feat: reasoning parser transformation (#3295)

Signed-off-by: ayushag <ayushag@nvidia.com>

lib/llm/src/engines.rs

@@ -159,12 +159,12 @@ impl
             for c in prompt.chars() {
                 // we are returning characters not tokens, so there will be some postprocessing overhead
                 tokio::time::sleep(*TOKEN_ECHO_DELAY).await;
-                let response = deltas.create_choice(0, Some(c.to_string()), None, None, None);
+                let response = deltas.create_choice(0, Some(c.to_string()), None, None);
                 yield Annotated{ id: Some(id.to_string()), data: Some(response), event: None, comment: None };
                 id += 1;
             }
 
-            let response = deltas.create_choice(0, None, None, Some(dynamo_async_openai::types::FinishReason::Stop), None);
+            let response = deltas.create_choice(0, None, Some(dynamo_async_openai::types::FinishReason::Stop), None);
             yield Annotated { id: Some(id.to_string()), data: Some(response), event: None, comment: None };
         };
 

lib/llm/src/preprocessor.rs

@@ -28,6 +28,7 @@ use crate::preprocessor::prompt::OAIChatLikeRequest;
 use crate::protocols::common::preprocessor::PreprocessedRequestBuilder;
 use crate::tokenizers::Encoding;
 
+use dynamo_parsers::{ReasoningParser, ReasoningParserType};
 use dynamo_runtime::engine::{AsyncEngine, AsyncEngineContextProvider, ResponseStream};
 use dynamo_runtime::pipeline::{
     AsyncEngineContext, Error, ManyOut, Operator, SingleIn, async_trait,
@@ -93,6 +94,12 @@ impl LLMMetricAnnotation {
     }
 }
 
+// Reasoning State for reasoning parsing transformation step
+struct ReasoningState {
+    stream: Pin<Box<dyn Stream<Item = Annotated<NvCreateChatCompletionStreamResponse>> + Send>>,
+    reasoning_parser: Option<Box<dyn ReasoningParser>>,
+}
+
 pub struct OpenAIPreprocessor {
     mdcsum: String,
     formatter: Arc<dyn OAIPromptFormatter>,
@@ -668,6 +675,56 @@ impl OpenAIPreprocessor {
             .build();
         jail.apply(stream)
     }
+
+    // Motivation: Each transformation on the stream should be a separate step to allow for more flexibility
+    // Earlier reasoning parser logic was nested under delta generation logic in choice_from_postprocessor
+    // Since we have tool calling parsing as separate step, it makes sense to have reasoning parser as separate step as well
+    pub fn parse_reasoning_content_from_stream<S>(
+        stream: S,
+        parser_name: String,
+    ) -> impl Stream<Item = Annotated<NvCreateChatCompletionStreamResponse>> + Send
+    where
+        S: Stream<Item = Annotated<NvCreateChatCompletionStreamResponse>> + Send + 'static,
+    {
+        // Initialize reasoning parser from parser_name
+        let reasoning_parser = Box::new(ReasoningParserType::get_reasoning_parser_from_name(
+            parser_name.as_ref(),
+        )) as Box<dyn ReasoningParser>;
+
+        let state = ReasoningState {
+            stream: Box::pin(stream),
+            reasoning_parser: Some(reasoning_parser),
+        };
+
+        stream::unfold(state, |mut state| async move {
+            if let Some(response) = state.stream.next().await {
+                // Process the response through reasoning parser if available
+                let processed_response = if let Some(ref mut parser) = state.reasoning_parser {
+                    response.map_data(|mut data| {
+                        // Process all choices, not just the first one
+                        for choice in data.choices.iter_mut() {
+                            if let Some(text) = choice.delta.content.as_ref() {
+                                let parser_result =
+                                    parser.parse_reasoning_streaming_incremental(text, &[]);
+
+                                // Update this specific choice with parsed content
+                                choice.delta.content = parser_result.get_some_normal_text();
+                                choice.delta.reasoning_content = parser_result.get_some_reasoning();
+                            }
+                        }
+                        Ok(data)
+                    })
+                } else {
+                    // No reasoning parser configured, pass through unchanged
+                    response
+                };
+
+                Some((processed_response, state))
+            } else {
+                None
+            }
+        })
+    }
 }
 
 // for pals, we do not want to add the generation prompt to the formatted prompt
@@ -715,9 +772,6 @@ impl
 
         let mut response_generator = Box::new(response_generator);
 
-        // set the runtime configuration
-        response_generator.set_reasoning_parser(self.runtime_config.clone());
-
         // update isl
         response_generator.update_isl(common_request.token_ids.len() as u32);
 
@@ -744,6 +798,25 @@ impl
             context.clone(),
         );
 
+        // Try to parse reasoning content only if parser is configured
+        let should_parse_reasoning = self.runtime_config.reasoning_parser.is_some();
+
+        // Reasoning Content Parsing Transformation Step
+        // Current Solution:
+        // This step operates on Deltas created by the transform_postprocessor_stream function
+        // Only access to text and not token_ids - so can not support parsing based on token_ids for now
+        // Future Solution:
+        // To address the limitation if needed in future: move this step before transform_postprocessor_stream and add new field of reasoning_content to the backend output
+        // Use backend_output.reasoning_content field to fill out the deltas.
+        let stream: Pin<Box<dyn Stream<Item = _> + Send>> = if should_parse_reasoning {
+            Box::pin(Self::parse_reasoning_content_from_stream(
+                stream,
+                self.runtime_config.reasoning_parser.clone().unwrap(), // Safety: We already checked that parser is some, so gtg
+            ))
+        } else {
+            Box::pin(stream)
+        };
+
         // Check if tools are present and if we should apply jail
         let has_tools =
             request.inner.tools.is_some() && !request.inner.tools.as_ref().unwrap().is_empty();

lib/llm/src/protocols/openai/chat_completions/delta.rs

@@ -7,7 +7,6 @@ use crate::{
     protocols::common::{self},
     types::TokenIdType,
 };
-use dynamo_parsers::{ParserResult, ReasoningParser, ReasoningParserType, ReasoningParserWrapper};
 
