[router] allow user to specify chat template path (#11549)

sgl-router/py_src/sglang_router/router_args.py

@@ -83,10 +83,9 @@ class RouterArgs:
     cb_timeout_duration_secs: int = 60
     cb_window_duration_secs: int = 120
     disable_circuit_breaker: bool = False
-    # Tokenizer configuration
     model_path: Optional[str] = None
     tokenizer_path: Optional[str] = None
-    # Parser configuration
+    chat_template: Optional[str] = None
     reasoning_parser: Optional[str] = None
     tool_call_parser: Optional[str] = None
 
@@ -449,6 +448,12 @@ class RouterArgs:
             default=None,
             help="Explicit tokenizer path (overrides model_path tokenizer if provided)",
         )
+        parser.add_argument(
+            f"--{prefix}chat-template",
+            type=str,
+            default=None,
+            help="Chat template path (optional)",
+        )
         parser.add_argument(
             f"--{prefix}reasoning-parser",
             type=str,

sgl-router/src/config/types.rs

@@ -67,6 +67,8 @@ pub struct RouterConfig {
     pub model_path: Option<String>,
     /// Explicit tokenizer path (overrides model_path tokenizer if provided)
     pub tokenizer_path: Option<String>,
+    /// Chat template path (optional)
+    pub chat_template: Option<String>,
     /// History backend configuration (memory or none, default: memory)
     #[serde(default = "default_history_backend")]
     pub history_backend: HistoryBackend,
@@ -450,6 +452,7 @@ impl Default for RouterConfig {
             connection_mode: ConnectionMode::Http,
             model_path: None,
             tokenizer_path: None,
+            chat_template: None,
             history_backend: default_history_backend(),
             oracle: None,
             reasoning_parser: None,
@@ -994,6 +997,7 @@ mod tests {
             connection_mode: ConnectionMode::Http,
             model_path: None,
             tokenizer_path: None,
+            chat_template: None,
             history_backend: default_history_backend(),
             oracle: None,
             reasoning_parser: None,
@@ -1061,6 +1065,7 @@ mod tests {
             connection_mode: ConnectionMode::Http,
             model_path: None,
             tokenizer_path: None,
+            chat_template: None,
             history_backend: default_history_backend(),
             oracle: None,
             reasoning_parser: None,
@@ -1124,6 +1129,7 @@ mod tests {
             connection_mode: ConnectionMode::Http,
             model_path: None,
             tokenizer_path: None,
+            chat_template: None,
             history_backend: default_history_backend(),
             oracle: None,
             reasoning_parser: None,

sgl-router/src/lib.rs

@@ -90,6 +90,7 @@ struct Router {
     connection_mode: config::ConnectionMode,
     model_path: Option<String>,
     tokenizer_path: Option<String>,
+    chat_template: Option<String>,
     reasoning_parser: Option<String>,
     tool_call_parser: Option<String>,
 }
@@ -216,6 +217,7 @@ impl Router {
             enable_igw: self.enable_igw,
             model_path: self.model_path.clone(),
             tokenizer_path: self.tokenizer_path.clone(),
+            chat_template: self.chat_template.clone(),
             history_backend: config::HistoryBackend::Memory,
             oracle: None,
             reasoning_parser: self.reasoning_parser.clone(),
@@ -284,6 +286,7 @@ impl Router {
         rate_limit_tokens_per_second = None,
         model_path = None,
         tokenizer_path = None,
+        chat_template = None,
         reasoning_parser = None,
         tool_call_parser = None,
     ))]
@@ -345,6 +348,7 @@ impl Router {
         rate_limit_tokens_per_second: Option<i32>,
         model_path: Option<String>,
         tokenizer_path: Option<String>,
+        chat_template: Option<String>,
         reasoning_parser: Option<String>,
         tool_call_parser: Option<String>,
     ) -> PyResult<Self> {
@@ -420,6 +424,7 @@ impl Router {
             connection_mode,
             model_path,
             tokenizer_path,
+            chat_template,
             reasoning_parser,
             tool_call_parser,
         })

sgl-router/src/main.rs

@@ -255,6 +255,9 @@ struct CliArgs {
     #[arg(long)]
     tokenizer_path: Option<String>,
 
+    #[arg(long)]
+    chat_template: Option<String>,
+
     #[arg(long, default_value = "memory", value_parser = ["memory", "none", "oracle"])]
     history_backend: String,
 
