path: root/epan/dissectors/packet-pcomtcp.c

/* packet-pcomtcp.c
 * Routines for PCOM/TCP dissection
 * Copyright 2018, Luis Rosa <lmrosa@dei.uc.pt>
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

/*
 * PCOM is a protocol to communicate with Unitronics PLCs either by serial or TCP.
 * Two modes are available, ASCII and Binary.
 *
 * See https://unitronicsplc.com/Download/SoftwareUtilities/Unitronics%20PCOM%20Protocol.pdf
 *
 */

#include <config.h>
#include <epan/packet.h>
#include <epan/expert.h>

void proto_reg_handoff_pcomtcp(void);
void proto_register_pcomtcp(void);

/* Initialize the protocol and registered fields */
static int proto_pcomtcp = -1;
static int proto_pcomascii = -1;
static int proto_pcombinary = -1;

static int hf_pcomtcp_transid = -1;
static int hf_pcomtcp_protocol = -1;
static int hf_pcomtcp_reserved = -1;
static int hf_pcomtcp_length = -1;

static int hf_pcomascii_stx = -1;
static int hf_pcomascii_unitid = -1;
static int hf_pcomascii_command = -1;
static int hf_pcomascii_checksum = -1;
static int hf_pcomascii_etx = -1;

static int hf_pcombinary_stx = -1;
static int hf_pcombinary_id = -1;
static int hf_pcombinary_reserved1 = -1;
static int hf_pcombinary_reserved2 = -1;
static int hf_pcombinary_reserved3 = -1;
static int hf_pcombinary_command = -1;
static int hf_pcombinary_reserved4 = -1;
static int hf_pcombinary_command_specific = -1;
static int hf_pcombinary_data_length = -1;
static int hf_pcombinary_header_checksum = -1;
static int hf_pcombinary_data = -1;
static int hf_pcombinary_footer_checksum = -1;
static int hf_pcombinary_etx = -1;

static expert_field ei_pcomtcp_reserved_bad_value = EI_INIT;
static expert_field ei_pcombinary_reserved1_bad_value = EI_INIT;
static expert_field ei_pcombinary_reserved2_bad_value = EI_INIT;
static expert_field ei_pcombinary_reserved3_bad_value = EI_INIT;
static expert_field ei_pcombinary_reserved4_bad_value = EI_INIT;

/* Initialize the subtree pointers */
static gint ett_pcomtcp = -1;
static gint ett_pcomascii = -1;
static gint ett_pcombinary = -1;

static dissector_handle_t pcomtcp_handle;
static dissector_handle_t pcomascii_handle;
static dissector_handle_t pcombinary_handle;

/* PCOM/TCP definitions */
#define PCOMTCP_MIN_LENGTH 6
#define PCOMTCP_TCP_PORT 20256
#define PCOM_ASCII 101
#define PCOM_BINARY 102

static guint global_pcomtcp_tcp_port = PCOMTCP_TCP_PORT; /* Port 20256, by default */

/* Translate pcomp_protocol to string */
static const value_string pcomp_protocol_vals[] = {
    { PCOM_ASCII,          "ASCII mode" },
    { PCOM_BINARY,         "Binary mode" },
    { 0,                    NULL },
};

/* Code to actually dissect the packets */
static int
dissect_pcomtcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
        void *data _U_)
{
    /* Set up structures needed to add the protocol subtree and manage it */
    proto_item  *ti;
    proto_tree  *pcomtcp_tree;

    tvbuff_t    *next_tvb;

    guint        offset = 0;
    const char  *pkt_type = "";
    guint8      pcom_mode;
    const char  *pcom_mode_str = "";

    proto_item    *hf_pcomtcp_reserved_item = NULL;

