gethostbyname use problem in webench source code - linux

source code here
inaddr = inet_addr(host);
if (inaddr != INADDR_NONE)
memcpy(&ad.sin_addr, &inaddr, sizeof(inaddr));
else
{
hp = gethostbyname(host);
if (hp == NULL)
return -1;
//does not have h_addr member
memcpy(&ad.sin_addr, hp->h_addr, hp->h_length);
}
I am new to network programming,one of my friend told me to read the code of webench to learn basic use.I see the book unp,find struct hostent does not have the member of h_addr,in the book the example shows that h_aliases and h_addrtype is pointer to pointer,which means we can use in this way:
#include "unp.h"
int
main(int argc, char **argv)
{
char *ptr, **pptr;
char str[INET_ADDRSTRLEN];
struct hostent *hptr;
while (--argc > 0) {
ptr = *++argv;
if ( (hptr = gethostbyname(ptr)) == NULL) {
err_msg("gethostbyname error for host: %s: %s",
ptr, hstrerror(h_errno));
continue;
}
printf("official hostname: %s\n", hptr->h_name);
for (pptr = hptr->h_aliases; *pptr != NULL; pptr++)
printf("\talias: %s\n", *pptr);
switch (hptr->h_addrtype) {
case AF_INET:
pptr = hptr->h_addr_list;
for ( ; *pptr != NULL; pptr++)
printf("\taddress: %s\n",
Inet_ntop(hptr->h_addrtype, *pptr, str, sizeof(str)));
break;
default:
err_ret("unknown address type");
break;
}
}
exit(0);
}
How can I modify this to corret code,since h_addr_list may have more than one ipaddr,which value should I copy to ad.sin_addr.

Related

why the system hang when I write characters to my dummy character device?

I am learning how to write Linux Device Driver.
I wrote a dummy character device driver, implemented open, release, write, read in fops;
When I read from device , everything was ok;
When I wrote to device by "echo xx > ", the OS was hang.
Even I comment out all codes in write function except pr_alert and return statements, It still hangs;
Could anybody help me figure it out?
#include <linux/init.h>
#include <linux/types.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/cdev.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/string.h>
struct hello_dev
{
char *buffer;
int length;
dev_t dev;
struct mutex lock;
struct cdev *pcdev;
};
struct hello_dev *pHelloDev;
int open_device(struct inode *pinode, struct file *filp)
{
filp->private_data = pHelloDev;
return 0;
}
int close_device(struct inode *pinode, struct file *filp)
{
struct hello_dev *pDev = filp->private_data;
if (pDev->buffer != NULL)
kfree(pDev->buffer);
pDev->buffer = NULL;
return 0;
}
ssize_t read_device(struct file *filp, char __user *buffer, size_t len, loff_t *loff)
{
pr_alert("read\n");
struct hello_dev *pDev = filp->private_data;
mutex_lock(&pDev->lock);
if (pDev->buffer == NULL)
{
mutex_unlock(&pDev->lock);
return 0;
}
int length = strlen(pDev->buffer);
// offset max than strlen in buffer, return
if (*loff > (length - 1))
{
mutex_unlock(&pDev->lock);
return 0;
} else {
// available to read
int len2read = length - *loff;
if (len < len2read)
{// buffer length less than available data
len2read = len;
}
int read = copy_to_user(buffer, pDev->buffer + *loff, len2read);
if (read)
{
*loff = *loff + read;
mutex_unlock(&pDev->lock);
return read;
} else {
*loff = *loff + len2read;
mutex_unlock(&pDev->lock);
return len2read;
}
}
}
ssize_t write_device(struct file *filp , const char __user *buffer, size_t len, loff_t* loff) {
pr_alert("write %s\n", buffer);
// struct hello_dev *pDev = filp->private_data;
// mutex_lock(&pDev->lock);
// if(pDev->buffer == NULL) {
// pDev->buffer = kmalloc(100, GFP_KERNEL);
// pDev->length = 100;
// }
// copy_from_user(pDev->buffer, buffer, len);
// *loff = *loff + len;
// mutex_unlock(&pDev->lock);
return len;
}
struct file_operations fops = {
.open = open_device,
.release = close_device,
.read = read_device,
.write = write_device
};
int init_device(void)
{
pr_alert("init device\n");
pHelloDev = kmalloc(sizeof(struct hello_dev), GFP_KERNEL);
pHelloDev->buffer = NULL;
pHelloDev->length = 0;
int ret = alloc_chrdev_region(&pHelloDev->dev, 0, 1, "hello");
if (ret)
goto alloc_error;
if (pHelloDev == NULL)
goto kmalloc_error;
pHelloDev->pcdev = cdev_alloc();
pHelloDev->pcdev->ops = &fops;
mutex_init(&pHelloDev->lock);
ret = cdev_add(pHelloDev->pcdev, pHelloDev->dev, 1);
if (ret)
goto cdev_add_error;
return 0;
alloc_error:
pr_alert("alloc_chrdev_region error, %d\n", ret);
return ret;
kmalloc_error:
pr_alert("alloc struct hello_dev error");
return -ENOMEM;
cdev_add_error:
pr_alert("cdev_add error, %d\n", ret);
return ret;
}
void cleanup_device(void)
{
pr_alert("unload ko\n");
cdev_del(pHelloDev->pcdev);
unregister_chrdev_region(pHelloDev->dev, 1);
}
MODULE_LICENSE("GPL");
module_init(init_device);
module_exit(cleanup_device);

