/* packet-sane.c

 * Routines for SANE dissection

 * Copyright 2024, James Ring <sjr@jdns.org>

 *

 * Wireshark - Network traffic analyzer

 * By Gerald Combs <gerald@wireshark.org>

 * Copyright 1998 Gerald Combs

 *

 * SPDX-License-Identifier: GPL-2.0-or-later

 */

/**

 * A dissector for the SANE protocol (https://sane-project.gitlab.io/standard/net.html).

 *

 * This dissector works only for the control protocol (typically between a

 * client on some ephemeral port and a server on port 6566). The data transfer

 * of scanned images is done on a separate connection. Future versions of this

 * dissector might provide dissected image information.

 *

 * SANE is a protocol layered on top of TCP. The main dissect_sane function

 * relies on tcp_dissect_pdus to reassemble large messages. The protocol has no

 * meta-information (e.g. length of packet, type of message), the only way you

 * can know the format of a response is to see the corresponding request. The

 * only way you can know the length of a PDU is to read and understand various

 * fields in the request/response.

 *

 * For these reasons, the get_sane_pdu_len function has to pretty much do all

 * the work of the dissector itself. There is probably a more elegant way to do

 * this without the duplication that exists between get_sane_pdu_len and

 * dissect_sane_pdu.

 */

/* TODO

 * - Setup proper request / response tracking, with

 *   - references to related packets,

 *   - response time indications.

 */

#include "config.h"

#include <wireshark.h>

#include <epan/packet.h>

#include <epan/proto_data.h>

#include <epan/prefs.h>

#include <epan/exceptions.h>

#include "packet-tcp.h"

#define SANE_WORD_LENGTH 4

#define SANE_MODULE_NAME "sane"

#define SANE_PORT "6566"

static range_t *sane_server_ports;

static dissector_handle_t sane_handle;

static int hf_sane_opcode;

static int hf_sane_version;

static int hf_sane_version_major;

static int hf_sane_version_minor;

static int hf_sane_version_build;

static int hf_sane_username;

static int hf_sane_password;

static int hf_sane_string;

static int hf_sane_string_length;

static int hf_sane_array_length;

static int hf_sane_device_descriptor;

static int hf_sane_device_name;

static int hf_sane_device_vendor;

static int hf_sane_device_model;

static int hf_sane_device_type;

static int hf_sane_resource_name;

static int hf_sane_device_handle;

static int hf_sane_option_descriptor;

static int hf_sane_option_index;

static int hf_sane_option_control_action;

static int hf_sane_option_value_type;

static int hf_sane_option_length;

static int hf_sane_option_count;

static int hf_sane_option_name;

static int hf_sane_option_value;

static int hf_sane_option_string_value;

static int hf_sane_option_numeric_value;

static int hf_sane_option_boolean_value;

static int hf_sane_option_title;

static int hf_sane_option_description;

static int hf_sane_option_unit;

static int hf_sane_option_size;

static int hf_sane_option_capabilities;

static int hf_sane_option_constraints;

static int hf_sane_option_constraint_type;

static int hf_sane_option_possible_string_value;

static int hf_sane_option_possible_word_value;

static int hf_sane_option_range_min;

static int hf_sane_option_range_max;

static int hf_sane_option_range_quant;

static int hf_sane_status;

static int hf_sane_data_port;

static int hf_sane_byte_order;

static int hf_sane_pointer_value;

static int hf_sane_frame_format;

static int hf_sane_scan_line_count;

static int hf_sane_scan_pixel_depth;

static int hf_sane_scan_pixels_per_line;

static int hf_sane_scan_bytes_per_line;

static int hf_sane_scan_is_last_frame;

static int hf_sane_dummy_value;

#define SANE_CAP_NONE 0x00000000

#define SANE_CAP_SOFT_SELECT 0x00000001

#define SANE_CAP_HARD_SELECT 0x00000002

#define SANE_CAP_SOFT_DETECT 0x00000004

#define SANE_CAP_EMULATED 0x00000008

#define SANE_CAP_AUTOMATIC 0x00000010

#define SANE_CAP_INACTIVE 0x00000020

#define SANE_CAP_ADVANCED 0x00000040

static int hf_sane_option_capability_soft_select;

static int hf_sane_option_capability_hard_select;

static int hf_sane_option_capability_soft_detect;

static int hf_sane_option_capability_emulated;

static int hf_sane_option_capability_automatic;

static int hf_sane_option_capability_inactive;

static int hf_sane_option_capability_advanced;

