prop289: Keep track of the last seen cell digests

This makes tor remember the last seen digest of a cell if that cell is the
last one before a SENDME on the Exit side.

Closes #26839

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

1 files changed, 8 insertions, 0 deletions

diff --git a/src/core/or/relay.c b/src/core/or/relay.c
index 76f2203a9a..b26360b245 100644
--- a/src/core/or/relay.c
+++ b/src/core/or/relay.c
@@ -639,6 +639,14 @@ relay_send_command_from_edge_,(streamid_t stream_id, circuit_t *circ,
     circuit_mark_for_close(circ, END_CIRC_REASON_INTERNAL);
     return -1;
   }
+
+  /* If applicable, note the cell digest for the SENDME version 1 purpose if
+   * we need to. This call needs to be after the circuit_package_relay_cell()
+   * because the cell digest is set within that function. */
+  if (relay_command == RELAY_COMMAND_DATA) {
+    sendme_note_cell_digest(circ);
+  }
+
   return 0;
 }