很多人对qmail smtp的认证机制，环境变量，执行顺序不太了解。
仔细看完这一大篇代码后相信你会明白很多你过去不太明白的问题。
当然你要有一点点c语言基础。也只要一点点。
Come from: ChongQing Gearbox co.,ltd
这份文件还不完善，如果您完善了它请发一份给我: beggar110@163.com
这份文件是给想深入了解qmail和想hacker qmail的人读的,如果你只是想建立一个能够运作的mail服务器,没有必要读下去了。它将浪费你很多的时间。
如果你对qmail控制文件还不是很了解，阅读这份文件之前，请先阅读rainbow的《qmail控制文件详解》
在这里你可以找到http://www.chinaunix.net/forum/viewtopic.php?t=1126
好的。开始我们qmail内部的漫游吧！！！Let's go!
代码:
qmail 总览
tcpserver MUA
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V V
qmail-smtpd qmail-inject
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+---------qmail-queue
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qmail-send
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+------------+------------+
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V V
qmail-rspawn qmail-lspawn
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V V
qmail-remote qmail-local
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V V
INTERNET
|
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vchkpw
|
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qmail-popup
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tcpserver--+
qmail-smtpd.c源代码分析(去掉了所有include)
qmail-smtpd是由tcpserver或由tcp-env启动。tcpserver负责监听端口，如果指定了-x rule.cbd，tcpserver会先决断是断开连接还是启动qmail子进程。如果没有指定-x参数启动tcpserver,那么直接启动 qmail-smtpd.启动qmail-smtpd之前将来自网络的数据连接重定向到qmail-smtpd的fd0,fd1.还会初始化一些 qmail-smtpd需要的环境变量，如TCPREMOTEIP.
tcp-env只会初始化qmail-smtpd的环境变量,不负责监听端口及重定向网络连接。所以tcp-env要和inetd配合使用。当然，由于初始化环境变量的工作tcpserver也会作，所以没有必要tcpserver和tcp-env配合使用.
qmail-smtpd完成邮件smtp命令的接收，并调用相应的处理程序。
检查mail 中的地址是否在control/badmailfrom中定义(MAIL命令)
检查是否设置了RELAYCLIENT环境变量或 rcpt 中的地址是否是control/rcpthosts中定义(RCPT命令)
需要明确的是qmail-smtpd只是简单的接收邮件内容传送给qmail-queue,并不对邮件进行转发(DATA命令)。
当然还要向qmail-queue传送mailfrom,mailto
代码:
#define MAXHOPS 100
unsigned int databytes = 0; //邮件最大长度：0=无限
int timeout = 1200; //默认超时20分钟
//向网络写，超时值为control/timeoutsmtpd指定的值。没有这个文件则取默认值20分钟
int safewrite(fd,buf,len) int fd; char *buf; int len;
{
int r;
r = timeoutwrite(timeout,fd,buf,len);
if (r
return r;
}
char ssoutbuf[512];
substdio ssout = SUBSTDIO_FDBUF(safewrite,1,ssoutbuf,sizeof ssoutbuf);
void flush() { substdio_flush(%26amp;ssout); }
void out(s) char *s; { substdio_puts(%26amp;ssout,s); }
//错误处理函数
void die_read() { _exit(1); }
void die_alarm() { out("451 timeout (#4.4.2)\r\n"); flush(); _exit(1); }
void die_nomem() { out("421 out of memory (#4.3.0)\r\n"); flush(); _exit(1); }
void die_control() { out("421 unable to read controls (#4.3.0)\r\n"); flush(); _exit(1); }
void die_ipme() { out("421 unable to figure out my IP addresses (#4.3.0)\r\n"); flush(); _exit(1); }
void straynewline() { out("451 See http://pobox.com/~djb/docs/smtplf.html.\r\n"); flush(); _exit(1); }
void err_bmf() { out("553 sorry, your envelope sender is in my badmailfrom list (#5.7.1)\r\n"); }
void err_nogateway() { out("553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)\r\n"); }
void err_unimpl() { out("502 unimplemented (#5.5.1)\r\n"); }
void err_syntax() { out("555 syntax error (#5.5.4)\r\n"); }
void err_wantmail() { out("503 MAIL first (#5.5.1)\r\n"); }
void err_wantrcpt() { out("503 RCPT first (#5.5.1)\r\n"); }
void err_noop() { out("250 ok\r\n"); }
void err_vrfy() { out("252 send some mail, i'll try my best\r\n"); }
void err_qqt() { out("451 qqt failure (#4.3.0)\r\n"); }
stralloc greeting = {0};
//输出提示信息*code
void smtp_greet(code) char *code;
{
substdio_puts(%26amp;ssout,code);
substdio_put(%26amp;ssout,greeting.s,greeting.len);
}
void smtp_help()
{
out("214 qmail home page: http://pobox.com/~djb/qmail.html\r\n");
}
void smtp_quit()
{
smtp_greet("221 "); out("\r\n"); flush(); _exit(0);
}
char *remoteip; //远端ip地址
char *remotehost; //远端主机名
char *remoteinfo; //远端信息
char *local; //本地主机
char *relayclient; //是否检查rcpthosts文件
stralloc helohost = {0};
char *fakehelo; /* pointer into helohost, or 0 */
void dohelo(arg) char *arg; {
if (!stralloc_copys(%26amp;helohost,arg)) die_nomem();
if (!stralloc_0(%26amp;helohost)) die_nomem();
//fakehelo变量，如果helo 参数指定的主机名与TCPREMOTEHOST环境变量中的主机名不同则
//fakehelo的值为helo命令的参数指定的主机名.如果两者相同则fekehelo为NULL;
//data命令处理程式用到这个变量
fakehelo = case_diffs(remotehost,helohost.s) ? helohost.s : 0;
}
int liphostok = 0;
stralloc liphost = {0};
int bmfok = 0;
stralloc bmf = {0};
struct constmap mapbmf;
void setup()
{
char *x;
unsigned long u;
if (control_init() == -1) die_control(); //control/me
//读入欢迎信息greeting，如果不存在则从me文件复制
if (control_rldef(%26amp;greeting,"control/smtpgreeting",1,(char *) 0) != 1)
die_control();
//读入localiphost,如果文件不存在则从me文件复制
liphostok = control_rldef(%26amp;liphost,"control/localiphost",1,(char *) 0);
if (liphostok == -1) die_control();
//读control/timeoutsmtpd存入timeout,用于控制超时的情况.
