/*

Copyright (c) 2004, 2005 Carl Byington - 510 Software Group, released
under the GPL version 2 or any later version at your choice available at
http://www.fsf.org/licenses/gpl.txt

Based on a sample milter Copyright (c) 2000-2003 Sendmail, Inc. and its
suppliers.  Inspired by the DCC by Rhyolite Software

-r port  The port used to talk to our internal dns resolver processes
-p port  The port through which the MTA will connect to this milter.
-t sec   The timeout value.
-c       Check the config, and print a copy to stdout. Don't start the
         milter or do anything with the socket.
-s       Stress test by loading and deleting the current config in a loop.
-d       Add debug syslog entries
-e f|t   Print the results of looking up from address f and to address
         t in the current config


TODO:

1) Add option for using smtp connections to verify addresses from backup
mx machines. This allows the backup mx to learn the valid addresses
on the primary machine.

*/


// from sendmail sample
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <sysexits.h>
#include <unistd.h>

// needed for socket io
#include <sys/ioctl.h>
#include <net/if.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <netdb.h>
#include <sys/socket.h>
#include <sys/un.h>

// needed for thread
#include <pthread.h>

// needed for std c++ collections
#include <set>
#include <map>
#include <list>

// for the dns resolver
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>

// misc stuff needed here
#include <ctype.h>
#include <syslog.h>
#include <pwd.h>
#include <sys/wait.h>   /* header for waitpid() and various macros */
#include <signal.h>     /* header for signal functions */

#include "includes.h"

static char* dnsbl_version="$Id$";


extern "C" {
    #include "libmilter/mfapi.h"
    sfsistat mlfi_connect(SMFICTX *ctx, char *hostname, _SOCK_ADDR *hostaddr);
    sfsistat mlfi_envfrom(SMFICTX *ctx, char **argv);
    sfsistat mlfi_envrcpt(SMFICTX *ctx, char **argv);
    sfsistat mlfi_body(SMFICTX *ctx, u_char *data, size_t len);
    sfsistat mlfi_eom(SMFICTX *ctx);
    sfsistat mlfi_abort(SMFICTX *ctx);
    sfsistat mlfi_close(SMFICTX *ctx);
    void sig_chld(int signo);
}

bool debug_syslog  = false;
bool syslog_opened = false;
bool use_syslog    = true;  // false to printf
bool loader_run    = true;  // used to stop the config loader thread
CONFIG   *config = NULL;    // protected by the config_mutex
int   generation = 0;       // protected by the config_mutex
const int maxlen = 1000;    // used for snprintf buffers

pthread_mutex_t  config_mutex;
pthread_mutex_t  syslog_mutex;
pthread_mutex_t  resolve_mutex;
pthread_mutex_t  fd_pool_mutex;

std::set<int>    fd_pool;
int    NULL_SOCKET       = -1;
char  *resolver_port     = NULL;         // unix domain socket to talk to the dns resolver process
int    resolver_socket   = NULL_SOCKET;  // socket used to listen for resolver requests
time_t ERROR_SOCKET_TIME = 60;           // number of seconds between attempts to open the spam filter socket
time_t last_error_time;
int    resolver_sock_count = 0;          // protected with fd_pool_mutex
int    resolver_pool_size  = 0;          // protected with fd_pool_mutex


struct ns_map {
    // all the strings are owned by the keys/values in the ns_host string map
    string_map  ns_host;    // nameserver name -> host name that uses this name server
    ns_mapper   ns_ip;      // nameserver name -> ip address of the name server
    ~ns_map();
    void add(char *name, char *refer);
};


ns_map::~ns_map() {
    for (string_map::iterator i=ns_host.begin(); i!=ns_host.end(); i++) {
        char *x = (*i).first;
        char *y = (*i).second;
        free(x);
        free(y);
    }
    ns_ip.clear();
    ns_host.clear();
}


void ns_map::add(char *name, char *refer) {
    string_map::iterator i = ns_host.find(name);
    if (i != ns_host.end()) return;
    char *x = strdup(name);
    char *y = strdup(refer);
    ns_ip[x]   = 0;
    ns_host[x] = y;

}

// packed structure to allow a single socket write to dump the
// length and the following answer. The packing attribute is gcc specific.
struct glommer {
    int    length;
    #ifdef NS_PACKETSZ
        u_char answer[NS_PACKETSZ];     // with a resolver, we return resolver answers
    #else
        int    answer;                  // without a resolver, we return a single ip4 address, 0 == no answer
    #endif
} __attribute__ ((packed));


////////////////////////////////////////////////
// helper to discard the strings held by a context_map
//
void discard(context_map &cm);
void discard(context_map &cm) {
    for (context_map::iterator i=cm.begin(); i!=cm.end(); i++) {
        char *x = (*i).first;
        free(x);
    }
    cm.clear();
}


////////////////////////////////////////////////
// helper to register a string in a context_map
//
void register_string(context_map &cm, char *name, CONTEXT *con);
void register_string(context_map &cm, char *name, CONTEXT *con) {
    context_map::iterator i = cm.find(name);
    if (i != cm.end()) return;
    char *x = strdup(name);
    cm[x] = con;
}


////////////////////////////////////////////////
// disconnect the fd from the dns resolver process
//
void my_disconnect(int sock, bool decrement = true);
void my_disconnect(int sock, bool decrement) {
    if (sock != NULL_SOCKET) {
        if (decrement) {
            pthread_mutex_lock(&fd_pool_mutex);
                resolver_sock_count--;
            pthread_mutex_unlock(&fd_pool_mutex);
        }
        shutdown(sock, SHUT_RDWR);
        close(sock);
    }
}


