[geary] Geary.RFC822.Subject: Handle long headers being folded

[Michael Gratton <mjog src gnome org>]

commit b51b933b6de8fbe880d6c6a657eff7a7b677db79
Author: Michael Gratton <mike vee net>
Date:   Wed Jan 20 19:20:30 2021 +1100

    Geary.RFC822.Subject: Handle long headers being folded
    
    Remove "\n " sequences from RFC822 text before decoding so that any
    long subject lines folded before the 80 char limit are unfolded.
    
    Fixes #895

 src/engine/rfc822/rfc822-message-data.vala       |  4 ++--
 src/engine/rfc822/rfc822-utils.vala              | 15 +++++++++++++--
 test/engine/rfc822/rfc822-message-data-test.vala |  9 +++++++++
 3 files changed, 24 insertions(+), 4 deletions(-)
---
diff --git a/src/engine/rfc822/rfc822-message-data.vala b/src/engine/rfc822/rfc822-message-data.vala
index d238bdec1..d36e57a0d 100644
--- a/src/engine/rfc822/rfc822-message-data.vala
+++ b/src/engine/rfc822/rfc822-message-data.vala
@@ -1,6 +1,6 @@
 /*
  * Copyright © 2016 Software Freedom Conservancy Inc.
- * Copyright © 2020 Michael Gratton <mike vee net>
+ * Copyright © 2020-2021 Michael Gratton <mike vee net>
  *
  * This software is licensed under the GNU Lesser General Public License
  * (version 2.1 or later).  See the COPYING file in this distribution.
@@ -367,7 +367,7 @@ public class Geary.RFC822.Subject :
     }
 
     public Subject.from_rfc822_string(string rfc822) {
-        base(GMime.utils_header_decode_text(get_parser_options(), rfc822).strip());
+        base(Utils.decode_rfc822_text_header_value(rfc822));
         this.rfc822 = rfc822;
     }
 
diff --git a/src/engine/rfc822/rfc822-utils.vala b/src/engine/rfc822/rfc822-utils.vala
index feb377eb8..e0b0bee55 100644
--- a/src/engine/rfc822/rfc822-utils.vala
+++ b/src/engine/rfc822/rfc822-utils.vala
@@ -1,6 +1,7 @@
 /*
- * Copyright 2016 Software Freedom Conservancy Inc.
- * Portions copyright (C) 2000-2013 Jeffrey Stedfast
+ * Copyright © 2016 Software Freedom Conservancy Inc.
+ * Copyright © 2021 Michael Gratton <mike vee net>
+ * Portions copyright © 2000-2013 Jeffrey Stedfast
  *
  * This software is licensed under the GNU Lesser General Public License
  * (version 2.1 or later). See the COPYING file in this distribution.
@@ -200,6 +201,16 @@ namespace Geary.RFC822.Utils {
         return Geary.String.reduce_whitespace(preview.make_valid());
     }
 
+    /**
+     * Decodes RFC-822 long header lines and RFC 2047 encoded text headers.
+     */
+    internal string decode_rfc822_text_header_value(string rfc822) {
+        return GMime.utils_header_decode_text(
+            get_parser_options(),
+            GMime.utils_header_unfold(rfc822)
+        );
+    }
+
     /**
      * Uses a GMime.FilterBest to determine the best charset.
      *
diff --git a/test/engine/rfc822/rfc822-message-data-test.vala 
b/test/engine/rfc822/rfc822-message-data-test.vala
index d6357ff95..613e4b9a1 100644
--- a/test/engine/rfc822/rfc822-message-data-test.vala
+++ b/test/engine/rfc822/rfc822-message-data-test.vala
@@ -9,6 +9,7 @@ class Geary.RFC822.MessageDataTest : TestCase {
 
     public MessageDataTest() {
         base("Geary.RFC822.MessageDataTest");
+        add_test("subject_from_rfc822", subject_from_rfc822);
         add_test("date_from_rfc822", date_from_rfc822);
         add_test("date_from_rfc822", date_from_rfc822);
         add_test("date_to_rfc822", date_to_rfc822);
@@ -21,6 +22,14 @@ class Geary.RFC822.MessageDataTest : TestCase {
         add_test("MessageIdList.merge", message_id_list_merge);
     }
 
+    public void subject_from_rfc822() throws GLib.Error {
+        Subject plain = new Subject.from_rfc822_string("hello");
+        assert_equal(plain.to_string(), "hello");
+
+        Subject new_line = new Subject.from_rfc822_string("hello\n there");
+        assert_equal(new_line.to_string(), "hello there");
+    }
+
     public void preview_text_with_header() throws GLib.Error {
         PreviewText plain_preview1 = new PreviewText.with_header(
             new Geary.Memory.StringBuffer(PLAIN_BODY1_HEADERS),