/*
 * The client for performing dynamic DNS updates, called by dotsd.c
 * 
 * (c) Columbia University, 2004-2006, All Rights Reserved.
 * Author: Weibin Zhao
 */

#include <sys/types.h>
#include <netinet/in.h>
// #include <arpa/nameser.h>
// #include <resolv.h>
// <res_update.h> can replace <arpa/nameser.h> and <resolv.h>
#include <res_update.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
#include "mod_dots.h"

/*
 * Make DNS query for IP address, use the first RR
 * Parameters:
 *     query:  query name 
 * Return value: 
 *     -1  error
 *      0  success
 */
int dns_ip_query(char *query, char *ip)
{
    union {
        HEADER hdr;
        u_char buf[8*1024];
    } response;
    ns_msg handle;
    ns_rr rr;
    int len;
    char name[MAXNAME];

    if (query == NULL)  {
        ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, NULL,
                     "DNS query is NULL");
        return -1;
    } 

    // add trailing dot if "query" does not have it
    len = strlen(query);
    if (query[len-1] == '.') {
        strcpy(name, query);
    } else {
        sprintf(name, "%s.", query);
    }

    // make query, the return value is response length
    len = res_query(name, C_IN, T_A, (u_char *)&response, sizeof(response));

    // initialize message handle
    ns_initparse(response.buf, len, &handle);

    // make sure that the answer section has at least one RR
    if (ns_msg_count(handle, ns_s_an) == 0) {
        ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, NULL,
                     "Answer section has zero RR");
        return -1;
    }

    // get the first RR from the answer section
    if (ns_parserr(&handle, ns_s_an, 0, &rr) < 0) {
        ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, NULL,
                     "Parse error for the first RR in answer section");
        return -1;
    }

    strcpy(ip, inet_ntoa(*(struct in_addr *)ns_rr_rdata(rr)));
    ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, NULL,
                 "name=%s, ip=%s", ns_rr_name(rr), ip);
    return 0;
}

/*
 * Make DNS query for SRV resource records, use the first RR
 * Parameters:
 *     query:  query name in the form of _Service._Proto.Name
 *     target: SRV target
 *     port:   SRV port
 * Return value: 
 *     -1  error
 *      0  success
 */
int dns_srv_query(char *query, char *target, short *port)
{
    union {
        HEADER hdr;
        u_char buf[4*1024];
    } response;
    ns_msg handle;
    ns_rr rr;
    u_char buf[256], *p;
    int t, len, priority, weight;

    // make query, the return value is response length
    len = res_query(query, C_IN, T_SRV, (u_char *)&response, sizeof(response));

    // initialize message handle
    ns_initparse(response.buf, len, &handle);

    // make sure that the answer section has at least one RR
    if (ns_msg_count(handle, ns_s_an) == 0) {
        ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, NULL,
                     "Answer section has zero RR");
        return -1;
    }

    // get the first RR from the answer section
    if (ns_parserr(&handle, ns_s_an, 0, &rr) < 0) {
        ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, NULL,
                     "Parse error for the first RR in answer section");
        return -1;
    }

    len = ns_rr_rdlen(rr);
    memcpy(buf, ns_rr_rdata(rr), len);
    p = buf;
    priority = ntohs(*(short *)p);
    p += 2;
    weight = ntohs(*(short *)p);
    p += 2;
    *port = ntohs(*(short *)p);
    p += 2;
    while (*p > 0) {
        t = *p;
        *p = '.';
        p += t+1;
    }
    p = buf + 7;
    strcpy(target, p);
    ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, NULL,
                 "name=%s port=%d target=%s", ns_rr_name(rr), *port, target);
    return 0;
}

/*
 * Performing dynamic updates in DNS (unsigned)
 * Parameters:
 *     update_opcode: ns_uop_delete, ns_uop_add 
 *     update_name:   FQDN
 *     update_type:   ns_t_a, ns_t_cname, ns_t_any, etc.
 *     update_data:   IP address, NULL, etc.
 * Return value: 
 *     -1  error
 *      0  update fail
 *      1  update success
 */
int dns_update_unsigned(int update_opcode, char *update_name, 
                        int update_type,   char *update_data)
{
    int        rval, r_ttl;
    ns_updrec *update_sec;
    char       opstr[10];