#define SANE_INFO_INEXACT 0x00000001

#define SANE_INFO_RELOAD_OPTIONS 0x00000002

#define SANE_INFO_RELOAD_PARAMS 0x00000004

static int hf_sane_control_option_info;

static int hf_sane_control_option_inexact;

static int hf_sane_control_option_reload_options;

static int hf_sane_control_option_reload_params;

static int* const sane_cap_bits[] = {

    &hf_sane_option_capability_soft_select,

    &hf_sane_option_capability_hard_select,

    &hf_sane_option_capability_soft_detect,

    &hf_sane_option_capability_emulated,

    &hf_sane_option_capability_automatic,

    &hf_sane_option_capability_inactive,

    &hf_sane_option_capability_advanced,

    NULL,

};

static int* const sane_control_option_info_bits[] = {

    &hf_sane_control_option_inexact,

    &hf_sane_control_option_reload_options,

    &hf_sane_control_option_reload_params,

    NULL,

};

static int proto_sane;

static int ett_sane;

static int ett_sane_version;

static int ett_sane_string;

static int ett_sane_option;

static int ett_sane_option_value;

static int ett_sane_option_capabilities;

static int ett_sane_option_constraints;

static int ett_sane_control_option_info;

static int ett_sane_device_descriptor;

typedef enum {

    SANE_NET_UNKNOWN = -1,

    SANE_NET_INIT = 0,

    SANE_NET_GET_DEVICES = 1,

    SANE_NET_OPEN = 2,

    SANE_NET_CLOSE = 3,

    SANE_NET_GET_OPTION_DESCRIPTORS = 4,

    SANE_NET_CONTROL_OPTION = 5,

    SANE_NET_GET_PARAMETERS = 6,

    SANE_NET_START = 7,

    SANE_NET_CANCEL = 8,

    SANE_NET_AUTHORIZE = 9,

    SANE_NET_EXIT = 10,

} sane_rpc_code;

static const value_string opcode_vals[] = {

    {SANE_NET_INIT,                   "SANE_NET_INIT"},

    {SANE_NET_GET_DEVICES,            "SANE_NET_GET_DEVICES"},

    {SANE_NET_OPEN,                   "SANE_NET_OPEN"},

    {SANE_NET_CLOSE,                  "SANE_NET_CLOSE"},

    {SANE_NET_GET_OPTION_DESCRIPTORS, "SANE_NET_GET_OPTION_DESCRIPTORS"},

    {SANE_NET_CONTROL_OPTION,         "SANE_NET_CONTROL_OPTION"},

    {SANE_NET_GET_PARAMETERS,         "SANE_NET_GET_PARAMETERS"},

    {SANE_NET_START,                  "SANE_NET_START"},

    {SANE_NET_CANCEL,                 "SANE_NET_CANCEL"},

    {SANE_NET_AUTHORIZE,              "SANE_NET_AUTHORIZE"},

    {SANE_NET_EXIT,                   "SANE_NET_EXIT"},

    {0, NULL},

};

typedef enum {

    SANE_NO_CONSTRAINT = 0,

    SANE_CONSTRAINT_RANGE = 1,

    SANE_CONSTRAINT_WORD_LIST = 2,

    SANE_CONSTRAINT_STRING_LIST = 3,

} sane_constraint_type;

static const value_string sane_constraint_type_names[] = {

    {SANE_NO_CONSTRAINT,          "SANE_NO_CONSTRAINT"},

    {SANE_CONSTRAINT_RANGE,       "SANE_CONSTRAINT_RANGE"},

    {SANE_CONSTRAINT_WORD_LIST,   "SANE_CONSTRAINT_WORD_LIST"},

    {SANE_CONSTRAINT_STRING_LIST, "SANE_CONSTRAINT_STRING_LIST"},

    {0, NULL},

};

typedef enum {

    SANE_TYPE_BOOL = 0,

    SANE_TYPE_INT = 1,

    SANE_TYPE_FIXED = 2,

    SANE_TYPE_STRING = 3,

    SANE_TYPE_BUTTON = 4,

    SANE_TYPE_GROUP = 5,

} sane_value_type;

static const value_string sane_value_types[] = {

    {SANE_TYPE_BOOL,   "SANE_TYPE_BOOL"},

    {SANE_TYPE_INT,    "SANE_TYPE_INT"},

    {SANE_TYPE_FIXED,  "SANE_TYPE_FIXED"},

    {SANE_TYPE_STRING, "SANE_TYPE_STRING"},

    {SANE_TYPE_BUTTON, "SANE_TYPE_BUTTON"},

    {SANE_TYPE_GROUP,  "SANE_TYPE_GROUP"},

    {0, NULL},

};

static const value_string control_types[] = {

    {0, "SANE_ACTION_GET_VALUE"},

    {1, "SANE_ACTION_SET_VALUE"},

    {2, "SANE_ACTION_SET_AUTO"},

    {0, NULL},

};

typedef enum {

    SANE_UNIT_NONE = 0,

    SANE_UNIT_PIXEL = 1,

    SANE_UNIT_BIT = 2,

    SANE_UNIT_MM = 3,

    SANE_UNIT_DPI = 4,

    SANE_UNIT_PERCENT = 5,

    SANE_UNIT_MICROSECOND = 6,

} sane_option_unit;

static const value_string sane_option_units[] = {

    {SANE_UNIT_NONE,        "SANE_UNIT_NONE"},

    {SANE_UNIT_PIXEL,       "SANE_UNIT_PIXEL"},

    {SANE_UNIT_BIT,         "SANE_UNIT_BIT"},

    {SANE_UNIT_MM,          "SANE_UNIT_MM"},

    {SANE_UNIT_DPI,         "SANE_UNIT_DPI"},

    {SANE_UNIT_PERCENT,     "SANE_UNIT_PERCENT"},

    {SANE_UNIT_MICROSECOND, "SANE_UNIT_MICROSECOND"},

    {0, NULL},

};

