dep update go-containerregistry

vendor/github.com/google/go-containerregistry/pkg/authn/helper.go

@@ -21,7 +21,7 @@ import (
 	"os/exec"
 	"strings"
 
-	"github.com/google/go-containerregistry/name"
+	"github.com/google/go-containerregistry/pkg/name"
 )
 
 // magicNotFoundMessage is the string that the CLI special cases to mean
@@ -72,17 +72,19 @@ func (h *helper) Authorization() (string, error) {
 
 	var out bytes.Buffer
 	cmd.Stdout = &out
-	if err := h.r.Run(cmd); err != nil {
-		return "", err
-	}
-	output := out.String()
+	err := h.r.Run(cmd)
 
 	// If we see this specific message, it means the domain wasn't found
 	// and we should fall back on anonymous auth.
+	output := out.String()
 	if output == magicNotFoundMessage {
 		return Anonymous.Authorization()
 	}
 
+	if err != nil {
+		return "", err
+	}
+
 	// Any other output should be parsed as JSON and the Username / Secret
 	// fields used for Basic authentication.
 	ho := helperOutput{}

vendor/github.com/google/go-containerregistry/pkg/authn/keychain.go

@@ -24,7 +24,7 @@ import (
 	"path"
 	"runtime"
 
-	"github.com/google/go-containerregistry/name"
+	"github.com/google/go-containerregistry/pkg/name"
 )
 
 // Keychain is an interface for resolving an image reference to a credential.

vendor/github.com/google/go-containerregistry/pkg/v1/empty/image.go

@@ -15,7 +15,7 @@
 package empty
 
 import (
-	"github.com/google/go-containerregistry/v1/random"
+	"github.com/google/go-containerregistry/pkg/v1/random"
 )
 
 // Image is a singleton empty image, think: FROM scratch.

vendor/github.com/google/go-containerregistry/pkg/v1/image.go

@@ -15,7 +15,7 @@
 package v1
 
 import (
-	"github.com/google/go-containerregistry/v1/types"
+	"github.com/google/go-containerregistry/pkg/v1/types"
 )
 
 // Image defines the interface for interacting with an OCI v1 image.

vendor/github.com/google/go-containerregistry/pkg/v1/manifest.go

@@ -18,7 +18,7 @@ import (
 	"encoding/json"
 	"io"
 
-	"github.com/google/go-containerregistry/v1/types"
+	"github.com/google/go-containerregistry/pkg/v1/types"
 )
 
 // Manifest represents the OCI image manifest in a structured way.

vendor/github.com/google/go-containerregistry/pkg/v1/mutate/mutate.go

@@ -16,6 +16,7 @@ package mutate
 
 import (
 	"archive/tar"
+	"bytes"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -23,9 +24,9 @@ import (
 	"path/filepath"
 	"strings"
 
-	"github.com/google/go-containerregistry/v1"
-	"github.com/google/go-containerregistry/v1/partial"
-	"github.com/google/go-containerregistry/v1/types"
+	"github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/partial"
+	"github.com/google/go-containerregistry/pkg/v1/types"
 )
 
 const whiteoutPrefix = ".wh."
@@ -110,10 +111,17 @@ func Append(base v1.Image, adds ...Addendum) (v1.Image, error) {
 	image.configFile.RootFS.DiffIDs = diffIDs
 	image.configFile.History = history
 	image.manifest.Layers = manifestLayers
-	image.manifest.Config.Digest, err = image.ConfigName()
+
+	rcfg, err := image.RawConfigFile()
 	if err != nil {
 		return nil, err
 	}
+	d, sz, err := v1.SHA256(bytes.NewBuffer(rcfg))
+	if err != nil {
+		return nil, err
+	}
+	image.manifest.Config.Digest = d
+	image.manifest.Config.Size = sz
 
