implemented a lot of features

lib/nntp/xref.ts

@@ -0,0 +1,13 @@
+/**
+ * Returns the group names from an Xref header,
+ * e.g. `news.eweka.nl alt.binaries.test:123 alt.binaries.x:456`.
+ */
+export function parseXrefGroups(xref: string | undefined): string[] {
+  if (!xref) return []
+  return xref
+    .trim()
+    .split(/\s+/)
+    .slice(1)
+    .map((entry) => entry.slice(0, entry.lastIndexOf(':')))
+    .filter(Boolean)
+}