Segmentation fault due to file descriptor in multi threaded client - c

Question

I have created a client-server file sharing system with multi threading. The client code is working correctly for a single client. When I increase the number of threads in client, segmentation fault is occurred in server code.
When I executed the code on gdb, it shows the error segmentation fault occurred, no such file or directory. Is this because of the threads sharing file descriptor? How to resolve the segmentation fault?
----------edit-----------
I considered all your suggestions. Most of the errors are resolved, but when I try to send a >10mb file, some send-recv call does not execute fully while sending it out with threads(It works fine with a single thread). I believe this is the reason memory leakage is happening and ultimately results in segmentation fault(file pointers not closed). The same is happening in gdb.
How to resolve this send receive blocking error?
client code
#include <time.h>
#include<arpa/inet.h>
#include<sys/socket.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<string.h>
#include<stdio.h>
#include <stdlib.h>
#include<pthread.h>
#include <semaphore.h>
#define PORT 8029
#define SIZE 1024
#define SERVER_ADDR "192.168.43.158" //"10.15.36.112"
//defining number of threads
struct ser_data
{
int sockfd;
int n;
};
void *client_req(void * data){
// printf("inside thread\n");
//sleep(1);
int s,c,n,read_size,r;
//login_id and password of the user
//array to choose file names randomly
//char f_name[20][20]={"f0.txt","f1.txt","f2.txt","f3.txt","f4.txt","f5.txt","f6.txt","f7.txt","f8.txt","f9.txt","f10.txt\0","f11.txt\0","f12.txt\0" ,"f13.txt\0","f14.txt\0","f15.txt\0","f16.txt\0","f17.txt\0","f18.txt","f19.txt"};
//socket address for client and server
//used for generation of random no
time_t t;
struct sockaddr_in cli,serv;
FILE *f;
char fname[SIZE]="file_cli/";
char f_name[SIZE];
char login_id[21], pswd[21], choice[2];
//msg_cli_rec= message recieved form server
char msg_cli_rec[SIZE];
//msg_cli_send =message sent by client
char msg_cli_send[SIZE];
time_t start, stop;
int brk=0;
start = time(NULL);
s=socket(AF_INET,SOCK_STREAM,0);
bzero((char*)&serv,sizeof(cli));
cli.sin_family=AF_INET;
cli.sin_port=htons(PORT);
cli.sin_addr.s_addr = inet_addr(SERVER_ADDR);
connect(s,(struct sockaddr*)&cli,sizeof(cli));
//printf("\nConnected with server");
strcpy(choice, "1");
/*msg_cli_rec = (char *) malloc(1000* sizeof(char));
msg_cli_send = (char *) malloc(1000* sizeof(char));*/
//if user wants to login
if(strcmp(choice,"1")==0)
{
strcpy(login_id, "prach");
send(s, login_id, sizeof(login_id), 0);
strcpy(pswd, "prach");
send(s, pswd, sizeof(pswd), 0);
}
//making default choice download 1
do {
strcpy(choice, "1\0");
strcpy(msg_cli_send, choice);
//send(s, choice, sizeof(choice), 0);
send(s,msg_cli_send,sizeof(msg_cli_send),0);
//random number generation
srand((unsigned) time(NULL));
//r=((unsigned)rand()*(i++))%20;
r=15;
if(strcmp(choice,"1")==0)
{
/*if(recv(s, msg_cli_rec, sizeof(msg_cli_rec), 0))
{
//if((strcmp("end",msg_cli_rec))==0)break;
printf("\n%s", msg_cli_rec);
}*/
/*printf("\nEnter the file name you want:");
scanf("%s", msg_cli_send);*/
// to select file name with index of the random number
sprintf(f_name,"file (%d).txt",r);
strcpy(msg_cli_send, "");
strcpy(msg_cli_send,f_name);
// printf("\n%s",msg_cli_send);
// printf("\n rand =%d\n", r );
send(s,msg_cli_send,sizeof(msg_cli_send),0);
// printf("\nThe received file content is:");
//receiving the file names
f = fopen(strcat(fname,f_name),"w");
bzero( msg_cli_rec, sizeof(msg_cli_rec));
while((recv(s, msg_cli_rec, sizeof(msg_cli_rec), 0)> 0)&&(*msg_cli_rec!='\0'))
{//fflush(stdout);
if((strcmp("quit",msg_cli_rec))==0)break;
fprintf(f, "%s", msg_cli_rec);
//printf("\n%s", msg_cli_rec);
bzero( msg_cli_rec, sizeof(msg_cli_rec));
}
// printf("File recieved");
fclose(f);
strcpy(fname,"\0" );
//sem_post(&sem);
}
stop = time(NULL);
// printf("\n%s\n", ctime(&stop));
//printf("%ld", (stop-start));
//set the timer to 300 seconds
}while(*choice == '1' && (stop-start)<10);
//tell the server that we are done with sending files
strcpy(choice, "0");
send(s, choice, sizeof(choice), 0);
printf("%ld\n", (stop-start) );
/* free(msg_cli_rec);
free(msg_cli_send);*/
close(s);
//pthread_exit(NULL);
}
int main()
{
int N_Threads=2, count =0;
struct ser_data data;