 	return image, nil
 }
@@ -136,9 +144,44 @@ func Config(base v1.Image, cfg v1.Config) (v1.Image, error) {
 		Image:      base,
 		manifest:   m.DeepCopy(),
 		configFile: cf.DeepCopy(),
-		diffIDMap:  make(map[v1.Hash]v1.Layer),
 		digestMap:  make(map[v1.Hash]v1.Layer),
 	}
+
+	rcfg, err := image.RawConfigFile()
+	if err != nil {
+		return nil, err
+	}
+	d, sz, err := v1.SHA256(bytes.NewBuffer(rcfg))
+	if err != nil {
+		return nil, err
+	}
+	image.manifest.Config.Digest = d
+	image.manifest.Config.Size = sz
+	return image, nil
+}
+
+// Created mutates the provided v1.Image to have the provided v1.Time
+func CreatedAt(base v1.Image, created v1.Time) (v1.Image, error) {
+	m, err := base.Manifest()
+	if err != nil {
+		return nil, err
+	}
+
+	cf, err := base.ConfigFile()
+	if err != nil {
+		return nil, err
+	}
+
+	cfg := cf.DeepCopy()
+	cfg.Created = created
+
+	image := &image{
+		Image:      base,
+		manifest:   m.DeepCopy(),
+		configFile: cfg,
+		digestMap:  make(map[v1.Hash]v1.Layer),
+	}
+
 	image.manifest.Config.Digest, err = image.ConfigName()
 	if err != nil {
 		return nil, err

vendor/github.com/google/go-containerregistry/pkg/v1/mutate/rebase.go

@@ -17,8 +17,8 @@ package mutate
 import (
 	"fmt"
 
-	"github.com/google/go-containerregistry/v1"
-	"github.com/google/go-containerregistry/v1/empty"
+	"github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/empty"
 )
 
 type RebaseOptions struct {

vendor/github.com/google/go-containerregistry/pkg/v1/partial/compressed.go

@@ -17,8 +17,8 @@ package partial
 import (
 	"io"
 
-	"github.com/google/go-containerregistry/v1"
-	"github.com/google/go-containerregistry/v1/v1util"
+	"github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/v1util"
 )
 
 // CompressedLayer represents the bare minimum interface a natively
@@ -50,6 +50,11 @@ func (ule *compressedLayerExtender) Uncompressed() (io.ReadCloser, error) {
 
 // DiffID implements v1.Layer
 func (ule *compressedLayerExtender) DiffID() (v1.Hash, error) {
+	// If our nested CompressedLayer implements DiffID,
+	// then delegate to it instead.
+	if wdi, ok := ule.CompressedLayer.(WithDiffID); ok {
+		return wdi.DiffID()
+	}
 	r, err := ule.Uncompressed()
 	if err != nil {
 		return v1.Hash{}, err

vendor/github.com/google/go-containerregistry/pkg/v1/partial/image.go

@@ -15,7 +15,7 @@
 package partial
 
 import (
-	"github.com/google/go-containerregistry/v1/types"
+	"github.com/google/go-containerregistry/pkg/v1/types"
 )
 
 // imageCore is the core set of properties without which we cannot build a v1.Image

vendor/github.com/google/go-containerregistry/pkg/v1/partial/uncompressed.go

@@ -19,9 +19,9 @@ import (
 	"io"
 	"sync"
 
-	"github.com/google/go-containerregistry/v1"
-	"github.com/google/go-containerregistry/v1/types"
-	"github.com/google/go-containerregistry/v1/v1util"
+	"github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/types"
+	"github.com/google/go-containerregistry/pkg/v1/v1util"
 )
 
 // UncompressedLayer represents the bare minimum interface a natively

vendor/github.com/google/go-containerregistry/pkg/v1/partial/with.go

@@ -20,8 +20,8 @@ import (
 	"fmt"
 	"io"
 
-	"github.com/google/go-containerregistry/v1"
-	"github.com/google/go-containerregistry/v1/v1util"
+	"github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/v1util"
 )
 
 // WithRawConfigFile defines the subset of v1.Image used by these helper methods
@@ -285,3 +285,8 @@ func UncompressedBlob(b WithBlob, h v1.Hash) (io.ReadCloser, error) {
 	}
 	return v1util.GunzipReadCloser(rc)
 }
+
+// WithDiffID defines the subset of v1.Layer for exposing the DiffID method.
+type WithDiffID interface {
+	DiffID() (v1.Hash, error)
+}

vendor/github.com/google/go-containerregistry/pkg/v1/random/image.go

@@ -22,10 +22,10 @@ import (
 	"io"
 	"time"
 