    /* Check that the packet is long enough for it to belong to us. */
    if (tvb_reported_length(tvb) < PCOMTCP_MIN_LENGTH)
        return 0;

    pcom_mode = tvb_get_guint8(tvb, 2);
    if ( pcom_mode != PCOM_ASCII && pcom_mode != PCOM_BINARY )
        return 0;

    pcom_mode_str = val_to_str(pcom_mode, pcomp_protocol_vals, "Unknown mode (%d)");

    if (pinfo->srcport == global_pcomtcp_tcp_port )
        pkt_type = "Reply";
    else
        pkt_type = "Query";

    col_set_str(pinfo->cinfo, COL_PROTOCOL, "PCOM/TCP");
    col_clear(pinfo->cinfo, COL_INFO);
    col_add_fstr(pinfo->cinfo, COL_INFO, "%s in %s",
            pkt_type, pcom_mode_str);


    /* create display subtree for the protocol */
    ti = proto_tree_add_item(tree, proto_pcomtcp, tvb, 0, -1, ENC_NA);
    pcomtcp_tree = proto_item_add_subtree(ti, ett_pcomtcp);

    proto_tree_add_item(pcomtcp_tree, hf_pcomtcp_transid, tvb,
            offset, 2, ENC_LITTLE_ENDIAN);
    offset += 2;
    proto_tree_add_item(pcomtcp_tree, hf_pcomtcp_protocol, tvb,
            offset, 1, ENC_NA);
    offset += 1;
    hf_pcomtcp_reserved_item = proto_tree_add_item(pcomtcp_tree, hf_pcomtcp_reserved, tvb,
            offset, 1, ENC_NA);
    if(tvb_get_guint8(tvb, offset) !=0){
            expert_add_info_format(pinfo, hf_pcomtcp_reserved_item,
                    &ei_pcomtcp_reserved_bad_value,"Isn't 0");
    }
    offset += 1;
    proto_tree_add_item(pcomtcp_tree, hf_pcomtcp_length, tvb,
            offset, 2, ENC_LITTLE_ENDIAN);


    /* dissect the PCOM Data */
    offset += 2;
    next_tvb = tvb_new_subset_length( tvb, offset, tvb_captured_length(tvb)-1);
    if( tvb_reported_length_remaining(tvb, offset) > 0 ){
        if ( pcom_mode == PCOM_ASCII)
            call_dissector_with_data(pcomascii_handle, next_tvb, pinfo, tree, &pcom_mode);
        else
            call_dissector_with_data(pcombinary_handle, next_tvb, pinfo, tree, &pcom_mode);
    }

    return tvb_captured_length(tvb);
}

static int
dissect_pcomascii(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
        void *data _U_)
{
    /* Set up structures needed to add the protocol subtree and manage it */
    proto_item  *ti;
    proto_tree  *pcomascii_tree;

    guint        offset = 0;

    /* Create protocol tree */
    ti = proto_tree_add_item(tree, proto_pcomascii, tvb, offset, 0, ENC_NA);
    pcomascii_tree = proto_item_add_subtree(ti, ett_pcomascii);

    if (pinfo->srcport == global_pcomtcp_tcp_port ){ // Reply
        proto_tree_add_item(pcomascii_tree, hf_pcomascii_stx, tvb,
                offset, 2, ENC_ASCII|ENC_NA); // "/A"
        offset += 2;
    }else{
        proto_tree_add_item(pcomascii_tree, hf_pcomascii_stx, tvb,
                offset, 1, ENC_ASCII|ENC_NA); // "/"
        offset += 1;
    }

    proto_tree_add_item(pcomascii_tree, hf_pcomascii_unitid, tvb,
            offset, 2, ENC_ASCII|ENC_NA);
    offset += 2;
    if (pinfo->srcport == global_pcomtcp_tcp_port ){ // Reply
        // (-2 stx -2 unitid -2 checksum -1 etx)
        proto_tree_add_item(pcomascii_tree, hf_pcomascii_command, tvb,
            offset, tvb_captured_length(tvb)-7, ENC_ASCII|ENC_NA);
        offset += tvb_captured_length(tvb)-7;
    }else{
        // (-1 stx -2 unitid -2 checksum -1 etx)
        proto_tree_add_item(pcomascii_tree, hf_pcomascii_command, tvb,
            offset, tvb_captured_length(tvb)-6, ENC_ASCII|ENC_NA);
        offset += tvb_captured_length(tvb)-6;
    }
    proto_tree_add_item(pcomascii_tree, hf_pcomascii_checksum, tvb,
            offset, 2, ENC_LITTLE_ENDIAN);
    offset += 2;
    proto_tree_add_item(pcomascii_tree, hf_pcomascii_etx, tvb,
            offset, 1, ENC_ASCII|ENC_NA);

