A few more usefull stuff for Buf.t

lib/buf.ml

@@ -29,6 +29,8 @@ let to_cstruct t = Cstruct.set_len t.cbuf t.coff
 
 let left t = t.tlen - t.coff
 
+let used t = t.coff
+
 let grow len t =
   let tlen = t.tlen + len in
   let cbuf = Cstruct.append t.cbuf (Cstruct.create len) in
@@ -39,6 +41,8 @@ let guard_space len t =
 
 let shift n t = { t with coff = t.coff + n }
 
+let reserve n t = shift n t
+
 let add_uint8 b t =
   let t = guard_space 1 t in
   Cstruct.set_uint8 t.cbuf t.coff b;
@@ -73,6 +77,9 @@ let add_raw buf t =
   Cstruct.blit buf 0 t.cbuf t.coff len;
   shift len t
 
+let add_random len t =
+  add_raw (Nocrypto.Rng.generate len) t
+
 let add_nl nl t =
   add_string (String.concat "," nl) t