fix: accept 200 with empty body in response to notifications in addition to 202 (#849)

crates/rmcp/src/transport/common/unix_socket.rs

@@ -257,12 +257,29 @@ impl StreamableHttpClient for UnixSocketHttpClient {
         }
 
         let content_type = response.headers().get(http::header::CONTENT_TYPE).cloned();
+        let content_length = response
+            .headers()
+            .get(http::header::CONTENT_LENGTH)
+            .and_then(|v| v.to_str().ok())
+            .and_then(|v| v.parse::<u64>().ok());
         let session_id = response
             .headers()
             .get(HEADER_SESSION_ID)
             .and_then(|v| v.to_str().ok())
             .map(|s| s.to_string());
 
+        if status.is_success()
+            && content_length == Some(0)
+            && matches!(
+                message,
+                ClientJsonRpcMessage::Notification(_)
+                    | ClientJsonRpcMessage::Response(_)
+                    | ClientJsonRpcMessage::Error(_)
+            )
+        {
+            return Ok(StreamableHttpPostResponse::Accepted);
+        }
+
         match content_type {
             Some(ref ct) if ct.as_bytes().starts_with(EVENT_STREAM_MIME_TYPE.as_bytes()) => {
                 let sse_stream = SseStream::new(response.into_body()).boxed();