I found why write to device hangs.
//this statements has problem
//maybe there is no \0 in buffer
//so I print it out, it will hang
//I wrote a program to write something to device
//and used strace to trace system call made by this program
//and found it hangs at write(...) system call
//and there was nothing printed out
//so, it must be this statement causing the problem
//when I removed this statement, everything was ok
pr_alert("write %s\n", buffer);

How do i print the char value from file c program?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define BUFFER_SIZE 128
const char *FILE_GAME_DATA_PATH = "./game.txt";
struct game_tag
{
char gname[20];
struct game_tag *next;
} * head;
//struct game_tag g;
typedef struct game_tag GAME;
//file functions
void read_file();
//util functions.
int menu();
void print_game(GAME *game);
void release(GAME *data);
//core
void display_game();
void quite();
//link
int count_elements(GAME *elements);
int count();
int main(void)
{
int selected;
read_file();
while (1)
{
selected = menu();
switch (selected)
{
case 1:
display_game();
break;
default:
printf("cannot find your option!");
break;
}
}
}
void display_game()
{
read_file();
GAME *game = head;
if(game == NULL)
{
printf("\nNo Game!\n");
return;
}
print_game(game);
}
void print_game(GAME *game)
{
int records_count = 0;
printf("\n========== GAME ==========\n");
while(game != NULL)
{
printf("\n");
printf("Game Name: %s\n ", game->gname);
game = game->next;
records_count++;
}
printf("\nRecords: %d has been loaded successfully!\n", records_count);
release(game);
}
int menu()
{
printf("\n(1) Display Game details\n");
int choosen;
printf("\nEnter your option: ");
scanf("%d", &choosen);
return choosen;
}
void add_game(char game_name[20])
{
GAME *temp, *iterator;
temp = (struct game_tag *)malloc(sizeof(struct game_tag));
GAME info;
memcpy(info.gname, game_name, 20);
//temp = head;
iterator = head;
if (head == NULL)
{
head = temp;
head->next = NULL;
}
else
{
while (iterator->next != NULL)
{
iterator = iterator->next;
}
temp->next = NULL;
iterator->next = temp;
}
}
void read_file()
{
if(head != NULL)
{
GAME *temp;
while(head != NULL)
{
temp = head;
head = head->next;
free(temp);
}
}
FILE *file;
file = fopen(FILE_GAME_DATA_PATH, "r");
if(file == NULL)
{
printf("Cannot read file: %s", FILE_GAME_DATA_PATH);
exit(EXIT_FAILURE);
}
char game_name[20];
int i;
while(!feof(file))
{
char no[BUFFER_SIZE];
fgets(game_name, sizeof(game_name), file);
i=0;
while(game_name[i] != '\0')
{
i++;
}
game_name[i] = '\0';
add_game(game_name);
}
fclose(file);
}
void quite()
{
printf("\nGoodbye!");
exit(EXIT_SUCCESS);
}
void release(GAME *data)
{
if (data == NULL)
{
return;
}
// free the nodes
// because it can be use in memory
// we need to clear it first
// before we re-initailize the new data
GAME *temp;
while (data != NULL)
{
temp = data;
data = data->next;
free(temp);
}
}
(1) At this point, I have created the main function
(2) I'm trying to print the value from txt file which is char value that less than 20byte
(3) My error is it read the file properly, but it returns the garbage value
!Error I'm concern that my read_file function doesn't read txt proper or there an error in my condition statement

