Performing sequential send and receive operation in TCP socket programming - c++

Question

I am trying to implement Socket where client send sentence to server and server replies back two integer valeus pcount and ncount. I can receive both this but first recv operation receives both values and also appends some other data to buffer.
Client.cpp
#include <fcntl.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <stdio.h>
#include <netinet/in.h>
#include <resolv.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
char *foo(char* buf)
{
char buffer[1024];
char *a='\0';
char *c=buf;
strcpy(buffer,buf);
int host_port= 1102;
char* host_name="127.0.0.1";
struct sockaddr_in my_addr;
//char buffer[1024];
int bytecount;
int buffer_len=0;
int hsock;
int * p_int;
int err;
hsock = socket(AF_INET, SOCK_STREAM, 0);
if(hsock == -1){
printf("Error initializing socket %d\n",errno);
goto FINISH;
}
p_int = (int*)malloc(sizeof(int));
*p_int = 1;
if( (setsockopt(hsock, SOL_SOCKET, SO_REUSEADDR, (char*)p_int, sizeof(int)) == -1 )||
(setsockopt(hsock, SOL_SOCKET, SO_KEEPALIVE, (char*)p_int, sizeof(int)) == -1 ) ){
printf("Error setting options %d\n",errno);
free(p_int);
goto FINISH;
}
free(p_int);
my_addr.sin_family = AF_INET ;
my_addr.sin_port = htons(host_port);
memset(&(my_addr.sin_zero), 0, 8);
my_addr.sin_addr.s_addr = inet_addr(host_name);
if( connect( hsock, (struct sockaddr*)&my_addr, sizeof(my_addr)) == -1 ){
if((err = errno) != EINPROGRESS){
fprintf(stderr, "Error connecting socket %d\n", errno);
goto FINISH;
}
}
//Now lets do the client related stuff
buffer_len = 1024;
memset(buf, '\0', buffer_len);
buf[strlen(buf)-1]='\0';
if( (bytecount=send(hsock, buffer, strlen(buffer),0))== -1){
fprintf(stderr, "Error sending data %d\n", errno);
go
to FINISH;
}
printf("Sent bytes %d\n", bytecount);
//-------
// may Needs to empty content of buffer here but dont know how to do. Tried with fflush, free(buffer) but does not work
//Two recv function which ideally recv pcount and ncount subsequently
if((bytecount = recv(hsock, buffer, buffer_len, 0))== -1){
fprintf(stderr, "Error receiving data %d\n", errno);
goto FINISH;
}
printf("Recieved bytes %d\nReceived string \"%s \n", bytecount, buffer);
//Needs to empty content of buffer here but dont know how to do. Tried with fflush, free(buffer) but does not work
if((bytecount = recv(hsock, buffer, buffer_len, 0))== -1){
fprintf(stderr, "Error receiving data %d\n", errno);
goto FINISH;
}
printf("Recieved bytes %d\nReceived string \"%s \n", bytecount, buffer);
close(hsock);
FINISH:
;
return buffer;
}
And server.cpp :
#include <fcntl.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <stdio.h>
#include <netinet/in.h>
#include <resolv.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <fcntl.h>
#include <string.h>
#include <stdlib.h>
//#include <errno.h>
#include <stdio.h>
#include <netinet/in.h>
#include <resolv.h>
#include <sys/socket.h>
#include <unistd.h>
//#include <sstream.h>
#include <pthread.h>
#include "serverFunction.cpp"
#include "serverFunction2.cpp"
#include <iostream>
#include <sstream>
#include <cstdio>
using namespace std;
void *SocketHandler(void *);
int main(int argv, char **argc)
{
int host_port = 1102;
char buf[20];
int k;
struct sockaddr_in my_addr;
int hsock;
int *p_int;
int err;
socklen_t addr_size = 0;
int *csock;
sockaddr_in sadr;
pthread_t thread_id = 0;
hsock = socket(AF_INET, SOCK_STREAM, 0);
if (hsock == -1) {
printf("Error initializing socket %dn", errno);
goto FINISH;
}
p_int = (int *) malloc(sizeof(int));
*p_int = 1;
if ((setsockopt(hsock, SOL_SOCKET, SO_REUSEADDR, (char *) p_int, sizeof(int)) == -1) || (setsockopt(hsock, SOL_SOCKET, SO_KEEPALIVE, (char *) p_int, sizeof(int)) == -1)) {
printf("Error setting options %dn", errno);
free(p_int);
goto FINISH;
}
free(p_int);
my_addr.sin_family = AF_INET;
my_addr.sin_port = htons(host_port);
memset(&(my_addr.sin_zero), 0, 8);
my_addr.sin_addr.s_addr = INADDR_ANY;
if (bind(hsock, (sockaddr *) & my_addr, sizeof(my_addr)) == -1) {
fprintf(stderr, "Error binding to socket, make sure nothing else is listening on this port %dn", errno);
goto FINISH;
}
if (listen(hsock, 10) == -1) {
fprintf(stderr, "Error listening %dn", errno);
goto FINISH;
}
//Now lets do the server stuff
addr_size = sizeof(sockaddr_in);
while (true) {
printf("waiting for a connectionn\n");
csock = (int *) malloc(sizeof(int));
if ((*csock = accept(hsock, (sockaddr *) & sadr, &addr_size)) != -1) {
printf("---------------------nReceived connection from %s\n", inet_ntoa(sadr.sin_addr));
pthread_create(&thread_id, 0, &SocketHandler, (void *) csock);
pthread_detach(thread_id);
} else {
fprintf(stderr, "Error accepting %dn", errno);
}
}
FINISH:
;
}
void *SocketHandler(void *lp)
{
int result=0;
//std::stringstream ss;
int *csock = (int *) lp;
char buf[20];
int k;
// char *target="my name is khan";
char *str;
char *str2;
int pcount = 0, ncount = 0;
char buffer[1024];
int buffer_len = 1024;
int bytecount;
int i = 0,t=0,q=0;
int j = 0;
char *ch[50] = { 0 }; /* stores references to 50 words. */
char *ch2[50] = { 0 };
char *word = strtok(buffer, " ");
char *word2 = strtok(buffer, " ");
char *portstring1=(char *)malloc(sizeof(buffer));
char *portstring2=(char *)malloc(sizeof(buffer));
memset(buffer, 0, buffer_len);
if ((bytecount = recv(*csock, buffer, buffer_len, 0)) == -1) {
fprintf(stderr, "Error receiving data %d \n", errno);
goto FINISH;
}
printf("Received bytes %d \n Received string %s \n ", bytecount, buffer);
/* stores references to 50 words. */
word = strtok(buffer, " ");
while ((NULL != word) && (50 > i)) {
ch[i] = strdup(word);
//printf("%s n", ch[i]);
str = BoyerMoore_positive(ch[i], strlen(ch[i]) - 1);
str2= BoyerMoore_negative(ch[i], strlen(ch[i]) - 1);
if (str == NULL)
t++;
else {
printf("%s \n", ch[i]);
// puts("true");
pcount += 1;
printf("Positive count is: %d \n",pcount);
}
if(str2== NULL)
q++;
else {
printf("%s \n", ch[i]);
// puts("true");
ncount += 1;
printf("Nagative count is: %d \n",ncount);
}
i++;
word = strtok(NULL, " ");
}
//I want to send pcount and ncount values to client
**sprintf(portstring1, "%d", pcount);
if ((bytecount = send(*csock, portstring1, 1, 0)) == -1) {
fprintf(stderr, "Error sending data %d\n", errno);
goto FINISH;
}
sprintf(portstring2, "%d", ncount);
if ((bytecount = send(*csock, portstring2, strlen(portstring2), 0)) == -1) {
fprintf(stderr, "Error sending data %d\n", errno);
goto FINISH;
}**
FINISH:
free(csock);
return 0;
}
I receive output like this:
Enter sentence to send to the server (press enter)
critic worst nice
Sent bytes 18
Recieved bytes 2
Received string 12itic worst nice //Here there should be only 1 2. Why 'itic ..' gets appended. And why 1 and 2 both does not get printed one after another

