From 6e316588f87f5a428b0fc46adb505b28a189a96d Mon Sep 17 00:00:00 2001
From: Simo Lin <linsimo.mark@gmail.com>
Date: Mon, 18 Aug 2025 09:26:09 -0700
Subject: [PATCH] [router] add reasoning parser base structure (#9310)

Co-authored-by: Chang Su <chang.s.su@oracle.com>
---
 .pre-commit-config.yaml                       |   2 +-
 sgl-router/src/lib.rs                         |   1 +
 sgl-router/src/reasoning_parser/factory.rs    | 232 +++++++++++
 sgl-router/src/reasoning_parser/mod.rs        |   7 +
 .../src/reasoning_parser/parsers/base.rs      | 382 ++++++++++++++++++
 .../src/reasoning_parser/parsers/mod.rs       |   3 +
 sgl-router/src/reasoning_parser/traits.rs     | 130 ++++++
 7 files changed, 756 insertions(+), 1 deletion(-)
 create mode 100644 sgl-router/src/reasoning_parser/factory.rs
 create mode 100644 sgl-router/src/reasoning_parser/mod.rs
 create mode 100644 sgl-router/src/reasoning_parser/parsers/base.rs
 create mode 100644 sgl-router/src/reasoning_parser/parsers/mod.rs
 create mode 100644 sgl-router/src/reasoning_parser/traits.rs

diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 346d8adf0..8f7455904 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -38,7 +38,7 @@ repos:
     hooks:
       - id: codespell
         additional_dependencies: ['tomli']
-        args: ['--toml', 'python/pyproject.toml', '-L', 'cann']
+        args: ['--toml', 'python/pyproject.toml', '-L', 'cann,thi']
         exclude: |
           (?x)^(
             test/srt/test_reasoning_parser\.py|
diff --git a/sgl-router/src/lib.rs b/sgl-router/src/lib.rs
index 299dfdcfa..00c8e910d 100644
--- a/sgl-router/src/lib.rs
+++ b/sgl-router/src/lib.rs
@@ -7,6 +7,7 @@ pub mod metrics;
 pub mod middleware;
 pub mod openai_api_types;
 pub mod policies;
+pub mod reasoning_parser;
 pub mod routers;
 pub mod server;
 pub mod service_discovery;
diff --git a/sgl-router/src/reasoning_parser/factory.rs b/sgl-router/src/reasoning_parser/factory.rs
new file mode 100644
index 000000000..1ac2232b6
--- /dev/null
+++ b/sgl-router/src/reasoning_parser/factory.rs
@@ -0,0 +1,232 @@
+// Factory and registry for creating model-specific reasoning parsers.
+
+use std::collections::HashMap;
+use std::sync::{Arc, RwLock};
+
+use crate::reasoning_parser::parsers::BaseReasoningParser;
+use crate::reasoning_parser::traits::{ParseError, ParserConfig, ReasoningParser};
+
+/// Type alias for parser creator functions.
+type ParserCreator = Arc<dyn Fn() -> Box<dyn ReasoningParser> + Send + Sync>;
+
+/// Registry for model-specific parsers.
+#[derive(Clone)]
+pub struct ParserRegistry {
+    parsers: Arc<RwLock<HashMap<String, ParserCreator>>>,
+    patterns: Arc<RwLock<Vec<(String, String)>>>, // (pattern, parser_name)
+}
+
+impl ParserRegistry {
+    /// Create a new empty registry.
+    pub fn new() -> Self {
+        Self {
+            parsers: Arc::new(RwLock::new(HashMap::new())),
+            patterns: Arc::new(RwLock::new(Vec::new())),
+        }
+    }
+
+    /// Register a parser creator for a given parser type.
+    pub fn register_parser<F>(&self, name: &str, creator: F)
+    where
+        F: Fn() -> Box<dyn ReasoningParser> + Send + Sync + 'static,
+    {
+        let mut parsers = self.parsers.write().unwrap();
+        parsers.insert(name.to_string(), Arc::new(creator));
+    }
+
+    /// Register a model pattern to parser mapping.
+    /// Patterns are checked in order, first match wins.
+    pub fn register_pattern(&self, pattern: &str, parser_name: &str) {
+        let mut patterns = self.patterns.write().unwrap();
+        patterns.push((pattern.to_string(), parser_name.to_string()));
+    }
+
+    /// Get a parser by exact name.