if (control_readint(%26amp;timeout,"control/timeoutsmtpd") == -1) die_control();
if (timeout
if (rcpthosts_init() == -1) die_control();
//读入badmailfrom文件存入 bmf
bmfok = control_readfile(%26amp;bmf,"control/badmailfrom",0);
if (bmfok == -1) die_control();
if (bmfok)
if (!constmap_init(%26amp;mapbmf,bmf.s,bmf.len,0)) die_nomem();
//读入databytes文件存入 databytes,如果该文件不存在，则将
//databytes的值设为0.
if (control_readint(%26amp;databytes,"control/databytes") == -1) die_control();
x = env_get("DATABYTES");
if (x) { scan_ulong(x,%26amp;u); databytes = u; }
if (!(databytes + 1)) --databytes;
//取tcp-environ环境变量，如果环境变量没有设置,将它的值设置为unknow.
//这些信息来自tcpserver,或tcp-env之类的程式
remoteip = env_get("TCPREMOTEIP");
if (!remoteip) remoteip = "unknown";
local = env_get("TCPLOCALHOST");
if (!local) local = env_get("TCPLOCALIP");
if (!local) local = "unknown";
remotehost = env_get("TCPREMOTEHOST");
if (!remotehost) remotehost = "unknown";
remoteinfo = env_get("TCPREMOTEINFO");
//从环境变量RELAYCLIENT读入.
//如果RELAYCLIENT变量没有设置那么relayclient将会是NULL.
relayclient = env_get("RELAYCLIENT");
dohelo(remotehost);
}
stralloc addr = {0}; /* will be 0-terminated, if addrparse returns 1 */
//对命令参数arg进行邮件地址分析
//并将分离出的email地址存入全局缓存addr
//成功返回值为1,失败返回0
int addrparse(arg)
char *arg;
{
int i;
char ch;
char terminator;
struct ip_address ip;
int flagesc;
int flagquoted;
//分离出邮件地址
//例如: arg="",或 arg=": email@eg.org "
//执行下面这段程式后arg="email@eg.org"
terminator = '';
i = str_chr(arg,'
if (arg[i])
arg += i + 1;
else { /* partner should go read rfc 821 */
terminator = ' ';
arg += str_chr(arg,':');
if (*arg == ':') ++arg;
while (*arg == ' ') ++arg;
}
/* strip source route */
if (*arg == '@') while (*arg) if (*arg++ == ':') break;
if (!stralloc_copys(%26amp;addr,"")) die_nomem();
flagesc = 0;
flagquoted = 0;
for (i = 0;ch = arg[i];++i) { /* copy arg to addr, stripping quotes */
if (flagesc) {
if (!stralloc_append(%26amp;addr,%26amp;ch)) die_nomem();
flagesc = 0;
}
else {
if (!flagquoted %26amp;%26amp; (ch == terminator)) break;
switch(ch) {
case '\': flagesc = 1; break;
case '"': flagquoted = !flagquoted; break;
default: if (!stralloc_append(%26amp;addr,%26amp;ch)) die_nomem();
}
}
}
/* could check for termination failure here, but why bother? */
if (!stralloc_append(%26amp;addr,"")) die_nomem();
//将ip地址转换为主机名:
//如 test@[10.0.6.21] 转换为 test@host.mydomain.org
//依据是control/localiphost文件中有host.mydomain.org
if (liphostok) {
i = byte_rchr(addr.s,addr.len,'@');
if (i if (addr.s[i + 1] == '[')//比较是否是用[]括起来的IP地址if (!addr.s[i + 1 + ip_scanbracket(addr.s + i + 1,%26amp;ip)])if (ipme_is(%26amp;ip)) {addr.len = i + 1;if (!stralloc_cat(%26amp;addr,%26amp;liphost)) die_nomem();if (!stralloc_0(%26amp;addr)) die_nomem();}}if (addr.len900) return 0; //地址太长，出错返回return 1;//成功返回}//简单的垃圾邮件检查//检查全局缓冲区addr中的地址是否有在badmailfrom中定义，//如果有则返回 1,否则返回 0.int bmfcheck(){int j;if (!bmfok) return 0;if (constmap(%26amp;mapbmf,addr.s,addr.len - 1)) return 1;j = byte_rchr(addr.s,addr.len,'@');if (jif (constmap(%26amp;mapbmf,addr.s + j,addr.len - j - 1)) return 1;return 0;}//检查全局缓存addr中的邮件地址是否要进行转发(依据control/rcpthosts文件)//可以进行转发返回1//拒绝转发返回0int addrallowed(){int r;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命令解释程式. 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; }flagbarf = bmfcheck(); //检查是否badmailfrom,如果是设置相应标志，这个标志在rcpt命令的处理程式中才起作用seenmail = 1;//指示已经执行过mail命令.if (!stralloc_copys(%26amp;rcptto,"")) die_nomem();//分配rcptto缓冲区if (!stralloc_copys(%26amp;mailfrom,addr.s)) die_nomem();//复制mail命令中指定的地址到mailfromif (!stralloc_0(%26amp;mailfrom)) die_nomem();out("250 ok\r\n");}//rcpt命令解释程式. 重要变量: [ rcptto /全局]void smtp_rcpt(arg) char *arg; {if (!seenmail) { err_wantmail(); return; }//mail命令是否已执行?if (!addrparse(arg)) { err_syntax(); return; }//分离邮件地址参数存入全局缓存addrif (flagbarf) { err_bmf(); return; }//如果mail命令中的地址在control/badmailfrom中有定义,返回//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="email@eg.org".