////////////////////////////////////////////////
// return fd connected to the dns resolver process
//
int my_connect();
int my_connect() {
    // if we have had recent errors, don't even try to open the socket
    time_t now = time(NULL);
    if ((now - last_error_time) < ERROR_SOCKET_TIME) return NULL_SOCKET;

    // nothing recent, maybe this time it will work
    int sock = NULL_SOCKET;
    sockaddr_un server;
    memset(&server, '\0', sizeof(server));
    server.sun_family = AF_UNIX;
    strncpy(server.sun_path, resolver_port, sizeof(server.sun_path)-1);
    sock = socket(AF_UNIX, SOCK_STREAM, 0);
    if (sock != NULL_SOCKET) {
        bool rc = (connect(sock, (sockaddr *)&server, sizeof(server)) == 0);
        if (!rc) {
            my_disconnect(sock, false);
            sock = NULL_SOCKET;
            last_error_time = now;
        }
    }
    else last_error_time = now;
    if (sock != NULL_SOCKET) {
        pthread_mutex_lock(&fd_pool_mutex);
            resolver_sock_count++;
        pthread_mutex_unlock(&fd_pool_mutex);
    }
    return sock;
}


mlfiPriv::mlfiPriv() {
    pthread_mutex_lock(&config_mutex);
        pc = config;
        pc->reference_count++;
    pthread_mutex_unlock(&config_mutex);
    get_fd();
    ip                  = 0;
    mailaddr            = NULL;
    queueid             = NULL;
    authenticated       = false;
    have_whites         = false;
    only_whites         = true;
    memory              = NULL;
    scanner             = NULL;
    content_suffix      = NULL;
    content_message     = NULL;
    content_host_ignore = NULL;
}

mlfiPriv::~mlfiPriv() {
    return_fd();
    pthread_mutex_lock(&config_mutex);
        pc->reference_count--;
    pthread_mutex_unlock(&config_mutex);
    reset(true);
}

void mlfiPriv::reset(bool final) {
    if (mailaddr) free(mailaddr);
    if (queueid)  free(queueid);
    discard(env_to);
    if (memory)  delete memory;
    if (scanner) delete scanner;
    if (!final) {
        mailaddr            = NULL;
        queueid             = NULL;
        authenticated       = false;
        have_whites         = false;
        only_whites         = true;
        memory              = NULL;
        scanner             = NULL;
        content_suffix      = NULL;
        content_message     = NULL;
        content_host_ignore = NULL;
    }
}

void mlfiPriv::get_fd() {
    err = true;
    fd  = NULL_SOCKET;
    int result = pthread_mutex_lock(&fd_pool_mutex);
    if (!result) {
        std::set<int>::iterator i;
        i = fd_pool.begin();
        if (i != fd_pool.end()) {
            // have at least one fd in the pool
            err = false;
            fd  = *i;
            fd_pool.erase(fd);
            resolver_pool_size--;
            pthread_mutex_unlock(&fd_pool_mutex);
        }
        else {
            // pool is empty, get a new fd
            pthread_mutex_unlock(&fd_pool_mutex);
            fd  = my_connect();
            err = (fd == NULL_SOCKET);
        }
    }
    else {
        // cannot lock the pool, just get a new fd
        fd  = my_connect();
        err = (fd == NULL_SOCKET);
    }
}

void mlfiPriv::return_fd() {
    if (err) {
        // this fd got a socket error, so close it, rather than returning it to the pool
        my_disconnect(fd);
    }
    else {
        int result = pthread_mutex_lock(&fd_pool_mutex);
        if (!result) {
            if ((resolver_sock_count > resolver_pool_size*5) || (resolver_pool_size < 5)) {
                // return the fd to the pool
                fd_pool.insert(fd);
                resolver_pool_size++;
                pthread_mutex_unlock(&fd_pool_mutex);
            }
            else {
                // more than 20% of the open resolver sockets are in the pool, and the
                // pool as at least 5 sockets. that is enough, so just close this one.
                pthread_mutex_unlock(&fd_pool_mutex);
                my_disconnect(fd);
            }
        }
        else {
            // could not lock the pool, so just close the fd
            my_disconnect(fd);
        }
    }
}

int mlfiPriv::my_write(char *buf, int len) {
    if (err) return 0;
    int rs = 0;
    while (len) {
        int ws = write(fd, buf, len);
        if (ws > 0) {
            rs  += ws;
            len -= ws;
            buf += ws;
        }
        else {
            // peer closed the socket!
            rs = 0;
            err = true;
            break;
        }
    }
    return rs;
}

int mlfiPriv::my_read(char *buf, int len) {
    if (err) return 0;
    int rs = 0;
    while (len > 1) {
        int ws = read(fd, buf, len);
        if (ws > 0) {
            rs  += ws;
            len -= ws;
            buf += ws;
        }
        else {
            // peer closed the socket!
            rs = 0;
            err = true;
            break;
        }
    }
    return rs;
}

void mlfiPriv::need_content_filter(char *rcpt, CONTEXT &con) {
    register_string(env_to, rcpt, &con);
    if (!memory) {
        // first recipient that needs content filtering sets all
        // the content filtering parameters
        memory        = new recorder(this, con.get_html_tags(), con.get_content_tlds());
        scanner       = new url_scanner(memory);
        content_suffix      = con.get_content_suffix();
        content_message     = con.get_content_message();
        content_host_ignore = &con.get_content_host_ignore();
    }
}

