| 1 | //! RPC bridge that services `llm_query` / `rlm_query` calls coming back |
| 2 | //! from the long-lived Python REPL during an RLM turn. |
| 3 | //! |
| 4 | //! This is the spiritual successor to the HTTP sidecar from earlier |
| 5 | //! versions — except instead of binding a localhost port and routing |
| 6 | //! through `urllib`, requests come in through stdin/stdout and we just |
| 7 | //! call the LLM client directly here in Rust. |
| 8 | //! |
| 9 | //! The bridge tracks cumulative token usage and the recursion budget. For |
| 10 | //! `Rlm` / `RlmBatch` requests it recursively calls `run_rlm_turn_inner` |
| 11 | //! at depth-1; the future-type cycle (bridge → run_rlm_turn_inner → |
| 12 | //! bridge) is broken by `run_rlm_turn_inner` returning a boxed dyn future. |
| 13 | |
| 14 | use std::sync::Arc; |
| 15 | use std::time::Duration; |
| 16 | use std::{future::Future, pin::Pin}; |
| 17 | |
| 18 | use anyhow::Result; |
| 19 | use futures_util::future::join_all; |
| 20 | use tokio::sync::Mutex; |
| 21 | |
| 22 | use crate::llm_client::LlmClient; |
| 23 | use crate::models::{ContentBlock, Message, MessageRequest, MessageResponse, SystemPrompt, Usage}; |
| 24 | use crate::repl::runtime::{BatchResp, RpcDispatcher, RpcRequest, RpcResponse, SingleResp}; |
| 25 | use crate::utils::spawn_supervised; |
| 26 | |
| 27 | /// Per-child completion timeout — same as the previous sidecar default. |
| 28 | const CHILD_TIMEOUT_SECS: u64 = 120; |
| 29 | /// Default `max_tokens` for one-shot child completions. |
| 30 | const DEFAULT_CHILD_MAX_TOKENS: u32 = 4096; |
| 31 | /// Hard cap on prompts per batch RPC. |
| 32 | pub const MAX_BATCH: usize = 16; |
| 33 | |
| 34 | /// Object-safe slice of the LLM client interface that the RLM bridge needs. |
| 35 | /// |
| 36 | /// `LlmClient` itself uses native async trait methods, which are not dyn-safe. |
| 37 | /// The bridge only needs non-streaming completions, so this boxed-future shim |
| 38 | /// gives tests a clean mock seam without changing the wider provider trait. |
| 39 | pub(crate) trait RlmLlmClient: Send + Sync { |
| 40 | fn create_message_boxed( |
| 41 | &self, |
| 42 | request: MessageRequest, |
| 43 | ) -> Pin<Box<dyn Future<Output = Result<MessageResponse>> + Send + '_>>; |
| 44 | } |
| 45 | |
| 46 | impl<T> RlmLlmClient for T |
| 47 | where |
| 48 | T: LlmClient + Send + Sync, |
| 49 | { |
| 50 | fn create_message_boxed( |
| 51 | &self, |
| 52 | request: MessageRequest, |
| 53 | ) -> Pin<Box<dyn Future<Output = Result<MessageResponse>> + Send + '_>> { |
| 54 | Box::pin(self.create_message(request)) |
| 55 | } |
| 56 | } |
| 57 | |
| 58 | /// State shared with the bridge across all RPC calls in one turn. |
| 59 | pub struct RlmBridge { |
| 60 | client: Arc<dyn RlmLlmClient>, |
| 61 | child_model: String, |
| 62 | /// Recursion budget remaining for `Rlm` / `RlmBatch` requests. When |
| 63 | /// zero, those requests fall back to plain `Llm` completions. |
| 64 | depth_remaining: u32, |
| 65 | usage: Arc<Mutex<Usage>>, |
| 66 | } |
| 67 | |
| 68 | impl RlmBridge { |
| 69 | pub(crate) fn new( |
| 70 | client: Arc<dyn RlmLlmClient>, |
| 71 | child_model: String, |
| 72 | depth_remaining: u32, |
| 73 | ) -> Self { |