+    pub fn get_parser(&self, name: &str) -> Option<Box<dyn ReasoningParser>> {
+        let parsers = self.parsers.read().unwrap();
+        parsers.get(name).map(|creator| creator())
+    }
+
+    /// Find a parser for a given model ID by pattern matching.
+    pub fn find_parser_for_model(&self, model_id: &str) -> Option<Box<dyn ReasoningParser>> {
+        let patterns = self.patterns.read().unwrap();
+        let model_lower = model_id.to_lowercase();
+
+        for (pattern, parser_name) in patterns.iter() {
+            if model_lower.contains(&pattern.to_lowercase()) {
+                return self.get_parser(parser_name);
+            }
+        }
+        None
+    }
+}
+
+impl Default for ParserRegistry {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+/// Factory for creating reasoning parsers based on model type.
+pub struct ParserFactory {
+    registry: ParserRegistry,
+}
+
+impl ParserFactory {
+    /// Create a new factory with default parsers registered.
+    pub fn new() -> Self {
+        let registry = ParserRegistry::new();
+
+        // Register base parser
+        registry.register_parser("base", || {
+            Box::new(BaseReasoningParser::new(ParserConfig::default()))
+        });
+
+        // Register DeepSeek-R1 parser
+        registry.register_parser("deepseek_r1", || {
+            let config = ParserConfig {
+                think_start_token: "<think>".to_string(),
+                think_end_token: "</think>".to_string(),
+                force_reasoning: true,
+                stream_reasoning: true,
+                max_buffer_size: 65536,
+            };
+            Box::new(BaseReasoningParser::new(config).with_model_type("deepseek_r1".to_string()))
+        });
+
+        // Register Qwen3 parser
+        registry.register_parser("qwen3", || {
+            let config = ParserConfig {
+                think_start_token: "<think>".to_string(),
+                think_end_token: "</think>".to_string(),
+                force_reasoning: false,
+                stream_reasoning: true,
+                max_buffer_size: 65536,
+            };
+            Box::new(BaseReasoningParser::new(config).with_model_type("qwen3".to_string()))
+        });
+
+        // Register Qwen3-thinking parser (forced reasoning)
+        registry.register_parser("qwen3_thinking", || {
+            let config = ParserConfig {
+                think_start_token: "<think>".to_string(),
+                think_end_token: "</think>".to_string(),
+                force_reasoning: true,
+                stream_reasoning: true,
+                max_buffer_size: 65536,
+            };
+            Box::new(BaseReasoningParser::new(config).with_model_type("qwen3_thinking".to_string()))
+        });
+
+        // Register Kimi parser with Unicode tokens
+        registry.register_parser("kimi", || {
+            let config = ParserConfig {
+                think_start_token: "◁think▷".to_string(),
+                think_end_token: "◁/think▷".to_string(),
+                force_reasoning: false,
+                stream_reasoning: true,
+                max_buffer_size: 65536,
+            };
+            Box::new(BaseReasoningParser::new(config).with_model_type("kimi".to_string()))
+        });
+
+        // Register model patterns
+        registry.register_pattern("deepseek-r1", "deepseek_r1");
+        registry.register_pattern("qwen3-thinking", "qwen3_thinking");
+        registry.register_pattern("qwen-thinking", "qwen3_thinking");
+        registry.register_pattern("qwen3", "qwen3");
+        registry.register_pattern("qwen", "qwen3");
+        registry.register_pattern("glm45", "qwen3"); // GLM45 uses same format as Qwen3
+        registry.register_pattern("kimi", "kimi");
+        registry.register_pattern("step3", "deepseek_r1"); // Step3 alias for DeepSeek-R1
+
+        Self { registry }
+    }
+
+    /// Create a parser for the given model ID.
+    /// Returns a no-op parser if model is not recognized.
+    pub fn create(&self, model_id: &str) -> Result<Box<dyn ReasoningParser>, ParseError> {
+        // First try to find by pattern
+        if let Some(parser) = self.registry.find_parser_for_model(model_id) {
+            return Ok(parser);
+        }
+
+        // Fall back to no-op parser (base parser without reasoning detection)
+        let config = ParserConfig {
+            think_start_token: "".to_string(),
+            think_end_token: "".to_string(),
+            force_reasoning: false,
+            stream_reasoning: true,
+            max_buffer_size: 65536,
+        };
+        Ok(Box::new(
+            BaseReasoningParser::new(config).with_model_type("passthrough".to_string()),
+        ))
+    }
+
+    /// Get the internal registry for custom registration.
