Move copy implementation into containers/image

copy/copy.go

@@ -0,0 +1,165 @@
+package copy
+
+import (
+	"crypto/sha256"
+	"crypto/subtle"
+	"encoding/hex"
+	"fmt"
+	"hash"
+	"io"
+	"strings"
+
+	"github.com/containers/image/image"
+	"github.com/containers/image/signature"
+	"github.com/containers/image/transports"
+	"github.com/containers/image/types"
+)
+
+// supportedDigests lists the supported blob digest types.
+var supportedDigests = map[string]func() hash.Hash{
+	"sha256": sha256.New,
+}
+
+type digestingReader struct {
+	source           io.Reader
+	digest           hash.Hash
+	expectedDigest   []byte
+	failureIndicator *bool
+}
+
+// newDigestingReader returns an io.Reader with contents of source, which will eventually return a non-EOF error
+// and set *failureIndicator to true if the source stream does not match expectedDigestString.
+func newDigestingReader(source io.Reader, expectedDigestString string, failureIndicator *bool) (io.Reader, error) {
+	fields := strings.SplitN(expectedDigestString, ":", 2)
+	if len(fields) != 2 {
+		return nil, fmt.Errorf("Invalid digest specification %s", expectedDigestString)
+	}
+	fn, ok := supportedDigests[fields[0]]
+	if !ok {
+		return nil, fmt.Errorf("Invalid digest specification %s: unknown digest type %s", expectedDigestString, fields[0])
+	}
+	digest := fn()
+	expectedDigest, err := hex.DecodeString(fields[1])
+	if err != nil {
+		return nil, fmt.Errorf("Invalid digest value %s: %v", expectedDigestString, err)
+	}
+	if len(expectedDigest) != digest.Size() {
+		return nil, fmt.Errorf("Invalid digest specification %s: length %d does not match %d", expectedDigestString, len(expectedDigest), digest.Size())
+	}
+	return &digestingReader{
+		source:           source,
+		digest:           digest,
+		expectedDigest:   expectedDigest,
+		failureIndicator: failureIndicator,
+	}, nil
+}
+
+func (d *digestingReader) Read(p []byte) (int, error) {
+	n, err := d.source.Read(p)
+	if n > 0 {
+		if n2, err := d.digest.Write(p[:n]); n2 != n || err != nil {
+			// Coverage: This should not happen, the hash.Hash interface requires
+			// d.digest.Write to never return an error, and the io.Writer interface
+			// requires n2 == len(input) if no error is returned.
+			return 0, fmt.Errorf("Error updating digest during verification: %d vs. %d, %v", n2, n, err)
+		}
+	}
+	if err == io.EOF {
+		actualDigest := d.digest.Sum(nil)
+		if subtle.ConstantTimeCompare(actualDigest, d.expectedDigest) != 1 {
+			*d.failureIndicator = true
+			return 0, fmt.Errorf("Digest did not match, expected %s, got %s", hex.EncodeToString(d.expectedDigest), hex.EncodeToString(actualDigest))
+		}
+	}
+	return n, err
+}
+
+// Options allows supplying non-default configuration modifying the behavior of CopyImage.
+type Options struct {
+	SignBy string // If non-empty, asks for a signature to be added during the copy, and specifies a key ID, as accepted by signature.NewGPGSigningMechanism().SignDockerManifest(),
+}
+
+// Image copies image from srcRef to destRef, using policyContext to validate source image admissibility.
+func Image(ctx *types.SystemContext, policyContext *signature.PolicyContext, destRef, srcRef types.ImageReference, options *Options) error {
+	dest, err := destRef.NewImageDestination(ctx)
+	if err != nil {
+		return fmt.Errorf("Error initializing destination %s: %v", transports.ImageName(destRef), err)
+	}
+	rawSource, err := srcRef.NewImageSource(ctx, dest.SupportedManifestMIMETypes())
+	if err != nil {
+		return fmt.Errorf("Error initializing source %s: %v", transports.ImageName(srcRef), err)
+	}
+	src := image.FromSource(rawSource)
+
+	// Please keep this policy check BEFORE reading any other information about the image.
+	if allowed, err := policyContext.IsRunningImageAllowed(src); !allowed || err != nil { // Be paranoid and fail if either return value indicates so.
+		return fmt.Errorf("Source image rejected: %v", err)
+	}
+
+	manifest, _, err := src.Manifest()
+	if err != nil {
+		return fmt.Errorf("Error reading manifest: %v", err)
+	}
+
+	sigs, err := src.Signatures()
+	if err != nil {
+		return fmt.Errorf("Error reading signatures: %v", err)
+	}
+
+	blobDigests, err := src.BlobDigests()
+	if err != nil {
+		return fmt.Errorf("Error parsing manifest: %v", err)
+	}
+	for _, digest := range blobDigests {
+		// TODO(mitr): do not ignore the size param returned here
+		stream, _, err := rawSource.GetBlob(digest)
+		if err != nil {
+			return fmt.Errorf("Error reading blob %s: %v", digest, err)
+		}
+		defer stream.Close()
+
+		// Be paranoid; in case PutBlob somehow managed to ignore an error from digestingReader,
+		// use a separate validation failure indicator.
+		// Note that we don't use a stronger "validationSucceeded" indicator, because
+		// dest.PutBlob may detect that the layer already exists, in which case we don't
+		// read stream to the end, and validation does not happen.
+		validationFailed := false // This is a new instance on each loop iteration.
+		digestingReader, err := newDigestingReader(stream, digest, &validationFailed)
+		if err != nil {
+			return fmt.Errorf("Error preparing to verify blob %s: %v", digest, err)
+		}
+		if err := dest.PutBlob(digest, digestingReader); err != nil {
+			return fmt.Errorf("Error writing blob: %v", err)
+		}
+		if validationFailed { // Coverage: This should never happen.
+			return fmt.Errorf("Internal error uploading blob %s, digest verification failed but was ignored", digest)
+		}
+	}
+
+	if options != nil && options.SignBy != "" {
+		mech, err := signature.NewGPGSigningMechanism()
+		if err != nil {
+			return fmt.Errorf("Error initializing GPG: %v", err)
+		}
+		dockerReference := dest.Reference().DockerReference()
+		if dockerReference == nil {
+			return fmt.Errorf("Cannot determine canonical Docker reference for destination %s", transports.ImageName(dest.Reference()))
+		}
+
+		newSig, err := signature.SignDockerManifest(manifest, dockerReference.String(), mech, options.SignBy)
+		if err != nil {
+			return fmt.Errorf("Error creating signature: %v", err)
+		}
+		sigs = append(sigs, newSig)
+	}
+
+	// FIXME: We need to call PutManifest after PutBlob and before PutSignatures. This seems ugly; move to a "set properties" + "commit" model?
+	if err := dest.PutManifest(manifest); err != nil {
+		return fmt.Errorf("Error writing manifest: %v", err)
+	}
+
+	if err := dest.PutSignatures(sigs); err != nil {
+		return fmt.Errorf("Error writing signatures: %v", err)
+	}
+	return nil
+}

