mimeparser: assume all Thunderbird users prefer encryption

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

CHANGELOG.md

@@ -10,6 +10,7 @@
 ### Fixes
 - Make sure malformed messsages will never block receiving further messages anymore #3771
 - strip leading/trailing whitespace from "Chat-Group-Name{,-Changed}:" headers content #3650
+- Assume all Thunderbird users prefer encryption #3774
 
 
 ## 1.102.0

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(())
+    }
 }

test-data/message/thunderbird_with_autocrypt.eml

@@ -0,0 +1,93 @@
+From - Thu, 24 Nov 2022 19:06:16 GMT
+X-Mozilla-Status: 0001
+X-Mozilla-Status2: 00800000
+Message-ID: <0bb9ffe1-2596-d997-95b4-1fef8cc4808e@example.org>
+Date: Thu, 24 Nov 2022 20:05:57 +0100
+MIME-Version: 1.0
+User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
+ Thunderbird/102.4.2
+From: Alice <alice@example.org>
+To: bob@example.net
+Content-Language: en-US
+Autocrypt: addr=alice@example.org; keydata=
+ xjMEXlh13RYJKwYBBAHaRw8BAQdAzfVIAleCXMJrq8VeLlEVof6ITCviMktKjmcBKAu4m5DN
+ GUFsaWNlIDxhbGljZUBleGFtcGxlLm9yZz7CkAQTFggAOBYhBC5vossjtTLXKGNLWGSwj2Gp
+ 7ZRDBQJeWHXdAhsDBQsJCAcCBhUKCQgLAgQWAgMBAh4BAheAAAoJEGSwj2Gp7ZRDE3oA/i4M
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+ RuI8A/8tEEXAA844BF5Ydd0SCisGAQQBl1UBBQEBB0AG7cjWy2SFAU8KnltlubVW67rFiyfp
+ 01JrRe6Xqy22HQMBCAfCeAQYFggAIBYhBC5vossjtTLXKGNLWGSwj2Gp7ZRDBQJeWHXdAhsM
+ AAoJEGSwj2Gp7ZRDLo8BAObE8GnsGVwKzNqCvHeWgJsqhjS3C6gvSlV3tEm9XmF6AQDXucIy
+ VfoBwoyMh2h6cSn/ATn5QJb35pgo+ivp3jsMAg==
+Subject: ...
+Content-Type: multipart/encrypted;
+ protocol="application/pgp-encrypted";
+ boundary="------------EOdOT2kJUL5hgCilmIhYyVZg"
+
+This is an OpenPGP/MIME encrypted message (RFC 4880 and 3156)
+--------------EOdOT2kJUL5hgCilmIhYyVZg
+Content-Type: application/pgp-encrypted
+Content-Description: PGP/MIME version identification
+
+Version: 1
+
+--------------EOdOT2kJUL5hgCilmIhYyVZg
+Content-Type: application/octet-stream; name="encrypted.asc"
+Content-Description: OpenPGP encrypted message
+Content-Disposition: inline; filename="encrypted.asc"
+
+-----BEGIN PGP MESSAGE-----
+
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+
+--------------EOdOT2kJUL5hgCilmIhYyVZg--