Function deltachat::tools::buf_compress

pub(crate) fn buf_compress(buf: &[u8]) -> Result<Vec<u8>>

Compresses buf to Vec using brotli. Note that it handles an empty buf as a special value that remains empty after compression, otherwise brotli would add its metadata to it which is not nice because this function is used for compression of strings stored in the db and empty strings are common there. This approach is not strictly correct because nowhere in the brotli documentation is said that an empty buffer can’t be a result of compression of some input, but i think this will never break.