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。
PRogrammer:夜未眠
Date:Apr 28,2003
Comefrom: 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!
[code:1:d803669f6f]
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
|
|
vchkpw
|
|
qmail-popup
|
|
tcpserver--+
[/code:1:d803669f6f]
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
[code:1:d803669f6f]
#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'rcpttest@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 (;
