Detecting that a file is not found or has no appropriate date information

[rpetrusha]

Detecting that a file is not found or has no appropriate date information

General

The following methods all return 12:00:00.00000 January 1, 1601 as the date if the file represented by a FileSystemInfo object does not exit or if the operating system cannot supply the requested information:

• FileSystemInfo.CreationTime
• FileSystemInfo.CreationTimeUtc
• FileSystemInfo.LastWriteTime
• FileSystemInfo.LastWriteTimeUtc

In PR #4453, @BillWagner raised the question of how to detect this missing/incomplete information -- whether there's a constant available, or whether the returned date should be compared with some date. Since the .NET Framework does not include a predefined constant for this purpose, detection requires comparison with a specific date. The best alternative is probably to implement a utility method that converts the returned date back to UTC and tests whether the result is less than or equal to 12:00:00.00000 January 1, 1601. It's also possible to avoid the UTC conversion and simply pick some arbitrary date after that, since presumably no file should legitimately have a creation/last write time in the seventeenth century.

//cc @BillWagner @JeremyKuhne

[JeremyKuhne]

When we can't determine a value it is returned as .FromFileTime(0). You can actually have time stamps of this value on Windows. Unix times, however don't go back before 1970-01-01 00:00:00 +0000 (UTC).

[mairaw]

Lowered the priority during triage,