fix(config_edit): tolerate Loxone's value-identical duplicate attributes

src/config_edit/mod.rs

@@ -311,7 +311,10 @@ impl ConfigEditor {
         let xml_data = if had_bom { &data[3..] } else { data };
 
         let (xml_data_cow, digit_attr_renames) = Self::sanitize_digit_attrs(xml_data);
-        let reader = BufReader::new(Cursor::new(xml_data_cow.as_ref()));
+        // Loxone emits the same attribute twice on some elements (value-identical).
+        // A strict parser rejects that; drop the redundant copy losslessly before parsing.
+        let deduped = Self::dedupe_duplicate_attrs(xml_data_cow.as_ref());
+        let reader = BufReader::new(Cursor::new(deduped.as_ref()));
         let root = Element::parse(reader).context("Failed to parse Loxone XML")?;
         Ok(ConfigEditor {
             root,
@@ -373,6 +376,112 @@ impl ConfigEditor {
         (std::borrow::Cow::Owned(result.into_bytes()), renames)
     }
 
+    /// Remove **value-identical** duplicate attributes from element start tags.
+    ///
+    /// Loxone Config emits the same attribute twice on some elements (observed on API
+    /// Connector elements: `Title` appears twice with the same value). A strict XML parser
+    /// rejects that ("Attribute 'Title' is redefined"). Since the duplicates are
+    /// value-identical, dropping the redundant copy is lossless. Duplicates with *different*
+    /// values are left untouched so a genuine conflict still surfaces at parse time.
+    ///
+    /// Quote-aware: attribute values may legitimately contain `<`, `>` and `=`
+    /// (e.g. `Unit="<v>%"`), so tag boundaries are found respecting `"…"`.
+    fn dedupe_duplicate_attrs(data: &[u8]) -> std::borrow::Cow<'_, [u8]> {
+        let text = match std::str::from_utf8(data) {
+            Ok(s) => s,
+            Err(_) => return std::borrow::Cow::Borrowed(data),
+        };
+        let bytes = text.as_bytes();
+        let len = bytes.len();
+        let ws = |b: u8| matches!(b, b' ' | b'\t' | b'\r' | b'\n');
+        let mut deletes: Vec<(usize, usize)> = Vec::new();
+        let mut i = 0;
+        while i < len {
+            // Start of an element tag: '<' not followed by '/', '?' or '!'.
+            if bytes[i] == b'<' && i + 1 < len && !matches!(bytes[i + 1], b'/' | b'?' | b'!') {
+                // Skip the element name.
+                let mut j = i + 1;
+                while j < len
+                    && (bytes[j].is_ascii_alphanumeric()
+                        || matches!(bytes[j], b'_' | b':' | b'-'))
+                {
+                    j += 1;
+                }
+                // Scan attributes until the end of the start tag.
+                let mut seen: Vec<(&str, &str)> = Vec::new();
+                loop {
+                    while j < len && ws(bytes[j]) {
+                        j += 1;
+                    }
+                    if j >= len || matches!(bytes[j], b'>' | b'/') {
+                        break;
+                    }
+                    let name_start = j;
+                    while j < len && !ws(bytes[j]) && !matches!(bytes[j], b'=' | b'>' | b'/') {
+                        j += 1;
+                    }
+                    let name_end = j;
+                    while j < len && ws(bytes[j]) {
+                        j += 1;
+                    }
+                    if j >= len || bytes[j] != b'=' {
+                        break; // not `name=…`, stop scanning this tag
+                    }
+                    j += 1;
+                    while j < len && ws(bytes[j]) {
+                        j += 1;
+                    }
+                    if j >= len || bytes[j] != b'"' {
+                        break;
+                    }
+                    let val_start = j + 1;
+                    j = val_start;
+                    while j < len && bytes[j] != b'"' {
+                        j += 1;
+                    }
+                    if j >= len {
+                        break;
+                    }
+                    let val_end = j;
+                    j += 1; // past closing quote
+                    let attr_end = j;
+                    let name = &text[name_start..name_end];
+                    let value = &text[val_start..val_end];
+                    if let Some(&(_, prev)) = seen.iter().find(|(n, _)| *n == name) {
+                        if prev == value {
+                            // Redundant copy → delete it plus one leading whitespace char.
+                            let del_start = if name_start > 0 && ws(bytes[name_start - 1]) {
+                                name_start - 1
+                            } else {
+                                name_start
+                            };
+                            deletes.push((del_start, attr_end));
+                        }
+                        // Different value: leave it, let the parser flag the conflict.
+                    } else {
+                        seen.push((name, value));
+                    }
+                }
+                i = j;
+                continue;
+            }
+            i += 1;
+        }
+        if deletes.is_empty() {
+            return std::borrow::Cow::Borrowed(data);
+        }
+        let mut out = String::with_capacity(text.len());
+        let mut last = 0;
+        for (s, e) in deletes {
+            if s >= last {
+                out.push_str(&text[last..s]);
+                last = e;
+            }
+        }
+        out.push_str(&text[last..]);
+        std::borrow::Cow::Owned(out.into_bytes())
+    }
+
     /// Get a mutable reference to an element by path.
     pub fn get_element_mut(&mut self, path: &[usize]) -> &mut Element {
         let mut current = &mut self.root;
@@ -572,6 +681,38 @@ mod tests {
         let _ = ConfigEditor::load(&output).unwrap();
     }
 
+    #[test]
+    fn test_dedupe_value_identical_duplicate_attr() {
+        // Loxone emits the same attribute twice, value-identical → must parse, redundant copy dropped.
+        let xml = br#"<?xml version="1.0" encoding="utf-8"?>
+<ControlList Version="267">
+  <C Type="Place" U="room-1" Title="Kitchen" WF="16384" Title="Kitchen"/>
+</ControlList>"#;
+        let editor = ConfigEditor::load(xml).unwrap();
+        let out = String::from_utf8(editor.to_bytes().unwrap()).unwrap();
+        assert_eq!(out.matches(r#"Title="Kitchen""#).count(), 1);
+    }
+
+    #[test]
+    fn test_dedupe_leaves_conflicting_duplicate() {
+        // Different values = a real conflict; must still surface at parse time.
+        let xml = br#"<ControlList><C U="x" Title="A" Title="B"/></ControlList>"#;
+        assert!(ConfigEditor::load(xml).is_err());
+    }
+
+    #[test]
+    fn test_dedupe_is_quote_aware() {
+        // A value may contain escaped angle brackets (e.g. Unit="&lt;v&gt;%"); tag scanning
+        // must not be confused, and an unrelated value-identical dup still collapses.
+        let xml = br#"<ControlList>
+  <C U="x" Unit="&lt;v&gt;%" Nio="1" Nio="1"/>
+</ControlList>"#;
+        let editor = ConfigEditor::load(xml).unwrap();
+        let out = String::from_utf8(editor.to_bytes().unwrap()).unwrap();
+        assert_eq!(out.matches(r#"Nio="1""#).count(), 1);
+        assert!(out.contains("&lt;v&gt;%"));
+    }
+
     #[test]
     fn test_bom_preservation() {
         let mut with_bom = Vec::new();