    return tvb_captured_length(tvb);
}

static int
dissect_pcombinary(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
        void *data _U_)
{
    /* Set up structures needed to add the protocol subtree and manage it */
    proto_item  *ti;
    proto_tree  *pcombinary_tree;

    guint        offset = 0;
    proto_item    *hf_pcombinary_reserved1_item = NULL;
    proto_item    *hf_pcombinary_reserved2_item = NULL;
    proto_item    *hf_pcombinary_reserved3_item = NULL;
    proto_item    *hf_pcombinary_reserved4_item = NULL;

    /* Create protocol tree */
    ti = proto_tree_add_item(tree, proto_pcombinary, tvb, offset, 0, ENC_NA);
    pcombinary_tree = proto_item_add_subtree(ti, ett_pcombinary);

    proto_tree_add_item(pcombinary_tree, hf_pcombinary_stx, tvb,
            offset, 6, ENC_ASCII|ENC_NA);

    offset += 6;
    if (pinfo->srcport == global_pcomtcp_tcp_port){ //these bytes are transposed
        hf_pcombinary_reserved1_item = proto_tree_add_item(pcombinary_tree,
                hf_pcombinary_reserved1, tvb, offset, 1, ENC_NA);
        if(tvb_get_guint8(tvb, offset) !=254){
            expert_add_info_format(pinfo, hf_pcombinary_reserved1_item,
                    &ei_pcombinary_reserved1_bad_value,"Isn't 0xfe");
        }
        offset += 1;
        proto_tree_add_item(pcombinary_tree, hf_pcombinary_id, tvb,
                offset, 1, ENC_NA);
        offset += 1;
    }else{
        proto_tree_add_item(pcombinary_tree, hf_pcombinary_id, tvb,
                offset, 1, ENC_NA);
        offset += 1;
        proto_tree_add_item(pcombinary_tree, hf_pcombinary_reserved1, tvb,
                offset, 1, ENC_NA);
        offset += 1;
    }
    hf_pcombinary_reserved2_item = proto_tree_add_item(pcombinary_tree,
            hf_pcombinary_reserved2, tvb, offset, 1, ENC_NA);
    if( tvb_get_guint8(tvb, offset) !=1)
        expert_add_info_format(pinfo, hf_pcombinary_reserved2_item,
                &ei_pcombinary_reserved2_bad_value,"Isn't 1");
    offset += 1;
    hf_pcombinary_reserved3_item = proto_tree_add_item(pcombinary_tree,
            hf_pcombinary_reserved3, tvb, offset, 3, ENC_LITTLE_ENDIAN);
    if( tvb_get_letoh24(tvb,offset) != 0)
        expert_add_info_format(pinfo, hf_pcombinary_reserved3_item,
                &ei_pcombinary_reserved3_bad_value,"Isn't 0");
    offset += 3;
    proto_tree_add_item(pcombinary_tree, hf_pcombinary_command, tvb,
            offset, 1, ENC_NA);
    offset += 1;
    hf_pcombinary_reserved4_item = proto_tree_add_item(pcombinary_tree,
            hf_pcombinary_reserved4, tvb, offset, 1, ENC_NA);
    if( tvb_get_guint8(tvb, offset) !=0)
        expert_add_info_format(pinfo, hf_pcombinary_reserved4_item,
                &ei_pcombinary_reserved4_bad_value,"Isn't 0");
    offset += 1;
    proto_tree_add_item(pcombinary_tree, hf_pcombinary_command_specific, tvb,
            offset, 6, ENC_NA);
    offset += 6;
    proto_tree_add_item(pcombinary_tree, hf_pcombinary_data_length, tvb,
            offset, 2, ENC_LITTLE_ENDIAN);
    offset += 2;
    proto_tree_add_item(pcombinary_tree, hf_pcombinary_header_checksum, tvb,
            offset, 2, ENC_NA);
    offset += 2;
    if ((tvb_captured_length(tvb) - 27) > 0) // ( -3 footer - 24 header)
        proto_tree_add_item(pcombinary_tree, hf_pcombinary_data, tvb,
                offset, tvb_captured_length(tvb)-27, ENC_NA);
    offset += (tvb_captured_length(tvb)-27);
    proto_tree_add_item(pcombinary_tree, hf_pcombinary_footer_checksum, tvb,
            offset, 2, ENC_LITTLE_ENDIAN);
    offset += 2;
    proto_tree_add_item(pcombinary_tree, hf_pcombinary_etx, tvb,
            offset, 1, ENC_ASCII|ENC_NA);

