/* Copyright (c) 2001 Matej Pfajfar. * Copyright (c) 2001-2004, Roger Dingledine. * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson. * Copyright (c) 2007-2017, The Tor Project, Inc. */ /* See LICENSE for licensing information */ #define BUFFERS_PRIVATE // XXXX remove. #include "or.h" #include "buffers.h" #include "proto_cell.h" #include "connection_or.h" /** True iff the cell command command is one that implies a * variable-length cell in Tor link protocol linkproto. */ static inline int cell_command_is_var_length(uint8_t command, int linkproto) { /* If linkproto is v2 (2), CELL_VERSIONS is the only variable-length cells * work as implemented here. If it's 1, there are no variable-length cells. * Tor does not support other versions right now, and so can't negotiate * them. */ switch (linkproto) { case 1: /* Link protocol version 1 has no variable-length cells. */ return 0; case 2: /* In link protocol version 2, VERSIONS is the only variable-length cell */ return command == CELL_VERSIONS; case 0: case 3: default: /* In link protocol version 3 and later, and in version "unknown", * commands 128 and higher indicate variable-length. VERSIONS is * grandfathered in. */ return command == CELL_VERSIONS || command >= 128; } } /** Check buf for a variable-length cell according to the rules of link * protocol version linkproto. If one is found, pull it off the buffer * and assign a newly allocated var_cell_t to *out, and return 1. * Return 0 if whatever is on the start of buf_t is not a variable-length * cell. Return 1 and set *out to NULL if there seems to be the start * of a variable-length cell on buf, but the whole thing isn't there * yet. */ int fetch_var_cell_from_buf(buf_t *buf, var_cell_t **out, int linkproto) { char hdr[VAR_CELL_MAX_HEADER_SIZE]; var_cell_t *result; uint8_t command; uint16_t length; const int wide_circ_ids = linkproto >= MIN_LINK_PROTO_FOR_WIDE_CIRC_IDS; const int circ_id_len = get_circ_id_size(wide_circ_ids); const unsigned header_len = get_var_cell_header_size(wide_circ_ids); *out = NULL; if (buf->datalen < header_len) return 0; peek_from_buf(hdr, header_len, buf); command = get_uint8(hdr + circ_id_len); if (!(cell_command_is_var_length(command, linkproto))) return 0; length = ntohs(get_uint16(hdr + circ_id_len + 1)); if (buf->datalen < (size_t)(header_len+length)) return 1; result = var_cell_new(length); result->command = command; if (wide_circ_ids) result->circ_id = ntohl(get_uint32(hdr)); else result->circ_id = ntohs(get_uint16(hdr)); buf_remove_from_front(buf, header_len); peek_from_buf((char*) result->payload, length, buf); buf_remove_from_front(buf, length); *out = result; return 1; }