这个变量是在addrparse函数中符值的//如果 RELAYCLIENT 环境变量设置将不进行rcpthosts,morercpthosts.cdb的比较//注意,打过smtp认证补丁，如果通过认证后会设置relayclient=""if (relayclient) {--addr.len;if (!stralloc_cats(%26amp;addr,relayclient)) die_nomem();if (!stralloc_0(%26amp;addr)) die_nomem();}else//如果没有指定RELAYCLIENT变量，则由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 test@eg.org' 命令将产生 rcptto="Temail@eg.org"//多次执行rcpt命令效果会是rcptto="Ttest@eg.orgTtwo@eg.org"if (!stralloc_cats(%26amp;rcptto,"T")) die_nomem();if (!stralloc_cats(%26amp;rcptto,addr.s)) die_nomem();if (!stralloc_0(%26amp;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 (rreturn 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(%26amp;qqt);qmail_put(%26amp;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 (;;) {substdio_get(%26amp;ssin,%26amp;ch,1);//从标准输入(也就是网络)读邮件内容直到读到仅有一个点的行.if (flaginheader) {if (posif (ch != "delivered"[pos]) if (ch != "DELIVERED"[pos]) flagmaybez = 0;if (flagmaybez) if (pos == 8) ++*hops;if (posif (ch != "received"[pos]) if (ch != "RECEIVED"[pos]) flagmaybex = 0;if (flagmaybex) if (pos == 7) ++*hops;if (posif (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(%26amp;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 命令解释程式//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，如果没有指定那么它的值将是0if (databytes) bytestooverflow = databytes + 1;if (qmail_open(%26amp;qqt) == -1) { err_qqt(); return; }//建立子进程执行qmail-queueqp = qmail_qp(%26amp;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(%26amp;qqt,"SMTP",local,remoteip,remotehost,remoteinfo,fakehelo);blast(%26amp;hops);hops = (hops= MAXHOPS);if (hops) qmail_fail(%26amp;qqt);//向qmail-queue传送邮件头信息.//如果hong@hg.org 向 lyx@hg.org发送邮件，那么向qmail-queue传送的字符串将是// Fhong@hg.orgTlyx@hg.orgqmail_from(%26amp;qqt,mailfrom.s);qmail_put(%26amp;qqt,rcptto.s,rcptto.len);qqx = qmail_close(%26amp;qqt);if (!*qqx) { acceptmessage(qp); return; }//如果接收成功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qamil-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tcpserver,或tcp-env之类的程式启动tcpserver,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");//从标准输入(网络连接)读入smtp命令.if (commands(%26amp;ssin,%26amp;smtpcommands) == 0) die_read();die_nomem();}==完==qmail-queue源代码分析Programmer:夜未眠Comefrom:ChongQing Gearbox co.,ltd程序主要完成的功能是：1.生成自已的邮件首部，也就是你在邮件头中见到的类似下面的东西Recevied (qmail 855 invoked by uid 0); 2 May 2003 12:18:09 -00002.建立3个文件queue/mess////邮件正文queue/intd/用户id,进程id,mailfrom,rcpttoqueue/todo/是intd目录下文件的复本.3.写命名管道lock/trigger通知新邮件代码:#define DEATH 86400 /* 24 hours; _must_ be below q-s's OSSIFIED (36 hours) */#define ADDR 1003char inbuf[2048];struct substdio ssin;char outbuf[256];struct substdio ssout;datetime_sec starttime;struct datetime dt;unsigned long mypid;unsigned long uid;char *pidfn;struct stat pidst;unsigned long messnum;char *messfn;char *todofn;char *intdfn;int messfd;int intdfd;int flagmademess = 0;int flagmadeintd = 0;//错误清理void cleanup(){if (flagmadeintd){seek_trunc(intdfd,0);if (unlink(intdfn) == -1) return;}if (flagmademess){seek_trunc(messfd,0);if (unlink(messfn) == -1) return;}}void die(e) int e; { _exit(e); }void die_write() { cleanup(); die(53); }void die_read() { cleanup(); die(54); }void sigalrm() { /* thou shalt not clean up here */ die(52); }void sigbug() { die(81); }unsigned int receivedlen;char *received;static unsigned int receivedfmt(s)char *s;{unsigned int i;unsigned int len;len = 0;/*生成/* "Received: (qmail-queue invoked by alias); 26 Sep 1995 04:46:54 -0000\n" */[日 月 年 时 分 秒]的形式.*/i = fmt_str(s,"Received: (qmail "); len += i; if (s) s += i;i = fmt_ulong(s,mypid); len += i; if (s) s += i;i = fmt_str(s," invoked "); len += i; if (s) s += i;if (uid == auto_uida){ i = fmt_str(s,"by alias"); len += i; if (s) s += i; }else if (uid == auto_uidd){ i = fmt_str(s,"from network"); len += i; if (s) s += i; }else if (uid == auto_uids){ i = fmt_str(s,"for bounce"); len += i; if (s) s += i; }else{i = fmt_str(s,"by uid "); len += i; if (s) s += i;i = fmt_ulong(s,uid); len += i; if (s) s += i;}i = fmt_str(s,"); "); len += i; if (s) s += i;i = date822fmt(s,%26amp;dt); len += i; if (s) s += i;return len;}void received_setup(){receivedlen = receivedfmt((char *) 0);received = alloc(receivedlen + 1);if (!received) die(51);receivedfmt(received);}unsigned int pidfmt(s,seq)char *s;unsigned long seq;{unsigned int i;unsigned int len;//生成类型pid/3434.34242424.1的字符串到s中//这个字符串实际上就是/var/qmail/queue/pid目录下一个文件名。