This allows the function to be used both with a double timestamp or a pointer
to a tm struct. With this, a similar implementation inside the tests can simply
use our regular function.
So far, the return value of strftime() was simply ignored and the output buffer
passed to the icinga::String constructor. However, there are error conditions
where strftime() returns 0 to signal an error, like if the buffer was too small
for the output. In that case, there's no guarantee on the buffer contents and
reading it can result in undefined behavior. Unfortunately, returning 0 can
also indicate success and strftime() doesn't set errno, so there's no reliable
way to distinguish both situations. Thus, the implementation now returns the
empty string in both cases.
I attempted to use std::put_time() at first as that allows for better error
handling, however, there were problems with the implementation on Windows (see
inline comment), so I put that plan on hold at left strftime() there for the
time being.
The previous implementation actually had undefined behavior when called with a
double that can't be represented as time_t. With boost::numeric_cast, there's a
convenient cast available that avoids this and throws an exceptions on
overflow.
It's undefined behavior ([0], where the implicit conversion rule comes into
play because the C-style cast uses static_cast [1] which in turn uses the
imlicit conversion as per rule 5 of [2]):
> A prvalue of floating-point type can be converted to a prvalue of any integer
> type. The fractional part is truncated, that is, the fractional part is
> discarded.
>
> * If the truncated value cannot fit into the destination type, the behavior
> is undefined (even when the destination type is unsigned, modulo arithmetic
> does not apply).
Note that on Linux amd64, the undefined behavior typically manifests itself in
the result being the minimal value of time_t which then results in localtime_r
failing with EOVERFLOW.
[0]: https://en.cppreference.com/w/cpp/language/implicit_conversion#Floating.E2.80.93integral_conversions
[1]: https://en.cppreference.com/w/cpp/language/explicit_cast
[2]: https://en.cppreference.com/w/cpp/language/static_cast
A day specification like "monday -1" refers to the last Monday of the month.
However, there was an off by one if the first day of the next month is the same
day of the week, i.e. a Monday in this example.
LegacyTimePeriod::FindNthWeekday() picks a day to start the search for the day
in question. When given a negative n to search for the n-th last day, it
wrongly used the first day of the following month as the start and counted it
as if it was within the current month. This resulted in a 1/7 chance that the
result was one week too late.
This is fixed by using the last day of the current month instead.
The old validation regex matched if the name consists only of invalid
character, not that it does not contain them, i.e. something like "foo/bar" was
considered valid.
This commit replaces the regex with a check that all characters in the name are
allowed characters.
The old test looked really strange where it reads 3 into a Value and then
checks that it's not 3. However, what's going on there is that operator>> for
Value actually always reads a String, so instead check for what v should be,
not what it should not be.
