Merge pull request #1430 from deltachat/fix-footer

regard line with ony '--' as footer mark partly

src/mimefactory.rs

@@ -15,6 +15,7 @@ use crate::message::{self, Message};
 use crate::mimeparser::SystemMessage;
 use crate::param::*;
 use crate::peerstate::{Peerstate, PeerstateVerifiedStatus};
+use crate::simplify::escape_message_footer_marks;
 use crate::stock::StockMessage;
 
 // attachments of 25 mb brutto should work on the majority of providers
@@ -807,7 +808,7 @@ impl<'a, 'b> MimeFactory<'a, 'b> {
         let message_text = format!(
             "{}{}{}{}{}",
             fwdhint.unwrap_or_default(),
-            &final_text,
+            escape_message_footer_marks(final_text),
             if !final_text.is_empty() && !footer.is_empty() {
                 "\r\n\r\n"
             } else {

src/simplify.rs

@@ -1,13 +1,41 @@
+// protect lines starting with `--` against being treated as a footer.
+// for that, we insert a ZERO WIDTH SPACE (ZWSP, 0x200B);
+// this should be invisible on most systems and there is no need to unescape it again
+// (which won't be done by non-deltas anyway)
+//
+// this escapes a bit more than actually needed by delta (eg. also lines as "-- footer"),
+// but for non-delta-compatibility, that seems to be better.
+// (to be only compatible with delta, only "[\r\n|\n]-- {0,2}[\r\n|\n]" needs to be replaced)
+pub fn escape_message_footer_marks(text: &str) -> String {
+    if text.starts_with("--") {
+        "-\u{200B}-".to_string() + &text[2..].replace("\n--", "\n-\u{200B}-")
+    } else {
+        text.replace("\n--", "\n-\u{200B}-")
+    }
+}
+
 /// Remove standard (RFC 3676, §4.3) footer if it is found.
 fn remove_message_footer<'a>(lines: &'a [&str]) -> &'a [&'a str] {
+    let mut nearly_standard_footer = None;
     for (ix, &line) in lines.iter().enumerate() {
-        // quoted-printable may encode `-- ` to `-- =20` which is converted
-        // back to `--  `
         match line {
+            // some providers encode `-- ` to `-- =20` which results in `--  `
             "-- " | "--  " => return &lines[..ix],
+            // some providers encode `-- ` to `=2D-` which results in only `--`;
+            // use that only when no other footer is found
+            // and if the line before is empty and the line after is not empty
+            "--" => {
+                if (ix == 0 || lines[ix - 1] == "") && ix != lines.len() - 1 && lines[ix + 1] != ""
+                {
+                    nearly_standard_footer = Some(ix);
+                }
+            }
             _ => (),
         }
     }
+    if let Some(ix) = nearly_standard_footer {
+        return &lines[..ix];
+    }
     lines
 }
 
@@ -156,7 +184,8 @@ fn render_message(lines: &[&str], is_cut_at_begin: bool, is_cut_at_end: bool) ->
     if is_cut_at_end && (!is_cut_at_begin || !empty_body) {
         ret += " [...]";
     }
-    ret
+    // redo escaping done by escape_message_footer_marks()
+    ret.replace("\u{200B}", "")
 }
 
 /**
@@ -268,4 +297,46 @@ mod tests {
         assert_eq!(lines, &["not a quote", "> first", "> second"]);
         assert!(!has_top_quote);
     }
+
+    #[test]
+    fn test_escape_message_footer_marks() {
+        let esc = escape_message_footer_marks("--\n--text --in line");
+        assert_eq!(esc, "-\u{200B}-\n-\u{200B}-text --in line");
+
+        let esc = escape_message_footer_marks("--\r\n--text");
+        assert_eq!(esc, "-\u{200B}-\r\n-\u{200B}-text");
+    }
+
+    #[test]
+    fn test_remove_message_footer() {
+        let input = "text\n--\nno footer".to_string();
+        let (plain, _) = simplify(input, true);
+        assert_eq!(plain, "text\n--\nno footer");
+
+        let input = "text\n\n--\n\nno footer".to_string();
+        let (plain, _) = simplify(input, true);
+        assert_eq!(plain, "text\n\n--\n\nno footer");
+
+        let input = "text\n\n-- no footer\n\n".to_string();
+        let (plain, _) = simplify(input, true);
+        assert_eq!(plain, "text\n\n-- no footer");
+
+        let input = "text\n\n--\nno footer\n-- \nfooter".to_string();
+        let (plain, _) = simplify(input, true);
+        assert_eq!(plain, "text\n\n--\nno footer");
+
+        let input = "text\n\n--\ntreated as footer when unescaped".to_string();
+        let (plain, _) = simplify(input.clone(), true);
+        assert_eq!(plain, "text"); // see remove_message_footer() for some explanations
+        let escaped = escape_message_footer_marks(&input);
+        let (plain, _) = simplify(escaped, true);
+        assert_eq!(plain, "text\n\n--\ntreated as footer when unescaped");
+
+        let input = "--\ntreated as footer when unescaped".to_string();
+        let (plain, _) = simplify(input.clone(), true);
+        assert_eq!(plain, ""); // see remove_message_footer() for some explanations
+        let escaped = escape_message_footer_marks(&input);
+        let (plain, _) = simplify(escaped, true);
+        assert_eq!(plain, "--\ntreated as footer when unescaped");
+    }
 }