+    pub fn registry(&self) -> &ParserRegistry {
+        &self.registry
+    }
+}
+
+impl Default for ParserFactory {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_factory_creates_deepseek_r1() {
+        let factory = ParserFactory::new();
+        let parser = factory.create("deepseek-r1-distill").unwrap();
+        assert_eq!(parser.model_type(), "deepseek_r1");
+    }
+
+    #[test]
+    fn test_factory_creates_qwen3() {
+        let factory = ParserFactory::new();
+        let parser = factory.create("qwen3-7b").unwrap();
+        assert_eq!(parser.model_type(), "qwen3");
+    }
+
+    #[test]
+    fn test_factory_creates_kimi() {
+        let factory = ParserFactory::new();
+        let parser = factory.create("kimi-chat").unwrap();
+        assert_eq!(parser.model_type(), "kimi");
+    }
+
+    #[test]
+    fn test_factory_fallback_to_passthrough() {
+        let factory = ParserFactory::new();
+        let parser = factory.create("unknown-model").unwrap();
+        assert_eq!(parser.model_type(), "passthrough");
+    }
+
+    #[test]
+    fn test_case_insensitive_matching() {
+        let factory = ParserFactory::new();
+        let parser1 = factory.create("DeepSeek-R1").unwrap();
+        let parser2 = factory.create("QWEN3").unwrap();
+        let parser3 = factory.create("Kimi").unwrap();
+
+        assert_eq!(parser1.model_type(), "deepseek_r1");
+        assert_eq!(parser2.model_type(), "qwen3");
+        assert_eq!(parser3.model_type(), "kimi");
+    }
+
+    #[test]
+    fn test_alias_models() {
+        let factory = ParserFactory::new();
+        let step3 = factory.create("step3-model").unwrap();
+        let glm45 = factory.create("glm45-v2").unwrap();
+
+        assert_eq!(step3.model_type(), "deepseek_r1");
+        assert_eq!(glm45.model_type(), "qwen3");
+    }
+}
diff --git a/sgl-router/src/reasoning_parser/mod.rs b/sgl-router/src/reasoning_parser/mod.rs
new file mode 100644
index 000000000..fd975a7bf
--- /dev/null
+++ b/sgl-router/src/reasoning_parser/mod.rs
@@ -0,0 +1,7 @@
+pub mod factory;
+pub mod parsers;
+pub mod traits;
+
+pub use factory::{ParserFactory, ParserRegistry};
+pub use parsers::BaseReasoningParser;
+pub use traits::{ParseError, ParserResult, ReasoningParser};
diff --git a/sgl-router/src/reasoning_parser/parsers/base.rs b/sgl-router/src/reasoning_parser/parsers/base.rs
new file mode 100644
index 000000000..78743b13d
--- /dev/null
+++ b/sgl-router/src/reasoning_parser/parsers/base.rs
@@ -0,0 +1,382 @@
+// Base implementation of reasoning parser that handles common logic
+// for detecting and extracting reasoning blocks from text.
+
+use crate::reasoning_parser::traits::{ParseError, ParserConfig, ParserResult, ReasoningParser};
+use tracing as log;
+
+/// Base reasoning parser implementation.
+///
+/// This parser handles the common logic for detecting reasoning blocks
+/// delimited by start and end tokens (e.g., <think> and </think>).
+#[derive(Debug, Clone)]
+pub struct BaseReasoningParser {
+    config: ParserConfig,
+    in_reasoning: bool,
+    buffer: String,
+    stripped_think_start: bool,
+    model_type: String,
+}
+
+impl BaseReasoningParser {
+    /// Create a new BaseReasoningParser with the given configuration.
+    pub fn new(config: ParserConfig) -> Self {
+        let in_reasoning = config.force_reasoning;
+        Self {
+            config,
+            in_reasoning,
+            buffer: String::new(),
+            stripped_think_start: false,
+            model_type: "base".to_string(),
+        }
+    }
+
+    /// Create with custom model type identifier.
