Remove nul chars from string before parsing to numerical values

[KowalczykBartek]

Looks like this change 353812f is causing following error (when SimpleConsumer is being run) - at least on OSX

librdkafka validated config value is valid u64: ParseIntError { kind: InvalidDigit }

That is because rd_kafka_conf_get returns null terminated string,

// Allocate a buffer of that size and call again to get the actual
// string.
let mut buf = vec![0_u8; size];
let res = unsafe {
    rdsys::rd_kafka_conf_get(
        self.ptr(),
        key_c.as_ptr(),
        buf.as_mut_ptr() as *mut c_char,
        &mut size,
    )
};

ends with buf equal:

[51, 48, 48, 48, 48, 48, 0];

I guess reverting this change will cause issues on windows, so maybe my PR will be good enough to handle this.

This pr should also fix this case #683

[chklauser]

Just as a heads up for maintainers: there seem to be 3 PRs for this issue

1. Use CStr::from_bytes_until_nul to read rdkafka config #671
2. Remove nul chars from string before parsing to numerical values #688 (this PR)
3. Fix null characters in configuration values #691

[mati865]

This PR feels like a workaround that is doomed to break in the future. Aby chance to revisit #671?

[fede1024]

I agree that #671 is a better solution. @mati865 any chance you could file a PR with from_bytes_until_nul? #671 has a few other changes that are conflicting with the master branch. Thanks

[mati865]

I'll wait for @chklauser to reply if he wants to revive his PR, otherwise I'll rebase hit work.

[chklauser]

I have rebased the change as #705 (forgot to re-open before pushing the new branch). With the unrelated bump of MSRV to 1.70 we can now just use CStr::from_bytes_until_nul 🥳

Thanks for tagging me @mati865

[andrei-ionescu]

I also created #706 for this issue, not knowing that there is this. Not sure which one would get merged to fix the problem.