指示当前进程的pid.len = 0;i = fmt_str(s,"pid/"); len += i; if (s) s += i;i = fmt_ulong(s,mypid); len += i; if (s) s += i;i = fmt_str(s,"."); len += i; if (s) s += i;i = fmt_ulong(s,starttime); len += i; if (s) s += i;i = fmt_str(s,"."); len += i; if (s) s += i;i = fmt_ulong(s,seq); len += i; if (s) s += i;++len; if (s) *s++ = 0;return len;}char *fnnum(dirslash,flagsplit)char *dirslash;int flagsplit;{char *s;s = alloc(fmtqfn((char *) 0,dirslash,messnum,flagsplit));if (!s) die(51);fmtqfn(s,dirslash,messnum,flagsplit);return s;}void pidopen() //建立类似/var/run/inet.pid之类的进程id文件.{unsigned int len;unsigned long seq;seq = 1;len = pidfmt((char *) 0,seq);pidfn = alloc(len);if (!pidfn) die(51);for (seq = 1;seq{if (pidfmt((char *) 0,seq)len) die(81); /* paranoia */pidfmt(pidfn,seq);messfd = open_excl(pidfn);if (messfd != -1) return;}die(63);}char tmp[FMT_ULONG];void main(){unsigned int len;char ch;sig_blocknone();umask(033);if (chdir(auto_qmail) == -1) die(61);if (chdir("queue") == -1) die(62);//改变工作目录到/var/qmail/queuemypid = getpid();uid = getuid();starttime = now();datetime_tai(%26amp;dt,starttime);//将起始时间转换为可读年月日时分秒的形式//生成自已的邮件头存入缓存reseived中//例如: received="Received: (qmail 3434 invoked by 34434); Apr 27 2003 14:55:34"received_setup();sig_pipeignore();sig_miscignore();sig_alarmcatch(sigalrm);//捕捉alarm信号,控制超时sig_bugcatch(sigbug);alarm(DEATH); //超时秒数，缺省值是86400(24小时) 后错误返回52pidopen();//建立进程id文件if (fstat(messfd,%26amp;pidst) == -1) die(63);messnum = pidst.st_ino; //进程id文件的inode节点号/*生成将要建立的文件的文件名几个文件都是根据刚才建立的pid文件的inode节点号命名的.inode不可能被两个文件同时占用，这保证了邮件唯一性。其中mess目录下的文件放置有一个%23的问题，tips: 因为是%23所以该目录名最大的可能只有22，明白queue/mess目录下目录为什么最大只22了吧比如说inode节点号为3455,那么3455%23=5,那么将生成/var/qmail/queue/mess/5/3455 这样一个文件来存放邮件。/var/qmail/queue/todo/3455与/var/qmail/queue/intd/3455是相同的,都是保存用户id,进程id,mailfrom,rcptto的。*/messfn = fnnum("mess/",1); //解释为message file nametodofn = fnnum("todo/",0); //todo file nameintdfn = fnnum("intd/",0); //intd file nameif (link(pidfn,messfn) == -1) die(64);if (unlink(pidfn) == -1) die(63);//进程id文件使命很快结束，死掉了//所以你不应该想在queue/pid目录中找到进程id文件。//另外,qmail-clean也将定期清理queue/pid目录下的pid文件，说定期其实也不是，qmail-clean会在每收到30个清理邮件的请求后清理pid目录一次.这在分析qmail-clean时我们将会看到.flagmademess = 1;//fd1关联到写mess/下新建的文件。 通过管道连接fde//也就是说qmail-smtpd进程写它的qqt-fde，那就相当于写mess/下新建立的邮件//注意是关联不是正式写substdio_fdbuf(%26amp;ssout,write,messfd,outbuf,sizeof(outbuf));//fd0关联到读标准输入到缓存区inbuf 通过管道连接fdm//也就是说读ssin将从qmail-smtpd的qqt-fdm端读substdio_fdbuf(%26amp;ssin,read,0,inbuf,sizeof(inbuf));//向mess/下的邮件文件写qmail-queue的头部信息if (substdio_bput(%26amp;ssout,received,receivedlen) == -1) die_write();//从fd1读smtpd设置的邮件首部switch(substdio_copy(%26amp;ssout,%26amp;ssin)){case -2: die_read();case -3: die_write();}if (substdio_flush(%26amp;ssout) == -1) die_write();if (fsync(messfd) == -1) die_write();intdfd = open_excl(intdfn);if (intdfd == -1) die(65);flagmadeintd = 1;//fd1关联到写intd/下新建立的文件 fd0关联到读inbuff缓冲区substdio_fdbuf(%26amp;ssout,write,intdfd,outbuf,sizeof(outbuf));substdio_fdbuf(%26amp;ssin,read,1,inbuf,sizeof(inbuf));/*向intd下新建立的文件写如下格式内容这些内容来自于qmail-smtpd.c中的data命令的解释函数。