Refactor connection_or_send_certs_cell() to use trunnel

We no longer generate certs cells by pasting the certs together one
by one. Instead we use trunnel to generate them.

Preliminary work for 19155 (send CERTS cell with ed certs)

src/or/connection_or.c

@@ -2130,8 +2130,8 @@ connection_or_send_certs_cell(or_connection_t *conn)
   const uint8_t *link_encoded = NULL, *id_encoded = NULL;
   size_t link_len, id_len;
   var_cell_t *cell;
-  size_t cell_len;
-  ssize_t pos;
+
+  certs_cell_t *certs_cell = NULL;
 
   tor_assert(conn->base_.state == OR_CONN_STATE_OR_HANDSHAKING_V3);
 
@@ -2140,34 +2140,44 @@ connection_or_send_certs_cell(or_connection_t *conn)
   const int conn_in_server_mode = ! conn->handshake_state->started_here;
   if (tor_tls_get_my_certs(conn_in_server_mode, &link_cert, &id_cert) < 0)
     return -1;
+
+  certs_cell = certs_cell_new();
+
   tor_x509_cert_get_der(link_cert, &link_encoded, &link_len);
   tor_x509_cert_get_der(id_cert, &id_encoded, &id_len);
 
-  cell_len = 1 /* 1 byte: num certs in cell */ +
-             2 * ( 1 + 2 ) /* For each cert: 1 byte for type, 2 for length */ +
-             link_len + id_len;
-  cell = var_cell_new(cell_len);
-  cell->command = CELL_CERTS;
-  cell->payload[0] = 2;
-  pos = 1;
-
+  certs_cell_cert_t *ccc = certs_cell_cert_new();
   if (conn_in_server_mode)
-    cell->payload[pos] = OR_CERT_TYPE_TLS_LINK; /* Link cert  */
+    ccc->cert_type = OR_CERT_TYPE_TLS_LINK; /* Link cert  */
   else
-    cell->payload[pos] = OR_CERT_TYPE_AUTH_1024; /* client authentication */
-  set_uint16(&cell->payload[pos+1], htons(link_len));
-  memcpy(&cell->payload[pos+3], link_encoded, link_len);
-  pos += 3 + link_len;
+    ccc->cert_type = OR_CERT_TYPE_AUTH_1024; /* client authentication */
+  ccc->cert_len = link_len;
+  certs_cell_cert_setlen_body(ccc, link_len);
+  memcpy(certs_cell_cert_getarray_body(ccc), link_encoded, link_len);
 
-  cell->payload[pos] = OR_CERT_TYPE_ID_1024; /* ID cert */
-  set_uint16(&cell->payload[pos+1], htons(id_len));
-  memcpy(&cell->payload[pos+3], id_encoded, id_len);
-  pos += 3 + id_len;
+  certs_cell_add_certs(certs_cell, ccc);
 
-  tor_assert(pos == (int)cell_len); /* Otherwise we just smashed the heap */
+  ccc = certs_cell_cert_new();
+  ccc->cert_type = OR_CERT_TYPE_ID_1024; /* ID cert */
+  ccc->cert_len = id_len;
+  certs_cell_cert_setlen_body(ccc, id_len);
+  memcpy(certs_cell_cert_getarray_body(ccc), id_encoded, id_len);
+
+  certs_cell_add_certs(certs_cell, ccc);
+
+  certs_cell->n_certs = certs_cell_getlen_certs(certs_cell);
+
+  ssize_t alloc_len = certs_cell_encoded_len(certs_cell);
+  tor_assert(alloc_len >= 0 && alloc_len <= UINT16_MAX);
+  cell = var_cell_new(alloc_len);
+  cell->command = CELL_CERTS;
+  ssize_t enc_len = certs_cell_encode(cell->payload, alloc_len, certs_cell);
+  tor_assert(enc_len > 0 && enc_len <= alloc_len);
+  cell->payload_len = enc_len;
 
   connection_or_write_var_cell_to_buf(cell, conn);
   var_cell_free(cell);
+  certs_cell_free(certs_cell);
 
   return 0;
 }