 /// Provides a method for generating a [`DeltaGenerator`] from a chat completion request.
 impl NvCreateChatCompletionRequest {
@@ -66,11 +65,6 @@ pub struct DeltaGenerator {
     msg_counter: u64,
     /// Configuration options for response generation.
     options: DeltaGeneratorOptions,
-
-    /// Reasoning Parser object
-    /// This is used to parse reasoning content in the response.
-    /// None means no reasoning parsing will be performed.
-    reasoning_parser: Option<ReasoningParserWrapper>,
 }
 
 impl DeltaGenerator {
@@ -101,14 +95,6 @@ impl DeltaGenerator {
             completion_tokens_details: None,
         };
 
-        // Reasoning parser type
-        // If no parser is specified (None), no reasoning parsing will be performed
-        let reasoning_parser = options
-            .runtime_config
-            .reasoning_parser
-            .as_deref()
-            .map(ReasoningParserType::get_reasoning_parser_from_name);
-
         let chatcmpl_id = format!("chatcmpl-{request_id}");
 
         Self {
@@ -121,21 +107,6 @@ impl DeltaGenerator {
             usage,
             msg_counter: 0,
             options,
-            reasoning_parser,
-        }
-    }
-
-    /// Update runtime configuration and reconfigure the reasoning parser accordingly.
-    pub fn set_reasoning_parser(&mut self, runtime_config: ModelRuntimeConfig) {
-        self.options.runtime_config = runtime_config.clone();
-        match self.options.runtime_config.reasoning_parser.as_deref() {
-            Some(name) => {
-                self.reasoning_parser =
-                    Some(ReasoningParserType::get_reasoning_parser_from_name(name));
-            }
-            None => {
-                self.reasoning_parser = None;
-            }
         }
     }
 
@@ -212,24 +183,6 @@ impl DeltaGenerator {
         })
     }
 
-    fn create_reasoning_content(
-        &mut self,
-        text: &Option<String>,
-        token_ids: &[u32],
-    ) -> Option<ParserResult> {
-        // If no reasoning parser is configured, return None
-        let reasoning_parser = self.reasoning_parser.as_mut()?;
-
-        let text_ref = text.as_deref().unwrap_or("");
-        if text_ref.is_empty() && token_ids.is_empty() {
-            return None;
-        }
-        let parser_result =
-            reasoning_parser.parse_reasoning_streaming_incremental(text_ref, token_ids);
-
-        Some(parser_result)
-    }
-
     /// Creates a choice within a chat completion response.
     ///
     /// # Arguments
@@ -245,7 +198,6 @@ impl DeltaGenerator {
         &mut self,
         index: u32,
         text: Option<String>,
-        reasoning_content: Option<String>,
         finish_reason: Option<dynamo_async_openai::types::FinishReason>,
         logprobs: Option<dynamo_async_openai::types::ChatChoiceLogprobs>,
     ) -> NvCreateChatCompletionStreamResponse {
@@ -259,7 +211,7 @@ impl DeltaGenerator {
                 None
             },
             refusal: None,
-            reasoning_content,
+            reasoning_content: None,
         };
 
         let choice = dynamo_async_openai::types::ChatChoiceStream {
@@ -371,25 +323,9 @@ impl crate::protocols::openai::DeltaGeneratorExt<NvCreateChatCompletionStreamRes
             None => None,
         };
 
-        // Handle reasoning parsing if enabled, otherwise treat all text as normal
-        let (normal_text, reasoning_content) =
-            match self.create_reasoning_content(&delta.text, &delta.token_ids) {
-                Some(reasoning_parser_result) => (
-                    reasoning_parser_result.get_some_normal_text(),
-                    reasoning_parser_result.get_some_reasoning(),
-                ),
-                None => (delta.text, None),
-            };
-
         // Create the streaming response.
         let index = 0;
-        let stream_response = self.create_choice(
-            index,
-            normal_text,
-            reasoning_content,
-            finish_reason,
-            logprobs,
-        );
+        let stream_response = self.create_choice(index, delta.text, finish_reason, logprobs);
 
         Ok(stream_response)
     }

lib/llm/tests/http-service.rs

@@ -89,7 +89,7 @@ impl
         let stream = stream! {
             tokio::time::sleep(std::time::Duration::from_millis(max_tokens)).await;
             for i in 0..10 {
-                let output = generator.create_choice(i,Some(format!("choice {i}")), None, None, None);
+                let output = generator.create_choice(i,Some(format!("choice {i}")), None, None);
 
                 yield Annotated::from_data(output);
             }

lib/llm/tests/http_metrics.rs

@@ -52,7 +52,7 @@ impl
 
             // Generate 5 response chunks
             for i in 0..5 {
-                let output = generator.create_choice(i, Some(format!("Mock response {i}")), None, None, None);
+                let output = generator.create_choice(i, Some(format!("Mock response {i}")), None, None);
                 yield Annotated::from_data(output);
             }
         };

lib/parsers/src/reasoning/base_parser.rs

@@ -119,7 +119,7 @@ impl ReasoningParser for BasicReasoningParser {
             };
             return ParserResult {
                 normal_text: normal_text.to_string(),
-                reasoning_text: reasoning_text.trim().to_string(),
+                reasoning_text: reasoning_text.to_string(),
             };
         }
         // Continue with reasoning content