static const value_string sane_option_unit_suffixes[] = {

    {1, "px"},

    {2, "bits"},

    {3, "mm"},

    {4, "dpi"},

    {5, "%"},

    {6, "ms"},

    {0, NULL},

};

typedef enum {

    SANE_STATUS_UNKNOWN = -1,

    SANE_STATUS_OK = 0,

} sane_status;

static const value_string status_values[] = {

    {0,  "SANE_STATUS_GOOD"},

    {1,  "SANE_STATUS_UNSUPPORTED"},

    {2,  "SANE_STATUS_CANCELLED"},

    {3,  "SANE_STATUS_DEVICE_BUSY"},

    {4,  "SANE_STATUS_INVAL"},

    {5,  "SANE_STATUS_EOF"},

    {6,  "SANE_STATUS_JAMMED"},

    {7,  "SANE_STATUS_NO_DOCS"},

    {8,  "SANE_STATUS_COVER_OPEN"},

    {9,  "SANE_STATUS_IO_ERROR"},

    {10, "SANE_STATUS_NO_MEM"},

    {11, "SANE_STATUS_ACCESS_DENIED"},

    {0, NULL},

};

static const value_string sane_frame_format_names[] = {

    {0, "SANE_FRAME_GRAY"},

    {1, "SANE_FRAME_RGB"},

    {2, "SANE_FRAME_RED"},

    {3, "SANE_FRAME_GREEN"},

    {4, "SANE_FRAME_BLUE"},

    {0, NULL},

};

typedef struct {

    bool is_request;

    sane_rpc_code opcode;

    uint32_t packet_num;

} sane_pdu;

/* Keep track of current request status during first pass.

   N.B. opcode is stored in per-frame data and read during subsequent passes.

   Could if necessary be expanded to include frame numbers and timestamps for

   more complete request/response tracking.

*/

typedef struct {

    bool     seen_request;

    sane_pdu last_request;

    bool     auth;

} sane_session;

typedef struct {

    tvbuff_t *tvb;

    unsigned offset;

    unsigned bytes_read;

} tvb_sane_reader;

static int

tvb_read_sane_word(tvb_sane_reader *r, uint32_t *dest) {

    if (tvb_captured_length_remaining(r->tvb, r->offset) < SANE_WORD_LENGTH) {

        return 0;

    }

    if (dest) {

        *dest = tvb_get_ntohl(r->tvb, r->offset);

    }

    r->offset += SANE_WORD_LENGTH;

    r->bytes_read += SANE_WORD_LENGTH;

    return SANE_WORD_LENGTH;

}

#define WORD_OR_RETURN(r, var) \

    do { if (tvb_read_sane_word((r), (var)) == 0) { return 0; } } while(0)

static int

tvb_read_sane_string(tvb_sane_reader *r, wmem_allocator_t *alloc, char **dest) {

    unsigned str_len;

    WORD_OR_RETURN(r, (uint32_t*)&str_len);

    if (tvb_captured_length_remaining(r->tvb, r->offset) < str_len) {

        return 0;

    }

    if (dest) {

        *dest = (char*)tvb_get_string_enc(alloc, r->tvb, r->offset, str_len, ENC_ASCII | ENC_NA);

    }

    r->offset += str_len;

    r->bytes_read += str_len;

    return SANE_WORD_LENGTH + str_len;

}

#define STRING_OR_RETURN(r) \

    do { if (tvb_read_sane_string((r), NULL, NULL) == 0) { return 0; } } while(0)

static unsigned

tvb_skip_bytes(tvb_sane_reader *r, unsigned len) {

    if (tvb_captured_length_remaining(r->tvb, r->offset) < len) {

        return 0;

    }

    r->offset += len;

    r->bytes_read += len;

    return len;

}

/**

 * Returns the expected response type for the (presumed) response in `pinfo`.

 * This usually returns the opcode of the last request seen in the conversation,

 * except for special handling of the authorization flow, for example:

 *

 * Client: SANE_NET_OPEN request (1)

 * Server: SANE_NET_OPEN response, authentication resource set (2)

 * Client: SANE_NET_AUTHORIZE request, username+password sent (3)

 * Server: SANE_NET_AUTHORIZE response sent, success (4)

 * Server: SANE_NET_OPEN response immediately sent (5)

 *

 * In this case, if the expected response type of PDU 5 is SANE_NET_OPEN,

 * because the server is responding to the request sent in PDU 2.

 */

static sane_rpc_code

get_sane_expected_response_type(sane_session *sess, packet_info *pinfo) {

    /* Look up any previous result. N.B. as called for length *and* dissecting,

       there may already be a value stored on first pass! */

    if (PINFO_FD_VISITED(pinfo) || p_get_proto_data(wmem_file_scope(), pinfo, proto_sane, 0)) {

        return (sane_rpc_code)GPOINTER_TO_UINT(p_get_proto_data(wmem_file_scope(), pinfo, proto_sane, 0));

    }

    /* First pass. Will be response to last_request if set, or AUTH request if flag set. */

    sane_rpc_code code = SANE_NET_UNKNOWN;

    if (sess->seen_request) {

        if (sess->auth) {

            code = SANE_NET_AUTHORIZE;

            sess->auth = false;

        }

        else {

            code = sess->last_request.opcode;

        }

    }

    /* Remember this code for later queries. */

    p_add_proto_data(wmem_file_scope(), pinfo, proto_sane, 0, GUINT_TO_POINTER(code));

    return code;

}

static proto_item *

dissect_sane_word(tvb_sane_reader *r, proto_tree *tree, int hfindex, int *word) {

    proto_item *item = proto_tree_add_item(tree, hfindex, r->tvb, r->offset, SANE_WORD_LENGTH,

                        ENC_BIG_ENDIAN);

    // safe to ignore the return value here, we're guaranteed to have enough bytes to

    // read a word.

