[SOLVED] UDP Client-Server scoket programming

bislinux · 12-17-2014, 07:11 AM

Hello Everyone
I am trying to test my client-server socket program wherein the client connects to the server,client sends a message, server receives it and echo back to the client.So far, in the program server receives the message from the client, prints it BUT when it tries to send the message back to the client it shows an error.

sendto(): Invalid argument.
I am new to socket programming and any help would be much appreciated. Thank you

Server

#include<stdio.h> //printf
#include<string.h> //memset
#include<stdlib.h> //exit(0)
#include<netinet/in.h>
#include<sys/socket.h>
#define BUFLEN 512 //Max length of buffer
#define PORT 10003 //The port on which to listen for incoming data

//error check fucntion
void die(char *sockS)
{
perror(sockS);
exit(1);
}

int main(void)
{

struct sockaddr_in S_Serv, S_Cli;

int sockS,slen=sizeof(S_Cli),recv_len;
char buf[BUFLEN];
char hostname[128];

//////////////////////// To get host name /////////////////////////////////////////
gethostname(hostname, sizeof hostname);
printf("My hostname: %s\n", hostname);

///////////////////////create a UDP server socket///////////////////////////////////

if((sockS=socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP))==-1)
{
die("socket");
}

/////////////////////////zero out the structure////////////////////////////////
memset((char *)&S_Serv,0,sizeof(S_Serv));

S_Serv.sin_family= AF_INET;
S_Serv.sin_port= htons(PORT);
S_Serv.sin_addr.s_addr=htonl(INADDR_ANY);

/////////////////////////bind socket to port/////////////////////////////////////
if (bind(sockS, (struct sockaddr *)&S_Serv,sizeof(S_Serv))==-1)
{

die("bind");
}

//////////////////////////keep listening for data//////////////////////////////
while(1)
{
printf("waiting for data.......");
fflush(stdout);

///////////try to receive some data (blocking call)/////////////////
if ((recv_len=recvfrom(sockS,buf,BUFLEN,0,(struct sockaddr *)&S_Cli,&slen)) == -1)

{
die("recvfrom()");

}

///////////print details of the client/peer and the data received/////
printf("Received packet from client %d:%d\n",inet_ntoa(S_Cli.sin_addr),ntohs(S_Cli.sin_port));
printf("data: %s\n",buf);

////////////reply the client with the same data//////////////////////
if(sendto(sockS, buf, recv_len,0,(struct sockaddr *) &S_Serv, &slen) == -1)
{
die("sendto()");

}

}
close(sockS);
return 0;

}

Client

#include<stdio.h> //printf
#include<string.h> //memset
#include<stdlib.h> //exit(0)
#include<netinet/in.h>
#include<sys/socket.h>
#define BUFLEN 512 //Max length of buffer
#define PORT 10003 //The port on which to send data
#define SERVER "127.0.0.1"

void die(char *sockC)
{
perror(sockC);
exit(0);
}

int main(void)
{
struct sockaddr_in S_Cli;
int sockC,slen=sizeof(S_Cli);
char buf[BUFLEN];
char message[BUFLEN];

if ((sockC=socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP))==-1)
{
die("socket");
}

memset((char *)& S_Cli,0,sizeof(S_Cli));
S_Cli.sin_family=AF_INET;
S_Cli.sin_port=htons(PORT);

if(inet_aton(SERVER,&S_Cli.sin_addr)==0)
{
fprintf(stderr,"inet_aton() failed \n");
exit(1);
}

while(1)
{

printf("enter message: ");
gets(message);

////////////////send the message///////////////////////////

if(sendto(sockC,message,strlen(message),0,(struct sockaddr *)&S_Cli, slen)==-1)
{
die("sendto()");

}

/////////////////receive a reply and print it//////////////
////////////////clear the buffer by filling null, as it might have previous received data/////////

memset(buf,'0',BUFLEN);

//////////////try to receive some data////////////////////
if (recvfrom(sockC,buf, BUFLEN,0,(struct sockaddr *)&S_Cli,&slen)==-1)
{
die("recvfrom()");

}

puts(buf);
}

close(sockC);
return 0;

}

The output(Server side)
My hostname: bis
waiting for data.......Received packet from client *.*.*.*:47883
data: bis
sendto(): Invalid argument

The output(Client side)
enter message: bis

When i try to compile this is the warning i get, which i suspect might be the reason for not receiving any message on the client side.

warning: passing argument 6 of ‘sendto’ makes integer from pointer without a cast [enabled by default]
if(sendto(sockS, buf, recv_len,0,(struct sockaddr *) &S_Serv, &slen) == -1)

Looking forward to any reply.

SoftSprocket · 12-17-2014, 08:23 AM

If you look in the man pages you'll see the sixth argument to sendto is "socklen_t addrlen" which is likely a signed integer type. You're passing the address of your variable.

