qmail-smtpd.c

linux下qmail的源码 本人加了一些注释

  r = rcpthosts(addr.s,str_len(addr.s));
  if (r == -1) die_control();
  return r;
}


int seenmail = 0;
int flagbarf; /* defined if seenmail */
stralloc mailfrom = {0};
stralloc rcptto = {0};

void smtp_helo(arg) char *arg;
{
  smtp_greet("250 "); out("\r\n");
  seenmail = 0; dohelo(arg);
}
void smtp_ehlo(arg) char *arg;
{
  smtp_greet("250-"); out("\r\n250-PIPELINING\r\n250 8BITMIME\r\n");
  seenmail = 0; dohelo(arg);
}

//重新初始化，调用helo或ehlo命令都会完成相同的功能
void smtp_rset()
{
  seenmail = 0;
  out("250 flushed\r\n");
}

//mail命令解释程序，重要变量：[mailfrom/全局]
//该函数完成检查mailfrom是否在badmailfrom中定义，设置标志指明mail命令已经执行
void smtp_mail(arg) char *arg;
{
  if (!addrparse(arg)) { err_syntax(); return; }

  //检查是否badmailfrom，如果是设置相应标志，这个标志在rcpt命令的处理程序中才起作用
  flagbarf = bmfcheck();
  seenmail = 1;		//指示已经执行过mail命令。
  if (!stralloc_copys(&rcptto,"")) die_nomem();		//分配rcptto缓冲区
  if (!stralloc_copys(&mailfrom,addr.s)) die_nomem();	//复制mail命令中指定的地址到mailfrom
  if (!stralloc_0(&mailfrom)) die_nomem();
  out("250 ok\r\n");
}

//rcpt命令解释程序，重要变量：[rcptto/全局]
void smtp_rcpt(arg) char *arg; {
  if (!seenmail) { err_wantmail(); return; }	//买了命令是否已经执行？
  if (!addrparse(arg)) { err_syntax(); return; }	//分离邮件地址参数存入全局缓存addr
  
  //如果mail命令中的地址在control/badmailfrom中有定义，返回
  if (flagbarf) { err_bmf(); return; }
  //至此addr缓存中包含了rcpt命令指定的email地址
  //如果rcpt命令，则有addr="[e-mail]"。这个变量是在addrparse函数中赋值的
  //如果RELAYCLIENT环境变量设置将不进行rcpthosts，morercpthosts.cdb的比较
  //足以，大国smtp认证补丁，如果通过认证后会设置relayclient=""
  if (relayclient) {
    --addr.len;
    if (!stralloc_cats(&addr,relayclient)) die_nomem();
    if (!stralloc_0(&addr)) die_nomem();
  }
  else		//如果没有指定RELAYCLIENT变量，则有control/rcpthosts决定是否进行转发
    if (!addrallowed()) { err_nogateway(); return; }

	//生成头连接到全局缓存rcptto：
	//例如地址"rcpt [e-mail]"命令将产生rcptto="[e-mail]"
	//多次执行rcpt命令效果会是rcptto=“[e-mail]@eg.org”
  if (!stralloc_cats(&rcptto,"T")) die_nomem();
  if (!stralloc_cats(&rcptto,addr.s)) die_nomem();
  if (!stralloc_0(&rcptto)) die_nomem();
  out("250 ok\r\n");
}


//saferead,从网络读len个字节到buf缓冲区
//返回实际读到的字节数.
//超时值为control/timeoutsmtpd文件中指定的值.见setup()函数，(默认值1200秒)
int saferead(fd,buf,len) int fd; char *buf; int len;
{
  int r;
  flush();
  r = timeoutread(timeout,fd,buf,len);
  if (r == -1) if (errno == error_timeout) die_alarm();
  if (r <= 0) die_read();
  return r;
}

char ssinbuf[1024];
substdio ssin = SUBSTDIO_FDBUF(saferead,0,ssinbuf,sizeof ssinbuf);

struct qmail qqt;
unsigned int bytestooverflow = 0;

void put(ch)
char *ch;
{
  if (bytestooverflow)
    if (!--bytestooverflow)
      qmail_fail(&qqt);
  qmail_put(&qqt,ch,1);
}

void blast(hops)
int *hops;
{
  char ch;
  int state;
  int flaginheader;
  int pos; /* number of bytes since most recent \n, if fih */
  int flagmaybex; /* 1 if this line might match RECEIVED, if fih */
  int flagmaybey; /* 1 if this line might match \r\n, if fih */
  int flagmaybez; /* 1 if this line might match DELIVERED, if fih */
 
  state = 1;
  *hops = 0;
  flaginheader = 1;
  pos = 0; flagmaybex = flagmaybey = flagmaybez = 1;
  for (;;) {

