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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 16:18:56 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 16:18:56 +0000
commitb7c15c31519dc44c1f691e0466badd556ffe9423 (patch)
treef944572f288bab482a615e09af627d9a2b6727d8 /src/util/sane_time.c
parentInitial commit. (diff)
downloadpostfix-b7c15c31519dc44c1f691e0466badd556ffe9423.tar.xz
postfix-b7c15c31519dc44c1f691e0466badd556ffe9423.zip
Adding upstream version 3.7.10.upstream/3.7.10
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+/*++
+/* NAME
+/* sane_time 3
+/* SUMMARY
+/* time(2) with backward time jump protection.
+/* SYNOPSIS
+/* #include <sane_time.h>
+/*
+/* time_t sane_time(void)
+/*
+/* DESCRIPTION
+/* This module provides time(2) like call for applications
+/* which need monotonically increasing time function rather
+/* than the real exact time. It eliminates the need for various
+/* workarounds all over the application which would handle
+/* potential problems if time suddenly jumps backward.
+/* Instead we choose to deal with this problem inside this
+/* module and let the application focus on its own tasks.
+/*
+/* sane_time() returns the current timestamp as obtained from
+/* time(2) call, at least most of the time. In case this routine
+/* detects that time has jumped backward, it keeps returning
+/* whatever timestamp it returned before, until this timestamp
+/* and the time(2) timestamp become synchronized again.
+/* Additionally, the returned timestamp is slowly increased to
+/* prevent the faked clock from freezing for too long.
+/* SEE ALSO
+/* time(2) get current time
+/* DIAGNOSTICS
+/* Warning message is logged if backward time jump is detected.
+/* LICENSE
+/* .ad
+/* .fi
+/* The Secure Mailer license must be distributed with this software.
+/* AUTHOR(S)
+/* Patrik Rak
+/* Modra 6
+/* 155 00, Prague, Czech Republic
+/*--*/
+
+/* System library. */
+
+#include <sys_defs.h>
+
+/* Utility library. */
+
+#include <msg.h>
+
+/* Application-specific. */
+
+#include "sane_time.h"
+
+/*
+ * How many times shall we slow down the real clock when recovering from
+ * time jump.
+ */
+#define SLEW_FACTOR 2
+
+/* sane_time - get current time, protected against time warping */
+
+time_t sane_time(void)
+{
+ time_t now;
+ static time_t last_time, last_real;
+ long delta;
+ static int fraction;
+ static int warned;
+
+ now = time((time_t *) 0);
+
+ if ((delta = now - last_time) < 0 && last_time != 0) {
+ if ((delta = now - last_real) < 0) {
+ msg_warn("%sbackward time jump detected -- slewing clock",
+ warned++ ? "another " : "");
+ } else {
+ delta += fraction;
+ last_time += delta / SLEW_FACTOR;
+ fraction = delta % SLEW_FACTOR;
+ }
+ } else {
+ if (warned) {
+ warned = 0;
+ msg_warn("backward time jump recovered -- back to normality");
+ fraction = 0;
+ }
+ last_time = now;
+ }
+ last_real = now;
+
+ return (last_time);
+}
+
+#ifdef TEST
+
+ /*
+ * Proof-of-concept test program. Repeatedly print current system time and
+ * time returned by sane_time(). Meanwhile, try stepping your system clock
+ * back and forth to see what happens.
+ */
+
+#include <stdlib.h>
+#include <msg_vstream.h>
+#include <iostuff.h> /* doze() */
+
+int main(int argc, char **argv)
+{
+ int delay = 1000000;
+ time_t now;
+
+ msg_vstream_init(argv[0], VSTREAM_ERR);
+
+ if (argc == 2 && (delay = atol(argv[1]) * 1000) > 0)
+ /* void */ ;
+ else if (argc != 1)
+ msg_fatal("usage: %s [delay in ms (default 1 second)]", argv[0]);
+
+ for (;;) {
+ now = time((time_t *) 0);
+ vstream_printf("real: %s", ctime(&now));
+ now = sane_time();
+ vstream_printf("fake: %s\n", ctime(&now));
+ vstream_fflush(VSTREAM_OUT);
+ doze(delay);
+ }
+}
+
+#endif