    /* Choose a right TTL based on update_opcode */
    if (update_opcode == ns_uop_add) {
        r_ttl = 1800;  /* 30 minutes */
        strcpy(opstr, "add");
    } else if (update_opcode == ns_uop_delete) {
        r_ttl = 0;     /* MUST be zero */
        strcpy(opstr, "delete");
    } else {           /* other update_opcode is NOT supported */
        ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, NULL,
                     "invalid update_opcode: %d", update_opcode);
        return -1;
    }

    /* 
     * Compose an update record for the update section "ns_s_ud".
     * We do not need to worry about the zone section since
     * res_update() will find the proper zone automatically
     * and prepend a zone section for us. However, we must
     * use "ns_c_in" as the CLASS
     */
    update_sec = (ns_updrec *) res_mkupdrec(ns_s_ud, update_name, 
                                            ns_c_in, update_type, r_ttl);
    if (update_sec == NULL) {
        ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, NULL,
                     "error in res_mkupdrec: %s", strerror(errno));
        return -1;
    }

    /* Set the update record properly: r_opcode/r_data/r_size */
    update_sec->r_opcode = update_opcode;
    if (update_data != NULL) {
        update_sec->r_size = strlen(update_data);
        update_sec->r_data = (u_char *) update_data;
    } else {
        update_sec->r_size = 0;
        update_sec->r_data = NULL;
    }

    // Set DNS update server for efficiency
    if (ddns_server_set == 1) dns_set_update_server(ddns_server, 53);

    /* Perform the real DNS update */
    rval = res_update(update_sec);
    ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, NULL,
                 "%d zone has been updated: %s %s(%s)", 
                 rval, opstr, update_name, update_data);

    /* Be sure to free the update record space */
    res_freeupdrec(update_sec);

    /* Indicate the number of zone has been updated */
    return rval;
}

// Set DNS update server for efficiency
int dns_set_update_server(char *serv, int serv_port)
{
    struct hostent *hp;
    char **p;
    static struct in_addr serv_addr;
    static int first_time = 1;

    if (first_time == 1) {
        hp = gethostbyname(serv);     // try domain name first
        if (hp == NULL) { // also try IP address if domain name fail
            hp = gethostbyaddr(serv, strlen(serv), AF_INET);
            if (hp == NULL) {
                ap_log_error(APLOG_MARK, APLOG_CRIT, 0, NULL,
                             "cannot resolve: %s", serv);
                return -1;
            }
        }
        first_time = 0;
        p = hp->h_addr_list;
        memcpy(&serv_addr.s_addr, *p, sizeof(serv_addr.s_addr));
        ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, NULL,
                     "DNS update server has been set to [%s:%d]", 
                     inet_ntoa(serv_addr), serv_port);
    }

    res_init();
    _res.nsaddr_list[0].sin_addr = serv_addr;
    _res.nsaddr_list[0].sin_port = htons(serv_port);

    return 0;
}

int dns_update(int op, char *name, char *ip)
{
    char opstr[10], cmd[1024], fname[64], server[64];
    int opcode, rval, i;

    if (op == DNS_ADD) {
        strcpy(opstr, "add");
        opcode = ns_uop_add;
    } else if (op == DNS_DEL) {
        strcpy(opstr, "delete");
        opcode = ns_uop_delete;
    } else {
        return -1;
    }

    if (name == NULL || ip == NULL) return -1;

    i = strlen(name);
    if (i>0 && name[i-1] == '.') {
        strcpy(fname, name);
    } else {
        sprintf(fname, "%s.", name);    // add trailing dot to name if needed
    }

    if (ddns_server_set) { // set the DNS server for sending updates
        strcpy(server, ddns_server);
    } else {
        strcpy(server, "NULL");
    }

    if (dns_tsig_set) { // signed
        sprintf(cmd, "%s %s:%s %s %s %s %s", ddns_script, my_tsigkey, 
                my_tsigsecret, opstr, fname, ip, server);
        rval = system(cmd);
        ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, NULL,
                     "nsupdate: %s %s(%s), rval=%d", opstr, fname, ip, rval);
    } else { // unsigned
        rval = dns_update_unsigned(opcode, fname, ns_t_a, ip);
    }

    return rval;
}