Add mail splitting

- If a mail has more then one recipient and not for all recipients an
  authenticated certificate can be obtained, the mail processing is
  split into 2 streams - one that encrypts and an other which sends the
  mail in plaintext.
- For both streams the header and the list of recipients is adjusted
  accordingly.
- As the milter interface only allows one stream, the second stream is
  reinjected into the MTA (via SMTP). The MTA is hardcoded to be
  localhost:25.

src/daemon/mod.rs

@@ -202,58 +202,143 @@ impl Daemon {
                 return Status::Accept;
             }
 
-            // possible protection
-            // none -> accept
-            // partial -> accept (later: split)
-            // full -> encrypt
+            let from = match context.mail.sender.clone() {
+                Some(f) => f,
+                None => {
+                    log::error!("No sender given");
+                    return Status::Tempfail;
+                }
+            };
 
-            let protection = ProtectionPossibility::from(&context.mail);
+            match ProtectionPossibility::from(&context.mail) {
+                ProtectionPossibility::Full => {
+                    log::debug!("completely encryptable");
+                    let inner_mail = MailContext::generate_inner_mail(&context.mail.header, body);
 
-            if protection == ProtectionPossibility::Full {
+                    // if an error occures the body is not exchanged
+                    match crypto::encrypt(context, inner_mail.to_string().as_bytes(), &context.mail.recipients) {
+                        Ok(encrypted) => {
+                            // replace the body of the mail with an encrypted,
+                            // mime encoded version.
+                            let outer_mail = MailContext::generate_outer_mail(encrypted);
+                            if cx.actions.replace_body(
+                                    outer_mail
+                                    .body_to_string()
+                                    .as_bytes()).await.is_err() {
+                                log::error!("Cannot exchange body");
+                                return Status::Continue;
+                            }
 
-                let inner_mail = context.mail.generate_inner_mail(body);
-
-                // if an error occures the body is not exchanged
-                match crypto::encrypt(context, inner_mail.to_string().as_bytes(), &context.mail.recipients) {
-                    Ok(encrypted) => {
-                        // replace the body of the mail with an encrypted,
-                        // mime encoded version.
-                        let outer_mail = MailContext::generate_outer_mail(encrypted);
-                        if cx.actions.replace_body(
-                                outer_mail
-                                .body_to_string()
-                                .as_bytes()).await.is_err() {
-                            log::error!("Cannot exchange body");
-                            return Status::Continue;
-                        }
-
-                        // adjust headers
-                        // This is mostly Content-Type related.
-                        for line in outer_mail.get_header().iter_lines() {
-                            // XXX: handle errors
-                            if let Ok(key) = line.key_as_cstring() {
-                                if let Ok(value) = line.value_as_cstring() {
-                                    let _ = cx.actions.change_header(
-                                        key, 1,
-                                        Some(value)
-                                    ).await;
+                            // adjust headers
+                            // This is mostly Content-Type related.
+                            for line in outer_mail.get_header().iter_lines() {
+                                // XXX: handle errors
+                                if let Ok(key) = line.key_as_cstring() {
+                                    if let Ok(value) = line.value_as_cstring() {
+                                        let _ = cx.actions.change_header(
+                                            key, 1,
+                                            Some(value)
+                                        ).await;
+                                    }
                                 }
                             }
+                            // Change the subject
+                            let _ = cx.actions.change_header(
+                                "Subject",
+                                1,
+                                Some(context.subject_replacement.clone())).await;
+                        },
+                        Err(e) => {
+                            log::error!("{}", e);
                         }
-                        // Change the subject
-                        let _ = cx.actions.change_header(
-                            "Subject",
-                            1,
-                            Some(context.subject_replacement.clone())).await;
-                    },
-                    Err(e) => {
-                        log::error!("{}", e);
                     }
+                },
+                ProtectionPossibility::Partial(encryptable, unencryptable) => {
+                    log::debug!("partially encryptable");
+                    // Generate a new mail for the unencryptable recipients.
+
+                    let header = context.mail.header.without_recipients(&encryptable);
+                    if mail::smtp_inject(
+                        from,
+                        &unencryptable,
+                        header,
+                        &body).await.is_err() {
+                            // smtp_inject() already logged the error.
+                            return Status::Tempfail;
+                    }
+
+                    // Encrypt for remaining recipients.
+                    let header = context.mail.header.without_recipients(&unencryptable);
+                    let inner_mail = MailContext::generate_inner_mail(&header, body);
+
+                    // If an error occures, the body is not exchanged.
+                    match crypto::encrypt(context, inner_mail.to_string().as_bytes(), &encryptable) {
+                        Ok(encrypted) => {
+                            // replace the body of the mail with an encrypted,
+                            // mime encoded version.
+                            let outer_mail = MailContext::generate_outer_mail(encrypted);
+                            if cx.actions.replace_body(
+                                    outer_mail
+                                    .body_to_string()
+                                    .as_bytes()).await.is_err() {
+                                log::error!("Cannot exchange body");
+                                return Status::Continue;
+                            }
+
+                            // Adjust headers
+                            // XXX error handling
+
+                            // Remove unencryptable recipients from 'to', 'cc'
+                            // and 'bcc'.
+                            for (key, value) in header.iter_lines() {
+                                match key.as_bytes().to_ascii_lowercase().as_slice() {
+                                    b"to"
+                                    | b"cc"
+                                    | b"bcc" => {
+                                        let _ = cx.actions.change_header(
+                                            key.clone(),
+                                            1,
+                                            Some(value.clone())
+                                        ).await;
+                                    },
+                                    _ => { }
+                                }
+                            }
+                            // Also remove recipients via the milter protocol.
+                            for rcpt in unencryptable {
+                                let _ = cx.actions.delete_recipient(rcpt.email).await;
+                            }
+
+                            // This is Content-Type related.
+                            for line in outer_mail.get_header().iter_lines() {
+                                // XXX: handle errors
+                                if let Ok(key) = line.key_as_cstring() {
+                                    if let Ok(value) = line.value_as_cstring() {
+                                        let _ = cx.actions.change_header(
+                                            key, 1,
+                                            Some(value)
+                                        ).await;
+                                    }
+                                }
+                            }
+                            // Change the subject.
+                            let _ = cx.actions.change_header(
+                                "Subject",
+                                1,
+                                Some(context.subject_replacement.clone())).await;
+                        },
+                        Err(e) => {
+                            log::error!("{}", e);
+                        }
+                    }
+                },
+                ProtectionPossibility::NoProtection => {
+                    log::debug!("not encryptable");
+                    // do nothing
                 }
             }
         }
 