-	"github.com/google/go-containerregistry/v1"
-	"github.com/google/go-containerregistry/v1/partial"
-	"github.com/google/go-containerregistry/v1/types"
-	"github.com/google/go-containerregistry/v1/v1util"
+	"github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/partial"
+	"github.com/google/go-containerregistry/pkg/v1/types"
+	"github.com/google/go-containerregistry/pkg/v1/v1util"
 )
 
 // uncompressedLayer implements partial.UncompressedLayer from raw bytes.

vendor/github.com/google/go-containerregistry/pkg/v1/remote/delete.go

@@ -20,9 +20,9 @@ import (
 	"net/http"
 	"net/url"
 
-	"github.com/google/go-containerregistry/authn"
-	"github.com/google/go-containerregistry/name"
-	"github.com/google/go-containerregistry/v1/remote/transport"
+	"github.com/google/go-containerregistry/pkg/authn"
+	"github.com/google/go-containerregistry/pkg/name"
+	"github.com/google/go-containerregistry/pkg/v1/remote/transport"
 )
 
 // DeleteOptions are used to expose optional information to guide or

vendor/github.com/google/go-containerregistry/pkg/v1/remote/image.go

@@ -23,13 +23,13 @@ import (
 	"net/url"
 	"sync"
 
-	"github.com/google/go-containerregistry/authn"
-	"github.com/google/go-containerregistry/name"
-	"github.com/google/go-containerregistry/v1"
-	"github.com/google/go-containerregistry/v1/partial"
-	"github.com/google/go-containerregistry/v1/remote/transport"
-	"github.com/google/go-containerregistry/v1/types"
-	"github.com/google/go-containerregistry/v1/v1util"
+	"github.com/google/go-containerregistry/pkg/authn"
+	"github.com/google/go-containerregistry/pkg/name"
+	"github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/partial"
+	"github.com/google/go-containerregistry/pkg/v1/remote/transport"
+	"github.com/google/go-containerregistry/pkg/v1/types"
+	"github.com/google/go-containerregistry/pkg/v1/v1util"
 )
 
 // remoteImage accesses an image from a remote registry
@@ -51,10 +51,19 @@ func Image(ref name.Reference, auth authn.Authenticator, t http.RoundTripper) (v
 	if err != nil {
 		return nil, err
 	}
-	return partial.CompressedToImage(&remoteImage{
+	img, err := partial.CompressedToImage(&remoteImage{
 		ref:    ref,
 		client: &http.Client{Transport: tr},
 	})
+	if err != nil {
+		return nil, err
+	}
+	// Wrap the v1.Layers returned by this v1.Image in a hint for downstream
+	// remote.Write calls to facilitate cross-repo "mounting".
+	return &mountableImage{
+		Image:      img,
+		Repository: ref.Context(),
+	}, nil
 }
 
 func (r *remoteImage) url(resource, identifier string) url.URL {
@@ -191,6 +200,17 @@ func (rl *remoteLayer) Size() (int64, error) {
 	return partial.BlobSize(rl, rl.digest)
 }
 
+// ConfigFile implements partial.WithManifestAndConfigFile so that we can use partial.BlobToDiffID below.
+func (rl *remoteLayer) ConfigFile() (*v1.ConfigFile, error) {
+	return partial.ConfigFile(rl.ri)
+}
+
+// DiffID implements partial.WithDiffID so that we don't recompute a DiffID that we already have
+// available in our ConfigFile.
+func (rl *remoteLayer) DiffID() (v1.Hash, error) {
+	return partial.BlobToDiffID(rl, rl.digest)
+}
+
 // LayerByDigest implements partial.CompressedLayer
 func (r *remoteImage) LayerByDigest(h v1.Hash) (partial.CompressedLayer, error) {
 	return &remoteLayer{

vendor/github.com/google/go-containerregistry/pkg/v1/remote/list.go

@@ -20,9 +20,9 @@ import (
 	"net/http"
 	"net/url"
 
