Daemon Process Acting as TCP Proxy Server - c

Question

I have a C program that I am trying to implement a daemon process that acts as a general TCP proxy server. I believe I have completed mostly everything correct but there is a while loop that I cannot figure out. Below is my code and I will put *** around what I am having trouble with.
Program descriptions
(1) The daemon listens for TCP connections on a specified port number.
(2) When a new client initiates a TCP connection request, the daemon accepts the request and
establishes a new TCP connection with the new client.
(a) The daemon forks a child process that is dedicated to handling the new client.
(b) The child process establishes a new TCP connection to a pre-assigned port on the actual
targeted server.
(c) The child process falls into a loop in which it acts as an intermediator exchanging data
(reading/writing or writing/reading) between the client and the targeted server.
(3) Once a child has been forked, the daemon process resumes listening for additional TCP
connections from other clients.
#ifndef unix
#define closesocket close
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdlib.h>
#include <stdio.h>
#endif
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#define PROTOPORT 5100 /* default protocol port number */
#define QLEN 6 /* size of request queue */
int visits = 0;
int argc;
char *argv[];
int main() // works as "server" side
{
struct hostent *ptrh; /* pointer to a host table entry */
struct protoent *ptrp; /* pointer to a protocol table entry */
struct sockaddr_in sad; /* structure to hold server's address */
struct sockaddr_in cad; /* structure to hold client's address */
int sd0, sd1; /* socket descriptors */
int port; /* protocol port number */
int addrlen; /* length of address */
pid_t pid;
memset((char *)&sad, 0, sizeof(sad)); /* clear sockaddr structure */
sad.sin_family = AF_INET; /* set family to Internet */
sad.sin_addr.s_addr = INADDR_ANY; /* set the local IP address(not specify, reserved */
if(argc > 1){
port = atoi(argv[1]);
}
else port = PROTOPORT; /* use the specified port number */
if (port > 0) /* test for illegal value */
sad.sin_port = htons((u_short)port);
else
{ /* print error message and exit */
fprintf(stderr,"bad port number %s\n", argv[1]);
exit(1);
}
/* Map TCP transport protocol name to protocol number */
if( ((int)(ptrp = getprotobyname("tcp"))) == 0) {
fprintf(stderr, "cannot map \"tcp\" to protocol number");
exit(1);
}
/* Create a socket */
sd0 = socket(PF_INET, SOCK_STREAM, ptrp->p_proto);
if(sd0 < 0){
fprintf(stderr, "socket creation failed\n");
exit(1);
}
/* Bind a local address to the socket */
// bind()
if (bind(sd0, (struct sockaddr *)&sad, sizeof(sad)) < 0) {
fprintf(stderr,"bind failed\n");
exit(1);
}
/* Listen at the port */
// listen()
/* Specify size of request queue */
if (listen(sd0, QLEN) < 0) {
fprintf(stderr,"listen failed\n");
exit(1);
}
/* Main server loop - accept and handle requests */
while (1)
{
// accept request
addrlen = sizeof(cad);
sd1 = accept(sd0, (struct sockaddr *)&cad, &addrlen);
// fork a process
pid = fork();
if(pid == 0) // child process
{
//close oldsocket;
close(sd0);
HandleClientConnection(sd1);
break;
}
else /*parant process */
{
close(sd1);
continue;
}
}
return 0;
}
// implement "HandleClientConnection(new socket1)" - works as "client" side
HandleClientConnection(newsocket1)
{
// general socket settings at the client side
struct hostent *ptrh; /* pointer to a host table entry */
struct protoent *ptrp; /* pointer to a protocol table entry */
struct sockaddr_in sad; /* structure to hold an IP address */
int newsocket2; /* socket descriptor */
int port; /* protocol port number */
char *host; /* pointer to host name */
int n, n2; /* number of characters read */
char buf[1000]; /* buffer for data from the server */
int i;
memset((char *)&sad,0,sizeof(sad)); /* clear sockaddr structure */
sad.sin_family = AF_INET; /* set family to Internet */
***while(1) /* get the real server's IP addr from "GET" command */
{
// read to buffer and compare, such as
if(strncmp("GET", buf[i-1], 3) == 0 || strncmp("CONNECT", buf[i-1], 7) == 0)
{
while(1)
{
//...; // read more
if(strncmp("Host", buf[i-1], 4) == 0)
{
//...;
printf("\nfound the host name.\n");
//...;
}
}
break;
}
}***
/* Convert real host name to equivalent IP address and copy to sad. */
// gethostbyname();
ptrh = gethostbyname(host);
if ( ((char *)ptrh) == NULL )
{
fprintf(stderr,"invalid host: %s\n", host);
exit(1);
}
memcpy(&sad.sin_addr, ptrh->h_addr, ptrh->h_length);
/* Map TCP transport protocol name to protocol number. */
if ( ((int)(ptrp = getprotobyname("tcp"))) == 0) {
fprintf(stderr, "cannot map \"tcp\" to protocol number");
exit(1);
}
/* Create a newsocket2. */
// socket();
newsocket2 = socket(PF_INET, SOCK_STREAM, ptrp->p_proto);
if (newsocket2 < 0) {
fprintf(stderr, "socket creation failed\n");
exit(1);
}
/* Connect the socket to the specified server. */
// connect()
if (connect(newsocket2, (struct sockaddr *)&sad, sizeof(sad)) < 0) {
fprintf(stderr,"connect failed\n");
exit(1);
}
// Repeatedly read data from client (newsocket1) and write to server' side (newsocket2)
n = recv(newsocket1, buf, sizeof(buf), 0);
while (n > 0) {
write(newsocket2,buf,n);
n = recv(newsocket1, buf, sizeof(buf), 0);
}
// Repeatedly read data from server' side (newsocket2) and write to client (newsocket1).
n2 = recv(newsocket2, buf, sizeof(buf), 0);
while (n2 > 0) {
write(newsocket1,buf,n2);
n2 = recv(newsocket2, buf, sizeof(buf), 0);
}
// Close the newsocket2
close(newsocket2);
}