pub fn decompress_len(input: &[u8]) -> Result<usize> {
    if input.is_empty() {
        return Ok(0);
    }
    Ok(Header::read(input)?.decompress_len)
}
Returns the decompressed size (in bytes) of the compressed bytes given.

`input` must be a sequence of bytes returned by a conforming Snappy
compressor.

# Errors

This function returns an error in the following circumstances:

* An invalid Snappy header was seen.
* The total space required for decompression exceeds `2^32 - 1`.
src/decompress.rs