Simple socket programming code working - c

Question

I am trying to study and understand BSD socket programming using these simple example C++ code for TCP-IP server and client. I have read the standard APIs like socket(), bind(), listen(), accept() and read/recv() and even got code below to compile on g++/Linux.
What I want to do is see it working in real-life, I mean run the server code, and then connect to it using the client and send data from client-to-server and vice-a-versa and verify the data received. All this within two linux boxes(Ubuntu) in my same network segment. I have private IPv4 addresses given to those two Linux machines.
What should be the setup to achieve this and what code changes in the server and client code below, would be needed to achieve this over the network setup described above? I want to really see it working over network in real time?
Also any further pointers to code, blog articles to study hands-on socket programming/network programming would help.
//TCP SERVER
#include<sys/socket.h>
#include<netinet/in.h>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include <arpa/inet.h>
//#include <fcntl.h>
#include <unistd.h>
main()
{
char buf[100];
socklen_t len;
int k,sock_desc,temp_sock_desc;
struct sockaddr_in client,server;
memset(&client,0,sizeof(client));
memset(&server,0,sizeof(server));
sock_desc = socket(AF_INET,SOCK_STREAM,0);
server.sin_family = AF_INET; server.sin_addr.s_addr = inet_addr("127.0.0.1");
server.sin_port = 7777;
k = bind(sock_desc,(struct sockaddr*)&server,sizeof(server));
k = listen(sock_desc,20); len = sizeof(client);
temp_sock_desc = accept(sock_desc,(struct sockaddr*)&client,&len);
while(1)
{
k = recv(temp_sock_desc,buf,100,0);
if(strcmp(buf,"exit")==0)
break;
if(k>0)
printf("%s",buf);
} close(sock_desc);
close(temp_sock_desc);
return 0;
}
//TCP CLIENT
#include<sys/socket.h>
#include<netinet/in.h>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include <arpa/inet.h>
//#include <fcntl.h>
#include <unistd.h>
main()
{
char buf[100];
struct sockaddr_in client;
int sock_desc,k;
sock_desc = socket(AF_INET,SOCK_STREAM,0);
memset(&client,0,sizeof(client));
client.sin_family = AF_INET;
client.sin_addr.s_addr = inet_addr("127.0.0.1");
client.sin_port = 7777;
k = connect(sock_desc,(struct sockaddr*)&client,sizeof(client));
while(1)
{
gets(buf);
k = send(sock_desc,buf,100,0);
if(strcmp(buf,"exit")==0)
break;
}
close(sock_desc);
return 0;
}

Answer 1

Add some error handling to your code, that will likely reveil something, eg:
Server:
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <arpa/inet.h>
//#include <fcntl.h>
#include <unistd.h>
main()
{
int sock_desc = socket(AF_INET, SOCK_STREAM, 0);
if (sock_desc == -1)
{
printf("cannot create socket!\n");
return 0;
}
struct sockaddr_in server;
memset(&server, 0, sizeof(server));
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons(7777);
if (bind(sock_desc, (struct sockaddr*)&server, sizeof(server)) != 0)
{
printf("cannot bind socket!\n");
close(sock_desc);
return 0;
}
if (listen(sock_desc, 20) != 0)
{
printf("cannot listen on socket!\n");
close(sock_desc);
return 0;
}
struct sockaddr_in client;
memset(&client, 0, sizeof(client));
socklen_t len = sizeof(client);
int temp_sock_desc = accept(sock_desc, (struct sockaddr*)&client, &len);
if (temp_sock_desc == -1)
{
printf("cannot accept client!\n");
close(sock_desc);
return 0;
}
char buf[100];
int k;
while(1)
{
k = recv(temp_sock_desc, buf, 100, 0);
if (recv == -1)
{
printf("\ncannot read from client!\n");
break;
}
if (recv == 0)
{
printf("\nclient disconnected.\n");
break;
}
if (k > 0)
printf("%*.*s", k, k, buf);
if (strcmp(buf, "exit") == 0)
break;
}
close(temp_sock_desc);
close(sock_desc);
printf("server disconnected\n");
return 0;
}
Client:
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <arpa/inet.h>
//#include <fcntl.h>
#include <unistd.h>
main()
{
int sock_desc = socket(AF_INET, SOCK_STREAM, 0);
if (sock_desc == -1)
{
printf("cannot create socket!\n");
return 0;
}
struct sockaddr_in client;
memset(&client, 0, sizeof(client));
client.sin_family = AF_INET;
client.sin_addr.s_addr = inet_addr("127.0.0.1");
client.sin_port = htons(7777);
if (connect(sock_desc, (struct sockaddr*)&client, sizeof(client)) != 0)
{
printf("cannot connect to server!\n");
close(sock_desc);
}
char buf[100];
char c = '\n';
char *p_buf;
int k, len;
while(1)
{
gets(buf);
len = strlen(buf);
p_buf = buf;
while (len > 0)
{
k = send(sock_desc, p_buf, len, 0);
if (k == -1)
{
printf("cannot write to server!\n");
break;
}
p_buf += k;
len -= k;
}
k = send(sock_desc, &c, 1, 0);
if (k == -1)
{
printf("cannot write to server!\n");
break;
}
if (strcmp(buf, "exit") == 0)
break;
}
close(sock_desc);
printf("client disconnected\n");
return 0;
}

Answer 2

On the server side you will need to change the address 127.0.0.1 to 0.0.0.0 to enable connections from anywhere. You can also use telnet instead of your client code and therefore check that the server is working as expected. Also investigate if you have the snoop command on your variety of Linux.
On the client side you need to use the IP address of the server machine

Answer 3

You need to make the following changes.
Port number - use htons i.e.
server - server.sin_port = htons(7777);
client - client.sin_port = htons(7777);
Server - get it to accept from any address - i.e. server.sin_addr.s_addr = INADDR_ANY;
Hope that helps somewhat

Answer 4

it should be like this.
if (connect(sock_desc, (struct sockaddr*)&client, sizeof(client)) != 0)