    return tvb_captured_length(tvb);
}

static void
apply_pcomtcp_prefs(void)
{
    global_pcomtcp_tcp_port = prefs_get_uint_value("pcomtcp", "tcp.port");
}

void
proto_register_pcomtcp(void)
{
    static hf_register_info hf_pcomtcp[] = {
        { &hf_pcomtcp_transid,
            { "Transaction Identifier", "pcomtcp.trans_id",
                FT_UINT16, BASE_DEC, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcomtcp_protocol,
            { "Protocol Mode", "pcomtcp.protocol",
                FT_UINT8, BASE_DEC, VALS(pcomp_protocol_vals), 0x0,
                NULL, HFILL }
        },
        { &hf_pcomtcp_reserved,
            { "Reserved", "pcomtcp.reserved",
                FT_UINT8, BASE_DEC, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcomtcp_length,
            { "Length (bytes)", "pcomtcp.length",
                FT_UINT16, BASE_DEC, NULL, 0x0,
                NULL, HFILL }
        },
    };


    static hf_register_info hf_pcomascii[] = {
        { &hf_pcomascii_stx,
            { "STX", "pcomascii.stx",
                FT_STRING, BASE_NONE, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcomascii_unitid,
            { "Unit Identifier", "pcomascii.unitid",
                FT_UINT16, BASE_HEX, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcomascii_command,
            { "Command", "pcomascii.command",
                FT_STRING, BASE_NONE, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcomascii_checksum,
            { "Checksum", "pcomascii.checksum",
                FT_UINT16, BASE_HEX, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcomascii_etx,
            { "ETX", "pcomascii.etx",
                FT_STRING, BASE_NONE, NULL, 0x0,
                NULL, HFILL }
        },
    };


    static hf_register_info hf_pcombinary[] = {
        { &hf_pcombinary_stx,
            { "STX", "pcombinary.stx",
                FT_STRING, BASE_NONE, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcombinary_id,
            { "ID (CANBUS or RS485)", "pcombinary.id",
                FT_UINT8, BASE_DEC, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcombinary_reserved1,
            { "Reserved", "pcombinary.reserved1",
                FT_UINT8, BASE_HEX, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcombinary_reserved2,
            { "Reserved", "pcombinary.reserved2",
                FT_UINT8, BASE_HEX, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcombinary_reserved3,
            { "Reserved", "pcombinary.reserved3",
                FT_UINT8, BASE_HEX, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcombinary_command,
            { "Command", "pcombinary.command",
                FT_BYTES, BASE_NONE, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcombinary_reserved4,
            { "Reserved", "pcombinary.reserved0",
                FT_UINT8, BASE_HEX, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcombinary_command_specific,
            { "Command Details", "pcombinary.command_specific",
                FT_BYTES, BASE_NONE, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcombinary_data_length,
            { "Data Length", "pcombinary.data_length",
                FT_UINT8, BASE_DEC, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcombinary_header_checksum,
            { "(Header) Checksum", "pcombinary.header_checksum",
                FT_UINT16, BASE_HEX, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcombinary_data,
            { "Data", "pcombinary.data",
                FT_BYTES, BASE_NONE, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcombinary_footer_checksum,
            { "(Footer) Checksum", "pcombinary.footer_checksum",
                FT_UINT16, BASE_HEX, NULL, 0x0,
                NULL, HFILL }
        },
        { &hf_pcombinary_etx,
            { "ETX", "pcombinary.etx",
                FT_STRING, BASE_NONE, NULL, 0x0,
                NULL, HFILL }
        },
    };