@@ -561,6 +564,7 @@ impl CliArgs {
             rate_limit_tokens_per_second: None,
             model_path: self.model_path.clone(),
             tokenizer_path: self.tokenizer_path.clone(),
+            chat_template: self.chat_template.clone(),
             history_backend,
             oracle,
             reasoning_parser: self.reasoning_parser.clone(),

sgl-router/src/server.rs

@@ -82,28 +82,40 @@ impl AppContext {
             }
         };
 
-        let (tokenizer, reasoning_parser_factory, tool_parser_factory) =
-            if router_config.connection_mode == ConnectionMode::Grpc {
-                let tokenizer_path = router_config
-                    .tokenizer_path
-                    .clone()
-                    .or_else(|| router_config.model_path.clone())
-                    .ok_or_else(|| {
-                        "gRPC mode requires either --tokenizer-path or --model-path to be specified"
-                            .to_string()
-                    })?;
+        let (tokenizer, reasoning_parser_factory, tool_parser_factory) = if router_config
+            .connection_mode
+            == ConnectionMode::Grpc
+        {
+            let tokenizer_path = router_config
+                .tokenizer_path
+                .clone()
+                .or_else(|| router_config.model_path.clone())
+                .ok_or_else(|| {
+                    "gRPC mode requires either --tokenizer-path or --model-path to be specified"
+                        .to_string()
+                })?;
 
-                let tokenizer = Some(
-                    tokenizer_factory::create_tokenizer(&tokenizer_path)
-                        .map_err(|e| format!("Failed to create tokenizer: {e}"))?,
+            let tokenizer = Some(
+                    tokenizer_factory::create_tokenizer_with_chat_template_blocking(
+                        &tokenizer_path,
+                        router_config.chat_template.as_deref(),
+                    )
+                    .map_err(|e| {
+                        format!(
+                            "Failed to create tokenizer from '{}': {}. \
+                            Ensure the path is valid and points to a tokenizer file (tokenizer.json) \
+                            or a HuggingFace model ID. For directories, ensure they contain tokenizer files.",
+                            tokenizer_path, e
+                        )
+                    })?,
                 );
-                let reasoning_parser_factory = Some(crate::reasoning_parser::ParserFactory::new());
-                let tool_parser_factory = Some(crate::tool_parser::ParserFactory::new());
+            let reasoning_parser_factory = Some(crate::reasoning_parser::ParserFactory::new());
+            let tool_parser_factory = Some(crate::tool_parser::ParserFactory::new());
 
-                (tokenizer, reasoning_parser_factory, tool_parser_factory)
-            } else {
-                (None, None, None)
-            };
+            (tokenizer, reasoning_parser_factory, tool_parser_factory)
+        } else {
+            (None, None, None)
+        };
 
         let worker_registry = Arc::new(WorkerRegistry::new());
         let policy_registry = Arc::new(PolicyRegistry::new(router_config.policy.clone()));

sgl-router/src/tokenizer/factory.rs

@@ -4,6 +4,7 @@ use std::fs::File;
 use std::io::Read;
 use std::path::Path;
 use std::sync::Arc;
+use tracing::{debug, info};
 
 use super::huggingface::HuggingFaceTokenizer;
 use super::tiktoken::TiktokenTokenizer;
@@ -189,14 +190,57 @@ pub fn discover_chat_template_in_dir(dir: &Path) -> Option<String> {
     None
 }
 
+/// Helper function to resolve and log chat template selection
+///
+/// Resolves the final chat template to use by prioritizing provided path over auto-discovery,
+/// and logs the source for debugging purposes.
+fn resolve_and_log_chat_template(
+    provided_path: Option<&str>,
+    discovery_dir: &Path,
+    model_name: &str,
+) -> Option<String> {
+    let final_chat_template = provided_path
+        .map(|s| s.to_string())
+        .or_else(|| discover_chat_template_in_dir(discovery_dir));
+
+    match (&provided_path, &final_chat_template) {
+        (Some(provided), _) => {
+            info!("Using provided chat template: {}", provided);
+        }
+        (None, Some(discovered)) => {
+            info!(
+                "Auto-discovered chat template in '{}': {}",
+                discovery_dir.display(),
+                discovered
+            );
+        }
+        (None, None) => {
+            debug!(
+                "No chat template provided or discovered for model: {}",
+                model_name
+            );
+        }
+    }
+
+    final_chat_template
+}
+
 /// Factory function to create tokenizer from a model name or path (async version)
 pub async fn create_tokenizer_async(
     model_name_or_path: &str,
+) -> Result<Arc<dyn traits::Tokenizer>> {
+    create_tokenizer_async_with_chat_template(model_name_or_path, None).await
+}
+
+/// Factory function to create tokenizer with optional chat template (async version)
+pub async fn create_tokenizer_async_with_chat_template(
+    model_name_or_path: &str,
+    chat_template_path: Option<&str>,
 ) -> Result<Arc<dyn traits::Tokenizer>> {
     // Check if it's a file path
     let path = Path::new(model_name_or_path);
     if path.exists() {
-        return create_tokenizer_from_file(model_name_or_path);
+        return create_tokenizer_with_chat_template(model_name_or_path, chat_template_path);
     }
 