    (void)tvb_read_sane_word(r, (uint32_t*)word);

    return item;

}

/**

 * Dissects and returns a SANE-encoded string from `r`.

 *

 * Also creates a proto_item representing the string. The `format` string should

 * contain a string format specifier (i.e. "%s"), which will be replaced with the

 * consumed string in the proto_item's text.

 */

static char *

dissect_sane_string(tvb_sane_reader *r, packet_info *pinfo, proto_tree *tree, int hfindex, const char *format) {

    int offset = r->offset;

    char *str = "";

    int len = tvb_read_sane_string(r, pinfo->pool, &str);

    proto_item *str_item = proto_tree_add_item(tree, hf_sane_string, r->tvb, offset, len, ENC_NA);

    proto_tree *str_tree = proto_item_add_subtree(str_item, ett_sane_string);

    proto_item_set_text(str_item, format, str);

    proto_tree_add_item(str_tree, hf_sane_string_length, r->tvb, offset, SANE_WORD_LENGTH, ENC_BIG_ENDIAN);

    proto_tree_add_item(str_tree, hfindex, r->tvb, offset + SANE_WORD_LENGTH, len - SANE_WORD_LENGTH, ENC_NA);

    return str;

}

static void

dissect_sane_net_init_request(tvb_sane_reader *r, packet_info *pinfo, proto_tree *tree) {

    int version = 0;

    int offset = r->offset;

    proto_item *version_item = dissect_sane_word(r, tree, hf_sane_version, &version);

    proto_item *version_tree = proto_item_add_subtree(version_item, ett_sane_version);

    proto_item_append_text(version_item, " (major: %d, minor: %d, build: %d)", version >> 24,

                           (version >> 16) & 0xff, version & 0xffff);

    proto_tree_add_item(version_tree, hf_sane_version_major, r->tvb, offset, 1, ENC_NA);

    proto_tree_add_item(version_tree, hf_sane_version_minor, r->tvb, offset + 1, 1, ENC_NA);

    proto_tree_add_item(version_tree, hf_sane_version_build, r->tvb, offset + 2, 2, ENC_BIG_ENDIAN);

    dissect_sane_string(r, pinfo, tree, hf_sane_username, "Username: %s");

}

static void

dissect_sane_net_open_request(tvb_sane_reader *r, packet_info *pinfo, proto_tree *tree) {

    dissect_sane_string(r, pinfo, tree, hf_sane_device_name, "Device name: %s");

}

static void

dissect_control_option_value(tvb_sane_reader *r, packet_info *pinfo, proto_tree *tree) {

    int value_type = 0;

    dissect_sane_word(r, tree, hf_sane_option_value_type, &value_type);

    proto_item *value_item = proto_tree_add_item(tree, hf_sane_option_value, r->tvb, r->offset, -1, ENC_NA);

    proto_tree *value_tree = proto_item_add_subtree(value_item, ett_sane_option_value);

    int array_length = 0;

    proto_item *length_item = dissect_sane_word(r, value_tree, hf_sane_option_length, &array_length);

    switch (value_type) {

    case SANE_TYPE_STRING:

        dissect_sane_string(r, pinfo, value_tree, hf_sane_option_string_value, "Option value: '%s'");

        break;

    case SANE_TYPE_FIXED:

    case SANE_TYPE_INT:

    case SANE_TYPE_BOOL:

        proto_item_append_text(length_item, " (vector of length %d)", array_length / SANE_WORD_LENGTH);

        dissect_sane_word(r, value_tree, hf_sane_array_length, &array_length);

        for (int i = 0; i < array_length; i++) {

            if (value_type == SANE_TYPE_FIXED) {

                int value = 0;

                proto_item *numeric_value = dissect_sane_word(r, value_tree, hf_sane_option_numeric_value, &value);

                proto_item_append_text(numeric_value, " (%f)", ((double) value) / (1 << 16));

            } else if (value_type == SANE_TYPE_INT) {

                int value = 0;

                proto_item *numeric_value = dissect_sane_word(r, value_tree, hf_sane_option_numeric_value, &value);

                proto_item_append_text(numeric_value, " (%d)", value);

            } else if (value_type == SANE_TYPE_BOOL) {

                dissect_sane_word(r, value_tree, hf_sane_option_boolean_value, NULL);

            }

        }

        break;

    case SANE_TYPE_BUTTON: /* Length supposed to be ignored, should be zero. */

        /* Since there is no value, presumably it doesn't include the

         * extra word for the array length? Need an example. */

    default: /* These violate the spec, and should have an expert info */

        if (tvb_skip_bytes(r, array_length) == 0) {

            /* Bogus length, didn't advance the offset. */

            /* We shouldn't get here because get_sane_pdu_len would have

             * returned 0. */

            THROW(ReportedBoundsError);

