		CacheImports: []CacheOptionsEntry{
+			{
+				Type: "registry",
+				Attrs: map[string]string{
+					"ref": target,
+				},
+			},
+		},
+	}, nil)
+	require.NoError(t, err)
+
+	dgst2uncompress, ok := resp.ExporterResponse[exptypes.ExporterImageDigestKey]
+	require.Equal(t, ok, true)
+
+	// dgst2uncompress != dgst, because the compression type is different
+	unique2uncompress, err := readFileInImage(sb.Context(), c, target+"@"+dgst2uncompress, "/unique")
+	require.NoError(t, err)
+	require.EqualValues(t, unique, unique2uncompress)
+
+	err = c.Prune(sb.Context(), nil, PruneAll)
+	require.NoError(t, err)
+
+	checkAllRemoved(t, c, sb)
+
 	resp, err = c.Solve(sb.Context(), def, SolveOpt{
 		Exports: []ExportEntry{
 			{

exporter/containerimage/export.go

@@ -19,6 +19,7 @@ import (
 	"github.com/moby/buildkit/exporter/containerimage/exptypes"
 	"github.com/moby/buildkit/session"
 	"github.com/moby/buildkit/snapshot"
+	"github.com/moby/buildkit/solver"
 	"github.com/moby/buildkit/util/buildinfo"
 	"github.com/moby/buildkit/util/compression"
 	"github.com/moby/buildkit/util/contentutil"
@@ -207,6 +208,15 @@ func (e *imageExporterInstance) Name() string {
 	return "exporting to image"
 }
 
+func (e *imageExporterInstance) Config() exporter.Config {
+	return exporter.Config{
+		Compression: solver.CompressionOpt{
+			Type:  e.layerCompression,
+			Force: e.forceCompression,
+		},
+	}
+}
+
 func (e *imageExporterInstance) Export(ctx context.Context, src exporter.Source, sessionID string) (map[string]string, error) {
 	if src.Metadata == nil {
 		src.Metadata = make(map[string][]byte)
@@ -287,11 +297,16 @@ func (e *imageExporterInstance) Export(ctx context.Context, src exporter.Source,
 			if e.push {
 				annotations := map[digest.Digest]map[string]string{}
 				mprovider := contentutil.NewMultiProvider(e.opt.ImageWriter.ContentStore())
+				compressionopt := solver.CompressionOpt{
+					Type:  e.layerCompression,
+					Force: e.forceCompression,
+				}
 				if src.Ref != nil {
-					remote, err := src.Ref.GetRemote(ctx, false, e.layerCompression, e.forceCompression, session.NewGroup(sessionID))
+					remotes, err := src.Ref.GetRemotes(ctx, false, compressionopt, false, session.NewGroup(sessionID))
 					if err != nil {
 						return nil, err
 					}
+					remote := remotes[0]
 					for _, desc := range remote.Descriptors {
 						mprovider.Add(desc.Digest, remote.Provider)
 						addAnnotations(annotations, desc)
@@ -299,10 +314,11 @@ func (e *imageExporterInstance) Export(ctx context.Context, src exporter.Source,
 				}
 				if len(src.Refs) > 0 {
 					for _, r := range src.Refs {
-						remote, err := r.GetRemote(ctx, false, e.layerCompression, e.forceCompression, session.NewGroup(sessionID))
+						remotes, err := r.GetRemotes(ctx, false, compressionopt, false, session.NewGroup(sessionID))
 						if err != nil {
 							return nil, err
 						}
+						remote := remotes[0]
 						for _, desc := range remote.Descriptors {
 							mprovider.Add(desc.Digest, remote.Provider)
 							addAnnotations(annotations, desc)
@@ -352,10 +368,15 @@ func (e *imageExporterInstance) unpackImage(ctx context.Context, img images.Imag
 		}
 	}
 
-	remote, err := topLayerRef.GetRemote(ctx, true, e.layerCompression, e.forceCompression, s)
+	compressionopt := solver.CompressionOpt{
+		Type:  e.layerCompression,
+		Force: e.forceCompression,
+	}
+	remotes, err := topLayerRef.GetRemotes(ctx, true, compressionopt, false, s)
 	if err != nil {
 		return err
 	}
+	remote := remotes[0]
 
