Add support for localtime_r() on Windows

Eshan Kelkarrequested to merge
eshankelkar/libssh-mirror-eshan:ssh_localtime into master

localtime() returns pointer to a static buffer and can hence lead to race conditions if multiple threads try access it at the same time. In cases where thread safety matters, localtime_r() should used instead.

But localtime_r() isn't available on Windows. This MR adds support for localtime_r() so that it can be used on Windows systems just like we can on POSIX systems.

Currently localtime is only used in logging to log the current time, hence even if a race condition occurs it shouldn't be much of a problem.

But the usage of localtime() in the OpenSSH certificate MR (!493 (ed0b86e8)) could be done for any arbitrary time in which case the race condition could be dangerous (Examle: A thread could overwrite another thread's time in localtime()'s static storage and the other thread could end up using the overwritten time)

Checklist

  • Commits have Signed-off-by: with name/author being identical to the commit author
  • Code modified for feature
  • Test suite updated with functionality tests
  • Test suite updated with negative tests
  • Documentation updated

Reviewer's checklist:

  • Any issues marked for closing are addressed
  • There is a test suite reasonably covering new functionality or modifications
  • Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTING.md
  • This feature/change has adequate documentation added
  • No obvious mistakes in the code
Edited by Jakub Jelen

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