-	"github.com/google/go-containerregistry/authn"
-	"github.com/google/go-containerregistry/name"
-	"github.com/google/go-containerregistry/v1/remote/transport"
+	"github.com/google/go-containerregistry/pkg/authn"
+	"github.com/google/go-containerregistry/pkg/name"
+	"github.com/google/go-containerregistry/pkg/v1/remote/transport"
 )
 
 type Tags struct {

vendor/github.com/google/go-containerregistry/pkg/v1/remote/mount.go

@@ -0,0 +1,77 @@
+// Copyright 2018 Google LLC All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package remote
+
+import (
+	"github.com/google/go-containerregistry/pkg/name"
+	"github.com/google/go-containerregistry/pkg/v1"
+)
+
+// MountableLayer wraps a v1.Layer in a shim that enables the layer to be
+// "mounted" when published to another registry.
+type MountableLayer struct {
+	v1.Layer
+
+	Repository name.Repository
+}
+
+// mountableImage wraps the v1.Layer references returned by the embedded v1.Image
+// in MountableLayer's so that remote.Write might attempt to mount them from their
+// source repository.
+type mountableImage struct {
+	v1.Image
+
+	Repository name.Repository
+}
+
+// Layers implements v1.Image
+func (mi *mountableImage) Layers() ([]v1.Layer, error) {
+	ls, err := mi.Image.Layers()
+	if err != nil {
+		return nil, err
+	}
+	mls := make([]v1.Layer, 0, len(ls))
+	for _, l := range ls {
+		mls = append(mls, &MountableLayer{
+			Layer:      l,
+			Repository: mi.Repository,
+		})
+	}
+	return mls, nil
+}
+
+// LayerByDigest implements v1.Image
+func (mi *mountableImage) LayerByDigest(d v1.Hash) (v1.Layer, error) {
+	l, err := mi.Image.LayerByDigest(d)
+	if err != nil {
+		return nil, err
+	}
+	return &MountableLayer{
+		Layer:      l,
+		Repository: mi.Repository,
+	}, nil
+}
+
+// LayerByDiffID implements v1.Image
+func (mi *mountableImage) LayerByDiffID(d v1.Hash) (v1.Layer, error) {
+	l, err := mi.Image.LayerByDiffID(d)
+	if err != nil {
+		return nil, err
+	}
+	return &MountableLayer{
+		Layer:      l,
+		Repository: mi.Repository,
+	}, nil
+}

vendor/github.com/google/go-containerregistry/pkg/v1/remote/transport/basic.go

@@ -17,7 +17,7 @@ package transport
 import (
 	"net/http"
 
-	"github.com/google/go-containerregistry/authn"
+	"github.com/google/go-containerregistry/pkg/authn"
 )
 
 type basicTransport struct {

vendor/github.com/google/go-containerregistry/pkg/v1/remote/transport/bearer.go

@@ -22,8 +22,8 @@ import (
 	"net/http"
 	"net/url"
 
-	"github.com/google/go-containerregistry/authn"
-	"github.com/google/go-containerregistry/name"
+	"github.com/google/go-containerregistry/pkg/authn"
+	"github.com/google/go-containerregistry/pkg/name"
 )
 
 type bearerTransport struct {

vendor/github.com/google/go-containerregistry/pkg/v1/remote/transport/ping.go

@@ -19,15 +19,15 @@ import (
 	"net/http"
 	"strings"
 
-	"github.com/google/go-containerregistry/name"
+	"github.com/google/go-containerregistry/pkg/name"
 )
 
 type challenge string
 
 const (
-	anonymous challenge = "Anonymous"
-	basic     challenge = "Basic"
-	bearer    challenge = "Bearer"
+	anonymous challenge = "anonymous"
+	basic     challenge = "basic"
+	bearer    challenge = "bearer"
 )
 
 type pingResp struct {
@@ -38,6 +38,10 @@ type pingResp struct {
 	parameters map[string]string
 }
 
