Bro Script to look up hostname from IP Address

I've wrote a bro script using the Input::add_table function to look up IPs and their corresponding hostnames and insert them into the conn_id record - so that I have id.source_name & id.destination_name in every log file. This works fine except when there are tunnel events and it crashes bro with a segmentation error. I suspect this is something to do with the encapsulation id but I don't really know. I know I could add the src & dest names to the Info record for each type but that would mean modifying every type. Is what I'm trying to do fundamentally incorrect or is there a bug in the tunnel code causing the crash ? Or is there a better way to do this

export {
global host_table: table[addr] of Val = table();
}

redef record conn_id += {
    src_name: string &optional &log;
    dest_name: string &optional &log;
};

const host_file = “hosts.txt”

event bro_init() &priority=20
{
    Input::add_table([$source=host_file, $name =“host_stream”, $idx=Idx, $val=Val, $destination=host_table]);
    Input::remove(“host_stream”);
}

event new_connection( c: connection ) {
    if( c$id$orig_h in host_table ) {
        c$id$src_name = host_table[c$id$orig_h]$host;
    }
    if( c$id$resp_h in host_table ) {
        c$id$dest_name = host_table[c$id$resp_h]$host;
    }
}

Unfortunately you don't want to extend the conn_id record. It is used internally in a number of ways which this change would impact. I would extend the Conn::Info record and add the data there.

Your script was missing some pieces and I wanted to make the answer more usable for people in the future so I filled out the missing areas:

@load base/protocols/conn

module MyHostNames;

export {
    ## File to load hostnames from.
    const host_file = "hosts.txt" &redef;
}

type Idx: record {
    host: addr;
};

type Val: record {
    hostname: string;
};

global host_table: table[addr] of Val = table();

redef record Conn::Info += {
    orig_name: string &optional &log;
    resp_name: string &optional &log;
};

event bro_init() &priority=5
    {
    Input::add_table([$source=host_file,
                      $name="myhostnames_stream",
                      $idx=Idx,
                      $val=Val,
                      $destination=host_table]);
    Input::remove("myhostnames_stream");
    }

event connection_state_remove(c: connection)
    {
    if ( c$id$orig_h in host_table )
        {
        c$conn$orig_name = host_table[c$id$orig_h]$hostname;
        }

    if ( c$id$resp_h in host_table )
        {
        c$conn$resp_name = host_table[c$id$resp_h]$hostname;
        }
    }

I used an input file that looks like this (keep in mind some literal tabs in this data between columns!):

#fields host    hostname
#types  addr    string
1.2.3.4 special-host