elektromail 0.1.1

A minimal, Rust-based IMAP + SMTP mail server for local development and testing
Documentation 
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use std::{
    io,
    pin::Pin,
    sync::Arc,
    task::{Context, Poll},
};

use rcgen::generate_simple_self_signed;
use rustls::{ServerConfig as RustlsServerConfig, pki_types::PrivateKeyDer};
use tokio::{
    io::{AsyncRead, AsyncWrite, ReadBuf},
    net::TcpStream,
};
use tokio_rustls::{TlsAcceptor, server::TlsStream};

/// Stream wrapper for IMAP connections that can be plain or TLS.
pub enum ImapStream {
    /// Plain TCP connection
    Plain(TcpStream),
    /// TLS-wrapped connection
    Tls(TlsStream<TcpStream>),
}

/// Stream wrapper for SMTP connections that can be plain or TLS.
pub enum SmtpStream {
    /// Plain TCP connection
    Plain(TcpStream),
    /// TLS-wrapped connection
    Tls(TlsStream<TcpStream>),
}

impl AsyncRead for ImapStream {
    fn poll_read(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<io::Result<()>> {
        match self.get_mut() {
            Self::Plain(stream) => Pin::new(stream).poll_read(cx, buf),
            Self::Tls(stream) => Pin::new(stream).poll_read(cx, buf),
        }
    }
}

impl AsyncWrite for ImapStream {
    fn poll_write(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        data: &[u8],
    ) -> Poll<io::Result<usize>> {
        match self.get_mut() {
            Self::Plain(stream) => Pin::new(stream).poll_write(cx, data),
            Self::Tls(stream) => Pin::new(stream).poll_write(cx, data),
        }
    }

    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        match self.get_mut() {
            Self::Plain(stream) => Pin::new(stream).poll_flush(cx),
            Self::Tls(stream) => Pin::new(stream).poll_flush(cx),
        }
    }

    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        match self.get_mut() {
            Self::Plain(stream) => Pin::new(stream).poll_shutdown(cx),
            Self::Tls(stream) => Pin::new(stream).poll_shutdown(cx),
        }
    }
}

impl Unpin for ImapStream {}

impl AsyncRead for SmtpStream {
    fn poll_read(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<io::Result<()>> {
        match self.get_mut() {
            Self::Plain(stream) => Pin::new(stream).poll_read(cx, buf),
            Self::Tls(stream) => Pin::new(stream).poll_read(cx, buf),
        }
    }
}

impl AsyncWrite for SmtpStream {
    fn poll_write(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        data: &[u8],
    ) -> Poll<io::Result<usize>> {
        match self.get_mut() {
            Self::Plain(stream) => Pin::new(stream).poll_write(cx, data),
            Self::Tls(stream) => Pin::new(stream).poll_write(cx, data),
        }
    }

    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        match self.get_mut() {
            Self::Plain(stream) => Pin::new(stream).poll_flush(cx),
            Self::Tls(stream) => Pin::new(stream).poll_flush(cx),
        }
    }

    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        match self.get_mut() {
            Self::Plain(stream) => Pin::new(stream).poll_shutdown(cx),
            Self::Tls(stream) => Pin::new(stream).poll_shutdown(cx),
        }
    }
}

impl Unpin for SmtpStream {}

pub fn build_tls_acceptor() -> io::Result<TlsAcceptor> {
    let rcgen::CertifiedKey { cert, key_pair } =
        generate_simple_self_signed(vec!["localhost".to_string()]).map_err(io::Error::other)?;
    let certs = vec![cert.der().clone()];
    let key_der = key_pair.serialize_der();
    let key = PrivateKeyDer::Pkcs8(key_der.into());

    let config = RustlsServerConfig::builder_with_provider(Arc::new(
        rustls::crypto::ring::default_provider(),
    ))
    .with_safe_default_protocol_versions()
    .map_err(io::Error::other)?
    .with_no_client_auth()
    .with_single_cert(certs, key)
    .map_err(io::Error::other)?;
    Ok(TlsAcceptor::from(Arc::new(config)))
}