From 1167650be97eaadd0e8f42acb4d0a28cdd145f67 Mon Sep 17 00:00:00 2001
From: "W. Trevor King" <wking@tremily.us>
Date: Fri, 9 Jun 2017 14:16:15 -0700
Subject: [PATCH] algorithm: Deprecate ErrDigestInvalidLength

This error was added in 97212540 (Validate digest length on parsing,
2015-12-02) and motivated with [1]:

> The new error is mostly so that digest.Set doesn't need a special
> way to figure out if invalid digest had a algorithm prefix or not.

That doesn't make sense to me, because Digest.Validate returns
ErrDigestUnsupported when there is no algorithm prefix (I've added a
test to confirm this as well), and that seems orthogonal to encoding
validation (which is the only place ErrDigestInvalidLength could
matter).  From the other changes in [1], I think the issue was just
that invalid lengths weren't raising errors at all.

I see no reason to distinguish between invalid lengths, invalid
characters, and other invalid-encoded-portion errors, so this commit
collapses the error into ErrDigestInvalidFormat.

The code I'm removing assumed hex (with '.Size() * 2'), so this commit
removes that assumption. The sha256 and other hex-based algorithms are
still getting their lengths validated via anchoredEncodedRegexps.

[1]: https://github.com/docker/distribution/pull/1231

Signed-off-by: W. Trevor King <wking@tremily.us>
---
 algorithm.go   |  5 -----
 digest.go      |  4 ++--
 digest_test.go | 10 +++++++---
 3 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/algorithm.go b/algorithm.go
index 8813bd2..158e83c 100644
--- a/algorithm.go
+++ b/algorithm.go
@@ -180,11 +180,6 @@ func (a Algorithm) Validate(encoded string) error {
 	if !ok {
 		return ErrDigestUnsupported
 	}
-	// Digests much always be hex-encoded, ensuring that their hex portion will
-	// always be size*2
-	if a.Size()*2 != len(encoded) {
-		return ErrDigestInvalidLength
-	}
 	if r.MatchString(encoded) {
 		return nil
 	}
diff --git a/digest.go b/digest.go
index ad398cb..ddc80c8 100644
--- a/digest.go
+++ b/digest.go
@@ -68,8 +68,8 @@ var (
 	// ErrDigestInvalidFormat returned when digest format invalid.
 	ErrDigestInvalidFormat = fmt.Errorf("invalid checksum digest format")
 
-	// ErrDigestInvalidLength returned when digest has invalid length.
-	ErrDigestInvalidLength = fmt.Errorf("invalid checksum digest length")
+	// ErrDigestInvalidLength is deprecated.  Please use ErrDigestInvalidFormat.
+	ErrDigestInvalidLength = ErrDigestInvalidFormat
 
 	// ErrDigestUnsupported returned when the digest algorithm is unsupported.
 	ErrDigestUnsupported = fmt.Errorf("unsupported digest algorithm")
diff --git a/digest_test.go b/digest_test.go
index cc3b648..a229061 100644
--- a/digest_test.go
+++ b/digest_test.go
@@ -35,6 +35,10 @@ func TestParseDigest(t *testing.T) {
 			algorithm: "sha384",
 			encoded:   "d3fc7881460b7e22e3d172954463dddd7866d17597e7248453c48b3e9d26d9596bf9c4a9cf8072c9d5bad76e19af801d",
 		},
+		{
+			input: "",
+			err:   ErrDigestInvalidFormat,
+		},
 		{
 			// empty hex
 			input: "sha256:",
@@ -53,17 +57,17 @@ func TestParseDigest(t *testing.T) {
 		{
 			// not hex
 			input: "sha256:d41d8cd98f00b204e9800m98ecf8427e",
-			err:   ErrDigestInvalidLength,
+			err:   ErrDigestInvalidFormat,
 		},
 		{
 			// too short
 			input: "sha256:abcdef0123456789",
-			err:   ErrDigestInvalidLength,
+			err:   ErrDigestInvalidFormat,
 		},
 		{
 			// too short (from different algorithm)
 			input: "sha512:abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789",
-			err:   ErrDigestInvalidLength,
+			err:   ErrDigestInvalidFormat,
 		},
 		{
 			input: "foo:d41d8cd98f00b204e9800998ecf8427e",