SMTP (Simple Mail Transfer Protocol )

tags: network programming linux SMTP protocol stack

請勿用於非法用途或塞垃圾, 詐騙, 等 郵件
Author: WhoAmI
e-mail: [e-mail]
Date: 20220726
Copyright: CC BY-NC-SA

請自行修改

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h> /* struct hostent, gethostbyname */

/*

S: 220 www.example.com ESMTP Postfix
C: HELO mydomain.com
S: 250 Hello mydomain.com
C: MAIL FROM: <[e-mail]>
S: 250 Ok
C: RCPT TO: <[e-mail]>
S: 250 Ok
C: DATA
S: 354 End data with <CR><LF>.<CR><LF>
C: Subject: test message
C: From:""< [e-mail]>
C: To:""< [e-mail]>
C:
C: Hello,
C: This is a test.
C: Goodbye.
C: .
S: 250 Ok: queued as 12345
C: quit
S: 221 Bye
*/
typedef struct _tsmtp{

char *c;
char *data;

}Tsmtp;


const char mailbody[]=
"Subject: test message\r\n"
"From:""< [e-mail]>\r\n"
"To:< [e-mail]>\r\n"
"\r\n"
"Hello,\r\n"
"This is a test.\r\n"
"Goodbye.\r\n"
"\r\n";




#define TOFCU 1
#ifdef TOFCU

Tsmtp smtp_c[]={{"HELO ","xyz.edu.tw\r\n"},\
{"MAIL FROM: ","[e-mail]\r\n"},\
{"RCPT TO: ","[e-mail]\r\n"},\
{"DATA","\r\n"},{mailbody,"\r\n.\r\n"},{"QUIT","\r\n"},NULL};

#else

Tsmtp smtp_c[]={{"HELO ","xyz.edu.tw\r\n"},\
{"MAIL FROM: ","[e-mail]\r\n"},\
{"RCPT TO: ","[e-mail]\r\n"},\
{"DATA","\r\n"},{mailbody,"\r\n.\r\n"},{"QUIT","\r\n"},NULL};


#endif

char smtp_from[256]="[e-mail]";



void error(const char *msg) { perror(msg); exit(0); }
static int read_delay_ms(int fd,int msec)
{
    struct timeval tval;
    fd_set readfds;
    int n;
 

    FD_ZERO(&readfds);
    FD_SET(fd, &readfds);

    tval.tv_sec = 0;
    tval.tv_usec = msec*1000;
 
    n = select(fd+1, &readfds, NULL, NULL,  &tval);
    return n;
}

static int read_delay_s(int fd,int sec)
{
    struct timeval tval;
    fd_set readfds;
    int n;
 

    FD_ZERO(&readfds);
    FD_SET(fd, &readfds);

    tval.tv_sec = sec;
    tval.tv_usec = 0;
 
    n = select(fd+1, &readfds, NULL, NULL,  &tval);
    return n;
}
int main(int argc,char *argv[])
{
    int i;

    /* SMPT port=25 */
    int portno= 25; 
    char *host ="mymail.fun.edu.tw"; /

    struct hostent *server;
    struct sockaddr_in serv_addr;
    int sockfd, bytes, sent, received, total, message_size;
    char response[4096];
    int step;
    char message[512];
    int tt;

  

    printf("Starting...%s\n",host);

    /* create the socket */
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) error("ERROR opening socket");

    /* lookup the ip address */
    server = gethostbyname(host);
    if (server == NULL) error("ERROR");

    /* fill in the structure */
    memset(&serv_addr,0,sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(portno);
    memcpy(&serv_addr.sin_addr.s_addr,server->h_addr,server->h_length);

    /* connect the socket */
    if (connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr)) < 0)
        error("ERROR connecting");

    /* send the request */
    step=0;
    printf("Starting...%s:%d\n",host,portno);
 
    for(step=0;step<8;step++){

    /* receive the response */
    printf("Step %d\n",step);

    memset(response,0,sizeof(response));
    total = sizeof(response)-1;
    received = 0;
    do {

        if(step==5){

           tt=read_delay_s(sockfd,15);
        }else tt=read_delay_ms(sockfd,1000);
        if(tt<=0)break;


        bytes = read(sockfd,response+received,total-received);
        if (bytes < 0)
            error("ERROR reading response from socket");
        if (bytes == 0)
            break;
        received+=bytes;
    } while (received < total);

    printf("Step %d: Recv %d bytes\n",step, received);
    if (received == total)
        error("ERROR storing complete response from socket");

    response[received]=0;
    printf("RECV form server:%s\n",response);

    if(smtp_c[step].c!=NULL){
       if(smtp_c[step].c[0]=='\0')goto END;
    }else goto END;

    sprintf(message,"%s%s",smtp_c[step].c,smtp_c[step].data);


    total = strlen(message);
    printf("SEND[%d]:%s\n",total,message);

 
    sent = 0;
    if(total>0){
    do {
        bytes = write(sockfd,message+sent,total-sent);
        if (bytes < 0)
            error("ERROR writing message to socket");
        if (bytes == 0)
            break;
        sent+=bytes;
    } while (sent < total);

    printf("write %d bytes\n",sent);

    }else break;
 
   }//for loop

END:

    /* close the socket */
    close(sockfd);

    /* process response */
    printf("Response:\n%s\n",response);

 
    return 0;
}


/*
$  ./smpt.exe smtp.xyz.edu.tw
Starting...mymail.xyz.edu.tw
Starting...mymail.xyz.edu.tw:25
Step 0
Step 0: Recv 99 bytes
RECV form server:220 Mymail ESMTP Service(Mail2000 ESMTP Server V6.00) ready Sat, 23 Feb 2019 14:16:24 +0800 (CST)

SEND[17]:HELO xyz.edu.tw

write 17 bytes
Step 1
Step 1: Recv 12 bytes
RECV form server:250 Mymail

SEND[29]:MAIL FROM: [e-mail]

write 29 bytes
Step 2
Step 2: Recv 34 bytes
RECV form server:250 Sender <[e-mail]> OK

SEND[27]:RCPT TO: [e-mail]

write 27 bytes
Step 3
Step 3: Recv 37 bytes
RECV form server:250 Recipient <[e-mail]> OK

SEND[6]:DATA

write 6 bytes
Step 4
Step 4: Recv 35 bytes
RECV form server:354 Enter mail, end <CRLF>.<CRLF>

SEND[123]:
Subject: test message
From:< [e-mail]>
To:< [e-mail]>

Hello,
This is a test.
Goodbye.


.

write 123 bytes
Step 5
Step 5: Recv 35 bytes
RECV form server:250 Message accepted for delivery

SEND[6]:QUIT

write 6 bytes
Step 6
Step 6: Recv 12 bytes
RECV form server:221 Mymail

Response:
221 Mymail


laikc@laikcpc ~
$
*/