From 89696582ada7f1ef76aec88a4aef7a14ec476e3d Mon Sep 17 00:00:00 2001
From: iequidoo <dgreshilov@gmail.com>
Date: Sat, 18 Feb 2023 22:39:58 -0300
Subject: [PATCH] mimeparser: Handle headers from the signed part of
 unencrypted signed message

This makes DC compatible with "multipart/signed" messages thus allowing switching to them someday
from the current "multipart/mixed" unencrypted message format.
---
 CHANGELOG.md      |  1 +
 src/mimeparser.rs | 26 +++++++++++++++++++++++++-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 39bb421be..3203bd410 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,7 @@
 - Updated provider database.
 - Disable DKIM-Checks again #4076
 - Switch from "X.Y.Z" and "py-X.Y.Z" to "vX.Y.Z" tags. #4089
+- mimeparser: handle headers from the signed part of unencrypted signed message #4013
 
 ### Fixes
 - Start SQL transactions with IMMEDIATE behaviour rather than default DEFERRED one. #4063
diff --git a/src/mimeparser.rs b/src/mimeparser.rs
index 075fd192f..50b71b092 100644
--- a/src/mimeparser.rs
+++ b/src/mimeparser.rs
@@ -224,8 +224,32 @@ impl MimeMessage {
 
         // Parse hidden headers.
         let mimetype = mail.ctype.mimetype.parse::<Mime>()?;
+        let (part, mimetype) =
+            if mimetype.type_() == mime::MULTIPART && mimetype.subtype().as_str() == "signed" {
+                if let Some(part) = mail.subparts.first() {
+                    // We don't remove "subject" from `headers` because currently just signed
+                    // messages are shown as unencrypted anyway.
+
+                    MimeMessage::merge_headers(
+                        context,
+                        &mut headers,
+                        &mut recipients,
+                        &mut from,
+                        &mut list_post,
+                        &mut chat_disposition_notification_to,
+                        &part.headers,
+                    );
+                    (part, part.ctype.mimetype.parse::<Mime>()?)
+                } else {
+                    // If it's a partially fetched message, there are no subparts.
+                    (&mail, mimetype)
+                }
+            } else {
+                // Currently we do not sign unencrypted messages by default.
+                (&mail, mimetype)
+            };
         if mimetype.type_() == mime::MULTIPART && mimetype.subtype().as_str() == "mixed" {
-            if let Some(part) = mail.subparts.first() {
+            if let Some(part) = part.subparts.first() {
                 for field in &part.headers {
                     let key = field.get_key().to_lowercase();