If you wrap your code in [code][/code] tags your formatting will be preserved.

NevemTeve · 12-17-2014, 09:36 AM

Code:

old:
sendto (sockS, buf, recv_len, 0, (struct sockaddr *)&S_Serv, &slen)

new: 
sendto (sockS, buf, recv_len, 0, (struct sockaddr *)&S_Serv, slen)

bislinux · 12-17-2014, 10:02 AM

Thank u SoftSprocket && NevemTeve for your quick responses...I did change the system call to
sendto (sockS, buf, recv_len, 0, (struct sockaddr *)&S_Serv, slen)

The error still remains
My hostname: bis
waiting for data.......Sock port 10004
Received packet from client ****:38187
data: bis
sendto(): Bad file descriptor

Please correct my logic if I am wrong::the sendto() will echo back the message to client through server.So effectively, if i send bis on client terminal, i am expecting to print out bis on server terminal and the server sends me back the same message.

Thanks

NevemTeve · 12-17-2014, 10:25 AM

As a start, paste the current state of your program(s) between [code] and [/code] tags.

bislinux · 12-17-2014, 10:29 AM

Code:

//Server

#include<stdio.h> //printf
#include<string.h> //memset
#include<stdlib.h> //exit(0)
#include<netinet/in.h>
#include<sys/socket.h>
#define BUFLEN 512 //Max length of buffer
#define PORT 10003 //The port on which to listen for incoming data


//error check fucntion
void die(char *sockS)
{
perror(sockS);
exit(1);
}



int main(void)
{

struct sockaddr_in S_Serv, S_Cli;

int sockS,slen=sizeof(S_Cli),recv_len;
char buf[BUFLEN];
char hostname[128];

// To get host name
gethostname(hostname, sizeof hostname);
printf("My hostname: %s\n", hostname);

//create a UDP server socket

if((sockS=socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP))==-1)
{
die("socket");
}

//zero out the structure
memset((char *)&S_Serv,0,sizeof(S_Serv));

S_Serv.sin_family= AF_INET;
S_Serv.sin_port= htons(PORT);
S_Serv.sin_addr.s_addr=htonl(INADDR_ANY);


//bind socket to port
if (bind(sockS, (struct sockaddr *)&S_Serv,sizeof(S_Serv))==-1)
{

die("bind");
}


//keep listening for data
while(1)
{
printf("waiting for data.......");
fflush(stdout);


//try to receive some data (blocking call)
if ((recv_len=recvfrom(sockS,buf,BUFLEN,0,(struct sockaddr *)&S_Cli,&slen)) == -1)


{
die("recvfrom()");

}

//print details of the client/peer and the data received
printf("Received packet from client %d:%d\n",inet_ntoa(S_Cli.sin_addr),ntohs(S_Cli.sin_port));
printf("data: %s\n",buf);

//reply the client with the same data
if(sendto(sockS, buf, recv_len,0,(struct sockaddr *) &S_Serv, slen) == -1)
{
die("sendto()");

}


}
close(sockS);
return 0;

}



Client

#include<stdio.h> //printf
#include<string.h> //memset
#include<stdlib.h> //exit(0)
#include<netinet/in.h>
#include<sys/socket.h>
#define BUFLEN 512 //Max length of buffer
#define PORT 10003 //The port on which to send data
#define SERVER "127.0.0.1"

void die(char *sockC)
{
perror(sockC);
exit(0);
}


int main(void)
{
struct sockaddr_in S_Cli;
int sockC,slen=sizeof(S_Cli);
char buf[BUFLEN];
char message[BUFLEN];

if ((sockC=socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP))==-1)
{
die("socket");
}


memset((char *)& S_Cli,0,sizeof(S_Cli));
S_Cli.sin_family=AF_INET;
S_Cli.sin_port=htons(PORT);

if(inet_aton(SERVER,&S_Cli.sin_addr)==0)
{
fprintf(stderr,"inet_aton() failed \n");
exit(1);
}


while(1)
{

printf("enter message: ");
gets(message);


//send the message

if(sendto(sockC,message,strlen(message),0,(struct sockaddr *)&S_Cli, slen)==-1)
{
die("sendto()");

}

//receive a reply and print it
//clear the buffer by filling null, as it might have previous received data

memset(buf,'0',BUFLEN);

//try to receive some data
if (recvfrom(sockC,buf, BUFLEN,0,(struct sockaddr *)&S_Cli,&slen)==-1)
{
die("recvfrom()");

}

puts(buf);
}

close(sockC);
return 0;

}

Silly me...learned a new trick

SoftSprocket · 12-17-2014, 10:42 AM

When you're running the compiler you can increase the warnings with the -Wall option. Read the warnings and try to understand them.

