Remove tarsum support for digest package

tarsum is not actually used by the registry. Remove support for it.

Convert numerous uses in unit tests to SHA256.

Update docs to remove mentions of tarsums (which were often inaccurate).

Remove tarsum dependency.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

digest.go

@@ -4,17 +4,11 @@ import (
 	"fmt"
 	"hash"
 	"io"
-	"io/ioutil"
 	"regexp"
 	"strings"
-
-	"github.com/docker/docker/pkg/tarsum"
 )
 
 const (
-	// DigestTarSumV1EmptyTar is the digest for the empty tar file.
-	DigestTarSumV1EmptyTar = "tarsum.v1+sha256:e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
-
 	// DigestSha256EmptyTar is the canonical sha256 digest of empty data
 	DigestSha256EmptyTar = "sha256:e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
 )
@@ -28,11 +22,6 @@ const (
 //
 // 	sha256:7173b809ca12ec5dee4506cd86be934c4596dd234ee82c0662eac04a8c2c71dc
 //
-// More important for this code base, this type is compatible with tarsum
-// digests. For example, the following would be a valid Digest:
-//
-// 	tarsum+sha256:e58fcf7418d4390dec8e8fb69d88c06ec07039d651fedd3aa72af9972e7d046b
-//
 // This allows to abstract the digest behind this type and work only in those
 // terms.
 type Digest string
@@ -78,25 +67,6 @@ func FromReader(rd io.Reader) (Digest, error) {
 	return Canonical.FromReader(rd)
 }
 
-// FromTarArchive produces a tarsum digest from reader rd.
-func FromTarArchive(rd io.Reader) (Digest, error) {
-	ts, err := tarsum.NewTarSum(rd, true, tarsum.Version1)
-	if err != nil {
-		return "", err
-	}
-
-	if _, err := io.Copy(ioutil.Discard, ts); err != nil {
-		return "", err
-	}
-
-	d, err := ParseDigest(ts.Sum(nil))
-	if err != nil {
-		return "", err
-	}
-
-	return d, nil
-}
-
 // FromBytes digests the input and returns a Digest.
 func FromBytes(p []byte) Digest {
 	digester := Canonical.New()
@@ -117,13 +87,6 @@ func FromBytes(p []byte) Digest {
 // error if not.
 func (d Digest) Validate() error {
 	s := string(d)
-	// Common case will be tarsum
-	_, err := ParseTarSum(s)
-	if err == nil {
-		return nil
-	}
-
-	// Continue on for general parser
 
 	if !DigestRegexpAnchored.MatchString(s) {
 		return ErrDigestInvalidFormat

digest_test.go

@@ -1,8 +1,6 @@
 package digest
 
 import (
-	"bytes"
-	"io"
 	"testing"
 )
 
@@ -13,21 +11,6 @@ func TestParseDigest(t *testing.T) {
 		algorithm Algorithm
 		hex       string
 	}{
-		{
-			input:     "tarsum+sha256:e58fcf7418d4390dec8e8fb69d88c06ec07039d651fedd3aa72af9972e7d046b",
-			algorithm: "tarsum+sha256",
-			hex:       "e58fcf7418d4390dec8e8fb69d88c06ec07039d651fedd3aa72af9972e7d046b",
-		},
-		{
-			input:     "tarsum.dev+sha256:e58fcf7418d4390dec8e8fb69d88c06ec07039d651fedd3aa72af9972e7d046b",
-			algorithm: "tarsum.dev+sha256",
-			hex:       "e58fcf7418d4390dec8e8fb69d88c06ec07039d651fedd3aa72af9972e7d046b",
-		},
-		{
-			input:     "tarsum.v1+sha256:220a60ecd4a3c32c282622a625a54db9ba0ff55b5ba9c29c7064a2bc358b6a3e",
-			algorithm: "tarsum.v1+sha256",
-			hex:       "220a60ecd4a3c32c282622a625a54db9ba0ff55b5ba9c29c7064a2bc358b6a3e",
-		},
 		{
 			input:     "sha256:e58fcf7418d4390dec8e8fb69d88c06ec07039d651fedd3aa72af9972e7d046b",
 			algorithm: "sha256",
@@ -97,25 +80,3 @@ func TestParseDigest(t *testing.T) {
 		}
 	}
 }
-
-// A few test cases used to fix behavior we expect in storage backend.
-
-func TestFromTarArchiveZeroLength(t *testing.T) {
-	checkTarsumDigest(t, "zero-length archive", bytes.NewReader([]byte{}), DigestTarSumV1EmptyTar)
-}
-
-func TestFromTarArchiveEmptyTar(t *testing.T) {
-	// String of 1024 zeros is a valid, empty tar file.
-	checkTarsumDigest(t, "1024 zero bytes", bytes.NewReader(bytes.Repeat([]byte("\x00"), 1024)), DigestTarSumV1EmptyTar)
-}
-
-func checkTarsumDigest(t *testing.T, msg string, rd io.Reader, expected Digest) {
-	dgst, err := FromTarArchive(rd)
-	if err != nil {
-		t.Fatalf("unexpected error digesting %s: %v", msg, err)
-	}
-
-	if dgst != expected {
-		t.Fatalf("unexpected digest for %s: %q != %q", msg, dgst, expected)
-	}
-}

digester.go

@@ -13,10 +13,9 @@ type Algorithm string
 
 // supported digest types
 const (
-	SHA256         Algorithm = "sha256"           // sha256 with hex encoding
-	SHA384         Algorithm = "sha384"           // sha384 with hex encoding
-	SHA512         Algorithm = "sha512"           // sha512 with hex encoding
-	TarsumV1SHA256 Algorithm = "tarsum+v1+sha256" // supported tarsum version, verification only
+	SHA256 Algorithm = "sha256" // sha256 with hex encoding
+	SHA384 Algorithm = "sha384" // sha384 with hex encoding
+	SHA512 Algorithm = "sha512" // sha512 with hex encoding
 
 	// Canonical is the primary digest algorithm used with the distribution
 	// project. Other digests may be used but this one is the primary storage

doc.go

@@ -1,7 +1,7 @@
 // Package digest provides a generalized type to opaquely represent message
 // digests and their operations within the registry. The Digest type is
 // designed to serve as a flexible identifier in a content-addressable system.
-// More importantly, it provides tools and wrappers to work with tarsums and
+// More importantly, it provides tools and wrappers to work with
 // hash.Hash-based digests with little effort.
 //
 // Basics
@@ -16,17 +16,7 @@
 // 	sha256:7173b809ca12ec5dee4506cd86be934c4596dd234ee82c0662eac04a8c2c71dc
 //
 // In this case, the string "sha256" is the algorithm and the hex bytes are
-// the "digest". A tarsum example will be more illustrative of the use case
-// involved in the registry:
-//
-// 	tarsum+sha256:e58fcf7418d4390dec8e8fb69d88c06ec07039d651fedd3aa72af9972e7d046b
-//
-// For this, we consider the algorithm to be "tarsum+sha256". Prudent
-// applications will favor the ParseDigest function to verify the format over
-// using simple type casts. However, a normal string can be cast as a digest
-// with a simple type conversion:
-//
-// 	Digest("tarsum+sha256:e58fcf7418d4390dec8e8fb69d88c06ec07039d651fedd3aa72af9972e7d046b")
+// the "digest".
 //
 // Because the Digest type is simply a string, once a valid Digest is
 // obtained, comparisons are cheap, quick and simple to express with the