Allow uppercase characters in hostnames

This allows hostnames to contain uppercase characters, matching behavior
in Docker versions before 1.10. It does not attempt to canonicalize
hostnames into a lowercase format before parsing, since this could lead
to corner cases (for example, making Hostname.Domain.Com/ref ambiguous
on a daemon which contains references for both hostname.domain.com/ref
and Hostname.Domain.Com/ref).

Fixes: #1433

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

reference/regexp_test.go

@@ -111,6 +111,10 @@ func TestHostRegexp(t *testing.T) {
 			input: "xn--n3h.com", // ☃.com in punycode
 			match: true,
 		},
+		{
+			input: "Asdf.com", // uppercase character
+			match: true,
+		},
 	}
 	r := regexp.MustCompile(`^` + hostnameRegexp.String() + `$`)
 	for i := range hostcases {
@@ -399,6 +403,14 @@ func TestFullNameRegexp(t *testing.T) {
 			match: true,
 			subs:  []string{"registry.io", "foo/project--id.module--name.ver---sion--name"},
 		},
+		{
+			input: "Asdf.com/foo/bar", // uppercase character in hostname
+			match: true,
+		},
+		{
+			input: "Foo/FarB", // uppercase characters in remote name
+			match: false,
+		},
 	}
 	for i := range testcases {
 		checkRegexp(t, anchoredNameRegexp, testcases[i])