-        log::logger().flush();
         Status::Continue
     }
 

src/mail.rs

@@ -1,8 +1,22 @@
 //! mail functions
 
+use anyhow::Result;
+use bytes::Bytes;
+use bytes::BytesMut;
 use std::ffi::CString;
 use sequoia_openpgp::packet::UserID;
+use lettre::transport::smtp::{
+    client::SmtpConnection, commands::*, extension::ClientId, SMTP_PORT,
+};
+use lettre::Address;
+use tokio::task::JoinSet;
+use std::time::Duration;
 
+use crate::types::cheader::CHeader;
+use crate::types::errors::HuskError;
+use crate::types::recipient::Recipient;
+
+/// Parse the user id fields from a string.
 pub fn to_userid(rcpt: &CString) -> Option<UserID> {
     match rcpt.to_str() {
         Ok(s) => Some(UserID::from(s)),
@@ -10,6 +24,7 @@ pub fn to_userid(rcpt: &CString) -> Option<UserID> {
     }
 }
 
+/// Get the email from the string representation of a user id.
 pub fn to_email(rcpt: &CString) -> Option<String> {
     if let Some(u) = to_userid(rcpt) {
        if let Ok(Some(e)) = u.email() { Some(e.to_string()) }
@@ -32,3 +47,84 @@ pub fn is_email(email: &str) -> bool {
 pub fn is_domain(domain: &str) -> bool {
     is_email(format!("test@{}", domain).as_str())
 }
+
+pub async fn smtp_inject(from: String, to: &Vec<Recipient<'_>>, header: CHeader, body: &Bytes) -> Result<()> {
+
+    let mut joinset: JoinSet<Result<()>> = JoinSet::new();
+
+    log::debug!("smtp inject: from {}", from);
+
+    // build message
+    let mut header_size = 0;
+    for (key, value) in header.iter_lines() {
+        header_size += key.count_bytes();
+        header_size += value.count_bytes();
+        header_size += 4; // 4 is ': ' plus '\r\n'
+    }
+
+    // The size of the whole message the sum of header and body size + '\r\n'
+    // as the dividing empty line.
+    let mut message = BytesMut::with_capacity(header_size + body.len() + 2);
+    for (key, value) in header.iter_lines() {
+        message.extend_from_slice(key.as_bytes());
+        message.extend_from_slice(": ".as_bytes());
+        message.extend_from_slice(value.as_bytes());
+        message.extend_from_slice("\r\n".as_bytes());
+    }
+    message.extend_from_slice(b"\r\n");
+    message.extend_from_slice(&body[..]);
+
+    // convert addresses
+    let from_email = CString::new(from.clone())?;
+    let from_email = to_email(&from_email).unwrap(); // XXX
+    let from_email: Address = from_email.try_into()?;
+
+    let mut rcpts: Vec<Address> = Vec::new();
+    for rcpt in to {
+        let rcpt = rcpt.email.clone();
+        rcpts.push(rcpt.try_into()?);
+    }
+
+    let my_id = ClientId::Domain("husk.reinject".to_owned()); // TODO: add secret token?
+    joinset.spawn(async move {
+
+        // XXX
+        // We connect to localhost - every other host would require implementing
+        // TLS. The milter protocol is unencrypted anyways.
+        match SmtpConnection::connect(("localhost", SMTP_PORT), Some(Duration::from_secs(5)), &my_id, None, None) {
+            Ok(mut client) => {
+                log::debug!("connected - start sending");
+
+                client.command(Mail::new(Some(from_email),vec![]))?;