u[uid]p[pid]F[mailfrom]T[rcptto1][rcptto2][rcptton]例如:lyx@hg.org向hong@hg.org和beggar@hg.org发邮件可能会有如下内容u6027p34234Flyx@hg.orgThong@hg.orgTbeggar@hg.org*/if (substdio_bput(%26amp;ssout,"u",1) == -1) die_write();if (substdio_bput(%26amp;ssout,tmp,fmt_ulong(tmp,uid)) == -1) die_write();if (substdio_bput(%26amp;ssout,"",1) == -1) die_write();if (substdio_bput(%26amp;ssout,"p",1) == -1) die_write();if (substdio_bput(%26amp;ssout,tmp,fmt_ulong(tmp,mypid)) == -1) die_write();if (substdio_bput(%26amp;ssout,"",1) == -1) die_write();if (substdio_get(%26amp;ssin,%26amp;ch,1)if (ch != 'F') die(91);if (substdio_bput(%26amp;ssout,%26amp;ch,1) == -1) die_write();for (len = 0;len{if (substdio_get(%26amp;ssin,%26amp;ch,1)if (substdio_put(%26amp;ssout,%26amp;ch,1) == -1) die_write();if (!ch) break;}//如有多个邮件接收人时,这些接收人的地址总不长度不能超过1023字节，如果每个邮件地址约为15个字节的话，//大约可能指定65个if (len= ADDR) die(11);if (substdio_bput(%26amp;ssout,QUEUE_EXTRA,QUEUE_EXTRALEN) == -1) die_write();for (;;){if (substdio_get(%26amp;ssin,%26amp;ch,1)if (!ch) break;if (ch != 'T') die(91);if (substdio_bput(%26amp;ssout,%26amp;ch,1) == -1) die_write();for (len = 0;len{if (substdio_get(%26amp;ssin,%26amp;ch,1)if (substdio_bput(%26amp;ssout,%26amp;ch,1) == -1) die_write();if (!ch) break;}if (len= ADDR) die(11);}if (substdio_flush(%26amp;ssout) == -1) die_write();if (fsync(intdfd) == -1) die_write();//复制intdfn到todofn 由此可见这两个是相同的文件if (link(intdfn,todofn) == -1) die(66);triggerpull(); //向命名管道 /var/qmail/queue/lock/trigger写一个字节(写的是0),通知有新的邮件die(0); //退出}==完==qmail-popup.c分析Programmer:夜未眠Come from:ChongQing Gearbox co.,ltdqmail-popup也是由tcpserver或tcp-env之类的程式启动。这些程式是通过管道与qmail-popup通信的。这也是qmail 的美妙之处，总观整个qmail源代码，除少量dns代码外。基本上没有使用网络编程。各个进程间大部分都是通管道通信。把监听，读写网络部分交给 inetd或tcpserver来作。使得qmail代码相当容易阅读理解。主要功能:1.从网络读pop3命令，进行相应处理。2.调用子进程(vchkpw或checkpassword，具体是哪一个由你在运行参数中指定,当然，仔细分析完doanddie函数后你也许就能编写自己的checkpw了，呵呵)完成检验密码，启动qmail-pop3d的工作重要的函数是doanddie. 理解这个函数基本上就能理解qmail pop密码的检验流程。几个程式间的关系是：代码:tcpserver--qmail-popup--vchkpw----认证成功-qmail-pop3d| || |==========================代码:void die() { _exit(1); }int saferead(fd,buf,len) int fd; char *buf; int len;{int r;r = timeoutread(1200,fd,buf,len);if (rreturn r;}int safewrite(fd,buf,len) int fd; char *buf; int len;{int r;r = timeoutwrite(1200,fd,buf,len);if (rreturn r;}char ssoutbuf[128];substdio ssout = SUBSTDIO_FDBUF(safewrite,1,ssoutbuf,sizeof ssoutbuf);char ssinbuf[128];substdio ssin = SUBSTDIO_FDBUF(saferead,0,ssinbuf,sizeof ssinbuf);void puts(s) char *s;{substdio_puts(%26amp;ssout,s);}void flush(){substdio_flush(%26amp;ssout);}void err(s) char *s;{puts("-ERR ");puts(s);puts("\r\n");flush();}void die_usage() { err("usage: popup hostname subprogram"); die(); }void die_nomem() { err("out of memory"); die(); }void die_pipe() { err("unable to open pipe"); die(); }void die_write() { err("unable to write pipe"); die(); }void die_fork() { err("unable to fork"); die(); }void die_childcrashed() { err("aack, child crashed"); }void die_badauth() { err("authorization failed"); }void err_syntax() { err("syntax error"); }void err_wantuser() { err("USER first"); }void err_authoriz() { err("authorization first"); }void okay() { puts("+OK \r\n"); flush(); }void pop3_quit() { okay(); die(); }//FMT_ULONG 40 /* enough space to hold 2^128 - 1 in decimal, plus \0 */char unique[FMT_ULONG + FMT_ULONG + 3];char *hostname;stralloc username = {0};int seenuser = 0;char **childargs;substdio ssup;char upbuf[128];void doanddie(user,userlen,pass)char *user;unsigned int userlen; /* including 0 byte */char *pass;{int child;int wstat;int pi[2];if (fd_copy(2,1) == -1) die_pipe();//关闭出错(fd2)，将标准输出(fd1),定向到标准出错(fd2)close(3);if (pipe(pi) == -1) die_pipe();if (pi[0] != 3) die_pipe(); //确保向子进程能够读到硬编码的fd 3switch(child = fork()) { //建立子进程执行subprogram给出的程式，一般是一个检验用户名和密码的程式case -1:die_fork();case 0:close(pi[1]);sig_pipedefault();//子进程执行checkpassword或vchkpw之类的程式，检验密码，如果认证通过execvp(*childargs,childargs);//这些再调用qmail-pop3d_exit(1);}//父进程向子进程的fd3传送用户名及密码,这是一个约定。如果你要写自已的检验密码的程式，记得//从fd3读密码哦。close(pi[0]);substdio_fdbuf(%26amp;ssup,write,pi[1],upbuf,sizeof upbuf);if (substdio_put(%26amp;ssup,user,userlen) == -1) die_write();if (substdio_put(%26amp;ssup,pass,str_len(pass) + 1) == -1) die_write();//父进程向子进程传送if (substdio_puts(%26amp;ssup,"if (substdio_puts(%26amp;ssup,unique) == -1) die_write();if (substdio_puts(%26amp;ssup,hostname) == -1) die_write();if (substdio_put(%26amp;ssup,"",2) == -1) die_write();if (substdio_flush(%26amp;ssup) == -1) die_write();close(pi[1]);//清除密码及用户名缓冲区byte_zero(pass,str_len(pass));byte_zero(upbuf,sizeof upbuf);if (wait_pid(%26amp;wstat,child) == -1) die();//等待子进程结束if (wait_crashed(wstat)) die_childcrashed();if (wait_exitcode(wstat)) die_badauth();//完成一次pop3对话退出die();}//显示欢迎信息void pop3_greet(){char *s;s = unique;s += fmt_uint(s,getpid());*s++ = '.';s += fmt_ulong(s,(unsigned long) now());*s++ = '@';*s++ = 0;puts("+OKputs(unique);puts(hostname);puts("\r\n");flush();}//设置标志，初始化用户名变量void pop3_user(arg) char *arg;{if (!