local_tzoffset: detect errors from tm_to_time_t

When we want to know the local timezone offset at a given
timestamp, we compute it by asking for localtime() at the
given time, and comparing the offset to GMT at that time.
However, there's some juggling between time_t and "struct
tm" which happens, which involves calling our own
tm_to_time_t().

If that function returns an error (e.g., because it only
handles dates up to the year 2099), it returns "-1", which
we treat as a time_t, and is clearly bogus, leading to
bizarre timestamps (that seem to always adjust the time back
to (time_t)(uint32_t)-1, in the year 2106).

It's not a good idea for local_tzoffset() to simply die
here; it would make it hard to run "git log" on a repository
with funny timestamps. Instead, let's just treat such cases
as "zero offset".

Reported-by: Norbert Kiesel <nkiesel@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/date.c b/date.c
index 7c9f76998ac7a00fb5f8781dd8e460f899edbfac..4c7aa9ba853c0924d49f4b8c2cc06826fe08956c 100644 (file)
--- a/date.c
+++ b/date.c
@@ -74,6 +74,8 @@ static int local_tzoffset(unsigned long time)
        localtime_r(&t, &tm);
        t_local = tm_to_time_t(&tm);
 
+       if (t_local == -1)
+               return 0; /* error; just use +0000 */
        if (t_local < t) {
                eastwest = -1;
                offset = t - t_local;

diff --git a/t/t0006-date.sh b/t/t0006-date.sh
index 57033ddcd175a9daf54da618141e1fdc93799c7b..04ce53509c57ad348d3adccf7f566396d69787b0 100755 (executable)
--- a/t/t0006-date.sh
+++ b/t/t0006-date.sh
@@ -48,6 +48,11 @@ check_show default "$TIME" 'Wed Jun 15 16:13:20 2016 +0200'
 check_show raw "$TIME" '1466000000 +0200'
 check_show iso-local "$TIME" '2016-06-15 14:13:20 +0000'
 
+# arbitrary time absurdly far in the future
+FUTURE="5758122296 -0400"
+check_show iso       "$FUTURE" "2152-06-19 18:24:56 -0400"
+check_show iso-local "$FUTURE" "2152-06-19 22:24:56 +0000"
+
 check_parse() {
        echo "$1 -> $2" >expect
        test_expect_${4:-success} "parse date ($1${3:+ TZ=$3})" "