+                for rcpt in rcpts {
+                    client.command(Rcpt::new(rcpt, vec![]))?;
+                }
+                client.command(Data)?;
+                client.message(&message)?;
+                client.command(Quit)?;
+
+                Ok(())
+            },
+            Err(e) => {
+                log::error!("cannot connect to localhost:{} - {:?}", SMTP_PORT, e);
+                Err(e.into())
+            }
+        }
+    });
+
+    match joinset.join_all().await.first() {
+        Some(Ok(_)) => {
+            log::debug!("mail injection done.");
+            Ok(())
+        },
+        Some(Err(e)) => {
+            log::error!("mail injection failed: {:?}", e);
+            Err(HuskError::SmtpInjectionFailure(e.to_string()).into())
+        },
+        _ => {
+            log::error!("mail injection failed without reason");
+            Err(HuskError::SmtpInjectionFailure("no reason".to_string()).into())
+        },
+    }
+}
+

src/types/cheader.rs

@@ -5,6 +5,11 @@
 use std::ffi::CString;
 use std::fmt;
 
+use anyhow::Result;
+
+use crate::types::recipient::Recipient;
+
+#[derive(Debug, PartialEq, Clone)]
 pub struct CHeader {
     lines: Vec<(CString, CString)>
 }
@@ -52,6 +57,47 @@ impl CHeader {
     pub fn iter_lines(&self) -> std::slice::Iter<'_, (CString, CString)> {
         self.lines.iter()
     }
+
+    /// Remove a recipient from a value taken from a to, cc or bcc header
+    /// line. Only the email address is matched.
+    pub fn remove_recipient(header_value: &CString, to_remove: &Vec<Recipient>) -> Result<CString> {
+        let content = String::from_utf8_lossy(header_value.as_bytes());
+        let parts = content.split(",")
+            .filter(|part| {
+                let mut keep = true;
+                let p = part.to_ascii_lowercase();
+                for rcpt in to_remove {
+                    let rcpt = rcpt.email.to_ascii_lowercase();
+                    if p.contains(&rcpt) { keep = false; break; }
+                }
+                keep
+            })
+            .collect::<Vec<&str>>();
+        CString::new(parts.join(","))
+            .map_err(|e| e.into())
+    }
+
+    /// Returns a new header with `to_remove` removed from to, cc and bcc.
+    pub fn without_recipients(&self, to_remove: &Vec<Recipient>) -> CHeader {
+        let mut result = CHeader::new();
+
+        for (key, value) in self.iter_lines() {
+            let new_value = match key.as_bytes().to_ascii_lowercase().as_slice() {
+                b"to"
+                | b"cc"
+                | b"bcc" => Self::remove_recipient(value, to_remove),
+                _ => Ok(value.clone())
+            };
+            if let Ok(value) = new_value {
+                if ! value.is_empty() {
+                    result.append(key.clone(), value);
+                }
+            }
+        }
+
+        result
+    }
+
 }
 
 impl fmt::Display for CHeader {
@@ -75,10 +121,12 @@ impl fmt::Display for CHeader {
 #[cfg(test)]
 pub mod tests {
     use std::ffi::CString;
+    use crate::types::recipient::Recipient;
+
     use super::CHeader;
 