LINUX msgget and ftok

Hello I'm trying IPC practice. But I have problem... Here is the code
Send_process.c (path : /home/John/h1/send_process.c)
struct mymsgbuf {
long mtype;
char mtext[80];
};
int main(void) {
key_t key;
int msgid;
struct mymsgbuf mesg;
char inputmsg[80];
if(msgid = msgget((key_t)123, IPC_CREAT | 0666) == -1) {
perror("Failed to create new MessageQueue");
exit(1);
}
printf("%d\n", msgid);
mesg.mtype = 1;
while(1) {
printf("Enter Sending Message. (Input exit, programm terminate) : ");
scanf("%s", inputmsg);
strcpy(mesg.mtext, inputmsg);
if(msgsnd(msgid, (void *)&mesg, sizeof(mesg.mtext), IPC_NOWAIT) == -1) {
perror("msgsnd");
exit(1);
}
if(strcmp(inputmsg, "exit") == 0) {
printf("Sending Process Terminated\n");
break;
}
}
return 0;
}
Receive_process.c (path : /home/John/h1/send_process.c)
struct mymsgbuf {
long mtype;
char mtext[80];
};
int main(void) {
struct mymsgbuf inmsg;
key_t key;
int msgid;
key = ftok("/home/John/h1/receive_process.c", 123);
if((msgid = msgget(key,0666)) < 0 ) { //here is error
perror("msgget");
exit(1);
}
printf("%d\n", msgid);
while(1) {
if(msgrcv(msgid, &inmsg, sizeof(inmsg.mtext), 0,0) == -1) {
perror("Message Receive");
exit(1);
}
printf("Received Message. Message is [%s]\n", inmsg.mtext);
if(strcmp(inmsg.mtext, "exit") == 0 ) {
printf("Receive_process end\n");
exit(0);
}
}
return 0;
}
Send_process is works very well, but Receive_process not works well. What is the problem?