/*while(N_Threads<=2)
{
pthread_t t;
pthread_create( &t , NULL , client_req , NULL);
N_Threads++;
if ( ! pthread_detach(t) )
printf("Thread detached successfully !!!\n");
//pthread_join(t, NULL);
}*/
while(count != N_Threads){
pthread_t handle;
count = count+1;
data.sockfd = count;
if(pthread_create(&handle, NULL, client_req,(void *)&data)<0)
error("Error creating thread");
else
printf("Thread allocation successful for fd: %d\n",data.sockfd);
}
pthread_exit(NULL);
}
server code
#include <time.h>
#include<arpa/inet.h>
#include<sys/socket.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<string.h>
#include<stdio.h>
#include<pthread.h>
#include<stdlib.h>
#include<dirent.h>
#include <mysql/mysql.h>
#include <semaphore.h>
#define PORT 8029
#define SIZE 1024
#define QUERY_SIZE 200
#define N_Threads 5
#define SERV_ADDR "192.168.43.158"
clock_t start, stop;
//login id and password of the user
int file_id=1;
/*Database variables*/
MYSQL *db_conn;
char *db_server = "localhost";
char *db_user = "root";
char *db_password = "root";
char *database = "file_db";
//for synchronization while accessing the db
sem_t sem;
/* A function which generates the and returns login query statement*/
char* query_login(char *query, char *login_id, char *pswd)
{
//generating query
strcpy(query,"SELECT * FROM user_info WHERE user_id='");
strcat(query, login_id);
strcat(query, "' AND pswd='");
strcat(query, pswd);
strcat(query, "'");
return query;
}
/* A function which generates and returns the register query statement*/
char* query_register(char *query, char *login_id, char *pswd)
{
strcpy(query, "INSERT INTO user_info VALUES ( '");
strcat(query, login_id);
strcat(query, "', '");
strcat(query, pswd);
strcat(query, "' )");
return query;
}
void *connect_client(void *socket)
{ int sock=*(int*)socket;
printf("\nFD %d",sock);
char msg_c_r[SIZE], msg_s_s[SIZE];
//for the choice given to the user to login or register
char choice='0';
char msg_serv_send[SIZE],msg_serv_rec[SIZE];
char msg_cli_rec[SIZE];
char fpath[SIZE] = "file_serv/";
char fname[SIZE];
int read_size;
int num_fields=0;
char * line = NULL;
size_t len = 0;
ssize_t read;
MYSQL_ROW row;
MYSQL_RES *db_res;
char login_id[21], pswd[21];
FILE *f;
FILE *fc;
char name[SIZE];
char query1[SIZE];
char query[QUERY_SIZE];
/*locking the database for mutual exclusion*/
//sem_wait(&sem);
//executing a query
choice = '1';
strcpy(query, "\0");
switch(choice)
{
//1 = login
case '1':
/*to find the login id and password of the user*/
bzero(login_id, sizeof(login_id));
recv(sock, login_id, sizeof(login_id), 0);
bzero(pswd, sizeof(pswd));
recv(sock, pswd, sizeof(pswd), 0);
printf("The login id is: %s\nThe Password is: %s\n", login_id, pswd);
//lock for accessing db in mutual exclusion
sem_wait(&sem);
query_login(query, login_id, pswd);
//checking the details given by client
if (mysql_query(db_conn, query)!=0) {
fprintf(stderr, "%s\n", mysql_error(db_conn));
}
strcpy(query, "\0");
strcat(query,"select * from user_info where user_id='");
strcat(query,login_id);
strcat(query,"'");
mysql_query(db_conn, query);
db_res = mysql_store_result(db_conn);
row = mysql_fetch_row(db_res);
if (row!=0) {
//send(sock,"T",sizeof("T"),0);
printf("\nT");
}
//freeing the result variable so it can be used further
mysql_free_result(db_res);
//release lock
sem_post(&sem);
break;
}//switch case
/*send(sock, "\nPlease enter your choice \n 1- File Download \n 2-File Upload\n 3-Rating\n", sizeof("\nPlease enter your choice \n 1- File Download \n 2-File Upload\n 3-Rating\n"), 0);*/
int nu=1;
do{
bzero(msg_serv_rec,sizeof(msg_serv_rec));
if(recv(sock, msg_serv_rec,sizeof(msg_serv_rec), 0)>0)
{
choice = msg_serv_rec ? *msg_serv_rec : '0';
printf("\n choice = %c\n", choice);
strcpy(query, "\0");
//printf("Client's choice is file Download\n" );
/*Sending File to the client line by line
checking the database connection*/
if(choice == '1'){
/*if(mysql_query(db_conn, "SELECT name FROM file_info")==0)
{
db_res = mysql_store_result(db_conn);
num_fields = mysql_num_fields(db_res);
if(num_fields>0)
{
while ((row = mysql_fetch_row(db_res)))
{
for(int i = 0; i < num_fields; i++)
{
char *fname1=row[i] ? row[i] : "NULL";
strcat(name,fname1);
strcat(name, "\n");
//send(sock,name,sizeof(name),0);
//printf("\n%s",name);
}
}
//sending list of all files to client
send(sock,name,sizeof(name),0);*/
/*emptying the name!!
