Unix Socket - Client Server program (Segmentation fault)

Question

I have been trying to establish a local client server using UNIX sockets and here are the two programs. After I run the server program on terminal, it shows "The socket was created" and "Binding Socket" but soon after when I run the client side program, and send the IP (127.0.0.1) as argument for it, the server program crashes with "Segmentation fault (core dumped)". Please help rectify.

Server Side->

    #include<sys/types.h>
    #include<sys/socket.h>
    #include<netinet/in.h>
    #include<sys/stat.h>
    #include<unistd.h>
    #include<stdlib.h>
    #include<stdio.h>
    #include<fcntl.h>
    int main(int argc,char *argv[])
    {
     int create_socket,new_socket,addrlen,cont,fd;
     int bufsize=1024;
     char *buffer=malloc(bufsize);
     char fname[256];
     struct sockaddr_in address;
      if((create_socket=socket(AF_INET,SOCK_STREAM,0))>0)
        printf("the socket was created\n");
        address.sin_family=AF_INET;
        address.sin_addr.s_addr=INADDR_ANY;
        address.sin_port=htons(15000);
       if(bind(create_socket,(struct sockaddr *)&address,sizeof(address))==0)
         printf("binding socket \n");
         listen(create_socket,3);
         addrlen=sizeof(struct sockaddr_in);
         new_socket=accept(create_socket,(struct sockaddr*)&address,&addrlen);
        if(new_socket>0)
          printf("the client %s is connected...\n",inet_ntoa(address.sin_addr));
          recv(new_socket,fname,255,0);
          printf("a request for filename %s received\n",fname);
         if((fd=open(fname,O_RDONLY))<0)
          {
        perror("file open failed ");
        exit(0);
          }
           while((cont=read(fd,buffer,bufsize))>0)
           {
         send(new_socket,buffer,cont,0);
           }
         printf("request completed \n");
         close(new_socket);
         return close(create_socket);
    }

Client Side->

    #include<sys/types.h>
    #include<sys/socket.h>
    #include<netinet/in.h>
    #include<sys/stat.h>
    #include<unistd.h>
    #include<stdlib.h>
    #include<stdio.h>
    int main(int argc,char *argv[])
    {
     int create_socket,cont;
     int bufsize=1024;
     char *buffer=malloc(bufsize);
     char fname[256];
     struct sockaddr_in address;
      if((create_socket=socket(AF_INET,SOCK_STREAM,0))>0)
       printf("the socket was created\n");
       address.sin_family=AF_INET;
       address.sin_port=htons(15000);
       inet_pton(AF_INET,argv[1],&address.sin_addr);
        if(connect(create_socket,(struct sockaddr*)&address,sizeof(address))==0)
          printf("the connection was accepted with the server %s",argv[1]);
          printf("enter the filename to request :");
          scanf("%s",fname);
          send(create_socket,fname,sizeof(fname),0);
          printf("request accepted .... receiving file  \n");
          printf("the contents of file are... \n");
        while((cont=recv(create_socket,buffer,bufsize,0))>0)
         {
           write(1,buffer,cont);
         } 
           printf("\n EOF\n");
           return close(create_socket);
    }

1st you want to fix the code to show no more warnings during compilation. — alk
– alk, Commented Oct 30, 2017 at 7:16
Calling this "Unix Socket" is misleading, as it can be understood as "Unix Domain Sockets", which it is not. It's TCP(/IP) sockets you are using. — alk
– alk, Commented Oct 30, 2017 at 7:28

peter__barnes · Accepted Answer · 2017-10-30 07:24:45Z

1

The core dump is caused by the "implicit declaration" , you didn't include enough header files. please use "man" command check the headers that a function need:

man inet_ntoa

then add this headers :

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

after fix these ,you can see this program work correctly(here is my server side out put after fix warnings):

./serv.out 
the socket was created
binding socket 
the client 127.0.0.1 is connected...
a request for filename a.txt received
request completed

and client side:

./cli.out 127.0.0.1
the socket was created
the connection was accepted with the server 127.0.0.1enter the filename to request :a.txt
request accepted .... receiving file  
the contents of file are... 
11111111111111

 EOF

edited Oct 30, 2017 at 7:24

answered Oct 30, 2017 at 7:18

peter__barnes

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Comments

alk · Accepted Answer · 2017-10-30 07:18:54Z

1

For starters:

Both, client and server, miss to include

#include <arpa/inet.h>

This causes non prototyped functions to be implicitly taken as functions returning int. As happening in the server code for inet_ntoa().

Passing an int to printf() as argument where a char* is expected

  printf("the client %s is connected...\n", inet_ntoa(address.sin_addr));

causes undefined behaviour. From this moment on anything can happend. In your case it's a crash.

answered Oct 30, 2017 at 7:18

alk

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