Unuseful warnings with --xattr/--remote-time + --output /dev/null

[vszakats]

When using the pattern curl <URL> --output /dev/null (typically in conjunction with --write-out '%{<format>}' to read the <format> value without actually retrieving the URL content), while having --xattr and/or --remote-time options enabled (e.g. via .curlrc or a curl alias), the warnings below may (remote time only when the server returns a Last-Modified: header) appear on stderr, respectively:

Warning: Error setting extended attributes: Operation not permitted
Failed to set filetime <unixtime> on outfile: Operation not permitted

Example (for *nix platforms):

$ curl --xattr --remote-time --output /dev/null https://example.org/ --write-out '%{content_type}'`

Actual console output:

Warning: Error setting extended attributes: Operation not permitted
Failed to set filetime <unixtime> on outfile: Operation not permitted
text/html; charset=UTF-8

Expected console output:

text/html; charset=UTF-8

An inconvenience rather than a bug per se, yet I think it'd be an improvement to try mitigating this, either by suppressing the warning when a non-file output is used, or by bringing --remote-time behavior closer to --xattr and omit the warning if the --silent option is used.

[bagder]

This is file output for all curl knows...

[vszakats]

Indeed, that's the difficult part. This specific value can be hard-coded (which is rather unelegant), but I was wondering if there is a better (and possibly platform-agnostic) option.

Many thanks for your quick PR, and if I read it correctly, this will also silence it like it is done with --xattr, which I think should resolve this nicely. Definitely LGTM.

[bagder]

Yes, the PR will make the time-setting error message truly respect --silent as well, which of course was a bug to begin with.