        }

    }

}

static void

dissect_sane_net_control_option_request(tvb_sane_reader *r, packet_info *pinfo, proto_tree *tree) {

    dissect_sane_word(r, tree, hf_sane_device_handle, NULL);

    dissect_sane_word(r, tree, hf_sane_option_index, NULL);

    dissect_sane_word(r, tree, hf_sane_option_control_action, NULL);

    dissect_control_option_value(r, pinfo, tree);

}

static void

dissect_sane_net_authorize_request(tvb_sane_reader *r, packet_info *pinfo, proto_tree *tree) {

    dissect_sane_string(r, pinfo, tree, hf_sane_resource_name, "Authentication resource: %s");

    dissect_sane_string(r, pinfo, tree, hf_sane_username, "Username: %s");

    dissect_sane_string(r, pinfo, tree, hf_sane_password, "Password: %s");

}

/** Dissects a message whose only payload is a device handle. */

static void

dissect_sane_device_handle_request(tvb_sane_reader *r, proto_tree *tree) {

    dissect_sane_word(r, tree, hf_sane_device_handle, NULL);

}

static int

dissect_sane_request(tvb_sane_reader *r, packet_info *pinfo, proto_tree *tree) {

    unsigned opcode = SANE_NET_UNKNOWN;

    char* str_opcode;

    dissect_sane_word(r, tree, hf_sane_opcode, (int*)&opcode);

    str_opcode = val_to_str(pinfo->pool, opcode, opcode_vals, "Unknown opcode (%u)");

    proto_item_append_text(tree, ": %s request", str_opcode);

    col_append_fstr(pinfo->cinfo, COL_INFO, "%s request", str_opcode);

    switch (opcode) {

        case SANE_NET_INIT:

            dissect_sane_net_init_request(r, pinfo, tree);

            break;

        case SANE_NET_GET_DEVICES:

            // no additional payload here

            break;

        case SANE_NET_OPEN:

            dissect_sane_net_open_request(r, pinfo, tree);

            break;

        case SANE_NET_CONTROL_OPTION:

            dissect_sane_net_control_option_request(r, pinfo, tree);

            break;

        case SANE_NET_CLOSE:

        case SANE_NET_START:

        case SANE_NET_CANCEL:

        case SANE_NET_GET_PARAMETERS:

        case SANE_NET_GET_OPTION_DESCRIPTORS:

            dissect_sane_device_handle_request(r, tree);

            break;

        case SANE_NET_AUTHORIZE:

            dissect_sane_net_authorize_request(r, pinfo, tree);

            break;

    }

    return r->bytes_read;

}

static proto_item *

dissect_sane_status(tvb_sane_reader *r, packet_info *pinfo, proto_tree *tree, unsigned *status_ptr) {

    int offset = r->offset;

    unsigned status = SANE_STATUS_UNKNOWN;

    char* str_status;

    // Safe to ignore the return value here, we're guaranteed to have enough bytes to

    // read a word.

    (void)tvb_read_sane_word(r, &status);

    str_status = val_to_str(pinfo->pool, status, status_values, "Unknown status (%u)");

    proto_item_append_text(tree, " (%s)", str_status);

    col_append_fstr(pinfo->cinfo, COL_INFO, " (%s)", str_status);

    proto_item *status_item = proto_tree_add_item(tree, hf_sane_status, r->tvb, offset, SANE_WORD_LENGTH, ENC_BIG_ENDIAN);

    proto_item_append_text(status_item, " (%s)", str_status);

    if (status_ptr) {

        *status_ptr = status;

    }

    return status_item;

}

static void

dissect_sane_net_init_response(tvb_sane_reader *r, packet_info *pinfo, proto_tree *tree) {

    unsigned status;

    dissect_sane_status(r, pinfo, tree, &status);

    int version = 0;

    proto_item *version_item = dissect_sane_word(r, tree, hf_sane_version, &version);

    proto_item *version_tree = proto_item_add_subtree(version_item, ett_sane_version);

    proto_item_append_text(version_item, " (major: %d, minor: %d, build: %d)", version >> 24,

                           (version >> 16) & 0xff, version & 0xffff);

    proto_tree_add_item(version_tree, hf_sane_version_major, r->tvb, SANE_WORD_LENGTH, 1, ENC_NA);

    proto_tree_add_item(version_tree, hf_sane_version_minor, r->tvb, SANE_WORD_LENGTH + 1, 1, ENC_NA);

    proto_tree_add_item(version_tree, hf_sane_version_build, r->tvb, SANE_WORD_LENGTH + 2, 2, ENC_BIG_ENDIAN);

}

static void

dissect_sane_net_open_response(tvb_sane_reader *r, packet_info *pinfo, proto_tree *tree) {

    unsigned status = SANE_STATUS_UNKNOWN;

    dissect_sane_status(r, pinfo, tree, &status);

    dissect_sane_word(r, tree, hf_sane_device_handle, NULL);

    dissect_sane_string(r, pinfo, tree, hf_sane_resource_name, "Authentication resource: '%s'");

