client server programming - buffer written - c++

Question

I am trying to develop client server program in c++ in which client is TCP echo client while server is TCP concurrent server using single process(using select system call). However i am succeed to develop it but problem with written buffer.
Server is writing some extra character from previous message after some message exchanged bet client and server,In starting it working fine for some message interchanged.
I am not getting why this happened?
//client code
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include <arpa/inet.h>
#include <iostream>
using namespace std;
#define MAXLINE 4096 /*max text line length*/
#define srv_PORT 3000 /*port*/
int main(int argc,char **argv)
{
int sockfd;
struct sockaddr_in srvaddr;
int sendchars,recvchar;
char buf[MAXLINE];
if (argc !=2)
{
cerr<<"Usage: Femto: <IP address of the srv"<<endl;
exit(1);
}
//Create a socket for the client
if ((sockfd = socket (AF_INET, SOCK_STREAM, 0)) <0)
{
cerr<<"Problem in creating the socket"<<endl;
exit(1);
}
//Creation of the socket
memset(&srvaddr, 0, sizeof(srvaddr));
srvaddr.sin_family = AF_INET;
srvaddr.sin_addr.s_addr= inet_addr(argv[1]);
srvaddr.sin_port = htons(srv_PORT);
//Connection of the client to the socket
if (connect(sockfd, (struct sockaddr *) &srvaddr, sizeof(srvaddr))<0)
{
cerr<<"Problem in connecting to the server"<<endl;
exit(1);
}
while (fgets(buf,sizeof(buf), stdin))
{
int n;
buf[MAXLINE]='\0';
sendchars=strlen(buf);
write(sockfd,buf,sendchars);
for(recvchar=0;recvchar<sendchars;recvchar+=n)
{
n=read(sockfd,&buf[recvchar],sendchars-recvchar);
if(n<0)
{
cerr<<"Read faild"<<endl;
}
cout<< "String received from the FGW: ";
fputs(buf, stdout);
}
}
}
//server code
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include <unistd.h>
#include <iostream>
#include <sys/select.h>
#include <sys/time.h>
using namespace std;
#define MAXLINE 4096 /*max text line length*/
#define srv_PORT 3000 /*port*/
#define LISTENQ 65535
int main (int argc, char **argv)
{
int msock,ssock;
fd_set rfds;
fd_set afds;
int fd,nfds;
socklen_t client_len ;
char buf[MAXLINE];
struct sockaddr_in clientaddr, srvaddr;
if ((msock = socket (AF_INET, SOCK_STREAM, 0)) <0)
{
cerr<<"Problem in creating the socket"<<endl;
exit(1);
}
srvaddr.sin_family = AF_INET;
srvaddr.sin_addr.s_addr = htonl(INADDR_ANY);
srvaddr.sin_port = htons(srv_PORT);
bind (msock, (struct sockaddr *) &srvaddr, sizeof(srvaddr));
listen (msock, LISTENQ);
nfds=getdtablesize();
FD_ZERO(&afds);
FD_SET(msock,&afds);
while(1)
{
memcpy(&rfds,&afds,sizeof(rfds));
if(select(nfds,&rfds,(fd_set *)0,(fd_set *)0,(struct timeval * )0)<0)
{
cerr<<"Error in select";
// exit(1);
}
if(FD_ISSET(msock,&rfds))
{
//int ssock;
ssock= accept(msock,(struct sockaddr *)&clientaddr,&client_len);
if(ssock<0)
{
cerr<<"Accept error";
}
FD_SET(ssock,&afds);
}
for(fd=0;fd<nfds;++fd)
if(fd!=msock && FD_ISSET (fd,&rfds))
{
int cc;
char buf[MAXLINE];
cc=read(fd,buf,sizeof(buf));
cout<<"String received from and resent to the client:"<<endl;
puts(buf);
if(cc<0)
{
cerr<<"Read error"<<endl;
exit(1);
}
if(cc && write(fd,buf,cc)<0)
{
cerr<<"Write error"<<endl;
exit(1);
}
}
close(fd);
FD_CLR(fd,&afds);
}
}

Answer 1

buf[MAXLINE]='\0';
Is out of bounds. That may cause any error at any time.
You could declare
char buf[MAXLINE+1]