diff --git a/lib/stream.c b/lib/stream.c
index ccd4623..9a6fcbc 100644
--- a/lib/stream.c
+++ b/lib/stream.c
@@ -154,6 +154,25 @@
   return (stream_copy (new, s));
 }
 
+struct stream *
+stream_dupcat (struct stream *s1, struct stream *s2, size_t offset)
+{
+  struct stream *new;
+
+  STREAM_VERIFY_SANE (s1);
+  STREAM_VERIFY_SANE (s2);
+
+  if ( (new = stream_new (s1->endp + s2->endp)) == NULL)
+    return NULL;
+
+  memcpy (new->data, s1->data, offset);
+  memcpy (new->data + offset, s2->data, s2->endp);
+  memcpy (new->data + offset + s2->endp, s1->data + offset,
+	  (s1->endp - offset));
+  new->endp = s1->endp + s2->endp;
+  return new;
+}
+
 size_t
 stream_resize (struct stream *s, size_t newsize)
 {
diff --git a/lib/stream.h b/lib/stream.h
index f10aa6d..f0c742c 100644
--- a/lib/stream.h
+++ b/lib/stream.h
@@ -122,6 +122,9 @@
   /* number of bytes still to be read */
 #define STREAM_READABLE(S) ((S)->endp - (S)->getp)
 
+#define STREAM_CONCAT_REMAIN(S1, S2, size) \
+  ((size) - (S1)->endp - (S2)->endp)
+
 /* deprecated macros - do not use in new code */
 #define STREAM_PNT(S)   stream_pnt((S))
 #define STREAM_DATA(S)  ((S)->data)
@@ -145,6 +148,14 @@
 extern size_t stream_get_size (struct stream *);
 extern u_char *stream_get_data (struct stream *);
 
+/**
+ * Create a new stream structure; copy offset bytes from s1 to the new
+ * stream; copy s2 data to the new stream; copy rest of s1 data to the
+ * new stream.
+ */
+extern struct stream *stream_dupcat(struct stream *s1, struct stream *s2,
+				    size_t offset);
+
 extern void stream_set_getp (struct stream *, size_t);
 extern void stream_set_endp (struct stream *, size_t);
 extern void stream_forward_getp (struct stream *, size_t);