Programming

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h> 

#ifndef PORT
#define PORT 30758  
#endif

#define MAXDATASIZE 1000 
#define CONSIGNMENT 8

typedef struct client_list {
    char *client_name;
    int client_socket_fd;
    struct client_list *next;
} client;

typedef struct item_list {
    char *name;
    char *number;
    char *current_price;
    char *minimum_price;
    char *num_of_bids_left;
    char *is_closed;
    struct item_list *next;
} item;

void error(const char *error_message) {
    perror(error_message);
    exit(1);
}

int str_len(char *string) {
    int count = 0;
    while(*(string+count)!= '\n' && *(string+count)!= '\0') count++;
    return count;
}

void send_message(int client_socket_fd, char *message, int length) {
    if (write(client_socket_fd, message, length) < 0) error("ERROR writing to socket");
}

void read_message(int socket_fd, char *buffer, int display) {
    size_t bytes; bzero(buffer,MAXDATASIZE);
    if((bytes = read(socket_fd, buffer, MAXDATASIZE)) < 0) error("ERROR reading from socket");    
    if (display) write(1,buffer,bytes);
}

void send_items(item *item_list, int client_socket_fd) {
    send_message(client_socket_fd, "Items available are:\n", 21);
    while(item_list) {
        send_message(client_socket_fd, item_list->number, str_len(item_list->number));
        send_message(client_socket_fd, ".\nItem Name: ", 13);
        send_message(client_socket_fd, item_list->name, str_len(item_list->name));
        send_message(client_socket_fd, "\nCurrent Price: $", 17);
        send_message(client_socket_fd, item_list->current_price, str_len(item_list->current_price));
        send_message(client_socket_fd, "\nNumber Of Bids Left: ", 22);
        send_message(client_socket_fd, item_list->num_of_bids_left, str_len(item_list->num_of_bids_left));
        send_message(client_socket_fd, "\nIs Closed: ", 12);
        send_message(client_socket_fd, item_list->is_closed, str_len(item_list->is_closed));
        send_message(client_socket_fd, "\n", 1);
        item_list = item_list->next;
    }
}

int already_there(client *current, char *username) {
    while(current) {
        if (strcmp(current->client_name, username)==0) return(1);
        current = current->next;
    }
    return(0);
}

client *add_client(char *username, client *client_list, int client_socket_fd) {
    client *new_client = (client *)malloc(sizeof(client)); 
    new_client->client_name = username;
    new_client->client_socket_fd = client_socket_fd;
    new_client->next = client_list;
    return new_client;
}

item *add_item(char *name, char *number, char *current_price, char *num_of_bids_left, char *is_closed, item *item_list) {
    item *new_item = (item *)malloc(sizeof(item)); 
    new_item->name=name;
    new_item->number=number;
    new_item->current_price=current_price;
    new_item->num_of_bids_left=num_of_bids_left;
    new_item->is_closed=is_closed;
    new_item->next=item_list;
    return new_item;
}

int main(int argc, char *argv[]) {
    int socket_fd;
    struct sockaddr_in server_address;
    struct hostent *server;
    char *username, buffer[MAXDATASIZE];
    if (argc == 3) username = getenv("USER");
    else if (argc == 4) username = argv[3];
    else error("Error, invalid number of arguments, need a hostname, port, and a user name (optional).\n"); 
    bzero(buffer,MAXDATASIZE); 
    socket_fd = socket(AF_INET, SOCK_STREAM, 0); 
    if (socket_fd < 0) error("Error opening socket");
    server = gethostbyname(argv[1]); 
    if (server == NULL) error("Error, no such host\n");
    bzero((char *) &server_address, sizeof(server_address)); 
    server_address.sin_family = AF_INET;
    bcopy((char *)server->h_addr, (char *)&server_address.sin_addr.s_addr, server->h_length); 
    server_address.sin_port = htons(PORT);
    if (connect(socket_fd,(struct sockaddr *) &server_address,sizeof(server_address)) < 0) error("Error connecting"); 
    send_message(socket_fd, username, str_len(username)); 
    read_message(socket_fd, buffer, 0); 
    if (strcmp(buffer, "Enter")==0) {
        write(1,username,str_len(username)); write(1," successfully connected to ",27); 
        write(1,argv[1],str_len(argv[1])); write(1,"!\n",2);
        send_message(socket_fd, "ok", 2); 
        read_message(socket_fd, buffer, 1); 
    }
    else { 
        write(1,"User ",5); write(1,username,str_len(username)); 
        write(1," already connected to ",22); write(1,argv[1],str_len(argv[1])); write(1,"!\n",2);
        send_message(socket_fd, "ok", 2); 
    }
    close(socket_fd); 
    return 0;
}

int pos=0;
bzero(buffer,MAXDATASIZE);

// Stop once we have an entire single line
while((buffer[pos] != '\n') && (pos < MAXDATASIZE))
{
        // Put new data 'pos' bytes ahead, so we don't overwrite the old
        ssize_t b=read(socket_fd, buffer+pos, 1); 
        if(b > 0) pos+=b;
        else break; // b<=0 means socket closed or socket error, so give up.
}

int pos=0; 
bzero(buffer,MAXDATASIZE);  // Stop once we have an entire single line 
while((buffer[pos] != '\0') && (pos < MAXDATASIZE)) {        
     // Put new data 'pos' bytes ahead, so we don't overwrite the old        
     ssize_t b=read(socket_fd, buffer+pos, 1);         
     if(b > 0) pos+=b;         
     else break; // b<=0 means socket closed or socket error, so give up. 
}