sendme: Add helper to note the cell digest

Signed-off-by: David Goulet <dgoulet@torproject.org>

src/core/or/sendme.c

@@ -286,10 +286,37 @@ send_circuit_level_sendme(circuit_t *circ, crypt_path_t *layer_hint,
   return 0;
 }
 
+/* Put the crypto.b_digest in the sendme_digest. */
+static void
+note_cell_digest(const relay_crypto_t *crypto)
+{
+  tor_assert(crypto);
+  crypto_digest_get_digest(crypto->b_digest, (char *) crypto->sendme_digest,
+                           sizeof(crypto->sendme_digest));
+}
+
 /*
  * Public API
  */
 
+/** Keep the current inbound cell digest for the next SENDME digest. This part
+ * is only done by the client as the circuit came back from the Exit. */
+void
+sendme_circuit_note_outbound_cell(or_circuit_t *or_circ)
+{
+  tor_assert(or_circ);
+  note_cell_digest(&or_circ->crypto);
+}
+
+/** Keep the current inbound cell digest for the next SENDME digest. This part
+ * is only done by the client as the circuit came back from the Exit. */
+void
+sendme_circuit_note_inbound_cell(crypt_path_t *cpath)
+{
+  tor_assert(cpath);
+  note_cell_digest(&cpath->crypto);
+}
+
 /** Return true iff the next cell for the given cell window is expected to be
  * a SENDME.
  *

src/core/or/sendme.h

@@ -36,6 +36,8 @@ int sendme_note_stream_data_packaged(edge_connection_t *conn);
 
 /* Track cell digest. */
 void sendme_note_cell_digest(circuit_t *circ);
+void sendme_circuit_note_inbound_cell(crypt_path_t *cpath);
+void sendme_circuit_note_outbound_cell(or_circuit_t *or_circ);
 
 /* Circuit level information. */
 bool sendme_circuit_is_next_cell(int window);