Add LMTP support

1 files changed, 263 insertions, 0 deletions

diff --git a/src/lmtp.rs b/src/lmtp.rs
new file mode 100644
index 0000000..049e119
--- /dev/null
+++ b/src/lmtp.rs
@@ -0,0 +1,263 @@
+use std::collections::HashMap;
+use std::net::SocketAddr;
+use std::{pin::Pin, sync::Arc};
+
+use anyhow::{bail, Result};
+use async_trait::async_trait;
+use duplexify::Duplex;
+use futures::{io, AsyncRead, AsyncReadExt, AsyncWrite};
+use futures::{stream, stream::FuturesUnordered, StreamExt};
+use log::*;
+use rusoto_s3::{PutObjectRequest, S3Client, S3};
+use tokio::net::{TcpListener, TcpStream};
+use tokio::select;
+use tokio::sync::watch;
+use tokio_util::compat::*;
+
+use smtp_message::{Email, EscapedDataReader, Reply, ReplyCode};
+use smtp_server::{reply, Config, ConnectionMetadata, Decision, MailMetadata, Protocol};
+
+use crate::config::*;
+use crate::cryptoblob::*;
+use crate::login::*;
+use crate::mail_ident::*;
+
+pub struct LmtpServer {
+    bind_addr: SocketAddr,
+    hostname: String,
+    login_provider: Arc<dyn LoginProvider + Send + Sync>,
+}
+
+impl LmtpServer {
+    pub fn new(
+        config: LmtpConfig,
+        login_provider: Arc<dyn LoginProvider + Send + Sync>,
+    ) -> Arc<Self> {
+        Arc::new(Self {
+            bind_addr: config.bind_addr,
+            hostname: config.hostname,
+            login_provider,
+        })
+    }
+
+    pub async fn run(self: &Arc<Self>, mut must_exit: watch::Receiver<bool>) -> Result<()> {
+        let tcp = TcpListener::bind(self.bind_addr).await?;
+        let mut connections = FuturesUnordered::new();
+
+        while !*must_exit.borrow() {
+            let wait_conn_finished = async {
+                if connections.is_empty() {
+                    futures::future::pending().await
+                } else {
+                    connections.next().await
+                }
+            };
+            let (socket, remote_addr) = select! {
+                a = tcp.accept() => a?,
+                _ = wait_conn_finished => continue,
+                _ = must_exit.changed() => continue,
+            };
+
+            let conn = tokio::spawn(smtp_server::interact(
+                socket.compat(),
+                smtp_server::IsAlreadyTls::No,
+                Conn { remote_addr },
+                self.clone(),
+            ));
+
+            connections.push(conn);
+        }
+        drop(tcp);
+
+        info!("LMTP server shutting down, draining remaining connections...");
+        while connections.next().await.is_some() {}
+
+        Ok(())
+    }
+}
+
+// ----
+
+pub struct Conn {
+    remote_addr: SocketAddr,
+}
+
+pub struct Message {
+    to: Vec<PublicCredentials>,
+}
+
+#[async_trait]
+impl Config for LmtpServer {
+    const PROTOCOL: Protocol = Protocol::Lmtp;
+
+    type ConnectionUserMeta = Conn;
+    type MailUserMeta = Message;
+
+    fn hostname(&self, _conn_meta: &ConnectionMetadata<Conn>) -> &str {
+        &self.hostname
+    }
+
+    async fn new_mail(&self, _conn_meta: &mut ConnectionMetadata<Conn>) -> Message {
+        Message { to: vec![] }
+    }
+
+    async fn tls_accept<IO>(
+        &self,
+        _io: IO,
+        _conn_meta: &mut ConnectionMetadata<Conn>,
+    ) -> io::Result<Duplex<Pin<Box<dyn Send + AsyncRead>>, Pin<Box<dyn Send + AsyncWrite>>>>
+    where
+        IO: Send + AsyncRead + AsyncWrite,
+    {
+        Err(io::Error::new(
+            io::ErrorKind::InvalidInput,
+            "TLS not implemented for LMTP server",
+        ))
+    }
+
+    async fn filter_from(
+        &self,
+        from: Option<Email>,
+        meta: &mut MailMetadata<Message>,
+        _conn_meta: &mut ConnectionMetadata<Conn>,
+    ) -> Decision<Option<Email>> {
+        Decision::Accept {
+            reply: reply::okay_from().convert(),
+            res: from,
+        }
+    }
+
+    async fn filter_to(
+        &self,
+        to: Email,
+        meta: &mut MailMetadata<Message>,
+        _conn_meta: &mut ConnectionMetadata<Conn>,
+    ) -> Decision<Email> {
+        let to_str = match to.hostname.as_ref() {
+            Some(h) => format!("{}@{}", to.localpart, h),
+            None => to.localpart.to_string(),