+    pub fn with_model_type(mut self, model_type: String) -> Self {
+        self.model_type = model_type;
+        self
+    }
+
+    /// Check if the current buffer is a prefix of one of the tokens.
+    fn is_partial_token(&self, text: &str) -> bool {
+        (self.config.think_start_token.starts_with(text) && self.config.think_start_token != text)
+            || (self.config.think_end_token.starts_with(text)
+                && self.config.think_end_token != text)
+    }
+}
+
+impl ReasoningParser for BaseReasoningParser {
+    fn detect_and_parse_reasoning(&mut self, text: &str) -> Result<ParserResult, ParseError> {
+        log::debug!("detect_and_parse_reasoning called with text: {:?}", text);
+
+        // Check input size against buffer limit
+        if text.len() > self.config.max_buffer_size {
+            return Err(ParseError::BufferOverflow(text.len()));
+        }
+
+        let in_reasoning = self.in_reasoning || text.contains(&self.config.think_start_token);
+        log::debug!("in_reasoning: {}", in_reasoning);
+
+        if !in_reasoning {
+            log::debug!("No reasoning detected, returning normal text.");
+            return Ok(ParserResult::normal(text.to_string()));
+        }
+
+        // The text is considered to be in a reasoning block.
+        let processed_text = text
+            .replace(&self.config.think_start_token, "")
+            .trim()
+            .to_string();
+        log::debug!(
+            "Processed text after removing think_start_token: {:?}",
+            processed_text
+        );
+
+        if !processed_text.contains(&self.config.think_end_token) {
+            log::debug!(
+                "Reasoning truncated, think_end_token not found. Returning reasoning text."
+            );
+            // Assume reasoning was truncated before end token
+            return Ok(ParserResult::reasoning(processed_text));
+        }
+
+        // Extract reasoning content
+        let splits: Vec<&str> = processed_text
+            .splitn(2, &self.config.think_end_token)
+            .collect();
+        let reasoning_text = splits.first().unwrap_or(&"").to_string();
+        let normal_text = splits
+            .get(1)
+            .map(|s| s.trim().to_string())
+            .unwrap_or_default();
+
+        log::debug!("Extracted reasoning_text: {:?}", reasoning_text);
+        log::debug!("Extracted normal_text: {:?}", normal_text);
+
+        Ok(ParserResult::new(normal_text, reasoning_text))
+    }
+
+    fn parse_reasoning_streaming_incremental(
+        &mut self,
+        text: &str,
+    ) -> Result<ParserResult, ParseError> {
+        // Check if adding this text would exceed buffer limit
+        if self.buffer.len() + text.len() > self.config.max_buffer_size {
+            return Err(ParseError::BufferOverflow(self.buffer.len() + text.len()));
+        }
+
+        // Incrementally parse the streaming text
+        self.buffer.push_str(text);
+        let mut current_text = self.buffer.clone();
+
+        log::debug!(
+            "parse_reasoning_streaming_incremental called with text: {:?}",
+            text
+        );
+        log::debug!("current buffer: {:?}", self.buffer);
+        log::debug!("current_text: {:?}", current_text);
+        log::debug!(
+            "in_reasoning: {}, stripped_think_start: {}, stream_reasoning: {}",
+            self.in_reasoning,
+            self.stripped_think_start,
+            self.config.stream_reasoning
+        );
+
+        // If the current text is a prefix of a token, keep buffering
+        if self.is_partial_token(&current_text) {
+            return Ok(ParserResult::default());
+        }
+
+        // Strip start token if present
+        if !self.stripped_think_start && current_text.contains(&self.config.think_start_token) {
+            current_text = current_text.replace(&self.config.think_start_token, "");
+            self.buffer = current_text.clone();
+            self.stripped_think_start = true;
+            self.in_reasoning = true;
+        }
+
+        // Handle end of reasoning block
+        let think_end_idx = if self.in_reasoning {
+            current_text
+                .find(&self.config.think_end_token)
+                .unwrap_or(current_text.len())
+        } else {
+            current_text.len()
+        };
+
+        if self.in_reasoning && think_end_idx < current_text.len() {
+            let reasoning_text = &current_text[..think_end_idx];
+            self.buffer.clear();
+            self.in_reasoning = false;
+            let start_idx = think_end_idx + self.config.think_end_token.len();
+            let normal_text = if start_idx < current_text.len() {
+                &current_text[start_idx..]
