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: secure_message_client_verify.rs
    path of file: ./repos/themis/docs/examples/rust
    
    the code of the file until where you have to start completion: // Copyright 2018 (c) rust-themis developers
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#![allow(clippy::needless_borrow)]

#[macro_use]
extern crate log;

use std::fs::File;
use std::io::{self, Read, Write};
use std::net::UdpSocket;
use std::process;
use std::thread;

use clap::clap_app;
use themis::keys::{PrivateKey, PublicKey};
use themis::secure_message::{SecureSign, SecureVerify};

fn main() {
    env_logger::init();

    let matches = clap_app!(secure_message_client_verify =>
        (version: env!("CARGO_PKG_VERSION"))
        (about: "Secure Message chat client (sign/verify).")
        (@arg private: --private [path] "Private key file (default: private.key)")
        (@arg public: --public [path] "Public key file (default: public.key)")
        (@arg address: -c --connect [addr] "Relay server address (default: localhost:7573)")
    )
    .get_matches();

    let private_path = matches.value_of("private").unwrap_or("private.key");
    let public_path = matches.value_of("public").unwrap_or("public.key");
    let remote_addr = matches.value_of("address").unwrap_or("localhost:7573");

    let private_key = read_file(private_path).expect("read private key");
    let private_key = PrivateKey::try_from_slice(private_key).expect("parse private key");
    let public_key = read_file(public_path).expect("read public key");
    let public_key = PublicKey::try_from_slice(public_key).expect("parse public key");

    let socket = UdpSocket::bind("localhost:0").expect("client socket");
    socket.connect(remote_addr).expect("client connection");

    let receive_socket = socket;
    let relay_socket = receive_socket.try_clone().unwrap();

    // Each of the threads is using its own object for message processing.
    // Also note that SecureSign/SecureVerify API is deliberately different from SecureMessage.
    let receive_secure = SecureVerify::new(public_key);
    let relay_secure = SecureSign::new(private_key);

    let final_message_server = format!("client {} left chat\n", process::id())
        .as_bytes()
        .to_vec();
    let final_message_client = final_message_server.clone();

    let receive = thread::spawn(move || {
        let receive_message = || -> io::Result<bool> {
            let buffer = recv(&receive_socket)?;
            if buffer == final_message_server {
                return Ok(false);
            }
            if buffer.starts_with(b"client") {
                return Ok(true);
            }
            let message = receive_secure.verify(&buffer).map_err(themis_as_io_error)?;
            io::stdout().write_all(&message)?;
            Ok(true)
        };
        loop {
            match receive_message() {
                Ok(true) => continue,
                Ok(false) => break,
                Err(e) => {
        
    
fn main() {
    env_logger::init();

    let matches = clap_app!(secure_message_client_verify =>
        (version: env!("CARGO_PKG_VERSION"))
        (about: "Secure Message chat client (sign/verify).")
        (@arg private: --private [path] "Private key file (default: private.key)")
        (@arg public: --public [path] "Public key file (default: public.key)")
        (@arg address: -c --connect [addr] "Relay server address (default: localhost:7573)")
    )
    .get_matches();

    let private_path = matches.value_of("private").unwrap_or("private.key");
    let public_path = matches.value_of("public").unwrap_or("public.key");
    let remote_addr = matches.value_of("address").unwrap_or("localhost:7573");

    let private_key = read_file(private_path).expect("read private key");
    let private_key = PrivateKey::try_from_slice(private_key).expect("parse private key");
    let public_key = read_file(public_path).expect("read public key");
    let public_key = PublicKey::try_from_slice(public_key).expect("parse public key");

    let socket = UdpSocket::bind("localhost:0").expect("client socket");
    socket.connect(remote_addr).expect("client connection");

    let receive_socket = socket;
    let relay_socket = receive_socket.try_clone().unwrap();

    // Each of the threads is using its own object for message processing.
    // Also note that SecureSign/SecureVerify API is deliberately different from SecureMessage.
    let receive_secure = SecureVerify::new(public_key);
    let relay_secure = SecureSign::new(private_key);

    let final_message_server = format!("client {} left chat\n", process::id())
        .as_bytes()
        .to_vec();
    let final_message_client = final_message_server.clone();

    let receive = thread::spawn(move || {
        let receive_message = || -> io::Result<bool> {
            let buffer = recv(&receive_socket)?;
            if buffer == final_message_server {
                return Ok(false);
            }
            if buffer.starts_with(b"client") {
                return Ok(true);
            }
            let message = receive_secure.verify(&buffer).map_err(themis_as_io_error)?;
            io::stdout().write_all(&message)?;
            Ok(true)
        };
        loop {
            match receive_message() {
                Ok(true) => continue,
                Ok(false) => break,
                Err(e) => {
                    error!("failed to receive message: {}", e);
                    break;
                }
            }
        }
    });

    let relay = thread::spawn(move || {
        let relay_message = || -> io::Result<bool> {
            let mut buffer = String::new();
            io::stdin().read_line(&mut buffer)?;
            if buffer.is_empty() {
                return Ok(false);
            }
            let message = relay_secure.sign(&buffer).map_err(themis_as_io_error)?;
            relay_socket.send(&message)?;
            Ok(true)
        };
        loop {
            match relay_message() {
                Ok(true) => continue,
                Ok(false) => break,
                Err(e) => {
                    error!("failed to relay message: {}", e);
                    break;
                }
            }
        }
        relay_socket
            .send(&final_message_client)
            .expect("final message");
    });

    receive.join().unwrap();
    relay.join().unwrap();
}