/* ratelimit.c   by Michael Thorpe   2020-08-06 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/time.h>

#define BUF_SIZE 2048	/* (BUF_SIZE+1)*1000000-1 must fit in a signed long */
#undef BUF_SIZE
#define BUF_SIZE 1024	/* This can yield better packetization on ethernet */
char buf[BUF_SIZE];

int main(int argc,char **argv) {
	struct timeval a,b;
	int i,r=0;
	size_t k;

	if(argc==2)
		r=atoi(argv[1]);
	if(argc != 2 || r<=0) {
		fprintf(stderr,"usage: ratelimit <bytes/sec>\n");
		return(1);
	}
	if(gettimeofday(&a,0)) {
		perror("gettimeofday");
		return(-1);
	}
	do {
		k=read(0,buf,BUF_SIZE);
		if(k==0)
			return(0);
		if(k==-1) {
			perror("read");
			return(-1);
		}
		if(0>=write(1,buf,k)) {
			perror("write");
			return(-1);
		}
		if(gettimeofday(&b,0)) {
			perror("gettimeofday");
			return(-1);
		}
		a.tv_usec+=1000000*k/r;
		i=a.tv_usec/1000000;
		a.tv_sec+=i;
		a.tv_usec-=1000000*i;
		if(a.tv_sec<b.tv_sec || (a.tv_sec==b.tv_sec && a.tv_usec<b.tv_usec))
			memcpy(&a,&b,sizeof(struct timeval));
		else
			usleep(1000000*(a.tv_sec-b.tv_sec)+a.tv_usec-b.tv_usec);
	} while(1);
	return(0);
}