Client hangs when tries to read back from server tcp - c

Question

i am trying to create a simple tcp server-client. My programm works fine if client sends data to server but when server tries to answer back the whole connection hangs. I am using write()/read() functions .
Server code :
#include <stdio.h>
#include <stdlib.h>
#include <netdb.h>
#include <netinet/in.h>
#include <string.h>
#include <stdbool.h>
#define SIZE 700000000
///////////////////////////////////////////////////////////////////////////
int main( int argc, char *argv[] ) {
int sockfd, newsockfd, portno, clilen;
char buffer[256];
struct sockaddr_in serv_addr, cli_addr;
int n;
/* First call to socket() function */
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0) {
perror("ERROR opening socket");
exit(1);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
portno = 5001;
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = INADDR_ANY;
serv_addr.sin_port = htons(portno);
if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) {
perror("ERROR on binding");
exit(1);
}
listen(sockfd, 10);
clilen = sizeof(cli_addr);
/* Accept actual connection from the client */
newsockfd = accept(sockfd, (struct sockaddr *)&cli_addr, &clilen);
if (newsockfd < 0) {
perror("ERROR on accept");
exit(1);
}
bzero(buffer, 255);
int readbyte = 0;
do {
readbyte = read(newsockfd, buffer, 1024);
if (readbyte < 0)
{
perror("ERROR on reading socket!");
break;
}
if (readbyte > 0)
{
//printf("Here is the message: %s\n",buffer);
}
} while (readbyte > 0); /* until EOF */
int writen = write(newsockfd, "I received your message", strlen("I received your message") + 1);
if (writen<0){
perror("Error");
}
//debug();
return 0;
}
Client code:
#include <stdio.h>
#include <stdlib.h>
#include <netdb.h>
#include <netinet/in.h>
#include <string.h>
//////////////////////////////////////////////////////////////////
int main(int argc, char *argv[]) {
int sockfd, portno, n;
struct sockaddr_in serv_addr;
struct hostent *server;
int mode;
char *code;
char buffer[256];
char *uptr = buffer;
int i;
if (argc < 3) {
fprintf(stderr, "Use: %s [hostname] [port] [args]\n", argv[1]);
exit(0);
}
portno = atoi(argv[2]);
/* Create a socket point */
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0) {
perror("ERROR opening socket");
exit(1);
}
server = gethostbyname(argv[1]);
if (server == NULL) {
fprintf(stderr, "ERROR, no such host\n");
exit(0);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *)server->h_addr, (char *)&serv_addr.sin_addr.s_addr, server->h_length);
serv_addr.sin_port = htons(portno);
int sock_et = connect(sockfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr);
/* Now connect to the server */
if (sock_et < 0) {
perror("ERROR connecting");
exit(1);
}
/* some code... */
while (len > 0) {
int writen = write(sockfd, buf, len + 1);
if (writen < 0)
{
printf("Error writting to socket!\n");
break;
}
len -= writen;
buf += writen; /* tricky pointer arythmetic */
}
printf("Finished writing to server\n");
bzero(buffer, 256);
int readbyte;
do {
readbyte = read(sock_et, buffer, 1024);
if (readbyte < 0)
{
perror("ERROR on reading socket!");
break;
}
if (readbyte > 0)
{
//printf("Here is the message: %s\n",buffer);
}
} while (readbyte > 0); /* until EOF */
printf("%s\n",buffer );
close(sockfd);
return 0;
}
Any help would be appreciated! Thanks!

Answer 1

Your client code doesn't compile
You are never going to get a 0 (EOF) from read while the socket is open (in either the client or server) -- so just add a break after a successful read for now.
You are not closing the socket in the server
In the client, you need to read from sockfd, not sock_et
There are probably other issues. It looks like you are trying to use client.c/server.c from here: http://www.linuxhowtos.org/C_C++/socket.htm
If I use those files, it works fine. So start over from them and apply your changes more carefully.