	//从标准输入(也就是网络)读邮件内容直到独到仅有一个点的行.
    substdio_get(&ssin,&ch,1);
    if (flaginheader) {
      if (pos < 9) {
        if (ch != "delivered"[pos]) if (ch != "DELIVERED"[pos]) flagmaybez = 0;
        if (flagmaybez) if (pos == 8) ++*hops;
        if (pos < 8)
          if (ch != "received"[pos]) if (ch != "RECEIVED"[pos]) flagmaybex = 0;
        if (flagmaybex) if (pos == 7) ++*hops;
        if (pos < 2) if (ch != "\r\n"[pos]) flagmaybey = 0;
        if (flagmaybey) if (pos == 1) flaginheader = 0;
      }
      ++pos;
      if (ch == '\n') { pos = 0; flagmaybex = flagmaybey = flagmaybez = 1; }
    }
    switch(state) {
      case 0:
        if (ch == '\n') straynewline();
        if (ch == '\r') { state = 4; continue; }
        break;
      case 1: /* \r\n */
        if (ch == '\n') straynewline();
        if (ch == '.') { state = 2; continue; }
        if (ch == '\r') { state = 4; continue; }
        state = 0;
        break;
      case 2: /* \r\n + . */
        if (ch == '\n') straynewline();
        if (ch == '\r') { state = 3; continue; }
        state = 0;
        break;
      case 3: /* \r\n + .\r */
        if (ch == '\n') return;
        put(".");
        put("\r");
        if (ch == '\r') { state = 4; continue; }
        state = 0;
        break;
      case 4: /* + \r */
        if (ch == '\n') { state = 1; break; }
        if (ch != '\r') { put("\r"); state = 0; }
    }
    put(&ch);
  }
}

char accept_buf[FMT_ULONG];
void acceptmessage(qp) unsigned long qp;
{
  datetime_sec when;
  when = now();
  out("250 ok ");
  accept_buf[fmt_ulong(accept_buf,(unsigned long) when)] = 0;
  out(accept_buf);
  out(" qp ");
  accept_buf[fmt_ulong(accept_buf,qp)] = 0;
  out(accept_buf);
  out("\r\n");
}

//data命令解释程序
//完成向qmail-queue投递邮件
void smtp_data() {
  int hops;
  unsigned long qp;
  char *qqx;
 
  if (!seenmail) { err_wantmail(); return; }	//如果没有执行过mail命令，出错返回
  if (!rcptto.len) { err_wantrcpt(); return; }	//如果没有执行rcpt命令，出错返回
  seenmail = 0;		//将mail命令标志失效

  //databytes邮件最大长度，如果没有指定那么值是0，代表无限
  if (databytes) bytestooverflow = databytes + 1;
  if (qmail_open(&qqt) == -1) { err_qqt(); return; }	//建立子进程执行qmail-queue
  qp = qmail_qp(&qqt);		//qp为qmail-queue process缩写，it's a process id。
  out("354 go ahead\r\n");
 
  //向新建立的进程传送邮件头
  received(&qqt,"SMTP",local,remoteip,remotehost,remoteinfo,fakehelo);
  blast(&hops);
  hops = (hops >= MAXHOPS);
  if (hops) qmail_fail(&qqt);

  //向qmail-queue传送邮件头信息,如果[e-mail]向[e-mail]发送邮件，那么向qmail-queue
  //传送的字符串将是 [e-mail]@hg.org
  qmail_from(&qqt,mailfrom.s);
  qmail_put(&qqt,rcptto.s,rcptto.len);
 
  qqx = qmail_close(&qqt);
  if (!*qqx) { acceptmessage(qp); return; }		//如果接受成功
  if (hops) { out("554 too many hops, this message is looping (#5.4.6)\r\n"); return; }
  if (databytes) if (!bytestooverflow) { out("552 sorry, that message size exceeds my databytes limit (#5.3.4)\r\n"); return; }
  if (*qqx == 'D') out("554 "); else out("451 ");
  out(qqx + 1);
  out("\r\n");
}


//smtp命令处理函数表
struct commands smtpcommands[] = {
  { "rcpt", smtp_rcpt, 0 }
, { "mail", smtp_mail, 0 }
, { "data", smtp_data, flush }		//建立子进程执行qmail-queue，并向其传送邮件.
, { "quit", smtp_quit, flush }
, { "helo", smtp_helo, flush }
, { "ehlo", smtp_ehlo, flush }
, { "rset", smtp_rset, 0 }
, { "help", smtp_help, flush }
, { "noop", err_noop, flush }		//实际上未实现的命令
, { "vrfy", err_vrfy, flush }		//实际上未实现的命令
, { 0, err_unimpl, flush }			//命令错误
} ;

/*
　　qmail-smtpd 是由tcp-env程序启动
　　tcp-env将来自网络的连接重定向到qmail-smtpd的标准输入及标准输出.
	这些程式建立一些环境变量(如TCPREMOTEHOST,TCPREMOTEIP)将由setup()函数使用
*/

void main()
{
  sig_pipeignore();		//忽略信号
  if (chdir(auto_qmail) == -1) die_control();	//改变当前目录到/var/qmail
  setup();		//读控制文件及相应的环境变量
  if (ipme_init() != 1) die_ipme();		//取本地接口的ip地址
  smtp_greet("220 ");		//显示欢迎信息
  out(" ESMTP\r\n");

  //从标准读入(网络连接)读入smtp命令
  if (commands(&ssin,&smtpcommands) == 0) die_read();
  die_nomem();
}