1 files changed, 114 insertions, 0 deletions
diff --git a/src/mqtt.rs b/src/mqtt.rs
new file mode 100644
index 0000000..f12d51c
--- /dev/null
+++ b/src/mqtt.rs
@@ -0,0 +1,114 @@
+// SPDX-FileCopyrightText: 2025 Tomasz Kramkowski <tomasz@kramkow.ski>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+pub fn topic_match(filter: &str, topic: &str) -> bool {
+    // TODO: Should probably just be a panic or prevented using types
+    if filter.is_empty() || topic.is_empty() {
+        return false;
+    }
+    if topic.starts_with('$') && (filter.starts_with('+') || filter.starts_with('#')) {
+        return false;
+    }
+
+    // zip_longest would be nice
+    let mut topic = topic.split('/');
+    let mut filter = filter.split('/');
+    loop {
+        let topic_level = topic.next();
+        return match filter.next() {
+            Some("#") => filter.next().is_none(),
+            Some("+") => {
+                if topic_level.is_none() {
+                    false
+                } else {
+                    continue;
+                }
+            }
+            Some(filter_level) => match topic_level {
+                Some(topic_level) if topic_level == filter_level => {
+                    continue;
+                }
+                _ => false,
+            },
+            None => topic_level.is_none(),
+        };
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::topic_match;
+
+    #[test]
+    fn topic_match_basic() {
+        assert!(topic_match("foo/bar/baz", "foo/bar/baz"));
+        assert!(!topic_match("foo/bar/baz", "foo/bar/qux"));
+        assert!(!topic_match("foo/bar", "foo/bar/baz"));
+        assert!(!topic_match("foo/bar/baz", "foo/bar"));
+    }
+
+    #[test]
+    fn topic_match_wildcard_hash() {
+        assert!(topic_match("foo/bar/baz/#", "foo/bar/baz"));
+        assert!(topic_match("foo/bar/baz/#", "foo/bar/baz/qux"));
+        assert!(topic_match("foo/bar/baz/#", "foo/bar/baz/qux/quux"));
+        assert!(topic_match("#", "foo/bar/baz"));
+        assert!(topic_match("#", "foo"));
+        assert!(topic_match("#", "/"));
+        assert!(topic_match("#", "/foo"));
+        assert!(!topic_match("foo/bar/#", "foo/baz/bar"));
+        assert!(!topic_match("foo/bar/#", "foo"));
+    }
+
+    #[test]
+    fn topic_match_wildcard_plus() {
+        assert!(topic_match("foo/bar/+", "foo/bar/baz"));
+        assert!(topic_match("foo/bar/+", "foo/bar/qux"));
+        assert!(!topic_match("foo/bar/+", "foo/bar/baz/qux"));
+        assert!(topic_match("foo/+", "foo/"));
+        assert!(!topic_match("foo/+", "foo"));
+        assert!(topic_match("+", "foo"));
+        assert!(topic_match("+/bar/#", "foo/bar/baz/qux"));
+        assert!(topic_match("+/bar/#", "qux/bar"));
+        assert!(topic_match("foo/+/baz", "foo/bar/baz"));
+        assert!(topic_match("foo/+/baz", "foo/qux/baz"));
+        assert!(!topic_match("foo/+/baz", "foo/bar/qux"));
+        assert!(topic_match("+/+", "/foo"));
+        assert!(topic_match("/+", "/foo"));
+        assert!(!topic_match("+", "/foo"));
+    }
+
+    #[test]
+    fn topic_match_dollar() {
+        assert!(!topic_match("#", "$foo/bar"));
+        assert!(!topic_match("+/bar/baz", "$foo/bar/baz"));
+        assert!(topic_match("$foo/#", "$foo/bar"));
+        assert!(topic_match("$foo/#", "$foo/bar/baz"));
+        assert!(topic_match("$foo/#", "$foo"));
+        assert!(topic_match("$foo/bar/+", "$foo/bar/baz"));
+        assert!(!topic_match("$foo/#", "foo/bar"));
+    }
+
+    #[test]
+    fn topic_match_edge_cases() {
+        assert!(!topic_match("foo", "FOO"));
+        assert!(topic_match("foo bar", "foo bar"));
+        assert!(!topic_match("foo bar", "foo  bar"));
+        assert!(!topic_match("foo  bar", "foo bar"));
+        assert!(!topic_match("/foo", "foo"));
+        assert!(!topic_match("foo", "/foo"));
+        assert!(topic_match("foo//bar", "foo//bar"));
+        assert!(!topic_match("foo/bar", "foo//bar"));
+        assert!(!topic_match("foo//bar", "foo/bar"));
+        assert!(!topic_match("foo//baz", "foo/bar/baz"));
+        assert!(!topic_match("foo/bar/baz", "foo//baz"));
+        assert!(topic_match("foo/+/baz", "foo//baz"));
+        assert!(topic_match("/", "/"));
+        assert!(!topic_match("/", "foo"));
+        assert!(!topic_match("foo", "/"));
+        assert!(!topic_match("", ""));
+        assert!(!topic_match("+", ""));
+        assert!(!topic_match("#", ""));
+        assert!(!topic_match("foo/#/baz", "foo/bar/baz"));
+    }
+}