Socket Programming Error in Connect

I am trying to do Socket programming. I've google and looked at problems like mine. However, I can't see to figure out my error.
Whenever I run my code, I get an error in connect() in main in client.c. The error is invalid argument.
Server.c
/* chatroom server */
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <netdb.h>
#include <pthread.h>
#include <signal.h>
#define MAX_ROOMS 36
#define MAX_NAME_SIZE 56
#define PORT_NUM 12333
#define MSG_SIZE 8
#define MAX_LOAD 246
#define MAX_CRC 64 //max clients
#define MAX_BUF 256
#define SERVER_IP 32
#define DEBUG 0
struct msg {
int type; //create, join, delete
int length; // length or port num
};
struct chat_room {
int socket_d; //socket descriptor
int port;
pthread_t id; //id of chatroom
char name[MAX_NAME_SIZE];
int clients[MAX_ROOMS]; // used to hold the client's master sockets
};
struct chat_room* findRoom(char* name, struct chat_room* chat){
int iterator;
for(iterator = 0; iterator < MAX_ROOMS; iterator++){
if(strcmp(name, chat[iterator].name) && (chat[iterator].port != 0)) {
return &chat[iterator];
}
}
//if room does not exist
return NULL;
}
struct chat_room* joinServer(int chat_socket, char* name, struct chat_room* chat){
struct chat_room* local_chat = findRoom(name, chat);
int i;
if(local_chat != NULL){ //if the chat exists
for(i= 0; i< MAX_CRC; i++){
if(local_chat->clients[i] == 0)
{
local_chat->clients[i] = chat_socket;
}
return local_chat;
}
}
//if server if full or else error
return NULL;
}
int createResponse(int chat_socket, int new_port_num, int type){
struct msg temp;
char temp_buff[MAX_LOAD];
memset(temp_buff, 0, MAX_LOAD);
temp.type = type;
temp.length = new_port_num;
memcpy(temp_buff, &temp, sizeof(temp));
write(chat_socket, temp_buff, MSG_SIZE);
return 0;
}
int joinResponse(int chat_socket, int new_port_num){
struct msg temp;
char temp_buff[MAX_LOAD];
memset(temp_buff, 0, MAX_LOAD);
temp.type = 11;
temp.length = new_port_num;
memcpy(temp_buff, &temp, sizeof(temp));
write(chat_socket, temp_buff, MSG_SIZE);
return 0;
}
int deleteResponse(int chat_socket, struct chat_room* chat){
struct msg temp;
char temp_buff[MAX_LOAD];
int i;
memset(temp_buff, 0, MAX_LOAD);
temp.type = 12;
memcpy(temp_buff, &temp, sizeof(temp));
for(i=0; i<MAX_CRC; i++){
if((chat->clients[i] != chat_socket) && (chat->clients[i] != 0))
write(chat->clients[i],temp_buff, MSG_SIZE);
}
return 0;
}
struct chat_room* addRoom(int chat_socket, char* name, struct chat_room* chat){
int socket_d;
int i;
struct sockaddr_in sock;
static int port = PORT_NUM;
memset(&sock, 0, sizeof(sock));
int temp = -1;
for(i = 0; i<MAX_ROOMS; i++){
if((strcmp(chat[i].name, name) == 0) && (chat[i].port != 0)){
createResponse(chat_socket, chat[i].port, 15);
return NULL;
}
else if((chat[i].port == 0) && (temp== -1)){
temp = i;
}
}
if(temp == -1){
return NULL;
}
socket_d = socket(AF_INET, SOCK_STREAM, 0);
if(socket_d == -1 && DEBUG){
perror("Error creating chatroom socket");
return NULL;
}
sock.sin_family = AF_INET;
port++;
sock.sin_port = htons(port);
if(bind(socket_d, (struct sockaddr*)&sock, sizeof(struct sockaddr_in)) == -1){
perror("error in binding ");
return NULL;
}
chat[temp].socket_d = socket_d;
chat[temp].port = port;
strcpy(chat[temp].name, name);
return &chat[temp];
}
void* chat_room_main(void* chat_room_cluster){
char buf[MAX_LOAD];
int socket_d, chat_socket;
int temp; //temp_fd
int read_val;
int num_clients = 0;
int i;
int clients[MAX_CRC];
fd_set allfd, modfd;
struct chat_room chat_room_para;
memcpy(&chat_room_para, (struct chat_room*)chat_room_cluster, sizeof(struct chat_room));
free(chat_room_cluster);
memset(clients, 0, sizeof(int)*MAX_CRC);
socket_d = chat_room_para.socket_d;
listen(socket_d, 1);
FD_ZERO(&allfd);
FD_SET(socket_d, &allfd);
printf("New Chatroom Started\n");
while(1){
modfd = allfd;
select(FD_SETSIZE, &modfd, NULL, NULL, NULL);
for(temp = 0; temp < FD_SETSIZE; temp++){
if(FD_ISSET(temp, &modfd)){
memset(buf, 0, sizeof(buf));
if(temp == socket_d) {
chat_socket = accept(socket_d, NULL, NULL);
FD_SET(chat_socket, &allfd);
