/* I wrote this program to test how feasible it was to fake a slow
* network connection by twiddling SO_RCVBUF. The idea is to read
* data from the socket relatively slowly, but keep SO_RCVBUF small
* from the beginning of the connection to make sure that the remote
* side's TCP is aware that (a) you really haven't read those 24K of
* data their application program has written to its output buffer, but
* (b) you are reading them, just very slowly, so don't hang up. It shows
* that it works reasonably well, at least on Linux 2.4.
*
* In a FoRKpost in 2001, Dave Long suggested that this was a possible
* alternative handling for things like the DUL and RBL --- rather
* than simply rejecting mail from blacklisted hosts, you could simply
* accept it very slowly, making you costly to deliver spam to.
*
* On my Linux 2.4 box, attempting to set SO_RCVBUF to 1 actually sets
* it to 256, which is probably good enough; the connection sockets do
* indeed inherit SO_RCVBUF from their server socket; and 256 bytes of
* buffer space actually means 96 or 192 bytes of TCP data, which
* tcpdump says is reflected in the window sizes advertised in TCP,
* even as early as the SYN-ACK packet when the connection opens. */
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdarg.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
void err(char *format, ...) {
va_list x;
va_start(x, format);
vfprintf(stderr, format, x);
if (errno) {fprintf(stderr, ": "); perror(""); }
va_end(x);
exit(1);
}
int main(int argc, char **argv) {
int serversocket, connectionsocket;
struct sockaddr_in me;
struct sockaddr_in them;
int themlen;
int one = 1;
int bufsiz;
#define charbufsiz 4096
char charbuf[charbufsiz];
int recvsiz;
int fucking_triplicate;
serversocket = socket(PF_INET, SOCK_STREAM, 0);
if (serversocket < 0) err("socket");
if (setsockopt(serversocket, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one))<0)
err("setsockopt with SO_REUSEADDR");
if (setsockopt(serversocket, SOL_SOCKET, SO_RCVBUF, &one, sizeof(one))<0)
err("setsockopt with SO_RCVBUF");
fucking_triplicate = sizeof(bufsiz);
if (getsockopt(serversocket, SOL_SOCKET, SO_RCVBUF, &bufsiz,
&fucking_triplicate)
< 0)
err("getsockopt with SO_RCVBUF");
printf("Receive buffer size on server socket is %d bytes\n", bufsiz);
me.sin_family = AF_INET;
me.sin_port = htons(5100); /* "sloo" -- slow */
me.sin_addr.s_addr = INADDR_ANY;
if (bind(serversocket, &me, sizeof(me)) < 0) err("bind");
if (listen(serversocket, 5) < 0) err("listen");
connectionsocket = accept(serversocket, &them, &themlen);
fucking_triplicate = sizeof(bufsiz);
if (getsockopt(connectionsocket, SOL_SOCKET, SO_RCVBUF, &bufsiz,
&fucking_triplicate)
< 0)
err("getsockopt with SO_RCVBUF on connection socket");
printf("Receive buffer size on connection socket is %d bytes\n", bufsiz);
for (;;) {
recvsiz = recv(connectionsocket, charbuf, charbufsiz, 0);
if (recvsiz == 0) {
printf("Received end of file on socket; exiting.\n");
exit(0);
}
printf("%d bytes\n", recvsiz);
sleep(1);
}
}