copy/copy_test.go

@@ -0,0 +1,62 @@
+package copy
+
+import (
+	"bytes"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewDigestingReader(t *testing.T) {
+	// Only the failure cases, success is tested in TestDigestingReaderRead below.
+	source := bytes.NewReader([]byte("abc"))
+	for _, input := range []string{
+		"abc",             // Not algo:hexvalue
+		"crc32:",          // Unknown algorithm, empty value
+		"crc32:012345678", // Unknown algorithm
+		"sha256:",         // Empty value
+		"sha256:0",        // Invalid hex value
+		"sha256:01",       // Invalid length of hex value
+	} {
+		validationFailed := false
+		_, err := newDigestingReader(source, input, &validationFailed)
+		assert.Error(t, err, input)
+	}
+}
+
+func TestDigestingReaderRead(t *testing.T) {
+	cases := []struct {
+		input  []byte
+		digest string
+	}{
+		{[]byte(""), "sha256:e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"},
+		{[]byte("abc"), "sha256:ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"},
+		{make([]byte, 65537, 65537), "sha256:3266304f31be278d06c3bd3eb9aa3e00c59bedec0a890de466568b0b90b0e01f"},
+	}
+	// Valid input
+	for _, c := range cases {
+		source := bytes.NewReader(c.input)
+		validationFailed := false
+		reader, err := newDigestingReader(source, c.digest, &validationFailed)
+		require.NoError(t, err, c.digest)
+		dest := bytes.Buffer{}
+		n, err := io.Copy(&dest, reader)
+		assert.NoError(t, err, c.digest)
+		assert.Equal(t, int64(len(c.input)), n, c.digest)
+		assert.Equal(t, c.input, dest.Bytes(), c.digest)
+		assert.False(t, validationFailed, c.digest)
+	}
+	// Modified input
+	for _, c := range cases {
+		source := bytes.NewReader(bytes.Join([][]byte{c.input, []byte("x")}, nil))
+		validationFailed := false
+		reader, err := newDigestingReader(source, c.digest, &validationFailed)
+		require.NoError(t, err, c.digest)
+		dest := bytes.Buffer{}
+		_, err = io.Copy(&dest, reader)
+		assert.Error(t, err, c.digest)
+		assert.True(t, validationFailed)
+	}
+}