// find an empty spot to add the chat room
for(i = 0; i<MAX_CRC; i++) {
if(clients[i] == 0){
clients[i] = chat_socket;
break;
}
}
sprintf(buf, "Number of people in chatroom: %d", num_clients);
write(chat_socket, buf, strlen(buf));
num_clients++;
}
else{
if(read_val = read(temp, buf, MAX_LOAD) > 0){
for(i = 0; i< MAX_CRC; i++){
if((clients[i] != temp) && (clients[i] != 0)){
write(clients[i], buf, read_val);
}
}
}
else if(read_val <= 0) {
FD_CLR(temp, &allfd);
for(i = 0; i<MAX_CRC; i++){
if(clients[i] == temp)
clients[i] = 0;
}
num_clients--;
close(chat_socket);
}
}
}
}
}
}
int main(int argc, char* argv[]){
int server_socket, chat_socket; //file descriptors for server and chat
int temp; //tempfd
int i, j;
char server_ip[SERVER_IP];
char buf[MAX_BUF];
char msg_buf[MSG_SIZE];
fd_set allfd, modfd;
struct sockaddr_in sock;
struct hostent* host_name;
struct chat_room chatrooms[MAX_ROOMS];
memset(chatrooms, '\0', sizeof(struct chat_room)* MAX_ROOMS);
memset(&sock, '\0', sizeof(sock));
server_socket = socket(AF_INET, SOCK_STREAM, 0);
if(server_socket == -1){
perror("Error creating socket");
return -1;
}
sock.sin_family = AF_INET;
sock.sin_port = htons(PORT_NUM);
sock.sin_addr.s_addr = INADDR_ANY;
if((bind(server_socket, (struct sockaddr*)&sock, sizeof(struct sockaddr_in))) == -1){
perror("Error in bind()");
return -1;
}
listen(server_socket, 1);
FD_ZERO(&allfd);
FD_SET(server_socket, &allfd);
FD_SET(0, &allfd);
printf("\n*******Chatroom Server*******");
while(1){
modfd = allfd;
select(FD_SETSIZE, &modfd, NULL, NULL, NULL);
for(temp = 0; temp < FD_SETSIZE; temp++) {
if(FD_ISSET(temp, &modfd)) {
switch(temp){
case 0:
break;
default:
if(temp == server_socket){
chat_socket = accept(server_socket, NULL, NULL);
}
else{
char msg_buf[MSG_SIZE];
char buf[MAX_LOAD];
char name[MAX_LOAD];
struct msg temp_message;
struct chat_room* local_chat = NULL;
void* (*init_chatroom)() = &chat_room_main;
void* thread_args;
pthread_attr_t attr;
pthread_t tid;
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
memset(buf, 0, sizeof(buf));
memset(msg_buf, 0, sizeof(msg_buf));
msg_buf[19]= 0;
int read_val = read(temp, msg_buf, MSG_SIZE);
if(read_val > 0){
memcpy(&temp_message, msg_buf, sizeof(temp_message));
read(temp, buf, temp_message.length - sizeof(temp_message));
memcpy(name, buf, temp_message.length - sizeof(temp_message));
if(temp_message.type == 0) {//if create
local_chat = addRoom(temp, name, chatrooms);
if(local_chat != NULL){
thread_args = (void*)malloc(sizeof(struct chat_room));
memcpy((struct chat_room*) thread_args, local_chat, sizeof(struct chat_room));
pthread_create(&tid, &attr, init_chatroom, thread_args);
local_chat->id = tid;
createResponse(temp, local_chat->port, 10);
}
}
else if(temp_message.type == 1){ //join
local_chat = joinServer(temp, name, chatrooms);
if(local_chat != NULL){
joinResponse(temp, local_chat->port);
}
}
else if(temp_message.type == 2){ //delete
local_chat = findRoom(name, chatrooms);
printf("Deleting Room\n");
if(local_chat != NULL) {
local_chat->port = 0;
close(local_chat->socket_d);
deleteResponse(temp, local_chat);
for(j = 0; j<MAX_CRC; j++){
if(local_chat->clients[j]!=0) {
FD_CLR(local_chat->clients[j], &modfd);
local_chat->clients[j] = 0;
}
}
pthread_cancel(local_chat->id);
}
}
}
else if(read_val <= 0){
FD_CLR(temp, &allfd);
close(temp);
}
}
}
}
}
}
return 0;
}
Client.c
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <netdb.h>
#include <pthread.h>
#define PORT_NUM 12333
#define MSG_SIZE 8
#define MAX_LOAD 246
#define MAX_BUF 256
#define SERVER_IP 32
struct msg {
int type;
int length;
};
struct thread_para {
int port;
struct hostent* host_name;
};
int sendCmd(int chat_socket, char* buf, int type){ //function for sending the command
struct msg temp;
char temp_buf[MAX_LOAD];
char name[MAX_LOAD];
int iterator;
if(type == 0){
iterator = 6;
}
else if(type == 1){
iterator = 4;
}
else if(type == 2){
iterator = 6;
}
for(; iterator < strlen(buf); iterator++){
if(buf[iterator] == ' ') {
continue;
}
else{
break;
}
}
strcpy(name, buf+iterator);
memset(temp_buf, 0, MAX_LOAD);