| 74 | Self { |
| 75 | client, |
| 76 | child_model, |
| 77 | depth_remaining, |
| 78 | usage: Arc::new(Mutex::new(Usage::default())), |
| 79 | } |
| 80 | } |
| 81 | |
| 82 | pub fn usage_handle(&self) -> Arc<Mutex<Usage>> { |
| 83 | Arc::clone(&self.usage) |
| 84 | } |
| 85 | |
| 86 | async fn dispatch_llm( |
| 87 | &self, |
| 88 | prompt: String, |
| 89 | _model: Option<String>, |
| 90 | max_tokens: Option<u32>, |
| 91 | system: Option<String>, |
| 92 | ) -> SingleResp { |
| 93 | let request = MessageRequest { |
| 94 | // The Python helper accepts `model=` for older snippets, but it is |
| 95 | // intentionally not authoritative. RLM child calls are pinned to |
| 96 | // the tool's configured child model so model-generated Python |
| 97 | // cannot silently upgrade cheap fanout work to an expensive model. |
| 98 | model: self.child_model.clone(), |
| 99 | messages: vec![Message { |
| 100 | role: "user".to_string(), |
| 101 | content: vec![ContentBlock::Text { |
| 102 | text: prompt, |
| 103 | cache_control: None, |
| 104 | }], |
| 105 | }], |
| 106 | max_tokens: max_tokens.unwrap_or(DEFAULT_CHILD_MAX_TOKENS), |
| 107 | system: system.map(SystemPrompt::Text), |
| 108 | tools: None, |
| 109 | tool_choice: None, |
| 110 | metadata: None, |
| 111 | thinking: None, |
| 112 | reasoning_effort: None, |
| 113 | stream: Some(false), |
| 114 | temperature: Some(0.4_f32), |
| 115 | top_p: Some(0.9_f32), |
| 116 | }; |
| 117 | |
| 118 | let fut = self.client.create_message_boxed(request); |
| 119 | let response = |
| 120 | match tokio::time::timeout(Duration::from_secs(CHILD_TIMEOUT_SECS), fut).await { |
| 121 | Ok(Ok(r)) => r, |
| 122 | Ok(Err(e)) => { |
| 123 | return SingleResp { |
| 124 | text: String::new(), |
| 125 | error: Some(format!("llm_query failed: {e}")), |
| 126 | }; |
| 127 | } |
| 128 | Err(_) => { |
| 129 | return SingleResp { |
| 130 | text: String::new(), |
| 131 | error: Some(format!("llm_query timed out after {CHILD_TIMEOUT_SECS}s")), |
| 132 | }; |
| 133 | } |
| 134 | }; |
| 135 | |
| 136 | let text = response |
| 137 | .content |
| 138 | .iter() |
| 139 | .filter_map(|b| match b { |
| 140 | ContentBlock::Text { text, .. } => Some(text.as_str()), |
| 141 | _ => None, |
| 142 | }) |
| 143 | .collect::<Vec<_>>() |
| 144 | .join("\n"); |
| 145 | |
| 146 | { |
| 147 | let mut u = self.usage.lock().await; |
| 148 | u.input_tokens = u.input_tokens.saturating_add(response.usage.input_tokens); |
| 149 | u.output_tokens = u.output_tokens.saturating_add(response.usage.output_tokens); |
| 150 | } |
| 151 | |
| 152 | SingleResp { text, error: None } |
| 153 | } |
| 154 | |
| 155 | async fn dispatch_llm_batch(&self, prompts: Vec<String>, _model: Option<String>) -> BatchResp { |
| 156 | if let Some(resp) = batch_guard(prompts.len()) { |
| 157 | return resp; |
| 158 | } |
| 159 | |
| 160 | let model = Arc::new(self.child_model.clone()); |
| 161 | |
| 162 | let futures = prompts.into_iter().map(|prompt| { |
| 163 | let model = Arc::clone(&model); |
| 164 | async move { |
| 165 | self.dispatch_llm((*prompt).to_string(), Some((*model).clone()), None, None) |
| 166 | .await |
| 167 | } |
| 168 | }); |
| 169 | |
| 170 | BatchResp { |
| 171 | results: join_all(futures).await, |
