feat(discovery): tag-agnostic image name normalisation

internal/discovery/matching.go

@@ -0,0 +1,33 @@
+package discovery
+
+import "strings"
+
+// NormaliseImage strips the tag and digest from an image reference,
+// returning the bare repository name.
+//
+// Tricky case: "localhost:5000/foo:v1" — the first colon is a port,
+// not a tag. We disambiguate by splitting on "/" first and only
+// treating colons in the last segment as tag separators.
+func NormaliseImage(ref string) string {
+	if at := strings.Index(ref, "@"); at >= 0 {
+		ref = ref[:at]
+	}
+	slash := strings.LastIndex(ref, "/")
+	if slash < 0 {
+		if colon := strings.Index(ref, ":"); colon >= 0 {
+			return ref[:colon]
+		}
+		return ref
+	}
+	prefix, last := ref[:slash], ref[slash+1:]
+	if colon := strings.Index(last, ":"); colon >= 0 {
+		last = last[:colon]
+	}
+	return prefix + "/" + last
+}
+
+// ImagesMatch reports whether two image references resolve to the same
+// repository, ignoring tag and digest. Case-sensitive per spec section 5.2.
+func ImagesMatch(a, b string) bool {
+	return NormaliseImage(a) == NormaliseImage(b)
+}