    /* Setup protocol subtree array */
    static gint *ett[] = {
        &ett_pcomtcp,
        &ett_pcomascii,
        &ett_pcombinary
    };

    static ei_register_info pcomtcp_ei[] = {
        { &ei_pcomtcp_reserved_bad_value,
          { "pcombinary.reserved.bad_value", PI_PROTOCOL, PI_CHAT,
            "Isn't 0", EXPFILL }
        },
    };

    static ei_register_info pcombinary_ei[] = {
        { &ei_pcombinary_reserved1_bad_value,
          { "pcombinary.reserved1.bad_value", PI_PROTOCOL, PI_CHAT,
            "Isn't  0xfe", EXPFILL }
        },
        { &ei_pcombinary_reserved2_bad_value,
          { "pcombinary.reserved2.bad_value", PI_PROTOCOL, PI_CHAT,
            "Isn't  1", EXPFILL }
        },
        { &ei_pcombinary_reserved3_bad_value,
          { "pcombinary.reserved3.bad_value", PI_PROTOCOL, PI_CHAT,
            "Isn't  0", EXPFILL }
        },
        { &ei_pcombinary_reserved4_bad_value,
          { "pcombinary.reserved4.bad_value", PI_PROTOCOL, PI_CHAT,
            "Isn't  0", EXPFILL }
        },
    };

    expert_module_t* expert_pcomtcp;
    expert_module_t* expert_pcombinary;

    /* Register the protocol name and description */
    proto_pcomtcp = proto_register_protocol("PCOM/TCP","PCOM/TCP", "pcomtcp");
    proto_pcomascii = proto_register_protocol("PCOM ASCII","PCOM ASCII", "pcomascii");
    proto_pcombinary = proto_register_protocol("PCOM BINARY","PCOM BINARY", "pcombinary");

    pcomtcp_handle = register_dissector("pcomtcp", dissect_pcomtcp, proto_pcomtcp);
    pcomascii_handle = register_dissector("pcomascii", dissect_pcomascii, proto_pcomascii);
    pcombinary_handle = register_dissector("pcombinary", dissect_pcombinary, proto_pcombinary);

    /* Required function calls to register the header fields and subtrees */
    proto_register_field_array(proto_pcomtcp, hf_pcomtcp, array_length(hf_pcomtcp));
    proto_register_field_array(proto_pcomascii, hf_pcomascii, array_length(hf_pcomascii));
    proto_register_field_array(proto_pcombinary, hf_pcombinary, array_length(hf_pcombinary));

    proto_register_subtree_array(ett, array_length(ett));
    expert_pcomtcp = expert_register_protocol(proto_pcomtcp);
    expert_pcombinary = expert_register_protocol(proto_pcombinary);

    expert_register_field_array(expert_pcomtcp, pcomtcp_ei, array_length(pcomtcp_ei));
    expert_register_field_array(expert_pcombinary, pcombinary_ei, array_length(pcombinary_ei));

    prefs_register_protocol(proto_pcomtcp, apply_pcomtcp_prefs);

}

void
proto_reg_handoff_pcomtcp(void)
{
    dissector_add_uint_with_preference("tcp.port", PCOMTCP_TCP_PORT, pcomtcp_handle);
}

/*
 * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
 *
 * Local variables:
 * c-basic-offset: 4
 * tab-width: 8
 * indent-tabs-mode: nil
 * End:
 *
 * vi: set shiftwidth=4 tabstop=8 expandtab:
 * :indentSize=4:tabSize=8:noTabs=true:
 */