*arg) { err_syntax(); return; }okay();seenuser = 1; //user命令已经执行的标志if (!stralloc_copys(%26amp;username,arg)) die_nomem(); //将参数存入usernameif (!stralloc_0(%26amp;username)) die_nomem();}void pop3_pass(arg) char *arg;{if (!seenuser) { err_wantuser(); return; }//如果没有执行user命令,返回if (!*arg) { err_syntax(); return; }doanddie(username.s,username.len,arg);//调用子进程验正密码并等待它完成}void pop3_apop(arg) char *arg;//用户名及密码在一个命令中给出的情况，见user,pass{char *space;space = arg + str_chr(arg,' ');if (!*space) { err_syntax(); return; }*space++ = 0;doanddie(arg,space - arg,space);}struct commands pop3commands[] = {//命令及相应的处理函数表{ "user", pop3_user, 0 }, { "pass", pop3_pass, 0 }, { "apop", pop3_apop, 0 }, { "quit", pop3_quit, 0 }, { "noop", okay, 0 }, { 0, err_authoriz, 0 }} ;void main(argc,argv)int argc;char **argv;{sig_alarmcatch(die);//捕获sigalrm信号sig_pipeignore();//忽略pipe信号hostname = argv[1]; //hostname 指向 程式的第一个参数if (!hostname) die_usage();childargs = argv + 2;if (!*childargs) die_usage();pop3_greet();//显示欢迎信息后进入命令循环，等待用户命令commands(%26amp;ssin,pop3commands);die();}qmail-start.c 分析Programmer:夜未眠Comefrom:ChongQing Gearbox co.,ltdqmail-start 是很简单的一个程式，他完成qmail-send,qmail-clean,qmail-lspawn,qmail-rspawn,splogger的启动，并通过管道将他们联系在一起，当然不是网状连接.具体如下代码:=====================================qmail-lspawn fd0qmail-lspawn fd1 ------ qmail-send fd2qmail-rspawn fd0qmail-rspawn fd1 ------ qmail-send fd4qmail-clean fd0qmail-clean fd1 ------ qmail-send fd6=====================================理解他们之间的关系(注意方向)对于理解qmail-send源代码非常重要。仔细再看一次。因为其比较简单，所以这里就不对他的源代码作过细的分析：代码:char *(qsargs[]) = { "qmail-send", 0 };char *(qcargs[]) = { "qmail-clean", 0 };char *(qlargs[]) = { "qmail-lspawn", "./Mailbox", 0 };char *(qrargs[]) = { "qmail-rspawn", 0 };void die() { _exit(111); }int pi0[2]; //splogger qmailint pi1[2]; //qmail-lspawn fd0int pi2[2]; //qmail-lspawn fd1 ------ qmail-send fd2int pi3[2]; //qmail-rspawn fd0int pi4[2]; //qmail-rspawn fd1 ------ qmail-send fd4int pi5[2]; //qmail-clean fd0int pi6[2]; //qmail-clean fd1 ------ qmail-send fd6void close23456() { close(2); close(3); close(4); close(5); close(6); }//****************////因为没有关闭pi0.//所以所有的子进程都可以通过写pi0来记录maillog.void closepipes() {close(pi1[0]); close(pi1[1]); close(pi2[0]); close(pi2[1]);close(pi3[0]); close(pi3[1]); close(pi4[0]); close(pi4[1]);close(pi5[0]); close(pi5[1]); close(pi6[0]); close(pi6[1]);}void main(argc,argv)int argc;char **argv;{if (chdir("/") == -1) die();umask(077);if (prot_gid(auto_gidq) == -1) die();if (fd_copy(2,0) == -1) die();if (fd_copy(3,0) == -1) die();if (fd_copy(4,0) == -1) die();if (fd_copy(5,0) == -1) die();if (fd_copy(6,0) == -1) die();if (argv[1]) {qlargs[1] = argv[1];++argv;}if (argv[1]) {if (pipe(pi0) == -1) die();switch(fork()) {case -1:die();case 0:if (prot_gid(auto_gidn) == -1) die();if (prot_uid(auto_uidl) == -1) die();close(pi0[1]);if (fd_move(0,pi0[0]) == -1) die();//重定向pi0[0]到splogger的fd0close23456();execvp(argv[1],argv + 1);//启动sploggerdie();}close(pi0[0]);if (fd_move(1,pi0[1]) == -1) die();}if (pipe(pi1) == -1) die();if (pipe(pi2) == -1) die();if (pipe(pi3) == -1) die();if (pipe(pi4) == -1) die();if (pipe(pi5) == -1) die();if (pipe(pi6) == -1) die();switch(fork()) {//启动qmail-lspawncase -1: die();case 0:if (fd_copy(0,pi1[0]) == -1) die();if (fd_copy(1,pi2[1]) == -1) die();close23456();closepipes();execvp(*qlargs,qlargs);die();}switch(fork()) {//启动qmail-rspawncase -1: die();case 0:if (prot_uid(auto_uidr) == -1) die();if (fd_copy(0,pi3[0]) == -1) die();if (fd_copy(1,pi4[1]) == -1) die();close23456();closepipes();execvp(*qrargs,qrargs);die();}switch(fork()) {//启动qmail-cleancase -1: die();case 0:if (prot_uid(auto_uidq) == -1) die();if (fd_copy(0,pi5[0]) == -1) die();if (fd_copy(1,pi6[1]) == -1) die();close23456();closepipes();execvp(*qcargs,qcargs);die();}if (prot_uid(auto_uids) == -1) die();if (fd_copy(0,1) == -1) die(); //重定向管道，把qmail-send 与上面各进程联系起来。