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Full Discussion: C socket issue with SMTP
Top Forums Programming C socket issue with SMTP Post 302385355 by Jess83 on Friday 8th of January 2010 12:08:38 AM
Old 01-08-2010
C socket issue with SMTP
Hey guys, im trying to write a program that'll create a report then email the report... my problem is when it comes to the socket trying to send the second command after EHLO smtp,*.*

When the first command is sent its working fine... but when the program tries to send the second command it jams on bzero(buffer,256);... My understanding is bzero resets all values to 0 hence... clear the array buffer[] so it can be used again right? Why would the program execution stop???

Code:
/*---------EHLO SMTP-------------*/

    printf("Sending EHLO to SMTP\n");
   
    
    
    buffer[255] = "EHLO smtp.primus.ca";

    n = write(sockfd,buffer,strlen(buffer));
    if (n < 0) 
         error("ERROR writing to socket");
    bzero(buffer,256);
    n = read(sockfd,buffer,255);
    if (n < 0) 
         error("ERROR reading from socket");
    printf("%s\n",buffer);

/*---------MAIL FROM-------------*/

    printf("Sending EHLO to SMTP\n");
   
    bzero(buffer,256);
    
    buffer[255] = "MAIL FROM: smtp.primus.ca";

    n = write(sockfd,buffer,strlen(buffer));
    if (n < 0) 
         error("ERROR writing to socket");
    bzero(buffer,256);
    n = read(sockfd,buffer,255);
    if (n < 0) 
         error("ERROR reading from socket");
    printf("%s\n",buffer);

/*------------------------------*/

When im doing a fgets as below and enter the the commands to be sent to the SMTP it works perfectly...

Code:
printf("SMTP Command to be sent\n");
    bzero(buffer,256);
    fgets(buffer,255,stdin);
    n = write(sockfd,buffer,strlen(buffer));
    if (n < 0) 
         error("ERROR writing to socket");
    bzero(buffer,256);
    n = read(sockfd,buffer,255);
    if (n < 0) 
         error("ERROR reading from socket");
    printf("%s\n",buffer);

BUT if I take off the fget because I need the things to be automated then it fails...

Code:
printf("Automated way\n");
    
    buffer[255] = "MAIL FROM: test@primustel.ca";

    n = write(sockfd,buffer,strlen(buffer));
    if (n < 0) 
         error("ERROR writing to socket");
    bzero(buffer,256);
    n = read(sockfd,buffer,255);
    if (n < 0) 
         error("ERROR reading from socket");
    printf("%s\n",buffer);

Now I assume it fails to SMTP code 500 (unrecognized command) because the buffer array values wasn't cleared but when I add the bzero the halt the execution of the software then timeout the connection...

Code:
printf("Automated way\n");
     
    bzero(buffer,255);
    
    buffer[255] = "MAIL FROM: test@primustel.ca";

     n = write(sockfd,buffer,strlen(buffer));
     if (n < 0) 
          error("ERROR writing to socket");
     bzero(buffer,256);
     n = read(sockfd,buffer,255);
     if (n < 0) 
          error("ERROR reading from socket");
     printf("%s\n",buffer);

-------------------Whole codes----------------------


Code:
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h> 

void error(char *msg)
{
    perror(msg);
    exit(0);
}

int main(int argc, char *argv[])
{

    int sockfd, portno, n;
    struct sockaddr_in serv_addr;
    struct hostent *server;

    char buffer[256];
    if (argc < 3) {
       fprintf(stderr,"usage %s hostname port\n", argv[0]);
       exit(0);
    }
    portno = atoi(argv[2]);
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) 
        error("ERROR opening socket");
    server = gethostbyname(argv[1]);
    if (server == NULL) {
        fprintf(stderr,"ERROR, no such host\n");
        exit(0);
    }
    bzero((char *) &serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    bcopy((char *)server->h_addr, 
         (char *)&serv_addr.sin_addr.s_addr,
         server->h_length);
    serv_addr.sin_port = htons(portno);
    if (connect(sockfd,&serv_addr,sizeof(serv_addr)) < 0) 
        error("ERROR connecting");


/*---------EHLO SMTP-------------*/

    printf("Sending EHLO to SMTP\n");
   
    
    
    buffer[255] = "EHLO smtp.primus.ca";

    n = write(sockfd,buffer,strlen(buffer));
    if (n < 0) 
         error("ERROR writing to socket");
    bzero(buffer,256);
    n = read(sockfd,buffer,255);
    if (n < 0) 
         error("ERROR reading from socket");
    printf("%s\n",buffer);

/*---------MAIL FROM-------------*/

    printf("Sending EHLO to SMTP\n");
   
    
    
    buffer[255] = "MAIL FROM: test@primustel.ca";

    n = write(sockfd,buffer,strlen(buffer));
    if (n < 0) 
         error("ERROR writing to socket");
    bzero(buffer,256);
    n = read(sockfd,buffer,255);
    if (n < 0) 
         error("ERROR reading from socket");
    printf("%s\n",buffer);

/*------------------------------*/    


return 0;
}

 

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