| 172 | } |
| 173 | } |
| 174 | |
| 175 | async fn dispatch_rlm(&self, prompt: String, _model: Option<String>) -> SingleResp { |
| 176 | if self.depth_remaining == 0 { |
| 177 | // Budget exhausted — fall back to a one-shot child completion |
| 178 | // rather than returning an error. Matches the paper's behaviour |
| 179 | // ("sub_RLM gracefully degrades to llm_query at depth=0"). |
| 180 | return self.dispatch_llm(prompt, None, None, None).await; |
| 181 | } |
| 182 | |
| 183 | // Build a drain channel to absorb status events from the nested |
| 184 | // turn (we don't surface them; this dispatch is invisible to the |
| 185 | // outer agent stream). |
| 186 | let (tx, mut rx) = tokio::sync::mpsc::channel(64); |
| 187 | let drain = spawn_supervised( |
| 188 | "rlm-bridge-drain", |
| 189 | std::panic::Location::caller(), |
| 190 | async move { while rx.recv().await.is_some() {} }, |
| 191 | ); |
| 192 | |
| 193 | let child_model = self.child_model.clone(); |
| 194 | |
| 195 | // Recursive call. The dyn-erasure on `run_rlm_turn_inner` breaks |
| 196 | // the `bridge → turn → bridge` opaque-future cycle. |
| 197 | let result = super::turn::run_rlm_turn_inner( |
| 198 | Arc::clone(&self.client), |
| 199 | child_model.clone(), |
| 200 | prompt, |
| 201 | None, |
| 202 | child_model, |
| 203 | tx, |
| 204 | self.depth_remaining.saturating_sub(1), |
| 205 | ) |
| 206 | .await; |
| 207 | |
| 208 | drain.abort(); |
| 209 | |
| 210 | { |
| 211 | let mut u = self.usage.lock().await; |
| 212 | u.input_tokens = u.input_tokens.saturating_add(result.usage.input_tokens); |
| 213 | u.output_tokens = u.output_tokens.saturating_add(result.usage.output_tokens); |
| 214 | } |
| 215 | |
| 216 | SingleResp { |
| 217 | text: result.answer, |
| 218 | error: result.error, |
| 219 | } |
| 220 | } |
| 221 | |
| 222 | async fn dispatch_rlm_batch(&self, prompts: Vec<String>, _model: Option<String>) -> BatchResp { |
| 223 | if let Some(resp) = batch_guard(prompts.len()) { |
| 224 | return resp; |
| 225 | } |
| 226 | |
| 227 | let futures = prompts |
| 228 | .into_iter() |
| 229 | .map(|p| async move { self.dispatch_rlm(p, None).await }); |
| 230 | BatchResp { |
| 231 | results: join_all(futures).await, |
| 232 | } |
| 233 | } |
| 234 | } |
| 235 | |
| 236 | fn batch_guard(prompt_count: usize) -> Option<BatchResp> { |
| 237 | if prompt_count == 0 { |
| 238 | return Some(BatchResp { results: vec![] }); |
| 239 | } |
| 240 | if prompt_count > MAX_BATCH { |
| 241 | return Some(BatchResp { |
| 242 | results: (0..prompt_count) |
| 243 | .map(|_| SingleResp { |
| 244 | text: String::new(), |
| 245 | error: Some(format!("batch too large: {prompt_count} > {MAX_BATCH}")), |
| 246 | }) |
| 247 | .collect(), |
| 248 | }); |
| 249 | } |
| 250 | None |
| 251 | } |
| 252 | |
| 253 | impl RpcDispatcher for RlmBridge { |
| 254 | fn dispatch<'a>( |
| 255 | &'a self, |
| 256 | req: RpcRequest, |
| 257 | ) -> std::pin::Pin<Box<dyn std::future::Future<Output = RpcResponse> + Send + 'a>> { |
| 258 | Box::pin(async move { |
| 259 | match req { |
| 260 | RpcRequest::Llm { |
| 261 | prompt, |
| 262 | model, |
| 263 | max_tokens, |
| 264 | system, |
| 265 | } => { |
| 266 | RpcResponse::Single(self.dispatch_llm(prompt, model, max_tokens, system).await) |