}

static void

append_option_value(proto_item *item, int value, unsigned units, unsigned type) {

    switch (type) {

        case SANE_TYPE_INT:

            if (units) {

                proto_item_append_text(item, " (%d %s)", value,

                                    val_to_str_const(units, sane_option_unit_suffixes, "(unknown unit)"));

            } else {

                proto_item_append_text(item, " (%d)", value);

            }

            break;

        case SANE_TYPE_FIXED: {

            double fixed_val = ((double) value) / (1 << 16);

            if (units) {

                proto_item_append_text(item, " (%f %s)", fixed_val,

                                    val_to_str_const(units, sane_option_unit_suffixes, "(unknown unit)"));

            } else {

                proto_item_append_text(item, " (%f)", fixed_val);

            }

            break;

        }

        case SANE_TYPE_BOOL:

            proto_item_append_text(item, " (%s)", (value == 1) ? "True" : ((value == 0) ? "False" : "Invalid"));

            break;

        default:

            break;

    }

}

static void

dissect_sane_net_get_option_descriptors_response(tvb_sane_reader *r, packet_info *pinfo, proto_tree *tree) {

    int option_count = 0;

    dissect_sane_word(r, tree, hf_sane_option_count, &option_count);

    for (int i = 0; i < option_count; i++) {

        int unit = 0;

        int type = 0;

        int start_offset = r->offset;

        proto_item *option_item = proto_tree_add_item(tree, hf_sane_option_descriptor, r->tvb, start_offset, 0, ENC_NA);

        proto_tree *option_tree = proto_item_add_subtree(option_item, ett_sane_option);

        proto_item_set_text(option_item, "Option descriptor %d", i);

        dissect_sane_word(r, option_tree, hf_sane_pointer_value, NULL);

        char *option_name = dissect_sane_string(r, pinfo, option_tree, hf_sane_option_name, "Option name: %s");

        if (option_name && *option_name) {

            proto_item_append_text(option_item, " (%s)", option_name);

        }

        char *option_title = dissect_sane_string(r, pinfo, option_tree, hf_sane_option_title, "Option title: %s");

        if (!(option_name && *option_name) && (option_title && *option_title)) {

            proto_item_append_text(option_item, " (%s)", option_title);

        }

        dissect_sane_string(r, pinfo, option_tree, hf_sane_option_description, "Option description: %s");

        dissect_sane_word(r, option_tree, hf_sane_option_value_type, &type);

        dissect_sane_word(r, option_tree, hf_sane_option_unit, &unit);

        dissect_sane_word(r, option_tree, hf_sane_option_size, NULL);

        proto_tree_add_bitmask(option_tree, r->tvb, r->offset, hf_sane_option_capabilities,

                               ett_sane_option_capabilities,

                               sane_cap_bits, ENC_BIG_ENDIAN);

        /* XXX - Add consistency checks (expert items):

         * SANE_CAP_SOFT_SELECT set and SANE_CAP_HARD_SELECT set

         * SANE_CAP_SOFT_SELECT set and SANE_CAP_SOFT_DETECT not set

         */

        tvb_skip_bytes(r, SANE_WORD_LENGTH);

        int constraint_start = r->offset;

        proto_item *constraint_item = proto_tree_add_item(option_tree, hf_sane_option_constraints, r->tvb, constraint_start, 0, ENC_NA);

        proto_tree *constraint_tree = proto_item_add_subtree(constraint_item, ett_sane_option_constraints);

        int constraint_type = SANE_NO_CONSTRAINT;

        dissect_sane_word(r, constraint_tree, hf_sane_option_constraint_type, &constraint_type);

        proto_item_set_text(constraint_item, "Constraint type: %s",

                            val_to_str(pinfo->pool, constraint_type, sane_constraint_type_names, "Unknown (%u)"));

        int array_length = 0;

        int min = 0;

        int max = 0;

        int quant = 0;

        switch (constraint_type) {

            case SANE_CONSTRAINT_STRING_LIST:

                dissect_sane_word(r, constraint_tree, hf_sane_array_length, &array_length);

                for (int j = 0; j < array_length; j++) {

                    dissect_sane_string(r, pinfo, constraint_tree, hf_sane_option_possible_string_value, "Possible value: %s");

                }

                break;

            case SANE_CONSTRAINT_WORD_LIST:

                dissect_sane_word(r, constraint_tree, hf_sane_array_length, &array_length);

                for (int j = 0; j < array_length; j++) {

                    int value = 0;

                    proto_item *value_item = dissect_sane_word(r, constraint_tree, hf_sane_option_possible_word_value,

                                                               &value);

                    append_option_value(value_item, value, unit, type);

                }

                break;

            case SANE_CONSTRAINT_RANGE:

                dissect_sane_word(r, constraint_tree, hf_sane_pointer_value, NULL);

                proto_item *min_item = dissect_sane_word(r, constraint_tree, hf_sane_option_range_min, &min);

                append_option_value(min_item, min, unit, type);

                proto_item *max_item = dissect_sane_word(r, constraint_tree, hf_sane_option_range_max, &max);

                append_option_value(max_item, max, unit, type);

                proto_item *quant_item = dissect_sane_word(r, constraint_tree, hf_sane_option_range_quant, &quant);

                append_option_value(quant_item, quant, unit, type);

                break;