if (fd_copy(1,pi1[1]) == -1) die();if (fd_copy(2,pi2[0]) == -1) die();if (fd_copy(3,pi3[1]) == -1) die();if (fd_copy(4,pi4[0]) == -1) die();if (fd_copy(5,pi5[1]) == -1) die();if (fd_copy(6,pi6[0]) == -1) die();closepipes();execvp(*qsargs,qsargs);//最后启动qmail-senddie();}==完==qmail-pop3d源代码分析Programmer:夜未眠Comefrom: ChongQing Gearbox co.,ltd关键数据结构队列: prioq这个数据结构在很多qmail很多程式中都有用到，最好记下来代码:struct prioq_elt {datetime_sec dt;//时间戳,优先级unsigned long id;//邮件唯一id,你可以把它同qmail-queue分析中介绍中pid文件inode联系起来} ;prioq在prioq.h中prioq是这样定义的GEN_ALLOC_typedef(prioq,struct prioq_elt,p,len,a)展开后实际上定义为typedef struct prioq{struct prioq_elt *p; // 指针unsigned int len; //队列的长度unsigned int a;}prioq;消息块: message 我把它叫作消息块是因为他并不包含消息内容，也许这样称呼它并不确切代码:struct message {int flagdeleted; //删除标记，在qmail-pop3d程式退出时进行实际删除动作unsigned long size; //消息文件大小char *fn; //消息文件名} *m;主要功能：qmail-pop3d是则vchkpw或checkpassword之类的程式启动的。这些程式(vchkpw)会更改环境变量USER，HOME，SHELL等等，并在启动qmail-pop3d前将工作目录改变到$HOME下.qmail-pop3d在启动时首先检查./Maildir/tmp(./Maildir是在argv中指定的)下最后访问时间超过36小时的文件，如果存在就将其删除。也正是由于qmail-pop3d在启动时就有chdir的动作，所以qmail-pop3d不支持mailbox形式的pop.扫描Maildir/cur及Maildir/new目录构造一个消息块数组 m(首先是构造一个临时队列pq,然后根据这个队列来构造消息块数组),输出+OK,进入命令循环，等待用户输入pop命令进行相应的处理.具体见代码分析.代码:void die() { _exit(0); }//超时读，超时时间为20分钟,正常返回读到的字节数，否则程式失败die()int saferead(fd,buf,len) int fd; char *buf; int len;{int r;r = timeoutread(1200,fd,buf,len);if (rreturn r;}//超时写，超时时间为20分钟，正常返回写的字节数，否则程式失败die()int safewrite(fd,buf,len) int fd; char *buf; int len;{int r;r = timeoutwrite(1200,fd,buf,len);if (rreturn r;}/*定义ssout为向fd1写，超时时间为20分钟定义ssin为从fd0读，超时时间为20分钟由于tcpserver或inetd已经重定向了fd1,fd0到网络，所以这就等同于向网络读写*/char ssoutbuf[1024];substdio ssout = SUBSTDIO_FDBUF(safewrite,1,ssoutbuf,sizeof ssoutbuf);char ssinbuf[128];substdio ssin = SUBSTDIO_FDBUF(saferead,0,ssinbuf,sizeof ssinbuf);void put(buf,len) char *buf; int len;{substdio_put(%26amp;ssout,buf,len);//将buf缓存中的内容向网络写}void puts(s) char *s;{substdio_puts(%26amp;ssout,s);//将s的内容向网络写,这个函数实际上是调用的substdio_put}void flush() //确保输出缓存中已经没有内容。{substdio_flush(%26amp;ssout);}void err(s) char *s;{puts("-ERR ");puts(s);puts("\r\n");flush();}//错误处理函数void die_nomem() { err("out of memory"); die(); }void die_nomaildir() { err("this user has no $HOME/Maildir"); die(); }void die_scan() { err("unable to scan $HOME/Maildir"); die(); }void err_syntax() { err("syntax error"); }void err_unimpl() { err("unimplemented"); }void err_deleted() { err("already deleted"); }void err_nozero() { err("messages are counted from 1"); }void err_toobig() { err("not that many messages"); }void err_nosuch() { err("unable to open that message"); }void err_nounlink() { err("unable to unlink all deleted messages"); }void okay() { puts("+OK \r\n"); flush(); }void printfn(fn) char *fn;{fn += 4;put(fn,str_chr(fn,':'));}char strnum[FMT_ULONG];stralloc line = {0};void blast(ssfrom,limit)//从ssfrom读数据输出到fd1,一次一行(用全局缓存line)substdio *ssfrom;unsigned long limit;//除开消息头部信息，最多读limit行,limit为0将全部读完{int match;int inheaders = 1;for (;;) {if (getln(ssfrom,%26amp;line,%26amp;match,'\n') != 0) die();if (!match %26amp;%26amp; !line.len) break;if (match) --line.len; /* no way to pass this info over POP */if (limit) if (!inheaders) if (!--limit) break;if (!line.len)inheaders = 0;elseif (line.s[0] == '.')put(".",1);put(line.s,line.len);put("\r\n",2);if (!match) break;}put("\r\n.