Answer 1

You forgot to design and implement a protocol. Network communication doesn't work by magic. If you have a notion of an application-level message, you have to write code to send and receive application-level messages. You haven't done this, so of course it won't happen.
Also:
printf("Received bytes %d \n Received string %s \n ", bytecount, buffer);
The %s format specifier is only for C-style strings. It's not suitable for arbitrary data. How would it know how many bytes to print?

Answer 2

The recv function does not add a nul character to terminate the received string. You have to add it yourself, like this:
if((bytecount = recv(hsock, buffer, buffer_len-1, 0))== -1){
fprintf(stderr, "Error receiving data %d\n", errno);
goto FINISH;
}
buffer[bytecount]=0;
Notice the -1 in buffer len, to make sure there's room for the nul character.

Answer 3

#Joni and David- Thanks for your support!
Problem solved:
at sender:
int ar[2];
if ((bytecount = send(*csock, (char *)ar, 2 *sizeof(int), 0)) == -1) { // Here we cant send lenth-1. It consider exact
fprintf(stderr, "Error sending data %d\n", errno);
goto FINISH;
}
at receiver side:
if((bytecount = recv(hsock, ar, 2 * sizeof(int), 0))== -1){
fprintf(stderr, "Error receiving data %d\n", errno);
goto FINISH;
}
for(k=0;k<2;k++)
{
printf("count is :%d",ar[k]);
}
just took and array, Now I can send any receive any numbers of values! It's so easy!