#define MLFIPRIV    ((struct mlfiPriv *) smfi_getpriv(ctx))


////////////////////////////////////////////////
// syslog a message
//
void my_syslog(mlfiPriv *priv, char *text) {
    char buf[maxlen];
    if (priv) {
        snprintf(buf, sizeof(buf), "%s: %s", priv->queueid, text);
        text = buf;
    }
    if (use_syslog) {
        pthread_mutex_lock(&syslog_mutex);
            if (!syslog_opened) {
                openlog("dnsbl", LOG_PID, LOG_MAIL);
                syslog_opened = true;
            }
            syslog(LOG_NOTICE, "%s", text);
            closelog();
            syslog_opened = false;
        pthread_mutex_unlock(&syslog_mutex);
    }
    else {
        printf("%s \n", text);
    }
}

void my_syslog(char *text) {
    my_syslog(NULL, text);
}


////////////////////////////////////////////////
//  read a resolver request from the socket, process it, and
//  write the result back to the socket.

void process_resolver_requests(int socket);
void process_resolver_requests(int socket) {
#ifdef NS_MAXDNAME
    char question[NS_MAXDNAME];
#else
    char question[1000];
#endif
    glommer glom;

    int maxq = sizeof(question);
    while (true) {
        // read a question
        int rs = 0;
        while (true) {
            int ns = read(socket, question+rs, maxq-rs);
            if (ns > 0) {
                rs += ns;
                if (question[rs-1] == '\0') {
                    // last byte read was the null terminator, we are done
                    break;
                }
            }
            else {
                // peer closed the socket
              //my_syslog("!!child worker process, peer closed socket while reading question");
                shutdown(socket, SHUT_RDWR);
                close(socket);
                return;
            }
        }

        // find the answer
#ifdef NS_PACKETSZ
      //char text[1000];
      //snprintf(text, sizeof(text), "!!child worker process has a question %s", question);
      //my_syslog(text);
        glom.length = res_search(question, ns_c_in, ns_t_a, glom.answer, sizeof(glom.answer));
        if (glom.length < 0) glom.length = 0;   // represent all errors as zero length answers
#else
        glom.length = sizeof(glom.answer);
        glom.answer = 0;
        struct hostent *host = gethostbyname(question);
        if (host && (host->h_addrtype == AF_INET)) {
            memcpy(&glom.answer, host->h_addr, sizeof(glom.answer));
        }
#endif

        // write the answer
        char *buf = (char *)&glom;
        int   len = glom.length + sizeof(glom.length);
      //snprintf(text, sizeof(text), "!!child worker process writing answer length %d for total %d", glom.length, len);
      //my_syslog(text);
        int    ws = 0;
        while (len > ws) {
            int ns = write(socket, buf+ws, len-ws);
            if (ns > 0) {
                ws += ns;
            }
            else {
                // peer closed the socket!
              //my_syslog("!!child worker process, peer closed socket while writing answer");
                shutdown(socket, SHUT_RDWR);
                close(socket);
                return;
            }
        }
    }
}


////////////////////////////////////////////////
//  ask a dns question and get an A record answer - we don't try
//  very hard, just using the default resolver retry settings.
//  If we cannot get an answer, we just accept the mail.
//
//
int dns_interface(mlfiPriv &priv, char *question, bool maybe_ip, ns_map *nameservers);
int dns_interface(mlfiPriv &priv, char *question, bool maybe_ip, ns_map *nameservers) {
    // this part can be done without locking the resolver mutex. Each
    // milter thread is talking over its own socket to a separate resolver
    // process, which does the actual dns resolution.
    if (priv.err) return 0; // cannot ask more questions on this socket.
    priv.my_write(question, strlen(question)+1);   // write the question including the null terminator
    glommer glom;
    char *buf = (char *)&glom;
    priv.my_read(buf, sizeof(glom.length));
    buf += sizeof(glom.length);
 ///char text[1000];
 ///snprintf(text, sizeof(text), "!!milter thread wrote question %s and has answer length %d", question, glom.length);
 ///my_syslog(text);
    if ((glom.length < 0) || (glom.length > sizeof(glom.answer))) {
        priv.err = true;
        return 0;  // cannot process overlarge answers
    }
    priv.my_read(buf, glom.length);