temp.type = type;
temp.length = sizeof(temp)+strlen(name)+1; //for \0
memcpy(temp_buf, &temp, sizeof(temp));
memcpy(temp_buf+sizeof(temp), name, strlen(name)+1);
write(chat_socket, temp_buf, temp.length);
return 0;
}
void* connectChat(int port_num, struct hostent* host_name, int master){
char buf[MAX_BUF];
char temp_buf[MAX_BUF];
int chat_socket;
int i;
int input;
int temp; //temp fd
fd_set allfd, modfd;
struct sockaddr_in sock;
printf("Successfully Joined Room\n");
memset(buf, 0, sizeof(buf));
memset(&sock, 0, sizeof(sock));
sock.sin_family = AF_INET;
sock.sin_port = htons(port_num);
memcpy((char*)&sock.sin_addr.s_addr, host_name->h_addr, host_name->h_length);
chat_socket = socket(AF_INET, SOCK_STREAM, 0);
if(chat_socket == -1){
perror("Error in creation");
return NULL;
}
if(connect(chat_socket, (struct sockaddr*)&sock, sizeof(struct sockaddr)) < 0 ){
perror("Error in connection");
return NULL;
}
FD_ZERO(&allfd);
FD_SET(chat_socket, &allfd);
FD_SET(0, &allfd);
FD_SET(master, &allfd);
while(1) {
modfd = allfd;
select(FD_SETSIZE, &modfd, NULL, NULL, NULL);
for(temp = 0; temp< FD_SETSIZE; temp++){
memset(buf, 0, sizeof(buf));
memset(temp, 0, sizeof(buf));
if(temp == 0) { //reading from standard in
input = read(0, buf, MAX_BUF);
buf[input-1] = '\0'; //add termination to end
write(chat_socket, buf, strlen(buf));
}
else if(temp == chat_socket){
input = read(0, buf, MAX_BUF);
buf[input] = '\0';
memcpy(temp, buf, input);
//display message
printf("%s \n", temp_buf);
}
else if(temp == master){
struct msg temp_message;
input = read(temp, buf, MSG_SIZE);
memcpy(&temp_message, buf, MSG_SIZE);
if(temp_message.type == 12){
printf("Chatroom has been deleted, Shutting down chatroom\n");
return NULL;
}
}
}
}
return 0;
}
int main(int argc, char* argv[]){
char buf[MAX_BUF];
int chat_socket;
int i;
int input;
int temp; //temp fd
int accept_input = 1; // take input for stdin to create a chat thread
fd_set allfd, modfd;
char server_ip[SERVER_IP];
struct hostent* host_name;
struct sockaddr_in sock;
struct msg temp_message;
pthread_attr_t tattr;
pthread_t tid;
if(argc < 2) {
printf("Please try ./crc <server IP> \n");
return -1;
}
pthread_attr_init(&tattr);
pthread_attr_setdetachstate(&tattr, PTHREAD_CREATE_DETACHED);
memset(&sock, '\0', sizeof(sock));
sock.sin_family = AF_INET;
sock.sin_port = htons(PORT_NUM);
strcpy(server_ip ,argv[1]);
if((host_name = (struct hostent*)gethostbyname(server_ip)) == NULL){
perror("failed to get host name");
return -1;
}
memcpy((char*)&sock.sin_addr.s_addr, host_name->h_addr, host_name->h_length);
chat_socket = socket(AF_INET, SOCK_STREAM, 0);
if(chat_socket == -1){
perror("Error creating socket");
return -1;
}
if((connect(chat_socket, (struct sockaddr*)&sock, sizeof(sock))) < 0) {
perror("Error connecting");
return -1;
}
FD_ZERO(&allfd); /* first, clear the allfd set */
FD_SET(chat_socket, &allfd); /* adding client to the set */
FD_SET(0, &allfd);
printf("*****Welcome to the Chatroom*****\n");
while(1){
modfd = allfd;
select(FD_SETSIZE, &modfd, NULL, NULL, NULL);
for(temp = 0; temp < FD_SETSIZE; temp++){
if(FD_ISSET(temp, &modfd)){
if(temp == 0){
input = read(0, buf, MAX_BUF);
buf[input-1] = '\0'; //remove \n inserts termination
if((strncasecmp(buf, "create ", 7) == 0)) {
sendCmd(chat_socket, buf, 0);
}
else if((strncasecmp(buf, "join ", 5) == 0)) {
sendCmd(chat_socket, buf, 1);
}
else if((strncasecmp(buf, "delete ", 7)==0)){
sendCmd(chat_socket, buf, 2);
}
else
{
printf("Enter a valid command: create <Room_name>, join <Room_name>, delete <Room_name>\n");
}
}
else if(temp == chat_socket){
input = read(temp, buf, MSG_SIZE);
memcpy(&temp_message, buf, sizeof(temp_message));
if(temp_message.type == 10) {
printf("Created Chatroom\n");
}
else if(temp_message.type == 11){
connectChat(temp_message.length, host_name, chat_socket);
fflush(stdin);
}
else if(temp_message.type == 15) {
printf("Chatroom exits. Type join <Room_name> to join\n");
}
}
}
}
}
close(chat_socket);
return 0;
}
I gave both sets of code just in case it was need. The program is designed to create multiple chat rooms.