Your server is still passing a pointer for the sixth argument of sendto.

NevemTeve · 12-18-2014, 02:49 AM

First, fix every compilation warning. Options -W -Wall -Wextra -pedantic -Werror will help

bislinux · 12-18-2014, 05:36 AM

I am at my wits ends....are there any more suggestions on solving this problem ?
thanks

NevemTeve · 12-18-2014, 08:12 AM

Have you fixed the warnings?
Have you tried yet?
Do you know what that means?
Why not?

bislinux · 12-18-2014, 11:17 AM

Thank you every one for your kind support....Yes i did manage to fix the bug...(eventually)...Sometimes the solution lies in front of your eyes while you are looking everywhere else....I am posting the new updated code for everybodies reference....Have a good day

Server side

Code:

#include<stdio.h>		//printf
#include<string.h>		//memset
#include<stdlib.h>		//exit(0)
#include<netinet/in.h>
#include<sys/socket.h>
#include<arpa/inet.h>
#define BUFLEN 512  //Max length of buffer
#define PORT 10005   //The port on which to listen for incoming data


//error check fucntion
void die(char *sockS)
{
perror(sockS);
exit(1);
}


int main(void)
{

struct sockaddr_in S_Serv, S_Cli;

int  sockS,recv_len;
socklen_t slen=sizeof(S_Cli);
char buf[BUFLEN];
char hostname[128];

//////////////////////// To get host name /////////////////////////////////////////
    gethostname(hostname, sizeof hostname);
    printf("My hostname: %s\n", hostname);

///////////////////////create a UDP server socket///////////////////////////////////

if((sockS=socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP))==-1)
{
die("socket");
}

/////////////////////////zero out the structure////////////////////////////////
memset((char *)&S_Serv,0,sizeof(S_Serv));

S_Serv.sin_family= AF_INET;
S_Serv.sin_port= htons(PORT);
S_Serv.sin_addr.s_addr=htonl(INADDR_ANY);


/////////////////////////bind socket to port/////////////////////////////////////
if (bind(sockS, (struct sockaddr*)&S_Serv,sizeof(S_Serv))==-1)
{
  
  die("bind");
}



//////////////////////////keep listening for data//////////////////////////////




while(1)
{
  
  printf("waiting for data.......\n\n");
  fflush(stdout);
  
  
///////////try to receive some data (blocking call)/////////////////
if (recv_len=recvfrom(sockS,buf,BUFLEN,0,(struct sockaddr*)&S_Cli,&slen) == -1)
   
  
  {
    die("recvfrom()");
    
  }

///////////print details of the client/peer and the data received/////
  printf("Received packet from client %d:%d\n",inet_ntoa(S_Cli.sin_addr),ntohs(S_Cli.sin_port));
  printf("data: %s\n",buf);

  
////////////reply the client with the same data//////////////////////struct sockaddr_in
  if(sendto(sockS, buf, BUFLEN,0,(struct sockaddr*) &S_Cli, slen) == -1)
  {
    die("sendto()");
    
  }
  

}
close(sockS);
return 0;

}

Client

Code:

#include<stdio.h>		//printf
#include<string.h>		//memset
#include<stdlib.h>		//exit(0)
#include<netinet/in.h>		
#include<sys/socket.h>
#define BUFLEN 512 		//Max length of buffer
#define PORT 10005		//The port on which to send data
#define SERVER "127.0.0.1"

void die(char *sockC)
{
  perror(sockC);
  exit(0);
}


int main(void)
{
  struct sockaddr_in S_Cli;
  int sockC,slen=sizeof(S_Cli);
  char buf[BUFLEN];
  char message[BUFLEN];
  
  if ((sockC=socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP))==-1)
  {
    die("socket");
  }
  
  
  memset((char *)& S_Cli,0,sizeof(S_Cli));
  S_Cli.sin_family=AF_INET;
  S_Cli.sin_port=htons(PORT);
  
  if(inet_aton(SERVER,&S_Cli.sin_addr)==0)
  {
    fprintf(stderr,"inet_aton() failed \n");
    exit(1);
  }
  
  
  while(1)
  {
    
    printf("enter message: ");
    gets(message);
    
    
////////////////send the message///////////////////////////
    
    if(sendto(sockC,message,strlen(message)+1,0,(struct sockaddr *)&S_Cli, slen)==-1)
    {
      die("sendto()");
      
    }

/////////////////receive a reply and print it//////////////
////////////////clear the buffer by filling null, as it might have previous received data/////////

memset(buf,'0',BUFLEN);

//////////////try to receive some data////////////////////
if (recvfrom(sockC,buf, BUFLEN,0,(struct sockaddr *)&S_Cli,&slen)==-1)
{
  die("recvfrom()");
  
}
    
    puts(buf);
  }
  
  close(sockC);	
  return 0;  
  
}