 	// ensure the content for each layer exists locally in case any are lazy
 	if unlazier, ok := remote.Provider.(cache.Unlazier); ok {

exporter/containerimage/writer.go

@@ -175,6 +175,10 @@ func (ic *ImageWriter) exportLayers(ctx context.Context, compressionType compres
 	layersDone := oneOffProgress(ctx, "exporting layers")
 
 	out := make([]solver.Remote, len(refs))
+	compressionopt := solver.CompressionOpt{
+		Type:  compressionType,
+		Force: forceCompression,
+	}
 
 	for i, ref := range refs {
 		func(i int, ref cache.ImmutableRef) {
@@ -182,10 +186,11 @@ func (ic *ImageWriter) exportLayers(ctx context.Context, compressionType compres
 				return
 			}
 			eg.Go(func() error {
-				remote, err := ref.GetRemote(ctx, true, compressionType, forceCompression, s)
+				remotes, err := ref.GetRemotes(ctx, true, compressionopt, false, s)
 				if err != nil {
 					return err
 				}
+				remote := remotes[0]
 				out[i] = *remote
 				return nil
 			})

exporter/exporter.go

@@ -4,6 +4,7 @@ import (
 	"context"
 
 	"github.com/moby/buildkit/cache"
+	"github.com/moby/buildkit/solver"
 )
 
 type Exporter interface {
@@ -12,6 +13,7 @@ type Exporter interface {
 
 type ExporterInstance interface {
 	Name() string
+	Config() Config
 	Export(ctx context.Context, src Source, sessionID string) (map[string]string, error)
 }
 
@@ -20,3 +22,7 @@ type Source struct {
 	Refs     map[string]cache.ImmutableRef
 	Metadata map[string][]byte
 }
+
+type Config struct {
+	Compression solver.CompressionOpt
+}

exporter/local/export.go

@@ -46,6 +46,10 @@ func (e *localExporterInstance) Name() string {
 	return "exporting to client"
 }
 
+func (e *localExporter) Config() exporter.Config {
+	return exporter.Config{}
+}
+
 func (e *localExporterInstance) Export(ctx context.Context, inp exporter.Source, sessionID string) (map[string]string, error) {
 
 	timeoutCtx, cancel := context.WithTimeout(ctx, 5*time.Second)

exporter/oci/export.go

@@ -15,6 +15,7 @@ import (
 	"github.com/moby/buildkit/exporter/containerimage/exptypes"
 	"github.com/moby/buildkit/session"
 	"github.com/moby/buildkit/session/filesync"
+	"github.com/moby/buildkit/solver"
 	"github.com/moby/buildkit/util/buildinfo"
 	"github.com/moby/buildkit/util/compression"
 	"github.com/moby/buildkit/util/contentutil"
@@ -144,6 +145,15 @@ func (e *imageExporterInstance) Name() string {
 	return "exporting to oci image format"
 }
 
+func (e *imageExporterInstance) Config() exporter.Config {
+	return exporter.Config{
+		Compression: solver.CompressionOpt{
+			Type:  e.layerCompression,
+			Force: e.forceCompression,
+		},
+	}
+}
+
 func (e *imageExporterInstance) Export(ctx context.Context, src exporter.Source, sessionID string) (map[string]string, error) {
 	if e.opt.Variant == VariantDocker && len(src.Refs) > 0 {
 		return nil, errors.Errorf("docker exporter does not currently support exporting manifest lists")
@@ -227,11 +237,16 @@ func (e *imageExporterInstance) Export(ctx context.Context, src exporter.Source,
 	}
 
 	mprovider := contentutil.NewMultiProvider(e.opt.ImageWriter.ContentStore())
+	compressionopt := solver.CompressionOpt{
+		Type:  e.layerCompression,
+		Force: e.forceCompression,
+	}
 	if src.Ref != nil {
-		remote, err := src.Ref.GetRemote(ctx, false, e.layerCompression, e.forceCompression, session.NewGroup(sessionID))
+		remotes, err := src.Ref.GetRemotes(ctx, false, compressionopt, false, session.NewGroup(sessionID))
 		if err != nil {
 			return nil, err
 		}
+		remote := remotes[0]
 		// unlazy before tar export as the tar writer does not handle
 		// layer blobs in parallel (whereas unlazy does)
 		if unlazier, ok := remote.Provider.(cache.Unlazier); ok {
@@ -245,10 +260,11 @@ func (e *imageExporterInstance) Export(ctx context.Context, src exporter.Source,
 	}
 	if len(src.Refs) > 0 {
 		for _, r := range src.Refs {
-			remote, err := r.GetRemote(ctx, false, e.layerCompression, e.forceCompression, session.NewGroup(sessionID))
+			remotes, err := r.GetRemotes(ctx, false, compressionopt, false, session.NewGroup(sessionID))
 			if err != nil {
 				return nil, err
 			}
+			remote := remotes[0]
 			if unlazier, ok := remote.Provider.(cache.Unlazier); ok {
 				if err := unlazier.Unlazy(ctx); err != nil {
 					return nil, err

