filter: add content filter

Signed-off-by: William Casarin <jb55@jb55.com>

src/filters/content.rs

@@ -0,0 +1,23 @@
+use crate::{Action, InputMessage, NoteFilter, OutputMessage};
+use serde::Deserialize;
+
+#[derive(Deserialize, Default)]
+pub struct Content {
+    filters: Vec<String>,
+}
+
+impl NoteFilter for Content {
+    fn filter_note(&mut self, msg: &InputMessage) -> OutputMessage {
+        for filter in &self.filters {
+            if msg.event.content.contains(filter) {
+                return OutputMessage::new(msg.event.id.clone(), Action::ShadowReject, None);
+            }
+        }
+
+        OutputMessage::new(msg.event.id.clone(), Action::Accept, None)
+    }
+
+    fn name(&self) -> &'static str {
+        "content"
+    }
+}

src/filters/mod.rs

@@ -1,3 +1,4 @@
+mod content;
 mod kinds;
 mod protected_events;
 mod ratelimit;
@@ -6,6 +7,7 @@ mod whitelist;
 #[cfg(feature = "forwarder")]
 mod forwarder;
 
+pub use content::Content;
 pub use kinds::Kinds;
 pub use protected_events::ProtectedEvents;
 pub use ratelimit::RateLimit;