#ifdef NS_PACKETSZ
    // now we need to lock the resolver mutex to keep the milter threads from
    // stepping on each other while parsing the dns answer.
    int ret_address = 0;
    pthread_mutex_lock(&resolve_mutex);
        if (glom.length > 0) {
            // parse the answer
            ns_msg handle;
            ns_rr  rr;
            if (ns_initparse(glom.answer, glom.length, &handle) == 0) {
                // look for ns names
                if (nameservers) {
                    ns_map &ns = *nameservers;
                    int rrnum = 0;
                    while (ns_parserr(&handle, ns_s_ns, rrnum++, &rr) == 0) {
                        if (ns_rr_type(rr) == ns_t_ns) {
                            char nam[NS_MAXDNAME+1];
                            char         *n = nam;
                            const u_char *p = ns_rr_rdata(rr);
                            while (((n-nam) < NS_MAXDNAME) && ((p-glom.answer) < glom.length) && *p) {
                                size_t s = *(p++);
                                if (s > 191) {
                                    // compression pointer
                                    s = (s-192)*256 + *(p++);
                                    if (s >= glom.length) break; // pointer outside bounds of answer
                                    p = glom.answer + s;
                                    s = *(p++);
                                }
                                if (s > 0) {
                                    if ((n-nam)         >= (NS_MAXDNAME-s)) break;  // destination would overflow name buffer
                                    if ((p-glom.answer) >= (glom.length-s)) break;  // source outside bounds of answer
                                    memcpy(n, p, s);
                                    n += s;
                                    p += s;
                                    *(n++) = '.';
                                }
                            }
                            if (n-nam) n--;             // remove trailing .
                            *n = '\0';                  // null terminate it
                            ns.add(nam, question);      // ns host to lookup later
                        }
                    }
                    rrnum = 0;
                    while (ns_parserr(&handle, ns_s_ar, rrnum++, &rr) == 0) {
                        if (ns_rr_type(rr) == ns_t_a) {
                            char* nam = (char*)ns_rr_name(rr);
                            ns_mapper::iterator i = ns.ns_ip.find(nam);
                            if (i != ns.ns_ip.end()) {
                                // we want this ip address
                                int address;
                                memcpy(&address, ns_rr_rdata(rr), sizeof(address));
                                ns.ns_ip[nam] = address;
                            }
                        }
                    }
                }
                int rrnum = 0;
                while (ns_parserr(&handle, ns_s_an, rrnum++, &rr) == 0) {
                    if (ns_rr_type(rr) == ns_t_a) {
                        int address;
                        memcpy(&address, ns_rr_rdata(rr), sizeof(address));
                        ret_address = address;
                    }
                }
            }
        }
        if (maybe_ip && !ret_address) {
            // might be a bare ip address
            in_addr ip;
            if (inet_aton(question, &ip)) {
                ret_address = ip.s_addr;
            }
        }
    pthread_mutex_unlock(&resolve_mutex);
    return ret_address;
#else
    return glom.answer;
#endif
}


////////////////////////////////////////////////
//  check a single dnsbl
//
bool check_single(mlfiPriv &priv, int ip, char *suffix);
bool check_single(mlfiPriv &priv, int ip, char *suffix) {
    // make a dns question
    const u_char *src = (const u_char *)&ip;
    if (src[0] == 127) return false;    // don't do dns lookups on localhost
#ifdef NS_MAXDNAME
    char question[NS_MAXDNAME];
#else
    char question[1000];
#endif
    snprintf(question, sizeof(question), "%u.%u.%u.%u.%s.", src[3], src[2], src[1], src[0], suffix);
    // ask the question, if we get an A record it implies a blacklisted ip address
    return dns_interface(priv, question, false, NULL);
}


////////////////////////////////////////////////
//  check a single dnsbl
//
bool check_single(mlfiPriv &priv, int ip, DNSBL &bl);
bool check_single(mlfiPriv &priv, int ip, DNSBL &bl) {
    return check_single(priv, ip, bl.suffix);
}


////////////////////////////////////////////////
//  check the dnsbls specified for this recipient
//
bool check_dnsbl(mlfiPriv &priv, dnsblp_list &dnsbll, DNSBLP &rejectlist);
bool check_dnsbl(mlfiPriv &priv, dnsblp_list &dnsbll, DNSBLP &rejectlist) {
    if (priv.authenticated) return false;
    for (dnsblp_list::iterator i=dnsbll.begin(); i!=dnsbll.end(); i++) {
        DNSBLP dp = *i;     // non null by construction
        bool st;
        map<DNSBLP, bool>::iterator f = priv.checked.find(dp);
        if (f == priv.checked.end()) {
            // have not checked this list yet
            st = check_single(priv, priv.ip, *dp);
            rejectlist = dp;
            priv.checked[dp] = st;
        }
        else {
            st = (*f).second;
            rejectlist = (*f).first;
        }
        if (st) return st;
    }
    return false;
}


////////////////////////////////////////////////
//  check the hosts from the body against the content dnsbl
//
bool check_hosts(mlfiPriv &priv, bool random, int limit, char *&host, int ip);
bool check_hosts(mlfiPriv &priv, bool random, int limit, char *&host, int ip) {
    CONFIG     &dc     = *priv.pc;
    string_set &hosts  = priv.memory->get_hosts();
    string_set &ignore = *priv.content_host_ignore;
    char       *suffix = priv.content_suffix;

    int count = 0;
    int   cnt = hosts.size();   // number of hosts we could look at
    int_set ips;
    ns_map  nameservers;
    for (string_set::iterator i=hosts.begin(); i!=hosts.end(); i++) {
        host = *i;  // a reference into hosts, which will live until this smtp transaction is closed

        // don't bother looking up hosts on the ignore list
        string_set::iterator j = ignore.find(host);
        if (j != ignore.end()) continue;