+func (c challenge) Canonical() challenge {
+	return challenge(strings.ToLower(string(c)))
+}
+
 func parseChallenge(suffix string) map[string]string {
 	kv := make(map[string]string)
 	for _, token := range strings.Split(suffix, ",") {
@@ -75,13 +79,13 @@ func ping(reg name.Registry, t http.RoundTripper) (*pingResp, error) {
 		if parts := strings.SplitN(wac, " ", 2); len(parts) == 2 {
 			// If there are two parts, then parse the challenge parameters.
 			return &pingResp{
-				challenge:  challenge(strings.Title(parts[0])),
+				challenge:  challenge(parts[0]).Canonical(),
 				parameters: parseChallenge(parts[1]),
 			}, nil
 		}
 		// Otherwise, just return the challenge without parameters.
 		return &pingResp{
-			challenge: challenge(strings.Title(wac)),
+			challenge: challenge(wac).Canonical(),
 		}, nil
 	default:
 		return nil, fmt.Errorf("unrecognized HTTP status: %v", resp.Status)

vendor/github.com/google/go-containerregistry/pkg/v1/remote/transport/scheme.go

@@ -18,7 +18,7 @@ import (
 	"regexp"
 	"strings"
 
-	"github.com/google/go-containerregistry/name"
+	"github.com/google/go-containerregistry/pkg/name"
 )
 
 // Detect more complex forms of local references.

vendor/github.com/google/go-containerregistry/pkg/v1/remote/transport/transport.go

@@ -18,8 +18,8 @@ import (
 	"fmt"
 	"net/http"
 
-	"github.com/google/go-containerregistry/authn"
-	"github.com/google/go-containerregistry/name"
+	"github.com/google/go-containerregistry/pkg/authn"
+	"github.com/google/go-containerregistry/pkg/name"
 )
 
 const (
@@ -49,7 +49,7 @@ func New(reg name.Registry, auth authn.Authenticator, t http.RoundTripper, scope
 		return nil, err
 	}
 
-	switch pr.challenge {
+	switch pr.challenge.Canonical() {
 	case anonymous:
 		return t, nil
 	case basic:

vendor/github.com/google/go-containerregistry/pkg/v1/remote/write.go

@@ -22,17 +22,15 @@ import (
 	"net/http"
 	"net/url"
 
-	"github.com/google/go-containerregistry/authn"
-	"github.com/google/go-containerregistry/name"
-	"github.com/google/go-containerregistry/v1"
-	"github.com/google/go-containerregistry/v1/remote/transport"
+	"github.com/google/go-containerregistry/pkg/authn"
+	"github.com/google/go-containerregistry/pkg/name"
+	"github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/remote/transport"
 )
 
 // WriteOptions are used to expose optional information to guide or
 // control the image write.
 type WriteOptions struct {
-	// The set of paths from which to attempt to mount blobs.
-	MountPaths []name.Repository
 	// TODO(mattmoor): Expose "threads" to limit parallelism?
 }
 
@@ -40,9 +38,15 @@ type WriteOptions struct {
 func Write(ref name.Reference, img v1.Image, auth authn.Authenticator, t http.RoundTripper,
 	wo WriteOptions) error {
 
+	ls, err := img.Layers()
+	if err != nil {
+		return err
+	}
 	scopes := []string{ref.Scope(transport.PushScope)}
-	for _, mp := range wo.MountPaths {
-		scopes = append(scopes, mp.Scope(transport.PullScope))
+	for _, l := range ls {
+		if ml, ok := l.(*MountableLayer); ok {
+			scopes = append(scopes, ml.Repository.Scope(transport.PullScope))
+		}
 	}
 
 	tr, err := transport.New(ref.Context().Registry, auth, t, scopes)
@@ -132,16 +136,16 @@ func (w *writer) initiateUpload(h v1.Hash) (location string, mounted bool, err e
 	uv := url.Values{
 		"mount": []string{h.String()},
 	}
-	var from []string
-	for _, m := range w.options.MountPaths {
-		from = append(from, m.RepositoryStr())
+	l, err := w.img.LayerByDigest(h)
+	if err != nil {
+		return "", false, err
 	}
 	// We currently avoid HEAD because it's semi-redundant with the mount that is part
 	// of initiating the blob upload.  GCR will perform an existence check on the initiation
 	// if "mount" is specified, even if no "from" sources are specified.  If this turns out
 	// to not be broadly applicable then we should replace mounts without "from"s with a HEAD.
-	if len(from) > 0 {
-		uv["from"] = from
+	if ml, ok := l.(*MountableLayer); ok {
+		uv["from"] = []string{ml.Repository.RepositoryStr()}
 	}
 	u.RawQuery = uv.Encode()
 