 
-#[test]
+    #[test]
     pub fn basic_functionality() {
         let cheader = CHeader::new()
             .add(CString::new("Content-Type").unwrap(), CString::new("text/plain").unwrap())
@@ -87,7 +135,7 @@ pub mod tests {
         assert_eq!("Content-Type: text/plain\r\nContent-Transfer-Encoding: 7bit\r\n", cheader.to_string());
     }
 
-#[test]
+    #[test]
     pub fn find() {
         let cheader = CHeader::new()
             .add(CString::new("Content-Type").unwrap(), CString::new("text/plain").unwrap())
@@ -103,7 +151,7 @@ pub mod tests {
         assert_eq!("text/plain", value);
     }
 
-#[test]
+    #[test]
     pub fn find_none() {
         let cheader = CHeader::new()
             .add(CString::new("Content-Type").unwrap(), CString::new("text/plain").unwrap())
@@ -114,7 +162,7 @@ pub mod tests {
         assert!(line.is_none());
     }
 
-#[test]
+    #[test]
     pub fn find_with_default() {
         let cheader = CHeader::new()
             .add(CString::new("Content-Type").unwrap(), CString::new("text/plain").unwrap())
@@ -124,5 +172,27 @@ pub mod tests {
 
         assert_eq!(value, "baaz");
     }
+
+    #[test]
+    pub fn remove_recipients() {
+        let header = CHeader::new()
+            .add(CString::new("To").unwrap(), CString::new("Alice <alice@example.com>, Bob <bob@other.org>").unwrap())
+            .add(CString::new("Cc").unwrap(), CString::new("carol@example.com").unwrap());
+
+        let modified_header = header.without_recipients(
+            &vec![ Recipient::from("bob@other.org".to_string()) ]
+        );
+        let expected_header = CHeader::new()
+            .add(CString::new("To").unwrap(), CString::new("Alice <alice@example.com>").unwrap())
+            .add(CString::new("Cc").unwrap(), CString::new("carol@example.com").unwrap());
+        assert_eq!(modified_header, expected_header);
+
+        let modified_header = header.without_recipients(
+            &vec![ Recipient::from("CaRol@exAmple.Com".to_string()) ]
+        );
+        let expected_header = CHeader::new()
+            .add(CString::new("To").unwrap(), CString::new("Alice <alice@example.com>, Bob <bob@other.org>").unwrap());
+        assert_eq!(modified_header, expected_header);
+    }
 }
 

src/types/errors.rs

@@ -24,4 +24,6 @@ pub enum HuskError {
     InvalidDomainName(String),
     #[error("Certificate has no user ids - {0}")]
     NoUserIDs(String),
+    #[error("Failing to send mail: {0}")]
+    SmtpInjectionFailure(String),
 }

src/types/mail_context.rs

@@ -15,17 +15,15 @@ use crate::types::mime::header::Header;
 use crate::types::mime::part::Part;
 use crate::types::mime::multi_part::MultiPart;
 
-#[derive(PartialEq)]
-pub enum ProtectionPossibility {
+pub enum ProtectionPossibility<'mc> {
     // no recipient has a cert
     NoProtection,
     // some recipients have a cert (but not all)
-    Partial,
+    Partial(Vec<Recipient<'mc>>, Vec<Recipient<'mc>>),
     // all recipients have a cert
     Full
 }
 
-
 pub struct MailContext<'mc> {
     pub sender:     Option<String>,
     pub recipients: Vec<Recipient<'mc>>,
@@ -84,8 +82,8 @@ impl<'mc> MailContext<'mc> {
         buffer.into()
     }
 
-    pub fn generate_inner_mail(&self, body: Bytes) -> MultiPart<'mc> {
-        let header = &self.header;
+    pub fn generate_inner_mail(header: &CHeader, body: Bytes) -> MultiPart<'mc> {
+        //let header = &self.header;
         let inner = Part::with_body(body)
             .set_header(Header::new()
                 .add(
@@ -158,22 +156,27 @@ impl<'mc> Default for MailContext<'mc> {
     }
 }
 
-impl From<&MailContext<'_>> for ProtectionPossibility {
-    fn from(mail_context: &MailContext<'_>) -> ProtectionPossibility {
+impl<'mc> From<&MailContext<'mc>> for ProtectionPossibility<'mc> {
+    fn from(mail_context: &MailContext<'mc>) -> ProtectionPossibility<'mc> {
         let mut can_encrypt = false;
         let mut cannot_encrypt = false;
 
