程序员眼中的qmail(qmail源代码分析)

12/3/2006来源:Qmail人气:7468

  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: [email protected]
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
| |
V V
qmail-smtpd qmail-inject
| |
+---------qmail-queue<-----------+
|
|
qmail-send
|
+------------+------------+
| |
V V
qmail-rspawn qmail-lspawn
| |
V V
qmail-remote qmail-local
| |
| |
V V
INTERNET <----qmail-pop3d
|
|
vchkpw
|
|
qmail-popup
|
|
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 <= 0) _exit(1);
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 <= 0) timeout = 1;

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 protected] "
//执行下面这段程式后arg="[email protected]"
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 [email protected][10.0.6.21] 转换为 [email protected]
//依据是control/localiphost文件中有host.mydomain.org
if (liphostok) {
i = byte_rchr(addr.s,addr.len,'@');
if (i < addr.len) /* if not, partner should go read rfc 821 */
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.len > 900) 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 (j < addr.len)
if (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0
int 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mailfrom
if (!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addr
if (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 protected]".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 [email protected]' 命令将产生 rcptto="[email protected]"
//多次执行rcpt命令效果会是rcptto="[email protected][email protected]"
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 (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(%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 (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(%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0
if (databytes) bytestooverflow = databytes + 1;
if (qmail_open(%26amp;qqt) == -1) { err_qqt(); return; }//建立子进程执行qmail-queue
qp = 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[email protected][email protected]发送邮件,那么向qmail-queue传送的字符串将是
// [email protected][email protected]
qmail_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 -0000
2.建立3个文件
queue/mess// //邮件正文
queue/intd/ 用户id,进程id,mailfrom,rcptto
queue/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 1003

char 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 < 10;++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/queue

mypid = 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52

pidopen();//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 name
todofn = fnnum("todo/",0); //todo file name
intdfn = fnnum("intd/",0); //intd file name

if (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<--------qmail-smtp 的 qqt->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 <---------qmail-smtp 的 qqt->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:[email protected][email protected][email protected]发邮件可能会有如下内容
u6027p34234[email protected][email protected][email protected]
*/

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) < 1) die_read();
if (ch != 'F') die(91);
if (substdio_bput(%26amp;ssout,%26amp;ch,1) == -1) die_write();
for (len = 0;len < ADDR;++len)
{
if (substdio_get(%26amp;ssin,%26amp;ch,1) < 1) die_read();
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) < 1) die_read();
if (!ch) break;
if (ch != 'T') die(91);
if (substdio_bput(%26amp;ssout,%26amp;ch,1) == -1) die_write();
for (len = 0;len < ADDR;++len)
{
if (substdio_get(%26amp;ssin,%26amp;ch,1) < 1) die_read();
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.,ltd


qmail-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
| |
| |
<---------- 认证失败-----------+


==========================

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 (r <= 0) die();
return r;
}

int safewrite(fd,buf,len) int fd; char *buf; int len;
{
int r;
r = timeoutwrite(1200,fd,buf,len);
if (r <= 0) die();
return 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 3
switch(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<进程ID.当前时间@主机名>
if (substdio_puts(%26amp;ssup,"<") == -1) die_write();
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("+OK <");
puts(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username
if (!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.,ltd

qmail-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 fd0 <-------- qmail-send fd1
qmail-lspawn fd1 ------ qmail-send fd2
qmail-rspawn fd0 <-------- qmail-send fd3
qmail-rspawn fd1 ------ qmail-send fd4
qmail-clean fd0 <-------- qmail-send fd5
qmail-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 qmail
int pi1[2]; //qmail-lspawn fd0 <-------- qmail-send fd1
int pi2[2]; //qmail-lspawn fd1 ------ qmail-send fd2
int pi3[2]; //qmail-rspawn fd0 <-------- qmail-send fd3
int pi4[2]; //qmail-rspawn fd1 ------ qmail-send fd4
int pi5[2]; //qmail-clean fd0 <-------- qmail-send fd5
int pi6[2]; //qmail-clean fd1 ------ qmail-send fd6

void 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fd0
close23456();
execvp(argv[1],argv + 1);//启动splogger
die();
}
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-lspawn
case -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-rspawn
case -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-clean
case -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-send
die();
}


==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 (r <= 0) die();
return 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 (r <= 0) die();
return 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;
else
if (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;i < numm;++i) {
if (!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;
else
m[i].size = st.st_size;
}
}


void pop3_stat() //打印类似 +OK <消息数量><删除标记未设置的消息所占空间>
{ //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;i < numm;++i) if (!m[i].flagdeleted) total += m[i].size;
puts("+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;i < numm;++i) m[i].flagdeleted = 0;
last = 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;i < numm;++i)
if (m[i].flagdeleted) {
if (unlink(m[i].fn) == -1) err_nounlink();
}
else
if (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-1
int 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 + 1 > last) 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;i < numm;++i)
if (!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*m

okay();
//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.