Add --dest-precompute-digests option for docker

This ensures layers are not uploaded that already exist on the
destination registry, in exchange for streaming layers to temporary
files when digests are unknown (ex. compressing "on the fly").

Signed-off-by: Paul Fisher <pfisher@lyft.com>

cmd/skopeo/utils.go

@@ -227,6 +227,7 @@ type imageDestOptions struct {
 	ociAcceptUncompressedLayers bool        // Whether to accept uncompressed layers in the oci: transport
 	compressionFormat           string      // Format to use for the compression
 	compressionLevel            optionalInt // Level to use for the compression
+	precomputeDigests           bool        // Precompute digests to dedup layers when saving to the docker: transport
 }
 
 // imageDestFlags prepares a collection of CLI flags writing into imageDestOptions, and the managed imageDestOptions structure.
@@ -240,6 +241,7 @@ func imageDestFlags(global *globalOptions, shared *sharedImageOptions, deprecate
 	fs.BoolVar(&opts.ociAcceptUncompressedLayers, flagPrefix+"oci-accept-uncompressed-layers", false, "Allow uncompressed image layers when saving to an OCI image using the 'oci' transport. (default is to compress things that aren't compressed)")
 	fs.StringVar(&opts.compressionFormat, flagPrefix+"compress-format", "", "`FORMAT` to use for the compression")
 	fs.Var(newOptionalIntValue(&opts.compressionLevel), flagPrefix+"compress-level", "`LEVEL` to use for the compression")
+	fs.BoolVar(&opts.precomputeDigests, flagPrefix+"precompute-digests", false, "Precompute digests to prevent uploading layers already on the registry using the 'docker' transport.")
 	return fs, &opts
 }
 
@@ -264,6 +266,7 @@ func (opts *imageDestOptions) newSystemContext() (*types.SystemContext, error) {
 	if opts.compressionLevel.present {
 		ctx.CompressionLevel = &opts.compressionLevel.value
 	}
+	ctx.DockerRegistryPushPrecomputeDigests = opts.precomputeDigests
 	return ctx, err
 }
 

cmd/skopeo/utils_test.go

@@ -167,6 +167,7 @@ func TestImageDestOptionsNewSystemContext(t *testing.T) {
 		"--dest-tls-verify=false",
 		"--dest-creds", "creds-user:creds-password",
 		"--dest-registry-token", "faketoken",
+		"--dest-precompute-digests=true",
 	})
 	res, err = opts.newSystemContext()
 	require.NoError(t, err)
@@ -187,6 +188,7 @@ func TestImageDestOptionsNewSystemContext(t *testing.T) {
 		DockerRegistryUserAgent:             defaultUserAgent,
 		DirForceCompress:                    true,
 		BigFilesTemporaryDir:                "/srv",
+		DockerRegistryPushPrecomputeDigests: true,
 	}, res)
 
 	// Global/per-command tlsVerify behavior is tested in TestTLSVerifyFlags.

completions/bash/skopeo

@@ -65,6 +65,7 @@ _skopeo_copy() {
     --src-no-creds
     --dest-no-creds
     --dest-oci-accept-uncompressed-layers
+    --dest-precompute-digests
     "
 
     local transports

docs/skopeo-copy.1.md

@@ -160,6 +160,10 @@ Bearer token for accessing the source registry.
 
 Bearer token for accessing the destination registry.
 
+**--dest-precompute-digests** _bool-value_
+
+Precompute digests to ensure layers are not uploaded that already exist on the destination registry. Layers with initially unknown digests (ex. compressing "on the fly") will be temporarily streamed to disk.
+
 **--retry-times**
 
 The number of times to retry. Retry wait time will be exponentially increased based on the number of failed attempts.