exporter/tar/export.go

@@ -45,6 +45,10 @@ func (e *localExporterInstance) Name() string {
 	return "exporting to client"
 }
 
+func (e *localExporterInstance) Config() exporter.Config {
+	return exporter.Config{}
+}
+
 func (e *localExporterInstance) Export(ctx context.Context, inp exporter.Source, sessionID string) (map[string]string, error) {
 	var defers []func()
 

solver/cachestorage.go

@@ -47,6 +47,6 @@ type CacheInfoLink struct {
 type CacheResultStorage interface {
 	Save(Result, time.Time) (CacheResult, error)
 	Load(ctx context.Context, res CacheResult) (Result, error)
-	LoadRemote(ctx context.Context, res CacheResult, s session.Group) (*Remote, error)
+	LoadRemotes(ctx context.Context, res CacheResult, compression *CompressionOpt, s session.Group) ([]*Remote, error)
 	Exists(id string) bool
 }

solver/exporter.go

@@ -78,7 +78,8 @@ func (e *exporter) ExportTo(ctx context.Context, t CacheExporterTarget, opt Cach
 		selector digest.Digest
 	}
 
-	rec := t.Add(rootKey(e.k.Digest(), e.k.Output()))
+	recKey := rootKey(e.k.Digest(), e.k.Output())
+	rec := t.Add(recKey)
 	allRec := []CacheExporterRecord{rec}
 
 	addRecord := true
@@ -93,6 +94,8 @@ func (e *exporter) ExportTo(ctx context.Context, t CacheExporterTarget, opt Cach
 
 	var remote *Remote
 	if v := e.record; v != nil && len(e.k.Deps()) > 0 && addRecord {
+		var variants []CacheExporterRecord
+
 		cm := v.cacheManager
 		key := cm.getID(v.key)
 		res, err := cm.backend.Load(key, v.ID)
@@ -100,21 +103,41 @@ func (e *exporter) ExportTo(ctx context.Context, t CacheExporterTarget, opt Cach
 			return nil, err
 		}
 
-		remote, err = cm.results.LoadRemote(ctx, res, opt.Session)
+		remotes, err := cm.results.LoadRemotes(ctx, res, opt.CompressionOpt, opt.Session)
 		if err != nil {
 			return nil, err
 		}
+		if len(remotes) > 0 {
+			remote, remotes = remotes[0], remotes[1:] // pop the first element
+		}
+		if opt.CompressionOpt != nil {
+			for _, r := range remotes { // record all remaining remotes as well
+				rec := t.Add(recKey)
+				rec.AddResult(v.CreatedAt, r)
+				variants = append(variants, rec)
+			}
+		}
 
-		if remote == nil && opt.Mode != CacheExportModeRemoteOnly {
+		if (remote == nil || opt.CompressionOpt != nil) && opt.Mode != CacheExportModeRemoteOnly {
 			res, err := cm.results.Load(ctx, res)
 			if err != nil {
 				return nil, err
 			}
-			remote, err = opt.Convert(ctx, res)
+			remotes, err := opt.ResolveRemotes(ctx, res)
 			if err != nil {
 				return nil, err
 			}
 			res.Release(context.TODO())
+			if remote == nil {
+				remote, remotes = remotes[0], remotes[1:] // pop the first element
+			}
+			if opt.CompressionOpt != nil {
+				for _, r := range remotes { // record all remaining remotes as well
+					rec := t.Add(recKey)
+					rec.AddResult(v.CreatedAt, r)
+					variants = append(variants, rec)
+				}
+			}
 		}
 
 		if remote != nil {
@@ -122,6 +145,7 @@ func (e *exporter) ExportTo(ctx context.Context, t CacheExporterTarget, opt Cach
 				rec.AddResult(v.CreatedAt, remote)
 			}
 		}
+		allRec = append(allRec, variants...)
 	}
 
 	if remote != nil && opt.Mode == CacheExportModeMin {
@@ -154,15 +178,17 @@ func (e *exporter) ExportTo(ctx context.Context, t CacheExporterTarget, opt Cach
 		}
 	}
 