+        let mut encrypted_rcpt = Vec::new();
+        let mut unencrypted_rcpt = Vec::new();
+
         for rcpt in mail_context.recipients.iter() {
             if rcpt.can_encrypt() {
                 can_encrypt = true;
+                encrypted_rcpt.push(rcpt.clone());
             } else {
                 cannot_encrypt = true;
+                unencrypted_rcpt.push(rcpt.clone());
             }
         }
 
         match (can_encrypt, cannot_encrypt) {
             (true, false) => ProtectionPossibility::Full,
-            (true, true) => ProtectionPossibility::Partial,
+            (true, true) => ProtectionPossibility::Partial(encrypted_rcpt, unencrypted_rcpt),
             (false, true) => ProtectionPossibility::NoProtection,
             // (false, false) occurs if there are no recipients
             (false, false) => ProtectionPossibility::NoProtection,
@@ -185,8 +188,17 @@ impl From<&MailContext<'_>> for ProtectionPossibility {
 mod tests {
 
     use std::ffi::CString;
+    use std::sync::Arc;
+
+    use anyhow::Result;
+    use sequoia_cert_store::LazyCert;
+    use sequoia_openpgp::cert::CertBuilder;
+
     use crate::types::cheader::CHeader;
     use crate::types::mail_context::MailContext;
+    use crate::types::recipient::Recipient;
+
+    use super::ProtectionPossibility;
 
     #[test]
     fn test_inner_mail() {
@@ -202,8 +214,7 @@ mod tests {
 
         let orig_body = "This is the body".as_bytes().to_vec();
 
-        let context = MailContext::from_header(orig_header);
-        let inner_mail = context.generate_inner_mail(orig_body.into());
+        let inner_mail = MailContext::generate_inner_mail(&orig_header, orig_body.into());
 
         let intended_result = [
             format!("Content-Type: multipart/mixed; boundary=\"{}\"; protected-headers=\"v1\"", inner_mail.get_boundary()),
@@ -220,5 +231,80 @@ mod tests {
 
         assert_eq!(intended_result, inner_mail.to_string());
     }
+
+    #[test]
+    fn test_recipient_splitting() -> Result<()> {
+        let (alice_cert, _) = CertBuilder::general_purpose(["alice@example.com"])
+            .generate()?;
+
+        // Mixed recipients: alice can encrypt, bob doesn't.
+        let mut mail_context = MailContext::new();
+        mail_context.recipients = vec![
+            Recipient {
+                email: "alice@example.com".to_string(),
+                certs: vec![Arc::new(LazyCert::from_cert(alice_cert))],
+            },
+            Recipient {
+                email: "bob@example.com".to_string(),
+                certs: Vec::new()
+            }
+        ];
+
+        let protection = ProtectionPossibility::from(&mail_context);
+
+        assert!(matches!(protection, ProtectionPossibility::Partial(_, _)));
+
+        if let ProtectionPossibility::Partial(a, b) = protection {
+            assert_eq!(a.len(), 1);
+            assert_eq!(b.len(), 1);
+
+            let alice = a.iter().next().unwrap();
+            assert_eq!(alice.email, "alice@example.com");
+
+            let bob = b.iter().next().unwrap();
+            assert_eq!(bob.email, "bob@example.com");
+        } else {
+            return Err(anyhow::anyhow!("this should be unreachable"));
+        }
+
+        // Both recipients can encrypt.
+        let (alice_cert, _) = CertBuilder::general_purpose(["alice@example.com"])
+            .generate()?;
+        let (bob_cert, _) = CertBuilder::general_purpose(["bob@example.com"])
+            .generate()?;
+        let mut mail_context = MailContext::new();
+        mail_context.recipients = vec![
+            Recipient {
+                email: "alice@example.com".to_string(),
+                certs: vec![Arc::new(LazyCert::from_cert(alice_cert))],
+            },
+            Recipient {
+                email: "bob@example.com".to_string(),
+                certs: vec![Arc::new(LazyCert::from_cert(bob_cert))],
+            }
+        ];
+
+        let protection = ProtectionPossibility::from(&mail_context);
+
+        assert!(matches!(protection, ProtectionPossibility::Full));
+
+        // No recipient can encrypt.
+        let mut mail_context = MailContext::new();
+        mail_context.recipients = vec![
+            Recipient {
+                email: "alice@example.com".to_string(),
+                certs: Vec::new()
+            },
+            Recipient {
+                email: "bob@example.com".to_string(),
+                certs: Vec::new()
+            }
+        ];
+
+        let protection = ProtectionPossibility::from(&mail_context);
+
+        assert!(matches!(protection, ProtectionPossibility::NoProtection));
+        Ok(())
+    }
 }