You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: impl_encryption.rs
    path of file: ./repos/tikv/components/tidb_query_expr/src
    
    the code of the file until where you have to start completion: // Copyright 2019 TiKV Project Authors. Licensed under Apache-2.0.

use std::io::Read;

use byteorder::{ByteOrder, LittleEndian};
use crypto::rand;
use flate2::{
    read::{ZlibDecoder, ZlibEncoder},
    Compression,
};
use openssl::hash::{self, MessageDigest};
use tidb_query_codegen::rpn_fn;
use tidb_query_common::{error::EvaluateError, Result};
use tidb_query_datatype::{
    codec::data_type::*,
    expr::{Error, EvalContext},
};

const SHA0: i64 = 0;
const SHA224: i64 = 224;
const SHA256: i64 = 256;
const SHA384: i64 = 384;
const SHA512: i64 = 512;

const MAX_RAND_BYTES_LENGTH: i64 = 1024;

#[rpn_fn(nullable)]
#[inline]
pub fn md5(arg: Option<BytesRef>)
    
    fn test_compress() {
        let test_cases = vec![
            (
                b"hello world".to_vec(),
                "0B000000789CCB48CDC9C95728CF2FCA4901001A0B045D",
            ),
            (b"".to_vec(), ""),
            (
                b"hello wor012".to_vec(),
                "0C000000789CCB48CDC9C95728CF2F32303402001D8004202E",
            ),
        ];
        for (arg, expect) in test_cases {
            let expect = Some(hex::decode(expect.as_bytes()).unwrap());

            let output = RpnFnScalarEvaluator::new()
                .push_param(arg)
                .evaluate::<Bytes>(ScalarFuncSig::Compress)
                .unwrap();
            assert_eq!(output, expect);
        }
        test_unary_func_ok_none::<BytesRef, Bytes>(ScalarFuncSig::Compress);
    }