ociregistry/ociref: add IsValidHost

This makes it easier for users to check that a bare hostname
is valid.

Also make it clearer in the docs that "host" also includes "host:port".

Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: I6308a4c30212addf270be3313237c8f2f6c5391c
Reviewed-on: https://review.gerrithub.io/c/cue-labs/oci/+/1170299
TryBot-Result: CUE porcuepine <cue.porcuepine@gmail.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

ociregistry/ociref/reference.go

@@ -100,11 +100,13 @@ var referencePat = regexp.MustCompile(
 		`)$`,
 )
 
+var hostPat = regexp.MustCompile(`^(?:` + domainAndPort + `)$`)
+
 // Reference represents an entry in an OCI repository.
 type Reference struct {
 	// Host holds the host name of the registry
-	// within which the repository is stored. This might
-	// be empty.
+	// within which the repository is stored, optionally in
+	// the form host:port. This might be empty.
 	Host string
 
 	// Repository holds the repository name.
@@ -120,10 +122,15 @@ type Reference struct {
 	Digest ociregistry.Digest
 }
 
+// IsValidHost reports whether s is a valid host (or host:port) part of a reference string.
+func IsValidHost(s string) bool {
+	return hostPat.MatchString(s)
+}
+
 // Parse parses a reference string that must include
-// a host name component.
+// a host name (or host:port pair) component.
 //
-// It is represented in string form as HOST/NAME[:TAG|@DIGEST]
+// It is represented in string form as HOST[:PORT]/NAME[:TAG|@DIGEST]
 // form: the same syntax accepted by "docker pull".
 // Unlike "docker pull" however, there is no default registry: when
 // presented with a bare repository name, Parse will return an error.
@@ -141,7 +148,7 @@ func Parse(refStr string) (Reference, error) {
 // ParseRelative parses a reference string that may
 // or may not include a host name component.
 //
-// It is represented in string form as [HOST/]NAME[:TAG|@DIGEST]
+// It is represented in string form as [HOST[:PORT]/]NAME[:TAG|@DIGEST]
 // form: the same syntax accepted by "docker pull".
 // Unlike "docker pull" however, there is no default registry: when
 // presented with a bare repository name, the Host field will be empty.

ociregistry/ociref/reference_test.go

@@ -376,3 +376,40 @@ func TestParseReference(t *testing.T) {
 		})
 	}
 }
+
+var isValidHostTests = []struct {
+	host string
+	want bool
+}{{
+	host: "foo.com:5000",
+	want: true,
+}, {
+	host: "foo.com",
+	want: true,
+}, {
+	host: "localhost:1234",
+	want: true,
+}, {
+	host: "localhost",
+	want: false,
+}, {
+	host: "foo",
+	want: false,
+}, {
+	host: "foo..com",
+	want: false,
+}, {
+	host: "[::1]",
+	want: true,
+}, {
+	host: "[::1]:3456",
+	want: true,
+}}
+
+func TestIsValidHost(t *testing.T) {
+	for _, test := range isValidHostTests {
+		t.Run(test.host, func(t *testing.T) {
+			qt.Assert(t, qt.Equals(IsValidHost(test.host), test.want))
+		})
+	}
+}