distributor/dist.c

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>

#include "utils.h"

extern char m_buffer[4096];

#define BANNER "220 " HOSTNAME " SMTP"
#define HELOANSWER "250 " HOSTNAME
#define CMDUNKNOWN "502 command unimplemented"
#define DOMAINUNKNOWN "553 unknown domain"
#define TEMPERROR "421 delivery error, please retry later"
#define DEFERROR "521 permanent delivery error, do not retry"
#define PORT 25

#define fail() do { perror(__FILE__ ":"); exit(-1); } while(0);
struct serverinfo
{
  char *address;
  unsigned port;
};

char *domains[]={"fakehermes.org","iteisa.net",NULL};
struct serverinfo servers[]={
  {"mail.gutierrezdequevedo.com",2525},
  {"94.23.193.98",25}
};

unsigned long connid=0;

struct serverinfo *get_server(char *domain)
{
  int i;
  for(i=0;domains[i];i++)
    if(!cmp(domain,domains[i]))
      return &servers[i];

  return NULL;
}

char *get_domain(char *line)
{
  char *strtmp=NULL;
  char *buf=NULL;

  safestrdup(buf,strchr(line,'@')+1);
  safestrdup(strtmp,strtok(buf," \"><"));

  condfree(buf);
  return strtmp;
}

void handle_new_connection(unsigned long p_connid,int fd)
{
  char *buf=NULL;
  char *from=NULL;
  char *to=NULL;
  char *domain=NULL;
  char *serveraddress=NULL;
  int fdin=-1;
  int fds[2];
  char databuffer[8192];
  int bytesread;
  int fdread,fdwrite;
  struct serverinfo *server;

  connid=p_connid;

  write_string(fd,BANNER);

  while(!socketeof(fd))
  {
    free_and_read_string(buf,fd);
    if(!cmp(buf,"HELO")||!cmp(buf,"EHLO"))
      write_string(fd,HELOANSWER);
    else if(!cmp(buf,"MAIL FROM"))
    {
      safestrdup(from,buf);
      write_string(fd,"250 Ok");
    }
    else if(!cmp(buf,"RCPT TO"))
    {
      safestrdup(to,buf);
      domain=get_domain(to);
      if(NULL==(server=get_server(domain)))
      {
        write_string(fd,DOMAINUNKNOWN);
        exit(-1);
      }
      condfree(domain);
      break;
    }
    else
      write_string(fd,CMDUNKNOWN);
  }
  if(-1==(fdin=create_connected_socket(server->address,server->port)))
  {
    write_string(fd,TEMPERROR);
    exit(-1);
  }
  do /* manage errors as we would do an exception, all in one point */
  {
    /* reproduce initial conversation on the new server */
    free_and_read_string(buf,fdin); /* read banner */
    write_string(fdin,"HELO " HOSTNAME); do { free_and_read_string(buf,fdin); } while('-'==buf[3]);
    write_string(fdin,from); do { free_and_read_string(buf,fdin); } while('-'==buf[3]);
    if(cmp(buf,"250")) { write_string(fd,DEFERROR); break; }
    write_string(fdin,to);
    /* now just copy data from one server to the other */
    while(1)
    {
      fds[0]=fd; fds[1]=fdin;
      can_read(fds,2,-1);
      if(can_read(&fd,1,0)) { fdread=fd; fdwrite=fdin; }
      else { fdread=fdin; fdwrite=fd; }
      bytesread=read(fdread,databuffer,sizeof(databuffer));
      if(bytesread<=0||write(fdwrite,databuffer,bytesread)<=0);
      {
        closeskt(fd);
	closeskt(fdin);
        break;
      }
    }
  }
  while(0);
  condfree(buf); condfree(to); condfree(from); closeskt(fd); closeskt(fdin);
  exit(0);
}

int main(int argc, char **argv)
{
  int fd_server=-1,fd=-1;
  unsigned long conn=0;

  /* ignore dying child */
  signal(SIGCHLD,SIG_IGN);
  openlog("dist",0,LOG_MAIL);
  if(-1==(fd_server=create_listening_socket(PORT))) fail();
  while(-1!=(fd=accept(fd_server,NULL,0)))
  {
    debug("New connection!");
    ++conn;
    switch(fork())
    {
      case 0: closeskt(fd_server); handle_new_connection(conn,fd);
      case -1: fail();
      default: closeskt(fd);
    }
  }
  close(fd_server);
  closelog();

  exit(0);
}