Simple socket proxy for Unix

[Gaal_Dornick]

It's compiling normally. This proxy can accept the incoming connection (int server_side()) and connect to 192.168.0.2 (int client_side()), but it stops right there -> in the second read(newsockfd_bnetd, buffer, MAXMSG);

What's wrong with my code? I just want to pass the packets through my proxy. Please, help me. It's very important to me.

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

#define MAXMSG 512

int server_side(void);
int client_side(void);

int main(void)
{
	int newsockfd, newsockfd_bnetd;
	char buffer[MAXMSG];

	newsockfd_bnetd = client_side();
	newsockfd       = server_side();
	for (;;)
	{
		bzero(buffer, MAXMSG);
		read(newsockfd, buffer, MAXMSG);
		write(newsockfd_bnetd, buffer, strlen(buffer));

		bzero(buffer, MAXMSG);
		read(newsockfd_bnetd, buffer, MAXMSG);
		write(newsockfd, buffer, strlen(buffer));
	}

	close(newsockfd_bnetd);
	close(newsockfd);
	return 0;
}



int server_side(void)
{
	int sockfd, newsockfd, portno, n;
	struct sockaddr_in serv_addr;

		sockfd = socket(AF_INET, SOCK_STREAM, 0);

	if (sockfd < 0)
		printf ("ERROR opening socket");

	fcntl(sockfd, F_SETFL, fcntl(sockfd, F_GETFL, 0) | O_NONBLOCK);

	bzero(&serv_addr, sizeof(serv_addr));

	serv_addr.sin_family = AF_INET;
	serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
	serv_addr.sin_port = htons(6112);

	if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
		printf ("ERROR on binding");

	n = listen(sockfd,5);
	if (n < 0)
		printf ("ERROR on listening");

	newsockfd = accept(sockfd, (struct sockaddr *) NULL, NULL);

	while ((newsockfd = accept(sockfd, (struct sockaddr *) NULL, NULL)) < 0);
	if (newsockfd < 0)
		printf ("accept error\n");

	return (newsockfd);
}

int client_side(void)
{
	int sockfd_bnetd, newsockfd_bnetd, n;
	struct sockaddr_in servaddr_bnetd;

	if ( (sockfd_bnetd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
		printf ("socket bnetd error\n");

	fcntl(sockfd_bnetd, F_SETFL, fcntl(sockfd_bnetd, F_GETFL, 0) | O_NONBLOCK);

	bzero(&servaddr_bnetd, sizeof(servaddr_bnetd));

	servaddr_bnetd.sin_family = AF_INET;
	servaddr_bnetd.sin_port   = htons(6003); 
	if (inet_pton(AF_INET, "192.168.0.2", &servaddr_bnetd.sin_addr) <= 0)
		printf ("inet_pton error for 192.168.0.2\n");

	while ((newsockfd_bnetd = connect(sockfd_bnetd, (struct sockaddr *) &servaddr_bnetd,
 sizeof(servaddr_bnetd))) < 0);
	if (n < 0)
		printf ("connect error\n");

	return (newsockfd_bnetd);
}

[Gaal_Dornick]

I made some changes, however, the proxy stops in the second write() (it seems he can't read. May it be a problem in the second socket?) The screen shows:

Ponto 1
Ponto 2
Ponto 3!

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

#define MAXMSG 512

int server_side(void);
int client_side(void);

int main(void)
{
	int newsockfd, newsockfd_bnetd, size;
	char buffer[MAXMSG];

	newsockfd_bnetd = client_side();
	printf ("Ponto 1\n");
	newsockfd       = server_side();
	printf ("Ponto 2\n");
	for (;;)
	{
		bzero(buffer, MAXMSG);
		size = read(newsockfd, buffer, MAXMSG);
		if (size > 0)
			write(newsockfd_bnetd, buffer, size);
		else
			printf ("Size: %d\n", size);
		printf ("Ponto 3!\n");
		bzero(buffer, MAXMSG);
		size = read(newsockfd_bnetd, buffer, MAXMSG);
		printf ("Ponto 4!\n");
		if (size > 0)
			write(newsockfd, buffer, size);
		else
			printf ("Size: %d\n", size);
	}// Fim for()

	close(newsockfd_bnetd);
	close(newsockfd);
	return 0;
}



int server_side(void)
{
	int sockfd, newsockfd, portno, n;
	struct sockaddr_in serv_addr;

		sockfd = socket(AF_INET, SOCK_STREAM, 0);

	if (sockfd < 0)
		printf ("ERROR opening socket");

	fcntl(sockfd, F_SETFL, fcntl(sockfd, F_GETFL, 0) | O_NONBLOCK);

	bzero(&serv_addr, sizeof(serv_addr));

	serv_addr.sin_family = AF_INET;
	serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
	serv_addr.sin_port = htons(6112);

	if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
		printf ("ERROR on binding");

	n = listen(sockfd,5);
	if (n < 0)
		printf ("ERROR on listening");

	while ((newsockfd = accept(sockfd, (struct sockaddr *) NULL, NULL)) < 0);
	if (newsockfd < 0)
		printf ("accept error\n");

	return (newsockfd);
}

int client_side(void)
{
	int sockfd_bnetd, newsockfd_bnetd, n;
	struct sockaddr_in servaddr_bnetd;

	if ( (sockfd_bnetd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
		printf ("socket bnetd error\n");

	fcntl(sockfd_bnetd, F_SETFL, fcntl(sockfd_bnetd, F_GETFL, 0) | O_NONBLOCK);

	bzero(&servaddr_bnetd, sizeof(servaddr_bnetd));

	servaddr_bnetd.sin_family = AF_INET;
	servaddr_bnetd.sin_port   = htons(6003); // Ele ira tentar conectar-se a porta 6003
	if (inet_pton(AF_INET, "192.168.0.2", &servaddr_bnetd.sin_addr) <= 0) // no endereco 192.168.0.2
		printf ("inet_pton error for 192.168.0.2\n");

	while ((newsockfd_bnetd = connect(sockfd_bnetd, (struct sockaddr *) &servaddr_bnetd, sizeof(servaddr_bnetd))) < 0);
	if (n < 0)
		printf ("connect error\n");

	return (newsockfd_bnetd);
}

[j0nas]

Let's see, you do (in a loop):
1. read from server
2. write to client
3. read from client
4. write to server

I see two problems with your code:
a) Read may (if it works the same as recv()) return anything from 0 to MAXMSG. So how do you know you have read all data from the other end?
b). Your code assume knowledge of the application protocol being proxy'd and I don't see any protocol parsing in your code

The reason why the second read() (step 3) blocks is obvious to me: the client isn't ready for sending data yet!
The client app probably wants to read more data from the server-end--the data that is lost due to problem a) above.

There are two possible solutions:
1. Obey the application protocol being proxy'd (can be very challenging)
2. Implement a generic TCP proxy (which is protocol independant)

I don't know what your proxy is supposed to do (you aren't trying to cheat in Starcraft/Warcraft 3/Diablo I hope?), but I recommend my 2:nd solution...
/Jonas

[cypher_soundz]

2. Implement a generic TCP proxy (which is protocol independant)

How would you implement a generic TCP proxy ?

cyph