+            } else {
+                ""
+            };
+            return Ok(ParserResult::new(
+                normal_text.to_string(),
+                reasoning_text.trim().to_string(),
+            ));
+        }
+
+        // Continue with reasoning content
+        if self.in_reasoning && self.config.stream_reasoning {
+            // Stream the content immediately
+            let reasoning_text = current_text;
+            self.buffer.clear();
+            Ok(ParserResult::reasoning(reasoning_text))
+        } else if !self.in_reasoning {
+            // If we're not in a reasoning block, return as normal text
+            // CRITICAL FIX: Return current_text (with buffer) not just text
+            // This prevents buffer loss when partial tokens are followed by normal text
+            let normal_text = current_text;
+            self.buffer.clear();
+            Ok(ParserResult::normal(normal_text))
+        } else {
+            // If we are in a reasoning block but no end token is found, buffer it
+            Ok(ParserResult::default())
+        }
+    }
+
+    fn reset(&mut self) {
+        self.in_reasoning = self.config.force_reasoning;
+        self.buffer.clear();
+        self.stripped_think_start = false;
+    }
+
+    fn model_type(&self) -> &str {
+        &self.model_type
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn create_test_parser(force_reasoning: bool, stream_reasoning: bool) -> BaseReasoningParser {
+        let config = ParserConfig {
+            think_start_token: "<think>".to_string(),
+            think_end_token: "</think>".to_string(),
+            force_reasoning,
+            stream_reasoning,
+            max_buffer_size: 65536,
+        };
+        BaseReasoningParser::new(config)
+    }
+
+    #[test]
+    fn test_detect_and_parse_reasoning() {
+        let mut parser = create_test_parser(false, true);
+        let result = parser
+            .detect_and_parse_reasoning("<think>with reasoning</think> and more text.")
+            .unwrap();
+        assert_eq!(result.normal_text, "and more text.");
+        assert_eq!(result.reasoning_text, "with reasoning");
+    }
+
+    #[test]
+    fn test_detect_and_parse_no_reasoning() {
+        let mut parser = create_test_parser(false, true);
+        let result = parser
+            .detect_and_parse_reasoning("This is a test without reasoning.")
+            .unwrap();
+        assert_eq!(result.normal_text, "This is a test without reasoning.");
+        assert_eq!(result.reasoning_text, "");
+    }
+
+    #[test]
+    fn test_detect_and_parse_truncated_reasoning() {
+        let mut parser = create_test_parser(false, true);
+        let result = parser
+            .detect_and_parse_reasoning("<think>with truncated reasoning")
+            .unwrap();
+        assert_eq!(result.normal_text, "");
+        assert_eq!(result.reasoning_text, "with truncated reasoning");
+    }
+
+    #[test]
+    fn test_parse_streaming_partial_token() {
+        let mut parser = create_test_parser(false, true);
+        let result = parser
+            .parse_reasoning_streaming_incremental("<thi")
+            .unwrap();
+        assert_eq!(result.normal_text, "");
+        assert_eq!(result.reasoning_text, "");
+    }
+
+    #[test]
+    fn test_parse_streaming_complete() {
+        let mut parser = create_test_parser(false, true);
+        let result = parser
+            .parse_reasoning_streaming_incremental("<think>with reasoning</think> and more text.")