        // try to only look at limit/cnt fraction of the available cnt host names in random mode
        if ((cnt > limit) && (limit > 0) && random) {
            int r = rand() % cnt;
            if (r >= limit) {
                char buf[maxlen];
                snprintf(buf, sizeof(buf), "host %s skipped", host);
                my_syslog(&priv, buf);
                continue;
            }
        }
        count++;
        ip = dns_interface(priv, host, true, &nameservers);
        if (debug_syslog) {
            char buf[maxlen];
            if (ip) {
                char adr[sizeof "255.255.255.255"];
                adr[0] = '\0';
                inet_ntop(AF_INET, (const u_char *)&ip, adr, sizeof(adr));
                snprintf(buf, sizeof(buf), "host %s found at %s", host, adr);
            }
            else {
                snprintf(buf, sizeof(buf), "host %s not found", host);
            }
            my_syslog(&priv, buf);
        }
        if (ip) {
            int_set::iterator i = ips.find(ip);
            if (i == ips.end()) {
                ips.insert(ip);
                if (check_single(priv, ip, suffix)) {
                    return true;
                }
            }
        }
    }
    limit *= 4;   // allow average of 3 ns per host name
    for (ns_mapper::iterator i=nameservers.ns_ip.begin(); i!=nameservers.ns_ip.end(); i++) {
        count++;
        if ((count > limit) && (limit > 0)) {
            if (random) continue; // don't complain
            return true;
        }
        host = (*i).first;  // a transient reference that needs to be replaced before we return it
        ip   = (*i).second;
        if (!ip) ip = dns_interface(priv, host, false, NULL);
        if (debug_syslog) {
            char buf[maxlen];
            if (ip) {
                char adr[sizeof "255.255.255.255"];
                adr[0] = '\0';
                inet_ntop(AF_INET, (const u_char *)&ip, adr, sizeof(adr));
                snprintf(buf, sizeof(buf), "ns %s found at %s", host, adr);
            }
            else {
                snprintf(buf, sizeof(buf), "ns %s not found", host);
            }
            my_syslog(&priv, buf);
        }
        if (ip) {
            int_set::iterator i = ips.find(ip);
            if (i == ips.end()) {
                ips.insert(ip);
                if (check_single(priv, ip, suffix)) {
                    string_map::iterator j = nameservers.ns_host.find(host);
                    if (j != nameservers.ns_host.end()) {
                        char *refer = (*j).second;
                        char buf[maxlen];
                        snprintf(buf, sizeof(buf), "%s with nameserver %s", refer, host);
                        host = register_string(hosts, buf);    // put a copy into hosts, and return that reference
                    }
                    else {
                        host = register_string(hosts, host);   // put a copy into hosts, and return that reference
                    }
                    return true;
                }
            }
        }
    }
    return false;
}


////////////////////////////////////////////////
// this email address is passed in from sendmail, and will
// always be enclosed in <>. It may have mixed case, just
// as the mail client sent it. We dup the string and convert
// the duplicate to lower case.
//
char *to_lower_string(char *email);
char *to_lower_string(char *email) {
    int n = strlen(email)-2;
    if (n < 1) return strdup(email);
    char *key = strdup(email+1);
    key[n] = '\0';
    for (int i=0; i<n; i++) key[i] = tolower(key[i]);
    return key;
}


////////////////////////////////////////////////
// start of sendmail milter interfaces
//
sfsistat mlfi_connect(SMFICTX *ctx, char *hostname, _SOCK_ADDR *hostaddr)
{
    // allocate some private memory
    mlfiPriv *priv = new mlfiPriv;
    if (hostaddr->sa_family == AF_INET) {
        priv->ip = ((struct sockaddr_in *)hostaddr)->sin_addr.s_addr;
    }

    // save the private data
    smfi_setpriv(ctx, (void*)priv);

    // continue processing
    return SMFIS_CONTINUE;
}

sfsistat mlfi_envfrom(SMFICTX *ctx, char **from)
{
    mlfiPriv &priv = *MLFIPRIV;
    priv.mailaddr      = to_lower_string(from[0]);
    priv.authenticated = (smfi_getsymval(ctx, "{auth_authen}") != NULL);
    return SMFIS_CONTINUE;
}

sfsistat mlfi_envrcpt(SMFICTX *ctx, char **rcpt)
{
    DNSBLP rejectlist = NULL;   // list that caused the reject
    mlfiPriv &priv = *MLFIPRIV;
    CONFIG &dc = *priv.pc;
    if (!priv.queueid) priv.queueid = strdup(smfi_getsymval(ctx, "i"));
    char *rcptaddr  = rcpt[0];
    char *loto      = to_lower_string(rcptaddr);
    CONTEXT    &con = *(dc.find_context(loto)->find_context(priv.mailaddr));
    if (debug_syslog) {
        char buf[maxlen];
        char msg[maxlen];
        snprintf(msg, sizeof(msg), "from <%s> to <%s> using context %s", priv.mailaddr, loto, con.get_full_name(buf,maxlen));
        my_syslog(&priv, msg);
    }
    char *fromvalue = con.find_from(priv.mailaddr);
    free(loto);
    status st;
    if (fromvalue == token_black) {
        st = black;
    }
    else if (fromvalue == token_white) {
        st = white;
    }
    else {
        // check the dns based lists
        st = (check_dnsbl(priv, con.get_dnsbl_list(), rejectlist)) ? black : oksofar;
    }
    if (st == reject) {
        // reject the recipient based on some dnsbl
        char adr[sizeof "255.255.255.255"];
        adr[0] = '\0';
        inet_ntop(AF_INET, (const u_char *)&priv.ip, adr, sizeof(adr));
        char buf[maxlen];
        snprintf(buf, sizeof(buf), rejectlist->message, adr, adr);
        smfi_setreply(ctx, "550", "5.7.1", buf);
        return SMFIS_REJECT;
    }
    else if (st == black) {
        // reject the recipient based on blacklisting either from or to
        smfi_setreply(ctx, "550", "5.7.1", "no such user");
        return SMFIS_REJECT;
    }
    else {
        // accept the recipient
        if (!con.get_content_filtering()) st = white;
        if (st == oksofar) {
            // but remember the non-whites
            priv.need_content_filter(rcptaddr, con);
            priv.only_whites = false;
        }
        if (st == white) {
            priv.have_whites = true;
        }
        return SMFIS_CONTINUE;
    }
}