        }

        proto_item_set_len(constraint_item, r->offset - constraint_start);

        proto_item_set_len(option_item, r->offset - start_offset);

    }

}

static void

dissect_sane_net_start_response(tvb_sane_reader *r, packet_info *pinfo, proto_tree *tree) {

    dissect_sane_status(r, pinfo, tree, NULL);

    dissect_sane_word(r, tree, hf_sane_data_port, NULL);

    dissect_sane_word(r, tree, hf_sane_byte_order, NULL);

    dissect_sane_string(r, pinfo, tree, hf_sane_resource_name, "Authentication resource: %s");

}

static void

dissect_sane_net_get_parameters_response(tvb_sane_reader *r, packet_info *pinfo, proto_tree *tree) {

    dissect_sane_status(r, pinfo, tree, NULL);

    dissect_sane_word(r, tree, hf_sane_frame_format, NULL);

    dissect_sane_word(r, tree, hf_sane_scan_is_last_frame, NULL);

    dissect_sane_word(r, tree, hf_sane_scan_bytes_per_line, NULL);

    dissect_sane_word(r, tree, hf_sane_scan_pixels_per_line, NULL);

    dissect_sane_word(r, tree, hf_sane_scan_line_count, NULL);

    dissect_sane_word(r, tree, hf_sane_scan_pixel_depth, NULL);

}

static void

dissect_sane_net_control_option_response(tvb_sane_reader *r, packet_info *pinfo, proto_tree *tree) {

    dissect_sane_status(r, pinfo, tree, NULL);

    proto_tree_add_bitmask(tree, r->tvb, r->offset, hf_sane_control_option_info,

                           ett_sane_control_option_info,

                           sane_control_option_info_bits, ENC_BIG_ENDIAN);

    tvb_skip_bytes(r, SANE_WORD_LENGTH);

    dissect_control_option_value(r, pinfo, tree);

    dissect_sane_string(r, pinfo, tree, hf_sane_resource_name, "Authentication resource: %s");

}

static void

dissect_sane_dummy_response(tvb_sane_reader *r, proto_tree *tree) {

    dissect_sane_word(r, tree, hf_sane_dummy_value, NULL);

}

static void

dissect_sane_net_get_devices_response(tvb_sane_reader *r, packet_info *pinfo, proto_tree *tree) {

    dissect_sane_status(r, pinfo, tree, NULL);

    int array_len = 0;

    dissect_sane_word(r, tree, hf_sane_array_length, &array_len);

    for (int i = 0; i < array_len - 1; i++) {

        int offset = r->offset;

        proto_item *device_item = proto_tree_add_item(tree, hf_sane_device_descriptor, r->tvb, r->offset, -1, ENC_NA);

        proto_tree *device_tree = proto_item_add_subtree(device_item, ett_sane_device_descriptor);

        proto_item_set_text(device_item, "Device[%d] descriptor", i);

        dissect_sane_word(r, device_tree, hf_sane_pointer_value, NULL);

        dissect_sane_string(r, pinfo, device_tree, hf_sane_device_name, "Device name: %s");

        dissect_sane_string(r, pinfo, device_tree, hf_sane_device_vendor, "Device vendor: %s");

        dissect_sane_string(r, pinfo, device_tree, hf_sane_device_model, "Device model: %s");

        dissect_sane_string(r, pinfo, device_tree, hf_sane_device_type, "Device type: %s");

        proto_item_set_len(device_item, r->offset - offset);

    }

    dissect_sane_word(r, tree, hf_sane_pointer_value, NULL);

}

static void

dissect_sane_response(tvb_sane_reader *r, sane_session *sess, packet_info *pinfo, proto_tree *tree) {

    sane_rpc_code opcode = get_sane_expected_response_type(sess, pinfo);

    char* str_opcode = val_to_str(pinfo->pool, opcode, opcode_vals, "Unknown opcode (%u)");

    proto_item_append_text(tree, ": %s response", str_opcode);

    col_append_fstr(pinfo->cinfo, COL_INFO, "%s response", str_opcode);

    switch (opcode) {

        case SANE_NET_INIT:

            dissect_sane_net_init_response(r, pinfo, tree);

            break;

        case SANE_NET_OPEN:

            dissect_sane_net_open_response(r, pinfo, tree);

            break;

        case SANE_NET_GET_OPTION_DESCRIPTORS:

            dissect_sane_net_get_option_descriptors_response(r, pinfo, tree);

            break;

        case SANE_NET_START:

            dissect_sane_net_start_response(r, pinfo, tree);

            break;

        case SANE_NET_GET_PARAMETERS:

            dissect_sane_net_get_parameters_response(r, pinfo, tree);

            break;

        case SANE_NET_CONTROL_OPTION:

            dissect_sane_net_control_option_response(r, pinfo, tree);

            break;

        case SANE_NET_GET_DEVICES:

            dissect_sane_net_get_devices_response(r, pinfo, tree);

            break;

        case SANE_NET_CLOSE:

        case SANE_NET_CANCEL:

        case SANE_NET_AUTHORIZE:

            dissect_sane_dummy_response(r, tree);

            break;

        default:

            break;