+            .unwrap();
+        assert_eq!(result.normal_text, " and more text.");
+        assert_eq!(result.reasoning_text, "with reasoning");
+    }
+
+    #[test]
+    fn test_parse_streaming_no_end_token() {
+        let mut parser = create_test_parser(true, true);
+        let result = parser
+            .parse_reasoning_streaming_incremental("<think>with reasoning")
+            .unwrap();
+        assert_eq!(result.normal_text, "");
+        assert_eq!(result.reasoning_text, "with reasoning");
+    }
+
+    #[test]
+    fn test_force_reasoning_mode() {
+        let mut parser = create_test_parser(true, true);
+        let result = parser
+            .detect_and_parse_reasoning("no think tags here")
+            .unwrap();
+        assert_eq!(result.normal_text, "");
+        assert_eq!(result.reasoning_text, "no think tags here");
+    }
+
+    #[test]
+    fn test_buffer_loss_bug_fix() {
+        // Critical test for buffer preservation
+        let mut parser = create_test_parser(false, true);
+
+        // Step 1: Send partial end tag when not in reasoning mode
+        let result1 = parser.parse_reasoning_streaming_incremental("</").unwrap();
+        assert_eq!(result1.normal_text, "");
+        assert_eq!(result1.reasoning_text, "");
+
+        // Step 2: Send normal text that doesn't complete the end tag
+        // Must return "</answer" not just "answer"
+        let result2 = parser
+            .parse_reasoning_streaming_incremental("answer")
+            .unwrap();
+        assert_eq!(result2.normal_text, "</answer");
+        assert_eq!(result2.reasoning_text, "");
+    }
+
+    #[test]
+    fn test_streaming_with_stream_reasoning_enabled() {
+        let mut parser = create_test_parser(false, true);
+
+        // Start reasoning block
+        let result1 = parser
+            .parse_reasoning_streaming_incremental("<think>reasoning ")
+            .unwrap();
+        assert_eq!(result1.normal_text, "");
+        assert_eq!(result1.reasoning_text, "reasoning ");
+
+        // Continue streaming reasoning
+        let result2 = parser
+            .parse_reasoning_streaming_incremental("content ")
+            .unwrap();
+        assert_eq!(result2.normal_text, "");
+        assert_eq!(result2.reasoning_text, "content ");
+
+        // End reasoning block
+        let result3 = parser
+            .parse_reasoning_streaming_incremental("more</think> normal")
+            .unwrap();
+        assert_eq!(result3.normal_text, " normal");
+        assert_eq!(result3.reasoning_text, "more");
+    }
+
+    #[test]
+    fn test_reset_state() {
+        let mut parser = create_test_parser(false, true);
+
+        // Process some text
+        parser
+            .parse_reasoning_streaming_incremental("<think>reasoning</think> normal")
+            .unwrap();
+
+        // Reset and verify state
+        parser.reset();
+        assert!(!parser.in_reasoning);
+        assert!(parser.buffer.is_empty());
+        assert!(!parser.stripped_think_start);
+    }
+
+    #[test]
+    fn test_buffer_overflow_detect_and_parse() {
+        let config = ParserConfig {
+            max_buffer_size: 10, // Set a very small buffer
+            ..Default::default()
+        };
+        let mut parser = BaseReasoningParser::new(config);
+
+        let large_text = "a".repeat(20);
+        let result = parser.detect_and_parse_reasoning(&large_text);
+
+        assert!(result.is_err());
+        match result {
+            Err(ParseError::BufferOverflow(size)) => {
+                assert_eq!(size, 20);
+            }
+            _ => panic!("Expected BufferOverflow error"),
+        }
+    }
+
+    #[test]
+    fn test_buffer_overflow_streaming() {
+        let config = ParserConfig {
+            max_buffer_size: 10, // Set a very small buffer
+            ..Default::default()
+        };
+        let mut parser = BaseReasoningParser::new(config);
+
+        // Send a partial token that will be buffered
+        let result1 = parser.parse_reasoning_streaming_incremental("<thi");
+        assert!(result1.is_ok());
+        assert_eq!(result1.unwrap().normal_text, "");
+
+        // Second chunk would exceed buffer
+        // Buffer has "<thi" (4 chars) + "this_is_too_large" (17 chars) = 21 total
+        let result2 = parser.parse_reasoning_streaming_incremental("this_is_too_large");
+        assert!(result2.is_err());
+        match result2 {
+            Err(ParseError::BufferOverflow(size)) => {
+                assert_eq!(size, 21); // 4 + 17
+            }
+            _ => panic!("Expected BufferOverflow error"),
+        }
+    }
+}
diff --git a/sgl-router/src/reasoning_parser/parsers/mod.rs b/sgl-router/src/reasoning_parser/parsers/mod.rs
new file mode 100644
index 000000000..64a00f864
--- /dev/null
+++ b/sgl-router/src/reasoning_parser/parsers/mod.rs
@@ -0,0 +1,3 @@
+pub mod base;
+
+pub use base::BaseReasoningParser;
diff --git a/sgl-router/src/reasoning_parser/traits.rs b/sgl-router/src/reasoning_parser/traits.rs
new file mode 100644
index 000000000..672b76813
--- /dev/null
+++ b/sgl-router/src/reasoning_parser/traits.rs
@@ -0,0 +1,130 @@
+use std::fmt;
+
+/// Result of parsing text for reasoning content.