sfsistat mlfi_body(SMFICTX *ctx, u_char *data, size_t len)
{
    mlfiPriv &priv = *MLFIPRIV;
    if (priv.authenticated)       return SMFIS_CONTINUE;
    if (priv.only_whites)         return SMFIS_CONTINUE;
    priv.scanner->scan(data, len);
    return SMFIS_CONTINUE;
}

sfsistat mlfi_eom(SMFICTX *ctx)
{
    sfsistat  rc;
    mlfiPriv &priv = *MLFIPRIV;
    CONFIG   &dc   = *priv.pc;
    char     *host = NULL;
    int       ip;
    status    st;
    // process end of message
    if (priv.authenticated || priv.only_whites) rc = SMFIS_CONTINUE;
    else {
        // assert env_to not empty
        char buf[maxlen];
        char *msg = NULL;
        string_set alive;
        bool random = false;
        int  limit  = 0;
        for (context_map::iterator i=priv.env_to.begin(); i!=priv.env_to.end(); i++) {
            char *rcpt   = (*i).first;
            CONTEXT &con = *((*i).second);
            if (!con.acceptable_content(*priv.memory, msg)) {
                // bad html tags or excessive hosts
                smfi_delrcpt(ctx, rcpt);
            }
            else {
                alive.insert(rcpt);
                random |= con.get_host_random();
                limit   = max(limit, con.get_host_limit());
            }
        }
        bool rejecting = alive.empty(); // if alive is empty, we must have set msg above in acceptable_content()
        if (!rejecting) {
            if (check_hosts(priv, random, limit, host, ip)) {
                char adr[sizeof "255.255.255.255"];
                adr[0] = '\0';
                inet_ntop(AF_INET, (const u_char *)&ip, adr, sizeof(adr));
                snprintf(buf, sizeof(buf), priv.content_message, host, adr);
                msg = buf;
                rejecting = true;
            }
        }
        if (!rejecting) {
            rc = SMFIS_CONTINUE;
        }
        else if (!priv.have_whites) {
            // can reject the entire message
            smfi_setreply(ctx, "550", "5.7.1", msg);
            rc = SMFIS_REJECT;
        }
        else {
            // need to accept it but remove the recipients that don't want it
            for (string_set::iterator i=alive.begin(); i!=alive.end(); i++) {
                char *rcpt = *i;
                smfi_delrcpt(ctx, rcpt);
            }
            rc = SMFIS_CONTINUE;
        }
    }
    // reset for a new message on the same connection
    mlfi_abort(ctx);
    return rc;
}

sfsistat mlfi_abort(SMFICTX *ctx)
{
    mlfiPriv &priv = *MLFIPRIV;
    priv.reset();
    return SMFIS_CONTINUE;
}

sfsistat mlfi_close(SMFICTX *ctx)
{
    mlfiPriv *priv = MLFIPRIV;
    if (!priv) return SMFIS_CONTINUE;
    delete priv;
    smfi_setpriv(ctx, NULL);
    return SMFIS_CONTINUE;
}

struct smfiDesc smfilter =
{
    "DNSBL",            // filter name
    SMFI_VERSION,       // version code -- do not change
    SMFIF_DELRCPT,      // flags
    mlfi_connect,       // connection info filter
    NULL,               // SMTP HELO command filter
    mlfi_envfrom,       // envelope sender filter
    mlfi_envrcpt,       // envelope recipient filter
    NULL,               // header filter
    NULL,               // end of header
    mlfi_body,          // body block filter
    mlfi_eom,           // end of message
    mlfi_abort,         // message aborted
    mlfi_close,         // connection cleanup
};


////////////////////////////////////////////////
//  reload the config
//
CONFIG* new_conf();
CONFIG* new_conf() {
    CONFIG *newc = new CONFIG;
    pthread_mutex_lock(&config_mutex);
        newc->generation = generation++;
    pthread_mutex_unlock(&config_mutex);
    char buf[maxlen];
    snprintf(buf, sizeof(buf), "loading configuration generation %d", newc->generation);
    my_syslog(buf);
    if (load_conf(*newc, "dnsbl.conf")) {
        newc->load_time = time(NULL);
        return newc;
    }
    delete newc;
    return NULL;
}


////////////////////////////////////////////////
//  thread to watch the old config files for changes
//  and reload when needed. we also cleanup old
//  configs whose reference count has gone to zero.
//
void* config_loader(void *arg);
void* config_loader(void *arg) {
    typedef set<CONFIG *> configp_set;
    configp_set old_configs;
    while (loader_run) {
        sleep(180);  // look for modifications every 3 minutes
        if (!loader_run) break;
        CONFIG &dc = *config;
        time_t then = dc.load_time;
        struct stat st;
        bool reload = false;
        for (string_set::iterator i=dc.config_files.begin(); i!=dc.config_files.end(); i++) {
            char *fn = *i;
            if (stat(fn, &st))           reload = true; // file disappeared
            else if (st.st_mtime > then) reload = true; // file modified
            if (reload) break;
        }
        if (reload) {
            CONFIG *newc = new_conf();
            // replace the global config pointer
            pthread_mutex_lock(&config_mutex);
                CONFIG *old = config;
                config = newc;
            pthread_mutex_unlock(&config_mutex);
            if (old) old_configs.insert(old);
        }
        // now look for old configs with zero ref counts
        for (configp_set::iterator i=old_configs.begin(); i!=old_configs.end(); ) {
            CONFIG *old = *i;
            if (!old->reference_count) {
                char buf[maxlen];
                snprintf(buf, sizeof(buf), "freeing memory for old configuration generation %d", old->generation);
                my_syslog(buf);
                delete old; // destructor does all the work
                old_configs.erase(i++);
            }
            else i++;
        }
    }
    return NULL;
}


