packet-sdlc.c

   1 /* packet-sdlc.c
   2  * Routines for SDLC frame disassembly
   3  *
   4  * $Id: packet-sdlc.c,v 1.1 2003/01/03 22:31:24 guy Exp $
   5  *
   6  * Ethereal - Network traffic analyzer
   7  * By Gerald Combs <gerald@ethereal.com>
   8  * Copyright 1998
   9  *
  10  * This program is free software; you can redistribute it and/or
  11  * modify it under the terms of the GNU General Public License
  12  * as published by the Free Software Foundation; either version 2
  13  * of the License, or (at your option) any later version.
  14  *
  15  * This program is distributed in the hope that it will be useful,
  16  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  17  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18  * GNU General Public License for more details.
  19  *
  20  * You should have received a copy of the GNU General Public License
  21  * along with this program; if not, write to the Free Software
  22  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  23  */
  24
  25 #ifdef HAVE_CONFIG_H
  26 # include "config.h"
  27 #endif
  28
  29 #include <stdio.h>
  30 #include <glib.h>
  31 #include <string.h>
  32 #include <epan/packet.h>
  33 #include "xdlc.h"
  34
  35 /*
  36  * See
  37  *
  38  *      http://www.protocols.com/pbook/sna.htm
  39  */
  40
  41 static int proto_sdlc = -1;
  42 static int hf_sdlc_address = -1;
  43 static int hf_sdlc_control = -1;
  44
  45 static gint ett_sdlc = -1;
  46 static gint ett_sdlc_control = -1;
  47
  48 static dissector_handle_t sna_handle;
  49 static dissector_handle_t data_handle;
  50
  51 static void
  52 dissect_sdlc(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
  53 {
  54         proto_tree      *sdlc_tree;
  55         proto_item      *sdlc_ti;
  56         guint8          address;
  57         guint16         control;
  58         int             sdlc_header_len;
  59         gboolean        is_response;
  60         tvbuff_t        *next_tvb;
  61
  62         if (check_col(pinfo->cinfo, COL_PROTOCOL))
  63                 col_set_str(pinfo->cinfo, COL_PROTOCOL, "SDLC");
  64         if (check_col(pinfo->cinfo, COL_INFO))
  65                 col_clear(pinfo->cinfo, COL_INFO);
  66
  67         address = tvb_get_guint8(tvb, 0);
  68         sdlc_header_len = 1;    /* address */
  69
  70         /*
  71          * XXX - is there something in the SDLC header that indicates
  72          * how to interpret "command vs. response" based on the
  73          * direction?
  74          */
  75         if (pinfo->p2p_dir == P2P_DIR_SENT) {
  76                 is_response = FALSE;
  77                 if (check_col(pinfo->cinfo, COL_RES_DL_DST))
  78                         col_set_str(pinfo->cinfo, COL_RES_DL_DST, "DCE");
  79                 if (check_col(pinfo->cinfo, COL_RES_DL_SRC))
  80                         col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "DTE");
  81         }
  82         else {
  83                 /* XXX - what if the direction is unknown? */
  84                 is_response = TRUE;
  85                 if (check_col(pinfo->cinfo, COL_RES_DL_DST))
  86                     col_set_str(pinfo->cinfo, COL_RES_DL_DST, "DTE");
  87                 if (check_col(pinfo->cinfo, COL_RES_DL_SRC))
  88                     col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "DCE");
  89         }
  90
  91         if (tree) {
  92                 sdlc_ti = proto_tree_add_item(tree, proto_sdlc, tvb, 0, -1,
  93                     FALSE);
  94                 sdlc_tree = proto_item_add_subtree(sdlc_ti, ett_sdlc);
  95
  96                 proto_tree_add_uint(sdlc_tree, hf_sdlc_address, tvb, 0, 1,
  97                     address);
  98         } else {
  99                 sdlc_ti = NULL;
 100                 sdlc_tree = NULL;
 101         }
 102
 103         /*
 104          * XXX - SDLC has a mod-128 mode as well as a mod-7 mode.
 105          * We can infer the mode from an SNRM/SRME frame, but if
 106          * we don't see one of them, we may have to have a preference
 107          * to control what to use.
 108          */
 109         control = dissect_xdlc_control(tvb, 1, pinfo, sdlc_tree, hf_sdlc_control,
 110             ett_sdlc_control, is_response, FALSE);
 111         sdlc_header_len += XDLC_CONTROL_LEN(control, FALSE);
 112
 113         if (tree)
 114                 proto_item_set_len(sdlc_ti, sdlc_header_len);
 115
 116         /*
 117          * XXX - is there an FCS at the end, at least in Sniffer
 118          * captures?  (There doesn't appear to be.)
 119          */
 120         next_tvb = tvb_new_subset(tvb, sdlc_header_len, -1, -1);
 121         if (XDLC_IS_INFORMATION(control)) {
 122                 /* call the SNA dissector */
 123                 call_dissector(sna_handle, next_tvb, pinfo, tree);
 124         } else
 125                 call_dissector(data_handle, next_tvb, pinfo, tree);
 126 }
 127
 128 void
 129 proto_register_sdlc(void)
 130 {
 131         static hf_register_info hf[] = {
 132                 { &hf_sdlc_address,
 133                   { "Address Field", "sdlc.address", FT_UINT8, BASE_HEX,
 134                      NULL, 0x0, "Address", HFILL }},
 135
 136                 { &hf_sdlc_control,
 137                   { "Control Field", "sdlc.control", FT_UINT16, BASE_HEX,
 138                     NULL, 0x0, "Control field", HFILL }},
 139         };
 140         static gint *ett[] = {
 141                 &ett_sdlc,
 142                 &ett_sdlc_control,
 143         };
 144
 145         proto_sdlc = proto_register_protocol(
 146             "Synchronous Data Link Control (SDLC)", "SDLC", "sdlc");
 147         proto_register_field_array(proto_sdlc, hf, array_length(hf));
 148         proto_register_subtree_array(ett, array_length(ett));
 149 }
 150
 151 void
 152 proto_reg_handoff_sdlc(void)
 153 {
 154         dissector_handle_t sdlc_handle;
 155
 156         /*
 157          * Get handle for the SNA dissector.
 158          */
 159         sna_handle = find_dissector("sna");
 160         data_handle = find_dissector("data");
 161
 162         sdlc_handle = create_dissector_handle(dissect_sdlc, proto_sdlc);
 163         dissector_add("wtap_encap", WTAP_ENCAP_SDLC, sdlc_handle);
 164 }