Support gzip and zstd HTTP transport compression to fetch remote resources

Co-authored-by: Nicolas De Loof <nicolas.deloof@gmail.com>
Signed-off-by: Laura Brehm <laurabrehm@hey.com>

remotes/docker/fetcher.go

@@ -17,6 +17,8 @@
 package docker
 
 import (
+	"compress/flate"
+	"compress/gzip"
 	"context"
 	"encoding/json"
 	"errors"
@@ -30,6 +32,7 @@ import (
 	"github.com/containerd/containerd/v2/images"
 	"github.com/containerd/containerd/v2/remotes"
 	"github.com/containerd/log"
+	"github.com/klauspost/compress/zstd"
 	digest "github.com/opencontainers/go-digest"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 )
@@ -262,6 +265,7 @@ func (r dockerFetcher) open(ctx context.Context, req *request, mediatype string,
 	} else {
 		req.header.Set("Accept", strings.Join([]string{mediatype, `*/*`}, ", "))
 	}
+	req.header.Set("Accept-Encoding", "zstd;q=1.0, gzip;q=0.8, deflate;q=0.5")
 
 	if offset > 0 {
 		// Note: "Accept-Ranges: bytes" cannot be trusted as some endpoints
@@ -320,5 +324,32 @@ func (r dockerFetcher) open(ctx context.Context, req *request, mediatype string,
 		}
 	}
 
-	return resp.Body, nil
+	body := resp.Body
+	encoding := strings.FieldsFunc(resp.Header.Get("Content-Encoding"), func(r rune) bool {
+		return r == ' ' || r == '\t' || r == ','
+	})
+	for i := len(encoding) - 1; i >= 0; i-- {
+		algorithm := strings.ToLower(encoding[i])
+		switch algorithm {
+		case "zstd":
+			r, err := zstd.NewReader(body)
+			if err != nil {
+				return nil, err
+			}
+			body = r.IOReadCloser()
+		case "gzip":
+			body, err = gzip.NewReader(body)
+			if err != nil {
+				return nil, err
+			}
+		case "deflate":
+			body = flate.NewReader(body)
+		case "identity", "":
+			// no content-encoding applied, use raw body
+		default:
+			return nil, errors.New("unsupported Content-Encoding algorithm: " + algorithm)
+		}
+	}
+
+	return body, nil
 }

remotes/docker/fetcher_test.go

@@ -17,6 +17,9 @@
 package docker
 
 import (
+	"bytes"
+	"compress/flate"
+	"compress/gzip"
 	"context"
 	"encoding/json"
 	"fmt"
@@ -28,6 +31,7 @@ import (
 	"strconv"
 	"testing"
 
+	"github.com/klauspost/compress/zstd"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -114,6 +118,152 @@ func TestFetcherOpen(t *testing.T) {
 	}
 }
 
+func TestContentEncoding(t *testing.T) {
+	t.Parallel()
+
+	zstdEncode := func(in []byte) []byte {
+		var b bytes.Buffer
+		zw, err := zstd.NewWriter(&b)
+		if err != nil {
+			t.Fatal(err)
+		}
+		_, err = zw.Write(in)
+		if err != nil {
+			t.Fatal()
+		}
+		err = zw.Close()
+		if err != nil {
+			t.Fatal(err)
+		}
+		return b.Bytes()
+	}
+	gzipEncode := func(in []byte) []byte {
+		var b bytes.Buffer
+		gw := gzip.NewWriter(&b)
+		_, err := gw.Write(in)
+		if err != nil {
+			t.Fatal(err)
+		}
+		err = gw.Close()
+		if err != nil {
+			t.Fatal(err)
+		}
+		return b.Bytes()
+	}
+	flateEncode := func(in []byte) []byte {
+		var b bytes.Buffer
+		dw, err := flate.NewWriter(&b, -1)
+		if err != nil {
+			t.Fatal(err)
+		}
+		_, err = dw.Write(in)
+		if err != nil {
+			t.Fatal(err)
+		}
+		err = dw.Close()
+		if err != nil {
+			t.Fatal(err)
+		}
+		return b.Bytes()
+	}
+
+	tests := []struct {
+		encodingFuncs  []func([]byte) []byte
+		encodingHeader string
+	}{
+		{
+			encodingFuncs:  []func([]byte) []byte{},
+			encodingHeader: "",
+		},
+		{
+			encodingFuncs:  []func([]byte) []byte{zstdEncode},
+			encodingHeader: "zstd",
+		},
+		{
+			encodingFuncs:  []func([]byte) []byte{gzipEncode},
+			encodingHeader: "gzip",
+		},
+		{
+			encodingFuncs:  []func([]byte) []byte{flateEncode},
+			encodingHeader: "deflate",
+		},
+		{
+			encodingFuncs:  []func([]byte) []byte{zstdEncode, gzipEncode},
+			encodingHeader: "zstd,gzip",
+		},
+		{
+			encodingFuncs:  []func([]byte) []byte{gzipEncode, flateEncode},
+			encodingHeader: "gzip,deflate",
+		},
+		{
+			encodingFuncs:  []func([]byte) []byte{gzipEncode, zstdEncode},
+			encodingHeader: "gzip,zstd",
+		},
+		{
+			encodingFuncs:  []func([]byte) []byte{gzipEncode, zstdEncode, flateEncode},
+			encodingHeader: "gzip,zstd,deflate",
+		},
+	}
+
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.encodingHeader, func(t *testing.T) {
+			t.Parallel()
+			content := make([]byte, 128)
+			rand.New(rand.NewSource(1)).Read(content)
+
+			s := httptest.NewServer(http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+				compressedContent := content
+				for _, enc := range tc.encodingFuncs {
+					compressedContent = enc(compressedContent)
+				}
+				rw.Header().Set("content-length", fmt.Sprintf("%d", len(compressedContent)))
+				rw.Header().Set("Content-Encoding", tc.encodingHeader)
+				rw.Write(compressedContent)
+			}))
+			defer s.Close()
+
+			u, err := url.Parse(s.URL)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			f := dockerFetcher{&dockerBase{
+				repository: "nonempty",
+			}}
+
+			host := RegistryHost{
+				Client: s.Client(),
+				Host:   u.Host,
+				Scheme: u.Scheme,
+				Path:   u.Path,
+			}
+
+			req := f.request(host, http.MethodGet)
+
+			rc, err := f.open(context.Background(), req, "", 0)
+			if err != nil {
+				t.Fatalf("failed to open for encoding %s: %+v", tc.encodingHeader, err)
+			}
+			b, err := io.ReadAll(rc)
+			if err != nil {
+				t.Fatal(err)
+			}
+			expected := content
+			if len(b) != len(expected) {
+				t.Errorf("unexpected length %d, expected %d", len(b), len(expected))
+				return
+			}
+			for i, c := range expected {
+				if b[i] != c {
+					t.Errorf("unexpected byte %x at %d, expected %x", b[i], i, c)
+					return
+				}
+			}
+		})
+	}
+}
+
 // New set of tests to test new error cases
 func TestDockerFetcherOpen(t *testing.T) {
 	tests := []struct {