void usage(char *prog);
void usage(char *prog)
{
    fprintf(stderr, "Usage: %s  [-d] [-c] [-s] [-e from|to] -r port -p sm-sock-addr [-t timeout]\n", prog);
    fprintf(stderr, "where port is for the connection to our own dns resolver processes\n");
    fprintf(stderr, "    and should be local-domain-socket-file-name\n");
    fprintf(stderr, "where sm-sock-addr is for the connection to sendmail\n");
    fprintf(stderr, "    and should be one of\n");
    fprintf(stderr, "        inet:port@ip-address\n");
    fprintf(stderr, "        local:local-domain-socket-file-name\n");
    fprintf(stderr, "-c will load and dump the config to stdout\n");
    fprintf(stderr, "-s will stress test the config loading code by repeating the load/free cycle\n");
    fprintf(stderr, "        in an infinte loop.\n");
    fprintf(stderr, "-d will add some syslog debug messages\n");
    fprintf(stderr, "-e will print the results of looking up the from and to addresses in the\n");
    fprintf(stderr, "        current config. The | character is used to separate the from and to\n");
    fprintf(stderr, "        addresses in the argument to the -e switch\n");
}



void setup_socket(char *sock);
void setup_socket(char *sock) {
    unlink(sock);
    //  sockaddr_un addr;
    //  memset(&addr, '\0', sizeof addr);
    //  addr.sun_family = AF_UNIX;
    //  strncpy(addr.sun_path, sock, sizeof(addr.sun_path)-1);
    //  int s = socket(AF_UNIX, SOCK_STREAM, 0);
    //  bind(s, (sockaddr*)&addr, sizeof(addr));
    //  close(s);
}


/*
 * The signal handler function -- only gets called when a SIGCHLD
 * is received, ie when a child terminates
 */
void sig_chld(int signo)
{
    int status;
    /* Wait for any child without blocking */
    while (waitpid(-1, &status, WNOHANG) > 0) {
        // ignore child exit status, we only do this to cleanup zombies
    }
}


int main(int argc, char**argv)
{
    token_init();
    bool check   = false;
    bool stress  = false;
    bool setconn = false;
    bool setreso = false;
    char *email = NULL;
    int c;
    const char *args = "r:p:t:e:cdhs";
    extern char *optarg;

    // Process command line options
    while ((c = getopt(argc, argv, args)) != -1) {
        switch (c) {
            case 'r':
                if (optarg == NULL || *optarg == '\0') {
                    fprintf(stderr, "Illegal resolver socket: %s\n", optarg);
                    exit(EX_USAGE);
                }
                resolver_port = strdup(optarg);
                setup_socket(resolver_port);
                setreso = true;
                break;

            case 'p':
                if (optarg == NULL || *optarg == '\0') {
                    fprintf(stderr, "Illegal sendmail socket: %s\n", optarg);
                    exit(EX_USAGE);
                }
                if (smfi_setconn(optarg) == MI_FAILURE) {
                    fprintf(stderr, "smfi_setconn failed\n");
                    exit(EX_SOFTWARE);
                }
                     if (strncasecmp(optarg, "unix:", 5) == 0)  setup_socket(optarg + 5);
                else if (strncasecmp(optarg, "local:", 6) == 0) setup_socket(optarg + 6);
                setconn = true;
                break;

            case 't':
                if (optarg == NULL || *optarg == '\0') {
                    fprintf(stderr, "Illegal timeout: %s\n", optarg);
                    exit(EX_USAGE);
                }
                if (smfi_settimeout(atoi(optarg)) == MI_FAILURE) {
                    fprintf(stderr, "smfi_settimeout failed\n");
                    exit(EX_SOFTWARE);
                }
                break;

            case 'e':
                if (email) free(email);
                email = strdup(optarg);
                break;

            case 'c':
                check = true;
                break;

            case 's':
                stress = true;
                break;

            case 'd':
                debug_syslog = true;
                break;

            case 'h':
            default:
                usage(argv[0]);
                exit(EX_USAGE);
        }
    }

    if (check) {
        use_syslog   = false;
        debug_syslog = true;
        CONFIG *conf = new_conf();
        if (conf) {
            conf->dump();
            delete conf;
            return 0;
        }
        else {
            return 1;   // config failed to load
        }
    }

    if (stress) {
        fprintf(stdout, "stress testing\n");
        while (1) {
            for (int i=0; i<10; i++) {
                CONFIG *conf = new_conf();
                if (conf) delete conf;
            }
            fprintf(stdout, ".");
            fflush(stdout);
            sleep(1);
        }
    }

    if (email) {
        char *x = strchr(email, '|');
        if (x) {
            *x = '\0';
            char *from = strdup(email);
            char *to   = strdup(x+1);
            use_syslog = false;
            CONFIG *conf = new_conf();
            if (conf) {
                CONTEXTP con = conf->find_context(to);
                char buf[maxlen];
                fprintf(stdout, "envelope to   <%s> finds context %s\n", to, con->get_full_name(buf,maxlen));
                CONTEXTP fc = con->find_context(from);
                fprintf(stdout, "envelope from <%s> finds context %s\n", from, fc->get_full_name(buf,maxlen));
                char *st = fc->find_from(from);
                fprintf(stdout, "envelope from <%s> finds status %s\n", from, st);
                delete conf;
            }
        }
        return 0;
    }

    if (!setconn) {
        fprintf(stderr, "%s: Missing required -p argument\n", argv[0]);
        usage(argv[0]);
        exit(EX_USAGE);
    }

    if (!setreso) {
        fprintf(stderr, "%s: Missing required -r argument\n", argv[0]);
        usage(argv[0]);
        exit(EX_USAGE);
    }

    if (smfi_register(smfilter) == MI_FAILURE) {
        fprintf(stderr, "smfi_register failed\n");
        exit(EX_UNAVAILABLE);
    }