    }

}

static int

dissect_sane_pdu(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data _U_) {

    tvb_sane_reader r = {.tvb = tvb, .bytes_read = 0, .offset = 0};

    conversation_t *conv = find_or_create_conversation(pinfo);

    if (!conv) {

        return 0;

    }

    sane_session *sess = conversation_get_proto_data(conv, proto_sane);

    DISSECTOR_ASSERT_HINT(sess, "no session found");

    col_set_str(pinfo->cinfo, COL_PROTOCOL, "SANE");

    col_clear(pinfo->cinfo, COL_INFO);

    proto_item *sane_item = proto_tree_add_item(tree, proto_sane, r.tvb, 0, -1, ENC_NA);

    proto_tree *sane_tree = proto_item_add_subtree(sane_item, ett_sane);

    if (value_is_in_range(sane_server_ports, pinfo->destport)) {

        dissect_sane_request(&r, pinfo, sane_tree);

    } else {

        dissect_sane_response(&r, sess, pinfo, sane_tree);

    }

    proto_item_set_len(sane_item, r.bytes_read);

    return r.bytes_read;

}

/**

 * Returns the length, in bytes, of the SANE PDU beginning at the given offset

 * within the buffer. If the PDU appears to be a response from a client and its

 * type cannot be determined (e.g. because Wireshark never saw the request),

 * or if the PDU appears to be truncated and its length cannot be determined,

 * this function returns 0.

 */

static unsigned

get_sane_pdu_len(packet_info *pinfo, tvbuff_t *tvb, int offset, void *data _U_) {

    tvb_sane_reader r = {.tvb = tvb, .offset = offset, .bytes_read = 0};

    conversation_t *conv = find_or_create_conversation(pinfo);

    if (!conv) {

        return 0;

    }

    sane_session *sess = conversation_get_proto_data(conv, proto_sane);

    if (!sess) {

        sess = wmem_new0(wmem_file_scope(), sane_session);

        conversation_add_proto_data(conv, proto_sane, sess);

    }

    if (value_is_in_range(sane_server_ports, pinfo->destport)) {

        /* REQUEST */

        unsigned opcode;

        WORD_OR_RETURN(&r, &opcode);

        sane_pdu pdu = {

            .is_request = true,

            .opcode = opcode,

            .packet_num = pinfo->num

        };

        if (!PINFO_FD_VISITED(pinfo)) {

            sess->seen_request = true;

            if (opcode == SANE_NET_AUTHORIZE) {

                /* Just set this flag, so can remember op being authorised */

                sess->auth = true;

            }

            else {

                /* Remember normal request */

                sess->last_request = pdu;

                sess->auth = false;

            }

        }

        switch (opcode) {

            case SANE_NET_INIT:

                WORD_OR_RETURN(&r, NULL);

                STRING_OR_RETURN(&r);

                break;

            case SANE_NET_GET_DEVICES:

            case SANE_NET_EXIT:

                break;

            case SANE_NET_OPEN:

                STRING_OR_RETURN(&r);

                break;

            case SANE_NET_CLOSE:

            case SANE_NET_GET_OPTION_DESCRIPTORS:

            case SANE_NET_GET_PARAMETERS:

            case SANE_NET_START:

            case SANE_NET_CANCEL:

                WORD_OR_RETURN(&r, NULL);

                break;

            case SANE_NET_CONTROL_OPTION:

                for (int i = 0; i < 4; i++) {

                    WORD_OR_RETURN(&r, NULL);

                }

                unsigned value_size;

                WORD_OR_RETURN(&r, &value_size);

                // Pointer to void, contains an extra word for whether the pointer is NULL

                if (tvb_skip_bytes(&r, SANE_WORD_LENGTH + value_size) == 0) {

                    return 0;

                }

                break;

            case SANE_NET_AUTHORIZE:

                STRING_OR_RETURN(&r);

                STRING_OR_RETURN(&r);

                STRING_OR_RETURN(&r);

                break;

        }

    } else {

        /* RESPONSE */

        sane_rpc_code opcode = get_sane_expected_response_type(sess, pinfo);

        unsigned array_len;

        switch (opcode) {

            case SANE_NET_INIT:

                for (int i = 0; i < 2; i++) {

                    WORD_OR_RETURN(&r, NULL);

                }

                break;

            case SANE_NET_OPEN:

                // Status word

                WORD_OR_RETURN(&r, NULL);

                // Device handle

                WORD_OR_RETURN(&r, NULL);

                // Authentication resource name

                STRING_OR_RETURN(&r);

                break;

            case SANE_NET_GET_OPTION_DESCRIPTORS:

                WORD_OR_RETURN(&r, &array_len);

                for (unsigned i = 0; i < array_len; i++) {

                    WORD_OR_RETURN(&r, NULL);

                    // read name, title and description

                    for (int j = 0; j < 3; j++) {

                        STRING_OR_RETURN(&r);

                    }

                    for (int j = 0; j < 4; j++) {

                        WORD_OR_RETURN(&r, NULL);

                    }

                    // constraint type

                    unsigned constraint_type;

                    WORD_OR_RETURN(&r, &constraint_type);

                    unsigned string_count;

                    unsigned value_list_length;

                    switch (constraint_type) {

                        case SANE_CONSTRAINT_STRING_LIST: