Improve FILE(DOWNLOAD ...):
- Add percent complete progress output to the FILE DOWNLOAD
command. This progress output is off by default to
preserve existing behavior. To turn it on, pass
SHOW_PROGRESS as an argument.
- Add EXPECTED_MD5 argument. Verify that the downloaded
file has the expected md5 sum after download is complete.
- Add documentation for SHOW_PROGRESS and EXPECTED_MD5.
When the destination file exists already and has the
expected md5 sum, then do not bother re-downloading
the file. ("Short circuit" return.)
Also, add a test that checks for the status output
indicating that the short circuit behavior is actually
occurring. Use a binary file for the test so that the
md5 sum is guaranteed to be the same on all platforms
regardless of "shifting text file line ending" issues.
Improve ExternalProject:
- Add argument URL_MD5.
- Add verify step that compares md5 sum of .tar.gz file
before extracting it.
- Add md5 check to download step, too, to prevent
unnecessary downloads.
- Emit a warning message when a file is not verified.
Indicate that the file may be corrupt or that no
checksum was specified.
David Cole