-	for i, srcs := range srcs {
+	for _, rec := range allRec {
-		for _, src := range srcs {
+		for i, srcs := range srcs {
-			rec.LinkFrom(src.r, i, src.selector.String())
+			for _, src := range srcs {
+				rec.LinkFrom(src.r, i, src.selector.String())
+			}
 		}
-	}
 
-	for cm, id := range e.k.ids {
+		for cm, id := range e.k.ids {
-		if _, err := addBacklinks(t, rec, cm, id, bkm); err != nil {
+			if _, err := addBacklinks(t, rec, cm, id, bkm); err != nil {
-			return nil, err
+				return nil, err
+			}
 		}
 	}
 

solver/llbsolver/result.go

@@ -8,7 +8,6 @@ import (
 	"github.com/moby/buildkit/cache/contenthash"
 	"github.com/moby/buildkit/session"
 	"github.com/moby/buildkit/solver"
-	"github.com/moby/buildkit/util/compression"
 	"github.com/moby/buildkit/worker"
 	digest "github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
@@ -82,13 +81,13 @@ func NewContentHashFunc(selectors []Selector) solver.ResultBasedCacheFunc {
 	}
 }
 
-func workerRefConverter(g session.Group) func(ctx context.Context, res solver.Result) (*solver.Remote, error) {
+func workerRefResolver(compressionopt solver.CompressionOpt, all bool, g session.Group) func(ctx context.Context, res solver.Result) ([]*solver.Remote, error) {
-	return func(ctx context.Context, res solver.Result) (*solver.Remote, error) {
+	return func(ctx context.Context, res solver.Result) ([]*solver.Remote, error) {
 		ref, ok := res.Sys().(*worker.WorkerRef)
 		if !ok {
 			return nil, errors.Errorf("invalid result: %T", res.Sys())
 		}
 
-		return ref.GetRemote(ctx, true, compression.Default, false, g)
+		return ref.GetRemotes(ctx, true, compressionopt, all, g)
 	}
 }

solver/llbsolver/solver.go

@@ -183,7 +183,7 @@ func (s *Solver) Solve(ctx context.Context, id string, sessionID string, req fro
 				inp.Metadata[exptypes.ExporterBuildInfo] = dtbi
 			}
 
-			dtic, err := inlineCache(ctx, exp.CacheExporter, r, session.NewGroup(sessionID))
+			dtic, err := inlineCache(ctx, exp.CacheExporter, r, e.Config().Compression, session.NewGroup(sessionID))
 			if err != nil {
 				return nil, err
 			}
@@ -215,7 +215,7 @@ func (s *Solver) Solve(ctx context.Context, id string, sessionID string, req fro
 						inp.Metadata[fmt.Sprintf("%s/%s", exptypes.ExporterBuildInfo, k)] = dtbi
 					}
 
-					dtic, err := inlineCache(ctx, exp.CacheExporter, r, session.NewGroup(sessionID))
+					dtic, err := inlineCache(ctx, exp.CacheExporter, r, e.Config().Compression, session.NewGroup(sessionID))
 					if err != nil {
 						return nil, err
 					}
@@ -247,7 +247,9 @@ func (s *Solver) Solve(ctx context.Context, id string, sessionID string, req fro
 				}
 				// all keys have same export chain so exporting others is not needed
 				_, err = r.CacheKeys()[0].Exporter.ExportTo(ctx, e, solver.CacheExportOpt{
-					Convert: workerRefConverter(g),
+					ResolveRemotes: workerRefResolver(solver.CompressionOpt{
+						Type: compression.Default, // TODO: make configurable
+					}, false, g),
 					Mode:    exp.CacheExportMode,
 					Session: g,
 				})
@@ -286,7 +288,7 @@ func (s *Solver) Solve(ctx context.Context, id string, sessionID string, req fro
 	}, nil
 }
 