+        };
+        match self.login_provider.public_login(&to_str).await {
+            Ok(creds) => {
+                meta.user.to.push(creds);
+                Decision::Accept {
+                    reply: reply::okay_to().convert(),
+                    res: to,
+                }
+            }
+            Err(e) => Decision::Reject {
+                reply: Reply {
+                    code: ReplyCode::POLICY_REASON,
+                    ecode: None,
+                    text: vec![smtp_message::MaybeUtf8::Utf8(e.to_string())],
+                },
+            },
+        }
+    }
+
+    async fn handle_mail<'a, R>(
+        &self,
+        reader: &mut EscapedDataReader<'a, R>,
+        _mail: MailMetadata<Message>,
+        _conn_meta: &mut ConnectionMetadata<Conn>,
+    ) -> Decision<()>
+    where
+        R: Send + Unpin + AsyncRead,
+    {
+        unreachable!();
+    }
+
+    async fn handle_mail_multi<'a, 'slife0, 'slife1, 'stream, R>(
+        &'slife0 self,
+        reader: &mut EscapedDataReader<'a, R>,
+        meta: MailMetadata<Message>,
+        conn_meta: &'slife1 mut ConnectionMetadata<Conn>,
+    ) -> Pin<Box<dyn futures::Stream<Item = Decision<()>> + Send + 'stream>>
+    where
+        R: Send + Unpin + AsyncRead,
+        'slife0: 'stream,
+        'slife1: 'stream,
+        Self: 'stream,
+    {
+        let err_response_stream = |meta: MailMetadata<Message>, msg: String| {
+            Box::pin(
+                stream::iter(meta.user.to.into_iter()).map(move |_| Decision::Reject {
+                    reply: Reply {
+                        code: ReplyCode::POLICY_REASON,
+                        ecode: None,
+                        text: vec![smtp_message::MaybeUtf8::Utf8(msg.clone())],
+                    },
+                }),
+            )
+        };
+
+        let mut text = Vec::new();
+        if reader.read_to_end(&mut text).await.is_err() {
+            return err_response_stream(meta, "io error".into());
+        }
+        reader.complete();
+
+        let encrypted_message = match EncryptedMessage::new(text) {
+            Ok(x) => Arc::new(x),
+            Err(e) => return err_response_stream(meta, e.to_string()),
+        };
+
+        Box::pin(stream::iter(meta.user.to.into_iter()).then(move |creds| {
+            let encrypted_message = encrypted_message.clone();
+            async move {
+                match encrypted_message.deliver_to(creds).await {
+                    Ok(()) => Decision::Accept {
+                        reply: reply::okay_mail().convert(),
+                        res: (),
+                    },
+                    Err(e) => Decision::Reject {
+                        reply: Reply {
+                            code: ReplyCode::POLICY_REASON,
+                            ecode: None,
+                            text: vec![smtp_message::MaybeUtf8::Utf8(e.to_string())],
+                        },
+                    },
+                }
+            }
+        }))
+    }
+}
+
+// ----
+
+struct EncryptedMessage {
+    key: Key,
+    encrypted_body: Vec<u8>,
+}
+
+impl EncryptedMessage {
+    fn new(body: Vec<u8>) -> Result<Self> {
+        let key = gen_key();
+        let encrypted_body = seal(&body, &key)?;
+        Ok(Self {
+            key,
+            encrypted_body,
+        })
+    }
+
+    async fn deliver_to(self: Arc<Self>, creds: PublicCredentials) -> Result<()> {
+        let s3_client = creds.storage.s3_client()?;
+
+        let encrypted_key =
+            sodiumoxide::crypto::sealedbox::seal(self.key.as_ref(), &creds.public_key);
+        let key_header = base64::encode(&encrypted_key);
+
+        let mut por = PutObjectRequest::default();
+        por.bucket = creds.storage.bucket.clone();
+        por.key = format!("incoming/{}", gen_ident().to_string());
+        por.metadata = Some(
+            [("Message-Key".to_string(), key_header)]
+                .into_iter()
+                .collect::<HashMap<_, _>>(),
+        );
+        por.body = Some(self.encrypted_body.clone().into());
+        s3_client.put_object(por).await?;
+
+        Ok(())
+    }
+}