+#[derive(Debug, Clone, Default, PartialEq)]
+pub struct ParserResult {
+    /// The normal text outside of reasoning blocks.
+    pub normal_text: String,
+
+    /// The extracted reasoning text from within reasoning blocks.
+    pub reasoning_text: String,
+}
+
+impl ParserResult {
+    /// Create a new ParserResult with the given normal and reasoning text.
+    pub fn new(normal_text: String, reasoning_text: String) -> Self {
+        Self {
+            normal_text,
+            reasoning_text,
+        }
+    }
+
+    /// Create a result with only normal text.
+    pub fn normal(text: String) -> Self {
+        Self {
+            normal_text: text,
+            reasoning_text: String::new(),
+        }
+    }
+
+    /// Create a result with only reasoning text.
+    pub fn reasoning(text: String) -> Self {
+        Self {
+            normal_text: String::new(),
+            reasoning_text: text,
+        }
+    }
+
+    /// Check if this result contains any text.
+    pub fn is_empty(&self) -> bool {
+        self.normal_text.is_empty() && self.reasoning_text.is_empty()
+    }
+}
+
+/// Trait for parsing reasoning content from LLM outputs.
+pub trait ReasoningParser: Send + Sync {
+    /// Detects and parses reasoning from the input text (one-time parsing).
+    ///
+    /// This method is used for non-streaming scenarios where the complete
+    /// text is available at once.
+    ///
+    /// Returns an error if the text exceeds buffer limits or contains invalid UTF-8.
+    fn detect_and_parse_reasoning(&mut self, text: &str) -> Result<ParserResult, ParseError>;
+
+    /// Parses reasoning incrementally from streaming input.
+    ///
+    /// This method maintains internal state across calls to handle partial
+    /// tokens and chunk boundaries correctly.
+    ///
+    /// Returns an error if the buffer exceeds max_buffer_size.
+    fn parse_reasoning_streaming_incremental(
+        &mut self,
+        text: &str,
+    ) -> Result<ParserResult, ParseError>;
+
+    /// Reset the parser state for reuse.
+    ///
+    /// This should clear any buffers and reset flags to initial state.
+    fn reset(&mut self);
+
+    /// Get the model type this parser is designed for.
+    fn model_type(&self) -> &str;
+}
+
+/// Error types for reasoning parsing operations.
+#[derive(Debug, thiserror::Error)]
+pub enum ParseError {
+    #[error("Invalid UTF-8 in stream: {0}")]
+    Utf8Error(#[from] std::str::Utf8Error),
+
+    #[error("Buffer overflow: {0} bytes exceeds maximum")]
+    BufferOverflow(usize),
+
+    #[error("Unknown model type: {0}")]
+    UnknownModel(String),
+
+    #[error("Parser configuration error: {0}")]
+    ConfigError(String),
+}
+
+/// Configuration for parser behavior.
+#[derive(Debug, Clone)]
+pub struct ParserConfig {
+    /// The token that marks the start of reasoning content.
+    pub think_start_token: String,
+
+    /// The token that marks the end of reasoning content.
+    pub think_end_token: String,
+
+    /// Whether to force all text to be treated as reasoning.
+    pub force_reasoning: bool,
+
+    /// Whether to stream reasoning content as it arrives.
+    pub stream_reasoning: bool,
+
+    /// Maximum buffer size in bytes.
+    pub max_buffer_size: usize,
+}
+
+impl Default for ParserConfig {
+    fn default() -> Self {
+        Self {
+            think_start_token: "<think>".to_string(),
+            think_end_token: "</think>".to_string(),
+            force_reasoning: false,
+            stream_reasoning: true,
+            max_buffer_size: 65536, // 64KB default
+        }
+    }
+}
+
+impl fmt::Display for ParserResult {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(
+            f,
+            "ParserResult {{ normal: {} chars, reasoning: {} chars }}",
+            self.normal_text.len(),
+            self.reasoning_text.len()
+        )
+    }
+}