| 267 | } |
| 268 | RpcRequest::LlmBatch { prompts, model } => { |
| 269 | RpcResponse::Batch(self.dispatch_llm_batch(prompts, model).await) |
| 270 | } |
| 271 | RpcRequest::Rlm { prompt, model } => { |
| 272 | RpcResponse::Single(self.dispatch_rlm(prompt, model).await) |
| 273 | } |
| 274 | RpcRequest::RlmBatch { prompts, model } => { |
| 275 | RpcResponse::Batch(self.dispatch_rlm_batch(prompts, model).await) |
| 276 | } |
| 277 | } |
| 278 | }) |
| 279 | } |
| 280 | } |
| 281 | |
| 282 | #[cfg(test)] |
| 283 | mod tests { |
| 284 | use super::*; |
| 285 | use crate::llm_client::mock::MockLlmClient; |
| 286 | |
| 287 | fn mock_response(text: &str, input_tokens: u32, output_tokens: u32) -> MessageResponse { |
| 288 | MessageResponse { |
| 289 | id: "mock_msg".to_string(), |
| 290 | r#type: "message".to_string(), |
| 291 | role: "assistant".to_string(), |
| 292 | content: vec![ContentBlock::Text { |
| 293 | text: text.to_string(), |
| 294 | cache_control: None, |
| 295 | }], |
| 296 | model: "mock-model".to_string(), |
| 297 | stop_reason: Some("end_turn".to_string()), |
| 298 | stop_sequence: None, |
| 299 | container: None, |
| 300 | usage: Usage { |
| 301 | input_tokens, |
| 302 | output_tokens, |
| 303 | ..Usage::default() |
| 304 | }, |
| 305 | } |
| 306 | } |
| 307 | |
| 308 | fn bridge_for(mock: Arc<MockLlmClient>, depth_remaining: u32) -> RlmBridge { |
| 309 | let client: Arc<dyn RlmLlmClient> = mock; |
| 310 | RlmBridge::new(client, "child-model".to_string(), depth_remaining) |
| 311 | } |
| 312 | |
| 313 | #[test] |
| 314 | fn batch_guard_allows_non_empty_batches_at_the_cap() { |
| 315 | assert!(batch_guard(MAX_BATCH).is_none()); |
| 316 | } |
| 317 | |
| 318 | #[test] |
| 319 | fn batch_guard_returns_empty_response_for_empty_batches() { |
| 320 | let response = batch_guard(0).expect("empty batch should be handled"); |
| 321 | assert!(response.results.is_empty()); |
| 322 | } |
| 323 | |
| 324 | #[test] |
| 325 | fn batch_guard_returns_one_error_per_oversized_prompt() { |
| 326 | let response = batch_guard(MAX_BATCH + 2).expect("oversized batch should be handled"); |
| 327 | assert_eq!(response.results.len(), MAX_BATCH + 2); |
| 328 | assert!(response.results.iter().all(|result| { |
| 329 | result.text.is_empty() |
| 330 | && result |
| 331 | .error |
| 332 | .as_deref() |
| 333 | .is_some_and(|err| err.contains("batch too large")) |
| 334 | })); |
| 335 | } |
| 336 | |
| 337 | #[tokio::test] |
| 338 | async fn llm_dispatch_pins_configured_child_model() { |
| 339 | let mock = Arc::new(MockLlmClient::new(Vec::new())); |
| 340 | mock.push_message_response(mock_response("child answer", 7, 11)); |
| 341 | let bridge = bridge_for(Arc::clone(&mock), 1); |
| 342 | |
| 343 | let response = bridge |
| 344 | .dispatch(RpcRequest::Llm { |
| 345 | prompt: "child prompt".to_string(), |
| 346 | model: Some("override-model".to_string()), |
| 347 | max_tokens: Some(123), |
| 348 | system: Some("child system".to_string()), |
| 349 | }) |
| 350 | .await; |
| 351 | |
| 352 | match response { |
| 353 | RpcResponse::Single(single) => { |
| 354 | assert_eq!(single.text, "child answer"); |
| 355 | assert!(single.error.is_none()); |