-func inlineCache(ctx context.Context, e remotecache.Exporter, res solver.CachedResult, g session.Group) ([]byte, error) {
+func inlineCache(ctx context.Context, e remotecache.Exporter, res solver.CachedResult, compressionopt solver.CompressionOpt, g session.Group) ([]byte, error) {
 	if efl, ok := e.(interface {
 		ExportForLayers([]digest.Digest) ([]byte, error)
 	}); ok {
@@ -295,10 +297,11 @@ func inlineCache(ctx context.Context, e remotecache.Exporter, res solver.CachedR
 			return nil, errors.Errorf("invalid reference: %T", res.Sys())
 		}
 
-		remote, err := workerRef.GetRemote(ctx, true, compression.Default, false, g)
+		remotes, err := workerRef.GetRemotes(ctx, true, compressionopt, false, g)
-		if err != nil || remote == nil {
+		if err != nil || len(remotes) == 0 {
 			return nil, nil
 		}
+		remote := remotes[0]
 
 		digests := make([]digest.Digest, 0, len(remote.Descriptors))
 		for _, desc := range remote.Descriptors {
@@ -306,9 +309,10 @@ func inlineCache(ctx context.Context, e remotecache.Exporter, res solver.CachedR
 		}
 
 		if _, err := res.CacheKeys()[0].Exporter.ExportTo(ctx, e, solver.CacheExportOpt{
-			Convert: workerRefConverter(g),
+			ResolveRemotes: workerRefResolver(compressionopt, true, g), // load as many compression blobs as possible
-			Mode:    solver.CacheExportModeMin,
+			Mode:           solver.CacheExportModeMin,
-			Session: g,
+			Session:        g,
+			CompressionOpt: &compressionopt, // cache possible compression variants
 		}); err != nil {
 			return nil, err
 		}

solver/memorycachestorage.go

@@ -298,7 +298,7 @@ func (s *inMemoryResultStore) Load(ctx context.Context, res CacheResult) (Result
 	return v.(Result), nil
 }
 
-func (s *inMemoryResultStore) LoadRemote(_ context.Context, _ CacheResult, _ session.Group) (*Remote, error) {
+func (s *inMemoryResultStore) LoadRemotes(_ context.Context, _ CacheResult, _ *CompressionOpt, _ session.Group) ([]*Remote, error) {
 	return nil, nil
 }
 

solver/scheduler_test.go

@@ -3789,11 +3789,11 @@ func testExporterOpts(all bool) CacheExportOpt {
 		mode = CacheExportModeMax
 	}
 	return CacheExportOpt{
-		Convert: func(ctx context.Context, res Result) (*Remote, error) {
+		ResolveRemotes: func(ctx context.Context, res Result) ([]*Remote, error) {
 			if dr, ok := res.Sys().(*dummyResult); ok {
-				return &Remote{Descriptors: []ocispecs.Descriptor{{
+				return []*Remote{{Descriptors: []ocispecs.Descriptor{{
 					Annotations: map[string]string{"value": fmt.Sprintf("%d", dr.intValue)},
-				}}}, nil
+				}}}}, nil
 			}
 			return nil, nil
 		},

solver/types.go

@@ -7,6 +7,7 @@ import (
 	"github.com/containerd/containerd/content"
 	"github.com/moby/buildkit/session"
 	"github.com/moby/buildkit/solver/pb"
+	"github.com/moby/buildkit/util/compression"
 	digest "github.com/opencontainers/go-digest"
 	ocispecs "github.com/opencontainers/image-spec/specs-go/v1"
 )
@@ -93,12 +94,21 @@ const (
 
 // CacheExportOpt defines options for exporting build cache
 type CacheExportOpt struct {
-	// Convert can convert a build result to transferable object
+	// ResolveRemotes can convert a build result to transferable objects
-	Convert func(context.Context, Result) (*Remote, error)
+	ResolveRemotes func(context.Context, Result) ([]*Remote, error)
 	// Mode defines a cache export algorithm
 	Mode CacheExportMode
 	// Session is the session group to client (for auth credentials etc)
 	Session session.Group
+	// CompressionOpt is an option to specify the compression of the object to load.
+	// If specified, all objects that meet the option will be cached.
+	CompressionOpt *CompressionOpt
+}
+
+// CompressionOpt is compression information of a blob
+type CompressionOpt struct {
+	Type  compression.Type
+	Force bool
 }
 
