Instant messenger app help
I was hoping someone could assist me on a text-based instant messaging client(using UDP) I am working on. I have the network communication basics already in place but, specifically, needed some further help on a "getting a user list" function. Eventually, I will get a "send message to user" function going, but I just wanted to get the user list working for now. The server code that the client will communicate with is not available to me, but I will list the implementation details below. Any help or advice on how to recieve a user list from the server would be greatly appreciated.
The client header fields include:
Type:
0x00-Login request
0x01-Login reply
0x02-Logout request
0x03-Logout reply
0x04-User list request
0x05-User list reply-Parameter indicates the number of users. Data contains list of users each separated by a comma.
User Len: Length of the From User Name field
Param Len: Length of the Optional Parameter field
Data Length: Length of the Optional Data field
Sequence Number: Used to match requests and replies between client and server. In other words, a request’s corresponding reply will have the same sequence number. The client should increment the sequence number (by one) with each new request.
From User Name: Client user name
Optional Parameter: Number of user names in a user list
Optional Data: List of user names
Implementation Details:
Here is an example sequence of events:
1. The client will prompt for a user name.
2. The client will issue a login request to the server, and receive a reply from the server.
3. Upon a successful login, the client will use the select() call and wait for input from:
a. User input (file descriptor 0)
i. Upon receiving user input, the client will determine if the user
wants to request a user list.
ii. If the user asks for a user list, the client will send a user list request
packet to the server, and display the response.
4. If the user chooses to quit, a logout request is sent to the server, and the client exits.
5. Repeat steps 3-4
Here is a rough go at the client code I have come up with so far. I have bolded the "user list" area.
Code:
#include <arpa/inet.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#define BUF_SIZE 4096
#define BUF_SIZE2 1024
void menu()
{
printf("*************** User Menu *******************\n");
printf("1 - Request list of users currently logged on\n");
printf("2 - Logout\n");
printf("Enter selection:");
}
union shortUnion
{
unsigned short num;
char bytes[2];
};
union shortUnion numUsers;
int main(int argc, char **argv)
{
int sock;
int nbytes;
int address_size;
int server_port;
int string_length;
int str_len;
int len;
int maxfd;
int k = 0;
int i = 0;
int usercount = 0;
char buf[BUF_SIZE];
char buffer[BUF_SIZE];
char choice;
char user_name[BUF_SIZE2];
char opt_par[BUF_SIZE2];
char data[BUF_SIZE2];
char user[BUF_SIZE2];
char recipient[BUF_SIZE2];
char message[BUF_SIZE];
char sendline[BUF_SIZE];
char recvline[BUF_SIZE];
struct hostent *host_name;
struct sockaddr_in ip_address;
struct sockaddr_in echo_address;
fd_set var;
// Header used for client requests and server replies
struct udphder
{
char type;
char result;
char user_len;
char param_len;
int data_len;
int sequence;
char data[1024];
} packet;
if (argc != 3)
{
fprintf(stderr, "Usage: %s <Server IP Address> <Port Number>\n", argv[0]);
exit(1);
}
server_port = atoi(argv[2]);
// Get network host entry
host_name = gethostbyname(argv[1]);
// Create a communication point
sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (sock < 0)
{
fprintf(stderr, "socket error.\n");
exit(1);
}
// Build server adress structure
memset(&ip_address, 0, sizeof(ip_address));
ip_address.sin_family= AF_INET;
memcpy(&ip_address.sin_addr.s_addr, host_name->h_addr, host_name->h_length);
ip_address.sin_port= htons(server_port);
address_size = sizeof(echo_address);
printf("Enter user name: ");
fgets(user_name,BUF_SIZE2,stdin);
printf("\n");
// Populate login request packet
printf("Logging in...\n\n");
packet.type = 0;
packet.result = 6;
packet.user_len = strlen(user_name);
packet.param_len = 0;
// Copy data from bufer to packet data
bcopy(&packet,buffer,8);
bcopy(user_name,buffer+8,strlen(user_name));
// Send entered data to server
if(sendto(sock, buffer, 8+strlen(user_name), 0, (struct sockaddr *)
&ip_address, sizeof(ip_address)) != 8+strlen(user_name))
{
fprintf(stderr, "send error.\n");
exit(1);
}
if ((recvfrom(sock, &packet, 8+strlen(user_name), 0,
(struct sockaddr *) &echo_address, &address_size)) < 0)
{
fprintf(stderr, "recv error.\n");
exit(1);
}
// Test login attempt status
/*switch (packet.result)
{
case 0:
printf("login successful...\n");\
case 1:
{
printf("Login Failure: user is already logged in...\n");
exit(1);
}
case 2:
{
printf("Login Failure: other cause (max num reached, bad request packet...)\n");
exit(1);
}
case 3:
{
printf("Login Failure: user is not logged in...\n");
exit(1);
}
case 4:
{
printf("Login Failure: other cause (server failure, bad request packet...\n");
exit(1);
}
}*/
menu ();
choice=getchar();
switch(choice)
{
case '1':
{
int index = 0;
// Prepare packet for user list request
packet.type = 0x04;
packet.result = 6;
packet.user_len = strlen(user_name);
packet.param_len = 0;
// Copy data from buffer to packet data
bcopy(&packet, buffer, 8);
bcopy(user_name, buffer+8, strlen(user_name));
if(sendto(sock, buffer, 8+strlen(user_name), 0, (struct sockaddr *)
&ip_address, sizeof(ip_address)) != 8+strlen(user_name))
{
fprintf(stderr, "send error.\n");
exit(1);
}
if ((recvfrom(sock, &packet, 8+strlen(user_name), 0,
(struct sockaddr *) &echo_address, &address_size)) < 0)
{
fprintf(stderr, "recv error.\n");
exit(1);
}
numUsers.bytes[0] = packet.data[index];
numUsers.bytes[1] = packet.data[index+1];
printf("User list reply: %d users logged in.\n",ntohs(numUsers.num));
}
case '2':
{
printf("Logging out\n");
packet.type=0x02;
packet.result = 6;
packet.user_len = strlen(user_name);
packet.param_len=0;
// Copy data from buffer to packet data
bcopy(&packet,buffer,8);
bcopy(user_name,buffer+8,strlen(user_name));
if(sendto(sock, buffer, 8+strlen(user_name), 0, (struct sockaddr *)
&ip_address, sizeof(ip_address)) != 8+strlen(user_name))
{
fprintf(stderr, "send error.\n");
exit(1);
}
if ((recvfrom(sock, &packet, 8+strlen(user_name), 0,
(struct sockaddr *) &echo_address, &address_size)) < 0)
{
fprintf(stderr, "recv error.\n");
exit(1);
}
}
}
}