invalid argument is the EINVAL error code, which in the context of connect() means:
An invalid argument was detected (e.g., address_len is not valid for the address family, the specified address family is invalid).
You have multiple calls to connect() in your client code (why?), but you did not indicate which call is the one that is failing. In connectChat() at least, sizeof(struct sockaddr) should be sizeof(struct sockaddr_in) instead, or better sizeof(sock), like you do in main().
Also, if either connect() fails, you are leaking the socket returned by socket(). You need to close() it.
Also, gethostbyname() is deprecated, you should be using getaddrinfo() instead. You are creating IPv4 sockets, which only work with IPv4 addresses. You are not checking if gethostbyname() actually returns an IPv4 address (host_name->h_addr_type == AF_INET) before copying the address bytes into your sock variable. At least with getaddrinfo(), you can restrict the output to IPv4 addresses only. You don't have that option with gethostbyname().

Since you're looking for a way to figure out your error, I'll suggest you to use the following Makefile:
CFLAGS=-Wall -g -O2
CC=gcc
LDFLAGS=-lpthread
all: Server Client
Server: Server.c
Client: Client.c
After running make command you'll see a lot of warnings. Some of them:
Server.c: In function ‘createResponse’:
Server.c:81:5: warning: ignoring return value of ‘write’, declared with attribute warn_unused_result [-Wunused-result]
write(chat_socket, temp_buff, MSG_SIZE);
^
Server.c: In function ‘chat_room_main’:
Server.c:237:25: warning: ‘chat_socket’ may be used uninitialized in this function [-Wmaybe-uninitialized]
close(chat_socket);
^
Server.c: In function ‘main’:
Server.c:319:36: warning: array subscript is above array bounds [-Warray-bounds]
msg_buf[19]= 0;
Client.c: In function ‘connectChat’:
Client.c:113:20: warning: passing argument 1 of ‘memset’ makes pointer from integer without a cast
memset(temp, 0, sizeof(buf));
^
So just try to fix these warnings. I mean all of them.

