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/*
 * Copyright Stalwart Labs Ltd.
 *
 * Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
 * https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
 * <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
 * option. This file may not be copied, modified, or distributed
 * except according to those terms.
 */

use std::{convert::TryFrom, io, sync::Arc};

use rustls::{
    client::danger::{HandshakeSignatureValid, ServerCertVerified, ServerCertVerifier},
    ClientConfig, ClientConnection, RootCertStore, SignatureScheme,
};
use rustls_pki_types::{ServerName, TrustAnchor};
use tokio::net::TcpStream;
use tokio_rustls::{client::TlsStream, TlsConnector};

use crate::{Error, SmtpClient};

use super::AssertReply;

impl SmtpClient<TcpStream> {
    /// Upgrade the connection to TLS.
    pub async fn start_tls(
        mut self,
        tls_connector: &TlsConnector,
        hostname: &str,
    ) -> crate::Result<SmtpClient<TlsStream<TcpStream>>> {
        // Send STARTTLS command
        self.cmd(b"STARTTLS\r\n")
            .await?
            .assert_positive_completion()?;

        self.into_tls(tls_connector, hostname).await
    }

    pub async fn into_tls(
        self,
        tls_connector: &TlsConnector,
        hostname: &str,
    ) -> crate::Result<SmtpClient<TlsStream<TcpStream>>> {
        tokio::time::timeout(self.timeout, async {
            Ok(SmtpClient {
                stream: tls_connector
                    .connect(
                        ServerName::try_from(hostname)
                            .map_err(|_| crate::Error::InvalidTLSName)?
                            .to_owned(),
                        self.stream,
                    )
                    .await
                    .map_err(|err| {
                        let kind = err.kind();
                        if let Some(inner) = err.into_inner() {
                            match inner.downcast::<rustls::Error>() {
                                Ok(error) => Error::Tls(error),
                                Err(error) => Error::Io(io::Error::new(kind, error)),
                            }
                        } else {
                            Error::Io(io::Error::new(kind, "Unspecified"))
                        }
                    })?,
                timeout: self.timeout,
            })
        })
        .await
        .map_err(|_| crate::Error::Timeout)?
    }
}

impl SmtpClient<TlsStream<TcpStream>> {
    pub fn tls_connection(&self) -> &ClientConnection {
        self.stream.get_ref().1
    }
}

pub fn build_tls_connector(allow_invalid_certs: bool) -> TlsConnector {
    let config = if !allow_invalid_certs {
        let mut root_cert_store = RootCertStore::empty();

        root_cert_store.extend(webpki_roots::TLS_SERVER_ROOTS.iter().map(|ta| TrustAnchor {
            subject: ta.subject.clone(),
            subject_public_key_info: ta.subject_public_key_info.clone(),
            name_constraints: ta.name_constraints.clone(),
        }));

        ClientConfig::builder()
            .with_root_certificates(root_cert_store)
            .with_no_client_auth()
    } else {
        ClientConfig::builder()
            .dangerous()
            .with_custom_certificate_verifier(Arc::new(DummyVerifier {}))
            .with_no_client_auth()
    };

    TlsConnector::from(Arc::new(config))
}

#[doc(hidden)]
#[derive(Debug)]
struct DummyVerifier;

impl ServerCertVerifier for DummyVerifier {
    fn verify_server_cert(
        &self,
        _end_entity: &rustls_pki_types::CertificateDer<'_>,
        _intermediates: &[rustls_pki_types::CertificateDer<'_>],
        _server_name: &rustls_pki_types::ServerName<'_>,
        _ocsp_response: &[u8],
        _now: rustls_pki_types::UnixTime,
    ) -> Result<ServerCertVerified, rustls::Error> {
        Ok(ServerCertVerified::assertion())
    }

    fn verify_tls12_signature(
        &self,
        _message: &[u8],
        _cert: &rustls_pki_types::CertificateDer<'_>,
        _dss: &rustls::DigitallySignedStruct,
    ) -> Result<HandshakeSignatureValid, rustls::Error> {
        Ok(HandshakeSignatureValid::assertion())
    }

    fn verify_tls13_signature(
        &self,
        _message: &[u8],
        _cert: &rustls_pki_types::CertificateDer<'_>,
        _dss: &rustls::DigitallySignedStruct,
    ) -> Result<HandshakeSignatureValid, rustls::Error> {
        Ok(HandshakeSignatureValid::assertion())
    }

    fn supported_verify_schemes(&self) -> Vec<SignatureScheme> {
        vec![
            SignatureScheme::RSA_PKCS1_SHA1,
            SignatureScheme::ECDSA_SHA1_Legacy,
            SignatureScheme::RSA_PKCS1_SHA256,
            SignatureScheme::ECDSA_NISTP256_SHA256,
            SignatureScheme::RSA_PKCS1_SHA384,
            SignatureScheme::ECDSA_NISTP384_SHA384,
            SignatureScheme::RSA_PKCS1_SHA512,
            SignatureScheme::ECDSA_NISTP521_SHA512,
            SignatureScheme::RSA_PSS_SHA256,
            SignatureScheme::RSA_PSS_SHA384,
            SignatureScheme::RSA_PSS_SHA512,
            SignatureScheme::ED25519,
            SignatureScheme::ED448,
        ]
    }
}