\r\n",5);flush();}stralloc filenames = {0};prioq pq = {0};struct message {int flagdeleted; //删除标记，在程式退出时进行实际删除动作unsigned long size; //文件大小char *fn; //文件名} *m;int numm;//全局变量记录队列长度int last = 0;void getlist(){struct prioq_elt pe;struct stat st;int i;maildir_clean(%26amp;line);//清除Maildir/tmp/目录下最后访问时间超过 36小时的文件if (maildir_scan(%26amp;pq,%26amp;filenames,1,1) == -1) die_scan();numm = pq.p ? pq.len : 0; //记录下队列长度//通过队列pq构造消息块数组,构建结束后队列pq删除m = (struct message *) alloc(numm * sizeof(struct message));//分配消息块if (!m) die_nomem();for (i = 0;iif (!prioq_min(%26amp;pq,%26amp;pe)) { numm = i; break; }prioq_delmin(%26amp;pq);m[i].fn = filenames.s + pe.id;m[i].flagdeleted = 0;if (stat(m[i].fn,%26amp;st) == -1)m[i].size = 0;elsem[i].size = st.st_size;}}void pop3_stat() //打印类似 +OK{ //如 +OK 3 3555表示总共有3条消息，占用空间3555(通过stat取得的)int i;unsigned long total;total = 0;for (i = 0;iputs("+OK ");put(strnum,fmt_uint(strnum,numm));puts(" ");put(strnum,fmt_ulong(strnum,total));puts("\r\n");flush();}void pop3_rset()//重置pop对话,清除所有删除标记{int i;for (i = 0;ilast = 0;okay();}void pop3_last()//显示最后一个消息块{puts("+OK ");put(strnum,fmt_uint(strnum,last));puts("\r\n");flush();}void pop3_quit()//结束一次pop对话，删除所有删除标记设置的消息,将new下的消息移到cur下{int i;for (i = 0;iif (m[i].flagdeleted) {if (unlink(m[i].fn) == -1) err_nounlink();}elseif (str_start(m[i].fn,"new/")) {if (!stralloc_copys(%26amp;line,"cur/")) die_nomem();if (!stralloc_cats(%26amp;line,m[i].fn + 4)) die_nomem();if (!stralloc_cats(%26amp;line,":2,")) die_nomem();if (!stralloc_0(%26amp;line)) die_nomem();rename(m[i].fn,line.s); /* if it fails, bummer */}okay();die();}//检查消息块是否存在。或消息块的删除标记是否已经设置了//成功返回消息块的位置int型//失败返回-1int msgno(arg) char *arg;{unsigned long u;if (!scan_ulong(arg,%26amp;u)) { err_syntax(); return -1; }if (!u) { err_nozero(); return -1; }--u;if (u= numm) { err_toobig(); return -1; }if (m[u].flagdeleted) { err_deleted(); return -1; }return u;}void pop3_dele(arg) char *arg;//将arg指定消息块设置删除标记,实际删除动作将在pop3退出时进行{int i;i = msgno(arg);if (i == -1) return;m[i].flagdeleted = 1;if (i + 1last) last = i + 1;okay();}void list(i,flaguidl)int i;int flaguidl;{//显示消息块的内容，如果flaguidl设置，输出消息文件名,否则消息大小put(strnum,fmt_uint(strnum,i + 1));puts(" ");if (flaguidl) printfn(m[i].fn);else put(strnum,fmt_ulong(strnum,m[i].size));puts("\r\n");}//如果指定了参数arg那么列出arg指定的消息块的内容，否则列出全部消息void dolisting(arg,flaguidl) char *arg; int flaguidl;{unsigned int i;if (*arg) {i = msgno(arg);if (i == -1) return;puts("+OK ");list(i,flaguidl);}else {okay();for (i = 0;iif (!m[i].flagdeleted)list(i,flaguidl);puts(".\r\n");}flush();}void pop3_uidl(arg) char *arg; { dolisting(arg,1); }void pop3_list(arg) char *arg; { dolisting(arg,0); }substdio ssmsg; char ssmsgbuf[1024];void pop3_top(arg) char *arg;//显示指定消息的内容{int i;unsigned long limit;int fd;i = msgno(arg);//邮件号if (i == -1) return;arg += scan_ulong(arg,%26amp;limit);//显示几行，如果未指定那么limit为0(balst函数打印全部内容)while (*arg == ' ') ++arg;if (scan_ulong(arg,%26amp;limit)) ++limit; else limit = 0;fd = open_read(m[i].fn);if (fd == -1) { err_nosuch(); return; }okay();//关系ssmsg为从指定的消息文件中读substdio_fdbuf(%26amp;ssmsg,read,fd,ssmsgbuf,sizeof(ssmsgbuf));//从ssmsg中读到fd1,如果limit大于0将只读取除消息头外的limit行，如果等于0读全部邮件blast(%26amp;ssmsg,limit);close(fd);}struct commands pop3commands[] = { //pop3命令及处理函数表{ "quit", pop3_quit, 0 }, { "stat", pop3_stat, 0 }, { "list", pop3_list, 0 }//显示消息大小, { "uidl", pop3_uidl, 0 }//显示消息文件名, { "dele", pop3_dele, 0 }, { "retr", pop3_top, 0 }//取一条消息的内容,与top实现是一样的, { "rset", pop3_rset, 0 }//重置pop对话，清除所有删除标记, { "last", pop3_last, 0 }, { "top", pop3_top, 0 }, { "noop", okay, 0 }, { 0, err_unimpl, 0 }} ;/*qmail-pop3d由vchkpw或checkpassword之类的程式起动，只有认证通过后才能执行本程式提供各种pop3命令*/void main(argc,argv)int argc;char **argv;{sig_alarmcatch(die);sig_pipeignore();if (!argv[1]) die_nomaildir();//由于vchkpw或checkpassword之类的程式在启动pop3之前已经将工作目录改变到HOME下了.//所以这里直接进入arg指定的Maildir目录.也是由于这个改变目录原因。qamil-pop3d不支持Mailbox.if (chdir(argv[1]) == -1) die_nomaildir();getlist(); //这里构造了我们前面提到了消息块数组*mokay();//进入命令循环commands(%26amp;ssin,pop3commands);die();}==自此qmail的pop3部分分析基本结束==小结Maildir/cur 只要用户进行了一次连接，qmail-pop3d就会将new下所有邮件移动这个目录下来(quit命令解释程式中有体现.)Maildir/new 用户还没看过新邮件可见qmail的pop3部分只与Maildir有联系，与smtp基本无关。也许有人会问怎么pop3代码都完了，怎么没看见有使用 Maildir/tmp目录的地方呢？(只见删除)其实这个tmp目录是qmail-local用来保证可靠的转发所用的临时文件目录。如果你想知道具体怎么可靠法可以看qmail-local的源代码分析或者man maildir 的HOW A MESSAGE IS DELIVERED节.
