Question

Hi,

I am stuck on a homework assignment where we use SMTP to transmit an email across a client/ server using read and send functions. I have read the unistd.h implementation of the functions read and send. Could someone possibly explain via pseudo or example how i could use this in terms of sockets? I will be using a while loop to read byte by byte the message. Not looking for a fully written program or anything , but if it helps understanding the function of sockets in an email transaction then by all means share the knowledge! ( The main function is written so just in terms of the parameters found in unix documentation.)

Answer 1

Instad of read byte by byte you can go for structure. it will work properly according to your expectation .

so create common structure for both side and use it . I am posting sample program here. go threw it. I hope it may helpful to you.

/*server.c*/

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <sys/time.h>

#include <sys/socket.h>

#include <sys/select.h>

#include <netinet/in.h>

#include <netinet/ip.h>

#include <pthread.h>

#include <unistd.h>

#include <stdio_ext.h>

#define SIZE 30

#define NAME_SIZE 15

int sock_fd,ret;

typedef struct cli_data {

char name[NAME_SIZE];

char data[SIZE];

}cli_data_t;   

int main(int argc,char **argv)

{

struct sockaddr_in connectAddr;

socklen_t len;

cli_data_t r_info;  

if(argc != 3) {

printf("Usage:./client port_number name\n");

goto done;

}

sock_fd = socket(AF_INET,SOCK_STREAM,0);

if (sock_fd == -1) {

perror("socket");

goto done;

}

printf("Client_fd: %d\n",sock_fd);

connectAddr.sin_family = AF_INET;

connectAddr.sin_port = htons(atoi(argv[1]));

connectAddr.sin_addr.s_addr = INADDR_ANY;

len = sizeof(connectAddr);

if (connect(sock_fd,(struct sockaddr *)&connectAddr,len) == -1) {

perror("connect_fail");

goto done;

}

perror("connect");

while(1) {

bzero(r_info.data,SIZE);

bzero(r_info.name,NAME_SIZE);

strcpy(r_info.name, argv[2]);

printf("Waiting for your input...............\n");

scanf(" %[^\n]",r_info.data);

if (write(sock_fd,&r_info,sizeof(cli_data_t)) == -1) {

perror("Write_Faild");

goto done;

}

if (read(sock_fd,&r_info,sizeof(cli_data_t)) == -1) {

perror("read");

goto done;

}

printf("\t\t\t\t\t\t\t\t\t\t\t%s: %s\n",r_info.name,r_info.data);   

}

done:

return 0;

}

/*client.c*/

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <sys/time.h>

#include <sys/socket.h>

#include <sys/select.h>

#include <netinet/in.h>

#include <netinet/ip.h>

#include <pthread.h>

#include <unistd.h>

#include <stdio_ext.h>

#define SIZE 30

#define NAME_SIZE 15

int sock_fd,ret;

typedef struct cli_data {

char name[NAME_SIZE];

char data[SIZE];

}cli_data_t;   

int main(int argc,char **argv)

{

struct sockaddr_in connectAddr;

socklen_t len;

cli_data_t r_info;  

if(argc != 3) {

printf("Usage:./client port_number name\n");

goto done;

}

sock_fd = socket(AF_INET,SOCK_STREAM,0);

if (sock_fd == -1) {

perror("socket");

goto done;

}

printf("Client_fd: %d\n",sock_fd);

connectAddr.sin_family = AF_INET;

connectAddr.sin_port = htons(atoi(argv[1]));

connectAddr.sin_addr.s_addr = INADDR_ANY;

len = sizeof(connectAddr);

if (connect(sock_fd,(struct sockaddr *)&connectAddr,len) == -1) {

perror("connect_fail");

goto done;

}

perror("connect");

while(1) {

bzero(r_info.data,SIZE);

bzero(r_info.name,NAME_SIZE);

strcpy(r_info.name, argv[2]);

printf("Waiting for your input...............\n");

scanf(" %[^\n]",r_info.data);

if (write(sock_fd,&r_info,sizeof(cli_data_t)) == -1) {

perror("Write_Faild");

goto done;

}

if (read(sock_fd,&r_info,sizeof(cli_data_t)) == -1) {

perror("read");

goto done;

}

printf("\t\t\t\t\t\t\t\t\t\t\t%s: %s\n",r_info.name,r_info.data);   

}

done:

return 0;

}

/////////////////////////////////////////////////////////////////////////

give ./server portNO form server side to run server code .

give ./client portNO YourName form client side to run client code.

It will convert your data into upper or lower case .