Add local in-memory pubsub

crates/geth-pubsub/Cargo.toml

@@ -7,4 +7,5 @@ license.workspace = true
 
 [dependencies]
 serde.workspace = true
+thiserror.workspace = true
 geth-types = { path = "../geth-types" }

crates/geth-pubsub/src/lib.rs

@@ -1,4 +1,4 @@
-use geth_types::{ResourceId, TopicId};
+use geth_types::{ResourceId, TopicId, UnixMillis};
 use serde::{Deserialize, Serialize};
 
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
@@ -8,7 +8,54 @@ pub struct PubsubTopic {
     pub name: String,
 }
 
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub struct PubsubMessage {
+    pub topic: TopicId,
+    pub message: String,
+    pub published_at: UnixMillis,
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum PubsubError {
+    #[error("invalid pubsub topic: {0}")]
+    InvalidTopic(String),
+    #[error("pubsub message must not be empty")]
+    EmptyMessage,
+}
+
+pub fn validate_topic(topic: &str) -> Result<(), PubsubError> {
+    if topic.is_empty()
+        || topic
+            .bytes()
+            .any(|byte| byte == 0 || byte == b'\n' || byte == b'\r')
+    {
+        return Err(PubsubError::InvalidTopic(topic.to_owned()));
+    }
+    Ok(())
+}
+
+pub fn validate_message(message: &str) -> Result<(), PubsubError> {
+    if message.is_empty() {
+        return Err(PubsubError::EmptyMessage);
+    }
+    Ok(())
+}
+
 #[must_use]
 pub fn pubsub_storage_warning() -> &'static str {
     "pubsub is lossy notification transport, not authoritative storage"
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn pubsub_validation_rejects_invalid_topics_and_empty_messages() {
+        assert!(validate_topic("presence/laptop").is_ok());
+        assert!(validate_topic("").is_err());
+        assert!(validate_topic("presence\nlaptop").is_err());
+        assert!(validate_message("online").is_ok());
+        assert!(validate_message("").is_err());
+    }
+}