 // CacheExporter can export the artifacts of the build chain

util/compression/compression.go

@@ -41,6 +41,21 @@ const (
 
 var Default = Gzip
 
+func Parse(t string) Type {
+	switch t {
+	case "uncompressed":
+		return Uncompressed
+	case "gzip":
+		return Gzip
+	case "estargz":
+		return EStargz
+	case "zstd":
+		return Zstd
+	default:
+		return UnknownCompression
+	}
+}
+
 func (ct Type) String() string {
 	switch ct {
 	case Uncompressed:
@@ -69,6 +84,14 @@ func (ct Type) DefaultMediaType() string {
 	}
 }
 
+func (ct Type) IsMediaType(mt string) bool {
+	mt, ok := toOCILayerType[mt]
+	if !ok {
+		return false
+	}
+	return mt == ct.DefaultMediaType()
+}
+
 func FromMediaType(mediaType string) Type {
 	switch toOCILayerType[mediaType] {
 	case ocispecs.MediaTypeImageLayer:

worker/cacheresult.go

@@ -66,7 +66,7 @@ func (s *cacheResultStorage) load(ctx context.Context, id string, hidden bool) (
 	return NewWorkerRefResult(ref, w), nil
 }
 
-func (s *cacheResultStorage) LoadRemote(ctx context.Context, res solver.CacheResult, g session.Group) (*solver.Remote, error) {
+func (s *cacheResultStorage) LoadRemotes(ctx context.Context, res solver.CacheResult, compressionopt *solver.CompressionOpt, g session.Group) ([]*solver.Remote, error) {
 	w, refID, err := s.getWorkerRef(res.ID)
 	if err != nil {
 		return nil, err
@@ -77,11 +77,16 @@ func (s *cacheResultStorage) LoadRemote(ctx context.Context, res solver.CacheRes
 	}
 	defer ref.Release(context.TODO())
 	wref := WorkerRef{ref, w}
-	remote, err := wref.GetRemote(ctx, false, compression.Default, false, g)
+	all := true // load as many compression blobs as possible
+	if compressionopt == nil {
+		compressionopt = &solver.CompressionOpt{Type: compression.Default}
+		all = false
+	}
+	remotes, err := wref.GetRemotes(ctx, false, *compressionopt, all, g)
 	if err != nil {
 		return nil, nil // ignore error. loadRemote is best effort
 	}
-	return remote, nil
+	return remotes, nil
 }
 func (s *cacheResultStorage) Exists(id string) bool {
 	ref, err := s.load(context.TODO(), id, true)

worker/result.go

@@ -6,7 +6,6 @@ import (
 	"github.com/moby/buildkit/cache"
 	"github.com/moby/buildkit/session"
 	"github.com/moby/buildkit/solver"
-	"github.com/moby/buildkit/util/compression"
 )
 
 func NewWorkerRefResult(ref cache.ImmutableRef, worker Worker) solver.Result {
@@ -26,16 +25,16 @@ func (wr *WorkerRef) ID() string {
 	return wr.Worker.ID() + "::" + refID
 }
 
-// GetRemote method abstracts ImmutableRef's GetRemote to allow a Worker to override.
+// GetRemotes method abstracts ImmutableRef's GetRemotes to allow a Worker to override.
 // This is needed for moby integration.
-// Use this method instead of calling ImmutableRef.GetRemote() directly.
+// Use this method instead of calling ImmutableRef.GetRemotes() directly.
-func (wr *WorkerRef) GetRemote(ctx context.Context, createIfNeeded bool, compressionType compression.Type, forceCompression bool, g session.Group) (*solver.Remote, error) {
+func (wr *WorkerRef) GetRemotes(ctx context.Context, createIfNeeded bool, compressionopt solver.CompressionOpt, all bool, g session.Group) ([]*solver.Remote, error) {
 	if w, ok := wr.Worker.(interface {
-		GetRemote(context.Context, cache.ImmutableRef, bool, compression.Type, bool, session.Group) (*solver.Remote, error)
+		GetRemotes(context.Context, cache.ImmutableRef, bool, solver.CompressionOpt, bool, session.Group) ([]*solver.Remote, error)
 	}); ok {
-		return w.GetRemote(ctx, wr.ImmutableRef, createIfNeeded, compressionType, forceCompression, g)
+		return w.GetRemotes(ctx, wr.ImmutableRef, createIfNeeded, compressionopt, all, g)
 	}
-	return wr.ImmutableRef.GetRemote(ctx, createIfNeeded, compressionType, forceCompression, g)
+	return wr.ImmutableRef.GetRemotes(ctx, createIfNeeded, compressionopt, all, g)
 }
 
 type workerRefResult struct {