@@ -286,7 +290,7 @@ func (w *writer) commitImage() error {
 	}
 
 	// The image was successfully pushed!
-	fmt.Printf("%v: digest: %v size: %d\n", w.ref, digest, len(raw))
+	log.Printf("%v: digest: %v size: %d", w.ref, digest, len(raw))
 	return nil
 }
 

vendor/github.com/google/go-containerregistry/pkg/v1/tarball/image.go

@@ -25,11 +25,11 @@ import (
 	"os"
 	"sync"
 
-	"github.com/google/go-containerregistry/name"
-	"github.com/google/go-containerregistry/v1"
-	"github.com/google/go-containerregistry/v1/partial"
-	"github.com/google/go-containerregistry/v1/types"
-	"github.com/google/go-containerregistry/v1/v1util"
+	"github.com/google/go-containerregistry/pkg/name"
+	"github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/partial"
+	"github.com/google/go-containerregistry/pkg/v1/types"
+	"github.com/google/go-containerregistry/pkg/v1/v1util"
 )
 
 type image struct {
@@ -298,7 +298,7 @@ type compressedLayerFromTarball struct {
 	filePath string
 }
 
-// DiffID implements partial.CompressedLayer
+// Digest implements partial.CompressedLayer
 func (clft *compressedLayerFromTarball) Digest() (v1.Hash, error) {
 	return clft.digest, nil
 }

vendor/github.com/google/go-containerregistry/pkg/v1/tarball/layer.go

@@ -20,8 +20,8 @@ import (
 	"io/ioutil"
 	"os"
 
-	"github.com/google/go-containerregistry/v1"
-	"github.com/google/go-containerregistry/v1/v1util"
+	"github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/v1util"
 )
 
 type layer struct {

vendor/github.com/google/go-containerregistry/pkg/v1/tarball/write.go

@@ -22,8 +22,8 @@ import (
 	"io"
 	"os"
 
-	"github.com/google/go-containerregistry/name"
-	"github.com/google/go-containerregistry/v1"
+	"github.com/google/go-containerregistry/pkg/name"
+	"github.com/google/go-containerregistry/pkg/v1"
 )
 
 // WriteOptions are used to expose optional information to guide or

vendor/github.com/google/go-containerregistry/pkg/v1/v1util/verify.go

@@ -20,7 +20,7 @@ import (
 	"hash"
 	"io"
 
-	"github.com/google/go-containerregistry/v1"
+	"github.com/google/go-containerregistry/pkg/v1"
 )
 
 type verifyReader struct {

vendor/github.com/google/go-containerregistry/pkg/v1/v1util/zip.go

@@ -24,14 +24,23 @@ var gzipMagicHeader = []byte{'\x1f', '\x8b'}
 
 // GzipReadCloser reads uncompressed input data from the io.ReadCloser and
 // returns an io.ReadCloser from which compressed data may be read.
+// This uses gzip.BestSpeed for the compression level.
 func GzipReadCloser(r io.ReadCloser) (io.ReadCloser, error) {
+	return GzipReadCloserLevel(r, gzip.BestSpeed)
+}
+
+// GzipReadCloserLevel reads uncompressed input data from the io.ReadCloser and
+// returns an io.ReadCloser from which compressed data may be read.
+// Refer to compress/gzip for the level:
+// https://golang.org/pkg/compress/gzip/#pkg-constants
+func GzipReadCloserLevel(r io.ReadCloser, level int) (io.ReadCloser, error) {
 	pr, pw := io.Pipe()
 
 	go func() {
 		defer pw.Close()
 		defer r.Close()
 
-		gw, _ := gzip.NewWriterLevel(pw, gzip.BestCompression)
+		gw, _ := gzip.NewWriterLevel(pw, level)
 		defer gw.Close()
 
 		_, err := io.Copy(gw, r)