Use a well-defined `.invalid` top-level domain instead of assuming there
is no `.png` top-level domain. Extend the timeout of this one case to
30 seconds to give DNS lookups a chance to fail instead of timing out.
Because the PASS_REGULAR_EXPRESSION test property is set,
the exit code of the test is ignored, so we can't just rely on using
message(SEND_ERROR) or the command itself failing. We have to
add an explicit error message for all unexpected status codes
and check for such messages with a FAIL_REGULAR_EXPRESSION.
We do not actually need to contact any real http servers.
The one attempt we make is to an intentionally bad domain name.
Unset any proxy configuration that may change behavior.
On a busy machine running many tests in parallel the `file(DOWNLOAD)`
step can take longer than 2 seconds even to simply copy a file.
Raise the timeout to 4 seconds to reduce spurious failures.
Since upstream curl commit curl-7_52_0~131 (URL-parser: for
file://[host]/ URLs, the [host] must be localhost, 2016-11-11) we can no
longer use URLs of the form `file://c:/...` on Windows. These worked
only accidentally before. Use `file:///c:/...` instead.
Make the EXPECTED_HASH option take only a single value instead of two to
avoid handling sub-keyword arguments. This is also consistent with
URL_HASH in ExternalProject.
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.
