/*
** Copyright (c) 2018 D. Richard Hipp
**
** This program is free software; you can redistribute it and/or
** modify it under the terms of the Simplified BSD License (also
** known as the "2-Clause License" or "FreeBSD License".)
**
** This program is distributed in the hope that it will be useful,
** but without any warranty; without even the implied warranty of
** merchantability or fitness for a particular purpose.
**
** Author contact information:
**   drh@hwaci.com
**   http://www.hwaci.com/drh/
**
*******************************************************************************
**
** Implementation of SMTP (Simple Mail Transport Protocol) according
** to RFC 5321.
*/
#include "config.h"
#include "smtp.h"
#include <assert.h>


#if !defined(FOSSIL_OMIT_SMTP)
#if defined(_WIN32)
   /* Don't yet know how to do this on windows */
#else
#  include <sys/types.h>
#  include <netinet/in.h>
#  include <arpa/nameser.h>
#  include <resolv.h>
#endif
#endif /* !defined(FOSSIL_OMIT_SMTP) */


/*
** Find the hostname for receiving email for the domain given
** in zDomain.  Return NULL if not found or not implemented.
** If multiple email receivers are advertized, pick the one with
** the lowest preference number.
**
** The returned string is obtained from fossil_malloc()
** and should be released using fossil_free().
*/
char *smtp_mx_host(const char *zDomain){
#if !defined(_WIN32) && !defined(FOSSIL_OMIT_SMTP)
  int nDns;                       /* Length of the DNS reply */
  int rc;                         /* Return code from various APIs */
  int i;                          /* Loop counter */
  int iBestPriority = 9999999;    /* Best priority */
  int nRec;                       /* Number of answers */
  ns_msg h;                       /* DNS reply parser */
  const unsigned char *pBest = 0; /* RDATA for the best answer */
  unsigned char aDns[5000];       /* Raw DNS reply content */
  char zHostname[5000];           /* Hostname for the MX */

  nDns = res_query(zDomain, C_IN, T_MX, aDns, sizeof(aDns));
  if( nDns<=0 ) return 0;
  res_init();
  rc = ns_initparse(aDns,nDns,&h);
  if( rc ) return 0;
  nRec = ns_msg_count(h, ns_s_an);
  for(i=0; i<nRec; i++){
    ns_rr x;
    int priority, sz;
    const unsigned char *p;
    rc = ns_parserr(&h, ns_s_an, i, &x);
    if( rc ) continue;
    p = ns_rr_rdata(x);
    sz = ns_rr_rdlen(x);
    if( sz>2 ){
      priority = p[0]*256 + p[1];
      if( priority<iBestPriority ){
        pBest = p;
        iBestPriority = priority;
      }
    }
  }
  if( pBest ){
    ns_name_uncompress(aDns, aDns+nDns, pBest+2,
                       zHostname, sizeof(zHostname));
    return fossil_strdup(zHostname);
  }
#endif /* not windows */
  return 0;
}

/*
** COMMAND: test-find-mx
**
** Usage: %fossil test-find-mx DOMAIN ...
**
** Do a DNS MX lookup to find the hostname for sending email for
** DOMAIN.
*/
void test_find_mx(void){
  int i;
  if( g.argc<2 ){
    usage("DOMAIN ...");
  }
  for(i=2; i<g.argc; i++){
    char *z = smtp_mx_host(g.argv[i]);
    fossil_print("%s: %s\n", g.argv[i], z);
    fossil_free(z);
  }
}