fix(translation): accept SSE data fields with no space after the colon

crates/switchyard-translation/src/sse.rs

@@ -29,14 +29,24 @@ pub(crate) fn done_marker(_format: WireFormat) -> Option<&'static str> {
     Some("[DONE]")
 }
 
+/// Value of a `data` field line; the space after the colon is optional framing.
+fn data_field_value(line: &str) -> Option<String> {
+    let value = match line.split_once(':') {
+        Some(("data", value)) => value,
+        None if line == "data" => "",
+        _ => return None,
+    };
+    Some(value.strip_prefix(' ').unwrap_or(value).to_string())
+}
+
 pub(crate) fn parse_json_sse_frame(
     frame: &str,
     done_marker: Option<&str>,
 ) -> Result<SseFrame, BoxError> {
     let data = frame
         .lines()
         .filter(|line| !line.is_empty() && !line.starts_with(':'))
-        .filter_map(|line| line.strip_prefix("data: ").map(|l| l.to_string()))
+        .filter_map(data_field_value)
         .fold(String::new(), |mut a, b| {
             a.reserve(b.len() + 1);
             a.push_str(&b);
@@ -83,6 +93,35 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn parses_a_data_line_without_a_space_after_the_colon() -> Result<(), BoxError> {
+        // The space after `data:` is optional framing, not part of the value.
+        let SseFrame::Data(value) = parse_json_sse_frame("data:{\"text\":\"hi\"}\n", DONE)? else {
+            return Err("expected a payload".into());
+        };
+        assert_eq!(value, json!({"text": "hi"}));
+        Ok(())
+    }
+
+    #[test]
+    fn done_marker_is_recognised_without_a_space() -> Result<(), BoxError> {
+        assert!(matches!(
+            parse_json_sse_frame("data:[DONE]\n", DONE)?,
+            SseFrame::Done
+        ));
+        Ok(())
+    }
+
+    #[test]
+    fn field_names_are_matched_exactly() -> Result<(), BoxError> {
+        // `database:` must not be read as a `data` field.
+        assert!(matches!(
+            parse_json_sse_frame("database: {\"n\":1}\n", DONE)?,
+            SseFrame::Empty
+        ));
+        Ok(())
+    }
+
     #[test]
     fn done_marker_yields_no_payload() -> Result<(), BoxError> {
         assert!(matches!(