    // switch to background mode
    if (daemon(1,0) < 0) {
        fprintf(stderr, "daemon() call failed\n");
        exit(EX_UNAVAILABLE);
    }

    // write the pid
    const char *pidpath = "/var/run/dnsbl.pid";
    unlink(pidpath);
    FILE *f = fopen(pidpath, "w");
    if (f) {
#ifdef linux
        // from a comment in the DCC source code:
        // Linux threads are broken.  Signals given the
        // original process are delivered to only the
        // thread that happens to have that PID.  The
        // sendmail libmilter thread that needs to hear
        // SIGINT and other signals does not, and that breaks
        // scripts that need to stop milters.
        // However, signaling the process group works.
        fprintf(f, "-%d\n", (u_int)getpgrp());
#else
        fprintf(f, "%d\n", (u_int)getpid());
#endif
        fclose(f);
    }

    // initialize the thread sync objects
    pthread_mutex_init(&config_mutex, 0);
    pthread_mutex_init(&syslog_mutex, 0);
    pthread_mutex_init(&resolve_mutex, 0);
    pthread_mutex_init(&fd_pool_mutex, 0);

    // drop root privs
    struct passwd *pw = getpwnam("dnsbl");
    if (pw) {
        if (setgid(pw->pw_gid) == -1) {
            my_syslog("failed to switch to group dnsbl");
        }
        if (setuid(pw->pw_uid) == -1) {
            my_syslog("failed to switch to user dnsbl");
        }
    }

    // fork off the resolver listener process
    pid_t child = fork();
    if (child < 0) {
        my_syslog("failed to create resolver listener process");
        exit(0);
    }
    if (child == 0) {
        // we are the child - dns resolver listener process
        resolver_socket = socket(AF_UNIX, SOCK_STREAM, 0);
        if (resolver_socket < 0) {
            my_syslog("child failed to create resolver socket");
            exit(0);   // failed
        }
        sockaddr_un server;
        memset(&server, '\0', sizeof(server));
        server.sun_family = AF_UNIX;
        strncpy(server.sun_path, resolver_port, sizeof(server.sun_path)-1);
        //try to bind the address to the socket.
        if (bind(resolver_socket, (sockaddr *)&server, sizeof(server)) < 0) {
            // bind failed
            shutdown(resolver_socket, SHUT_RDWR);
            close(resolver_socket);
            my_syslog("child failed to bind resolver socket");
            exit(0);   // failed
        }
        //listen on the socket.
        if (listen(resolver_socket, 10) < 0) {
            // listen failed
            shutdown(resolver_socket, SHUT_RDWR);
            close(resolver_socket);
            my_syslog("child failed to listen to resolver socket");
            exit(0);   // failed
        }
        // setup sigchld handler to prevent zombies
        struct sigaction act;
        act.sa_handler = sig_chld;      // Assign sig_chld as our SIGCHLD handler
        sigemptyset(&act.sa_mask);      // We don't want to block any other signals in this example
        act.sa_flags = SA_NOCLDSTOP;    // only want children that have terminated
        if (sigaction(SIGCHLD, &act, NULL) < 0) {
            my_syslog("child failed to setup SIGCHLD handler");
            exit(0);   // failed
        }
        while (true) {
            sockaddr_un client;
            socklen_t   clientlen = sizeof(client);
            int s = accept(resolver_socket, (sockaddr *)&client, &clientlen);
            if (s > 0) {
                // accept worked, it did not get cancelled before we could accept it
                // fork off a process to handle this connection
                int newchild = fork();
                if (newchild == 0) {
                    // this is the worker process
                    // child does not need the listening socket
                    close(resolver_socket);
                  //my_syslog("child forked a worker process");
                    process_resolver_requests(s);
                  //my_syslog("child terminated a worker process");
                    exit(0);
                }
                else {
                    // this is the parent
                    // parent does not need the accepted socket
                    close(s);
                }
            }
        }
        exit(0);    // make sure we don't fall thru.
    }
    else {
        sleep(2);   // allow child to get started
    }

    // load the initial config
    config = new_conf();

    // only create threads after the fork() in daemon
    pthread_t tid;
    if (pthread_create(&tid, 0, config_loader, 0))
        my_syslog("failed to create config loader thread");
    if (pthread_detach(tid))
        my_syslog("failed to detach config loader thread");

    time_t starting = time(NULL);
    int rc = smfi_main();
    if ((rc != MI_SUCCESS) && (time(NULL) > starting+5*60)) {
        my_syslog("trying to restart after smfi_main()");
        loader_run = false;     // eventually the config loader thread will terminate
        execvp(argv[0], argv);
    }
    exit((rc == MI_SUCCESS) ? 0 : EX_UNAVAILABLE);
}