Do not initialize event data on comments (#38)

As we process a stream, we build up the event_data instance with the
data as it is parsed. When we receive an empty line (e.g. "\n\r"), we
try to dispatch any event we have pending.

However, this event_data instance should only be created and / or
updated if the line we are parsing isn't a comment. Otherwise, we can
skip the initialization and return a comment event without furthering
processing.

Author: keelerm84

eventsource-client/src/event_parser.rs

@@ -206,14 +206,17 @@ impl EventParser {
                 }
 
                 if let Some((key, value)) = parse_field(&line)? {
+                    if key == "comment" {
+                        self.sse.push_back(SSE::Comment(value.to_string()));
+                        continue;
+                    }
+
                     let id = &self.last_event_id;
                     let event_data = self
                         .event_data
                         .get_or_insert_with(|| EventData::new().with_id(id.clone()));
 
-                    if key == "comment" {
-                        self.sse.push_back(SSE::Comment(value.to_string()));
-                    } else if key == "event" {
+                    if key == "event" {
                         event_data.event_type = value.to_string()
                     } else if key == "data" {
                         event_data.append_data(value);
@@ -534,6 +537,18 @@ mod tests {
         assert!(parser.get_event().is_none());
     }
 
+    #[test]
+    fn test_comment_with_trailing_blank_line() {
+        let mut parser = EventParser::new();
+        let result = parser.process_bytes(Bytes::from(":comment\n\r\n\r"));
+        assert!(result.is_ok());
+
+        let comment = parser.get_event();
+        assert!(matches!(comment, Some(SSE::Comment(_))));
+
+        assert!(parser.get_event().is_none());
+    }
+
     #[test_case(&["data:", "hello\n\n"], event("message", "hello"); "data split")]
     #[test_case(&["data:hell", "o\n\n"], event("message", "hello"); "data truncated")]
     fn test_decode_message_split_across_chunks(chunks: &[&'static str], event: SSE) {