From DTraceBook

httpclients.d

#!/usr/sbin/dtrace -s

#pragma D option quiet

dtrace:::BEGIN
{
	trace("Tracing... output every 10 seconds, or Ctrl-C.\n");
}

http*:::request-done
{
	@rbytes[args[0]->ci_remote] = sum(args[1]->hri_bytesread);
	@wbytes[args[0]->ci_remote] = sum(args[1]->hri_byteswritten);
}

profile:::tick-10sec,
dtrace:::END
{
	normalize(@rbytes, 1024);
	normalize(@wbytes, 1024);
	printf("\n %-32s %10s %10s\n", "HTTP CLIENT", "FROM(KB)", "TO(KB)");
	printa(" %-32s %@10d %@10d\n", @rbytes, @wbytes);
	trunc(@rbytes);
	trunc(@wbytes);
}