add -L limit bitrate option (#14)

src/bwlimit.c

@@ -0,0 +1,94 @@
+/* SPDX-License-Identifier: GPL-3.0-only */
+#include <errno.h>
+
+#include <bwlimit.h>
+#include <platform.h>
+
+#define timespeczerorize(ts)    \
+	do {                    \
+		ts.tv_sec = 0;  \
+		ts.tv_nsec = 0; \
+	} while (0)
+
+int bwlimit_init(struct bwlimit *bw, uint64_t bps, uint64_t win)
+{
+	if (!(bw->sem = sem_create(1)))
+		return -1;
+
+	bw->bps = bps;
+	bw->win = win; /* msec window */
+	bw->amt = (double)bps / 8 / 1000 * win; /* bytes in a window (msec) */
+	bw->credit = bw->amt;
+	timespeczerorize(bw->wstart);
+	timespeczerorize(bw->wend);
+
+	return 0;
+}
+
+#define timespecisset(ts) ((ts).tv_sec || (ts).tv_nsec)
+
+#define timespecmsadd(a, msec, r)                                \
+	do {                                                     \
+		(r).tv_sec = (a).tv_sec;                         \
+		(r).tv_nsec = (a).tv_nsec + (msec * 1000000);    \
+		if ((r).tv_nsec > 1000000000) {                  \
+			(r).tv_sec += (r.tv_nsec) / 1000000000L; \
+			(r).tv_nsec = (r.tv_nsec) % 1000000000L; \
+		}                                                \
+	} while (0)
+
+#define timespecsub(a, b, r)                             \
+	do {                                             \
+		(r).tv_sec = (a).tv_sec - (b).tv_sec;    \
+		(r).tv_nsec = (a).tv_nsec - (b).tv_nsec; \
+		if ((r).tv_nsec < 0) {                   \
+			(r).tv_sec -= 1;                 \
+			(r).tv_nsec += 1000000000;       \
+		}                                        \
+	} while (0)
+
+#define timespeccmp(a, b, expr) \
+	((a.tv_sec * 1000000000 + a.tv_nsec) expr(b.tv_sec * 1000000000 + b.tv_nsec))
+
+#include <stdio.h>
+
+int bwlimit_wait(struct bwlimit *bw, size_t nr_bytes)
+{
+	struct timespec now, end, rq, rm;
+
+	if (bw->bps == 0)
+		return 0; /* no bandwidth limit */
+
+	if (sem_wait(bw->sem) < 0)
+		return -1;
+
+	clock_gettime(CLOCK_MONOTONIC, &now);
+
+	if (!timespecisset(bw->wstart)) {
+		bw->wstart = now;
+		timespecmsadd(bw->wstart, bw->win, bw->wend);
+	}
+
+	bw->credit -= nr_bytes;
+
+	if (bw->credit < 0) {
+		/* no more credit on this window. sleep until the end
+		 * of this window + additional time for the remaining
+		 * bytes. */
+		uint64_t addition = (double)(bw->credit * -1) / (bw->bps / 8);
+		timespecmsadd(bw->wend, addition * 1000, end);
+		if (timespeccmp(end, now, >)) {
+			timespecsub(end, now, rq);
+			while (nanosleep(&rq, &rm) == -1) {
+				if (errno != EINTR)
+					break;
+				rq = rm;
+			}
+		}
+		bw->credit = bw->amt;
+		timespeczerorize(bw->wstart);
+	}
+
+	sem_post(bw->sem);
+	return 0;
+}