Reuse char * pointer needs to free and malloc again?

I would like to implement a main function such as in order to execute system commands. The following code is currently used :
int main(int argc, char *argv[])
{
size_t cmd_length;
char *cmd_buffer = NULL;
char *file = NULL;
char *ip = NULL;
int size;
if(argc == 3)
{
size = strlen(argv[1]);
file = (char*)malloc((size + 1)*sizeof(char));
strcpy(file, argv[1]);
size = strlen(argv[2]);
ip = (char*)malloc((size + 1)*sizeof(char));
strcpy(ip, argv[2]);
}
cmd_length = snprintf(NULL, 0, "tftp -g -r %s %s", file, ip);
cmd_buffer = malloc(cmd_length + 1);
if (cmd_buffer == NULL)
{
return -1;
}
snprintf(cmd_buffer, cmd_length + 1, "tftp -g -r %s %s", file, ip);
if(system(cmd_buffer) == 0)
{
then ...
}
{
return -1;
}
free(cmd_buffer);
cmd_buffer = NULL;
cmd_length = snprintf(NULL, 0, "tftp -g -r %s %s", DFT_FILE, DFT_IP);
cmd_buffer = malloc(cmd_length + 1);
if (cmd_buffer == NULL)
{
return -1;
}
snprintf(cmd_buffer, cmd_length + 1, "tftp -g -r %s %s", DFT_FILE, DFT_IP);
if(system(cmd_buffer) == 0)
{
then ...
}
{
return -1;
}
free(cmd_buffer);
free(file);
free(ip);
cmd_buffer = NULL;
file = NULL;
ip = NULL;
return 0;
}
Because I need to enter other commands, I am currently using the same cmd_buffer by using free() before reallocating memory. Is it the right way to do ? Some other commands might be required in the future.

Your program can be be greatly simplified if you use a common function to execute the system call. It doesn't even need to use malloc at all. Here's a partial implementation [Please pardon the gratuitous style cleanup]:
#include <stdarg.h>
int
execute_command(const char *fmt,...)
{
char cmd_buffer[5000];
int cmd_length;
va_list ap;
// NOTE: much simpler to used a fixed size buffer that is larger than
// needed
va_start(ap,fmt);
cmd_length = vsnprintf(cmd_buffer,sizeof(cmd_buffer),fmt,ap);
va_end(ap);
if (system(cmd_buffer) != 0)
return -1;
return 0;
}
int
main(int argc, char *argv[])
{
char *file = NULL;
char *ip = NULL;
// NOTE: I had to guess the intent if fewer arguments are passed (e.g. just
// skip as I did here, print message and abort?)
if (argc == 3) {
// NOTE: no need to malloc these, but if you did, see strdup(3)
file = argv[1];
ip = argv[2];
execute_command("tftp -g -r %s %s", file, ip);
}
execute_command("tftp -g -r %s %s", DFT_FILE, DFT_IP);
return 0;
}

Yes, you are essentially just re-using the pointer variable cmd_buffer which is fine. And for every malloc() there is a matching free(), which is good.
You should factor our common code into a function, for example runCommand(const char *command, ...) (using varargs).

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