| 356 | } |
| 357 | other => panic!("expected single response, got {other:?}"), |
| 358 | } |
| 359 | |
| 360 | let captured = mock.captured_requests(); |
| 361 | assert_eq!(captured.len(), 1); |
| 362 | assert_eq!(captured[0].model, "child-model"); |
| 363 | assert_eq!(captured[0].max_tokens, 123); |
| 364 | assert_eq!( |
| 365 | captured[0].system, |
| 366 | Some(SystemPrompt::Text("child system".to_string())) |
| 367 | ); |
| 368 | |
| 369 | let usage = bridge.usage.lock().await; |
| 370 | assert_eq!(usage.input_tokens, 7); |
| 371 | assert_eq!(usage.output_tokens, 11); |
| 372 | } |
| 373 | |
| 374 | #[tokio::test] |
| 375 | async fn llm_batch_dispatch_pins_configured_child_model() { |
| 376 | let mock = Arc::new(MockLlmClient::new(Vec::new())); |
| 377 | mock.push_message_response(mock_response("one", 1, 2)); |
| 378 | mock.push_message_response(mock_response("two", 3, 4)); |
| 379 | mock.push_message_response(mock_response("three", 5, 6)); |
| 380 | let bridge = bridge_for(Arc::clone(&mock), 1); |
| 381 | |
| 382 | let response = bridge |
| 383 | .dispatch(RpcRequest::LlmBatch { |
| 384 | prompts: vec!["a".to_string(), "b".to_string(), "c".to_string()], |
| 385 | model: Some("batch-model".to_string()), |
| 386 | }) |
| 387 | .await; |
| 388 | |
| 389 | match response { |
| 390 | RpcResponse::Batch(batch) => { |
| 391 | let texts: Vec<_> = batch |
| 392 | .results |
| 393 | .iter() |
| 394 | .map(|result| result.text.as_str()) |
| 395 | .collect(); |
| 396 | assert_eq!(texts, ["one", "two", "three"]); |
| 397 | assert!(batch.results.iter().all(|result| result.error.is_none())); |
| 398 | } |
| 399 | other => panic!("expected batch response, got {other:?}"), |
| 400 | } |
| 401 | |
| 402 | let captured = mock.captured_requests(); |
| 403 | assert_eq!(captured.len(), 3); |
| 404 | assert!( |
| 405 | captured |
| 406 | .iter() |
| 407 | .all(|request| request.model == "child-model") |
| 408 | ); |
| 409 | |
| 410 | let usage = bridge.usage.lock().await; |
| 411 | assert_eq!(usage.input_tokens, 9); |
| 412 | assert_eq!(usage.output_tokens, 12); |
| 413 | } |
| 414 | |
| 415 | #[tokio::test] |
| 416 | async fn rlm_dispatch_at_depth_zero_pins_configured_child_model() { |
| 417 | let mock = Arc::new(MockLlmClient::new(Vec::new())); |
| 418 | mock.push_message_response(mock_response("fallback answer", 3, 5)); |
| 419 | let bridge = bridge_for(Arc::clone(&mock), 0); |
| 420 | |
| 421 | let response = bridge |
| 422 | .dispatch(RpcRequest::Rlm { |
| 423 | prompt: "nested prompt".to_string(), |
| 424 | model: Some("override-model".to_string()), |
| 425 | }) |
| 426 | .await; |
| 427 | |
| 428 | match response { |
| 429 | RpcResponse::Single(single) => { |
| 430 | assert_eq!(single.text, "fallback answer"); |
| 431 | assert!(single.error.is_none()); |
| 432 | } |
| 433 | other => panic!("expected single response, got {other:?}"), |
| 434 | } |
| 435 | |
| 436 | let usage = bridge.usage.lock().await; |
| 437 | assert_eq!(usage.input_tokens, 3); |
| 438 | assert_eq!(usage.output_tokens, 5); |
| 439 | |
| 440 | let captured = mock.captured_requests(); |
| 441 | assert_eq!(captured.len(), 1); |
| 442 | assert_eq!(captured[0].model, "child-model"); |
| 443 | } |
| 444 | } |
| 445 |