strcpy(name, "");*/
//freeing the result variable so it can be used further
/*mysql_free_result(db_res);
sem_post(&sem);*/
bzero(msg_serv_rec,sizeof(msg_serv_rec));
if(recv(sock, msg_serv_rec,sizeof(msg_serv_rec), 0)>0)
{//which file recieved
printf("%s\n", msg_serv_rec );
// sem_wait(&sem);
f = fopen(strcat(fpath, msg_serv_rec),"r");
while(fgets(msg_serv_send, sizeof(msg_serv_send), f) !=NULL)
{
if((*msg_serv_send!=EOF || *msg_serv_send!='\n'))
{
send(sock, msg_serv_send, sizeof(msg_serv_send), 0);
//printf("\n%s", msg_serv_send);
}
else
break;
}
send(sock,"quit",sizeof("quit"),0);
fclose(f);
strcpy(fpath, "file_serv/");
//sem_post(&sem);
printf("\nFile sent to the client\n");
}
}
else if (choice == '0')
break;
strcpy(msg_serv_rec, "");
//stop = clock();
//time(NULL);
}
else
{
choice = '0';
}
}while ( choice != 'f' && choice != '0');
nu++;
/* unblocking the semaphores to allow other threads to access*/
//sem_post(&sem);
if(read_size == 0)
{
puts("\nClient disconnected\n");
fflush(stdout);
}
/*else if(read_size == -1)
{perror("recv failed");}
fclose(f);*/
close(sock);
pthread_exit(NULL);
}
int main()
{ int s,n,i, clilen;
int c;
int newsockfd;
int *new_sock;
start = clock();
//pthread_t handle;
struct sockaddr_in cli,serv;//socket address for client and server
MYSQL_ROW row;
MYSQL_RES *db_res;
//initializing the semaphore
sem_init(&sem, 0, 1);
//synchronization in DB
sem_wait(&sem);
/*Database connectivity*/
db_conn = mysql_init(NULL);
/* Connect to database */
if (!mysql_real_connect(db_conn, db_server, db_user, db_password, database, 0, NULL, 0)) {
fprintf(stderr, "%s\n", mysql_error(db_conn));
exit(1);
}
/* send SQL query */
if (mysql_query(db_conn, "show tables")) {
fprintf(stderr, "%s\n", mysql_error(db_conn));
exit(1);
}
db_res = mysql_use_result(db_conn);
/* output table name */
printf("MySQL Tables in mysql database:\n");
while ((row = mysql_fetch_row(db_res)) != NULL)
printf("%s \n", row[0]);
//freeing the result variable so it can be used further
mysql_free_result(db_res);
sem_post(&sem);
//Server socket
s=socket(AF_INET,SOCK_STREAM,0);
bzero((char*)&serv,sizeof(serv));
serv.sin_family=AF_INET;
serv.sin_port=htons(PORT);
serv.sin_addr.s_addr=inet_addr( SERV_ADDR);//"10.15.36.112");
/*printf("\nServer is waiting for client to respond");
i=0*/
//accept the incomming connections from client
bind(s,(struct sockaddr *)&serv,sizeof(serv));
printf("\nAddress bind successful");
listen(s,3000);//4 is the limit of the number of outstanding connections
n=sizeof(cli);
/*
i=0;
//accept the incomming connections from client
while( (c = accept(s, (struct sockaddr *)&cli, (socklen_t*)&n))) //&& (stop-start)<300 )
{ puts("Connection accepted\n");
pthread_t t;
printf("sock =%d\n", c);
if( pthread_create( &t , NULL , connect_client , (void*) c) < 0)
{
perror("could not create thread");
return 1;
}
i++;
/*Now detach the thread ,When a detached thread terminates, its resources are
automatically released back to the system without the need for
another thread to join with the terminated thread.*/
/* if ( ! pthread_detach(t) )
printf("Thread detached successfully !!!\n");
puts("Handler assigned");
stop = clock();
}*/
clilen=sizeof(cli);
while(newsockfd = accept(s, (struct sockaddr *) &cli, &clilen))
{
if(newsockfd < 0)
error("ERROR on accept");
else{
pthread_t handle;
new_sock = malloc(1);
*new_sock = newsockfd;
if(pthread_create(&handle, NULL,connect_client ,(void *)new_sock)<0)
error("Error creating thread");
else
printf("Thread fd: %d\n",newsockfd);
if ( ! pthread_detach(handle) )
printf("Thread detached successfully !!!\n");
}
}
/* close database connection */
mysql_free_result(db_res);
mysql_close(db_conn);
close(s);
/*destroying the mutex */
sem_destroy(&sem);
return 0;
}