mimeparser: assume all Thunderbird users prefer encryption

Co-Authored-By: missytake <missytake@systemli.org>

src/decrypt.rs

@@ -5,7 +5,7 @@ use std::collections::HashSet;
 use anyhow::{Context as _, Result};
 use mailparse::ParsedMail;
 
-use crate::aheader::Aheader;
+use crate::aheader::{Aheader, EncryptPreference};
 use crate::authres;
 use crate::authres::handle_authres;
 use crate::contact::addr_cmp;
@@ -60,11 +60,18 @@ pub(crate) async fn prepare_decryption(
     mail: &ParsedMail<'_>,
     from: &str,
     message_time: i64,
+    is_thunderbird: bool,
 ) -> Result<DecryptionInfo> {
-    let autocrypt_header = Aheader::from_headers(from, &mail.headers)
+    let mut autocrypt_header = Aheader::from_headers(from, &mail.headers)
         .ok_or_log_msg(context, "Failed to parse Autocrypt header")
         .flatten();
 
+    if is_thunderbird {
+        if let Some(autocrypt_header) = &mut autocrypt_header {
+            autocrypt_header.prefer_encrypt = EncryptPreference::Mutual;
+        }
+    }
+
     let dkim_results = handle_authres(context, mail, from, message_time).await?;
 
     let peerstate = get_autocrypt_peerstate(

src/mimeparser.rs

@@ -216,9 +216,16 @@ impl MimeMessage {
         headers.remove("secure-join-fingerprint");
         headers.remove("chat-verified");
 
+        let is_thunderbird = if let Some(user_agent) = headers.get("user-agent") {
+            info!(context, "Detected thunderbird");
+            user_agent.contains("Thunderbird")
+        } else {
+            false
+        };
+
         let from = from.context("No from in message")?;
         let mut decryption_info =
-            prepare_decryption(context, &mail, &from.addr, message_time).await?;
+            prepare_decryption(context, &mail, &from.addr, message_time, is_thunderbird).await?;
 
         // Memory location for a possible decrypted message.
         let mut mail_raw = Vec::new();

src/receive_imf.rs

@@ -2277,6 +2277,7 @@ mod tests {
 
     use super::*;
 
+    use crate::aheader::EncryptPreference;
     use crate::chat::get_chat_contacts;
     use crate::chat::{get_chat_msgs, ChatItem, ChatVisibility};
     use crate::chatlist::Chatlist;
@@ -5299,4 +5300,20 @@ Reply from different address
 
         Ok(())
     }
+
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_thunderbird_autocrypt() -> Result<()> {
+        let t = TestContext::new_bob().await;
+        t.set_config(Config::ShowEmails, Some("2")).await?;
+
+        let raw = include_bytes!("../test-data/message/thunderbird_with_autocrypt.eml");
+        receive_imf(&t, raw, false).await?;
+
+        let peerstate = Peerstate::from_addr(&t, "alice@example.org")
+            .await?
+            .unwrap();
+        assert_eq!(peerstate.prefer_encrypt, EncryptPreference::Mutual);
+
+        Ok(())
+    }
 }