quickbrownfox quickbrownfox - 2 months ago 8
C Question

C Client Server Connection Refused

I have a laptop running windows 10 and intalled ubuntu in Oracle VM Virtualbox Machine. I have the following server and and client source code. I run the server first then the client. But it gave me a connection refused. Tried netstat -ntlp then found out that there is actually no port listening to the specific port I typed.

enter image description here

server.c

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/utsname.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<netdb.h>
#include<unistd.h>

int _GetHostName(char *buffer, int lenght);

const char MESSAGE[]="Hello, World!\n";
const int BACK_LOG=5;

int main(int argc, char *argv[]){
int serverSocket=0, on=0, port=0, status=0, childPid=0;
struct hostent *hostPtr=NULL;
char hostname[80]="";
struct sockaddr_in serverName={0};

if(2!= argc){
fprintf(stderr, "Usage : %s <port>\n", argv[0]);
exit(1);
}
port=atoi(argv[1]);
serverSocket=socket(PF_INET,SOCK_STREAM, IPPROTO_TCP);
if(-1==serverSocket){
perror("socket()");
exit(1);
}

on=1;
status=setsockopt(serverSocket, SOL_SOCKET, SO_REUSEADDR, (const char *)&on, sizeof(on));
if(-1==status){
perror("setsockopt(...,SO_REUSEADDRE,...)");
}

{
struct linger linger={0};
linger.l_onoff=1;
linger.l_linger=30;
status=setsockopt(serverSocket, SOL_SOCKET, SO_LINGER, (const char*)&linger, sizeof(linger));
if(-1==status){
perror("setsockopt(...,SO_LINGER,...)");
}
}

status=_GetHostName(hostname, sizeof(hostname));
if(-1==status){
perror("_GetHostName()");
exit(1);
}

hostPtr=gethostbyname(hostname);
if(NULL==hostPtr){
perror("gethostbyname()");
exit(1);
}

(void)memset(&serverName,0,sizeof(serverName));
(void)memcpy(&serverName.sin_addr, hostPtr->h_addr,hostPtr->h_length);

serverName.sin_family=AF_INET;
serverName.sin_port=htons(port);

status=bind(serverSocket, (struct sockaddr*)&serverName,sizeof(serverName));
if(-1==status){
perror("bind");
exit(1);
}


status=listen(serverSocket, BACK_LOG);
if(-1==status){
perror("listen()");
exit(1);
}

for(;;){
struct sockaddr_in clientName={0};
int slaveSocket, clientLength=sizeof(clientName);

(void)memset(&clientName,0,sizeof(clientName));

slaveSocket=accept(serverSocket,(struct sockaddr*)&clientName, & clientLength);
if(-1==slaveSocket){
perror("accept()");
exit(1);
}

childPid=fork();

switch(childPid){
case -1:perror("fork()");
exit(1);
case 0: close(serverSocket);
if(-1==getpeername(slaveSocket, (struct sockaddr*)&clientName, &clientLength)){
perror("getpeername()");
}else{
printf("Connection request from %s \n", inet_ntoa(clientName.sin_addr));
}

/*
Server Application specific code here
response to client
*/
write(slaveSocket,MESSAGE,strlen(MESSAGE));
close(slaveSocket);
exit(0);
default:close(slaveSocket);
}
}
return 0;
}

int _GetHostName(char *buffer,int length){
struct utsname sysname={0};
int status=0;

status=uname(&sysname);
if(-1!=status){
strncpy(buffer,sysname.nodename,length);
}
return(status);
}


client.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <string.h>

int main(int argc, char *argv[]){
int clientSocket, remotePort, status=0;
struct hostent *hostPtr=NULL;
struct sockaddr_in serverName={0};
char buffer[256]="";
char *remoteHost=NULL;

if(3!=argc){
fprintf(stderr, "Usage: %s <serverHost> <serverPort> \n",argv[0]);
exit(1);
}
remoteHost=argv[1];
remotePort=atoi(argv[2]);
clientSocket=socket(PF_INET,SOCK_STREAM,IPPROTO_TCP);
if(-1==clientSocket){
perror("socket()");
exit(1);
}

hostPtr=gethostbyname(remoteHost);
if(NULL==hostPtr){
hostPtr=gethostbyaddr(remoteHost,strlen(remoteHost), AF_INET);
if(NULL==hostPtr){
perror("Error resolving server address ");
exit(1);
}
}
serverName.sin_family=AF_INET;
serverName.sin_port=htons(remotePort);
(void)memcpy(&serverName.sin_addr,hostPtr->h_addr,hostPtr->h_length);
status=connect(clientSocket,(struct sockaddr*)&serverName,sizeof(serverName));
if(-1==status){
perror("connect()");
exit(1);
}
//CLIENT SPECIFIC HERE

while(0 < (status=read(clientSocket, buffer,sizeof(buffer)-1)))
printf("%d: %s", status, buffer);
if(-1==status)perror("read()");
close(clientSocket);
return 0;

}

Answer

Just figured it out. There is actually no problem in the code. The reason why I got an error particularly in the following line is that because just after I installed ubuntu in the virtual box, I changed the device name of the ubuntu without changing the etc/hosts.

hostPtr=gethostbyname(hostname);
if(NULL==hostPtr){
    perror("gethostbyname()");
    exit(1);
}
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