     // Check if it's a GPT model name that should use Tiktoken
@@ -216,8 +260,13 @@ pub async fn create_tokenizer_async(
             // Look for tokenizer.json in the cache directory
             let tokenizer_path = cache_dir.join("tokenizer.json");
             if tokenizer_path.exists() {
-                // Try to find a chat template file in the cache directory
-                let chat_template_path = discover_chat_template_in_dir(&cache_dir);
+                // Resolve chat template: provided path takes precedence over auto-discovery
+                let final_chat_template = resolve_and_log_chat_template(
+                    chat_template_path,
+                    &cache_dir,
+                    model_name_or_path,
+                );
+
                 let tokenizer_path_str = tokenizer_path.to_str().ok_or_else(|| {
                     Error::msg(format!(
                         "Tokenizer path is not valid UTF-8: {:?}",
@@ -226,7 +275,7 @@ pub async fn create_tokenizer_async(
                 })?;
                 create_tokenizer_with_chat_template(
                     tokenizer_path_str,
-                    chat_template_path.as_deref(),
+                    final_chat_template.as_deref(),
                 )
             } else {
                 // Try other common tokenizer file names
@@ -234,13 +283,19 @@ pub async fn create_tokenizer_async(
                 for file_name in &possible_files {
                     let file_path = cache_dir.join(file_name);
                     if file_path.exists() {
-                        let chat_template_path = discover_chat_template_in_dir(&cache_dir);
+                        // Resolve chat template: provided path takes precedence over auto-discovery
+                        let final_chat_template = resolve_and_log_chat_template(
+                            chat_template_path,
+                            &cache_dir,
+                            model_name_or_path,
+                        );
+
                         let file_path_str = file_path.to_str().ok_or_else(|| {
                             Error::msg(format!("File path is not valid UTF-8: {:?}", file_path))
                         })?;
                         return create_tokenizer_with_chat_template(
                             file_path_str,
-                            chat_template_path.as_deref(),
+                            final_chat_template.as_deref(),
                         );
                     }
                 }
@@ -258,11 +313,22 @@ pub async fn create_tokenizer_async(
 }
 
 /// Factory function to create tokenizer from a model name or path (blocking version)
+///
+/// This delegates to `create_tokenizer_with_chat_template_blocking` with no chat template,
+/// which handles both local files and HuggingFace Hub downloads uniformly.
 pub fn create_tokenizer(model_name_or_path: &str) -> Result<Arc<dyn traits::Tokenizer>> {
+    create_tokenizer_with_chat_template_blocking(model_name_or_path, None)
+}
+
+/// Factory function to create tokenizer with optional chat template (blocking version)
+pub fn create_tokenizer_with_chat_template_blocking(
+    model_name_or_path: &str,
+    chat_template_path: Option<&str>,
+) -> Result<Arc<dyn traits::Tokenizer>> {
     // Check if it's a file path
     let path = Path::new(model_name_or_path);
     if path.exists() {
-        return create_tokenizer_from_file(model_name_or_path);
+        return create_tokenizer_with_chat_template(model_name_or_path, chat_template_path);
     }
 
     // Check if it's a GPT model name that should use Tiktoken
@@ -280,11 +346,19 @@ pub fn create_tokenizer(model_name_or_path: &str) -> Result<Arc<dyn traits::Toke
     // Check if we're already in a tokio runtime
     if let Ok(handle) = tokio::runtime::Handle::try_current() {
         // We're in a runtime, use block_in_place
-        tokio::task::block_in_place(|| handle.block_on(create_tokenizer_async(model_name_or_path)))
+        tokio::task::block_in_place(|| {
+            handle.block_on(create_tokenizer_async_with_chat_template(
+                model_name_or_path,
+                chat_template_path,
+            ))
+        })
     } else {
         // No runtime, create a temporary one
         let rt = tokio::runtime::Runtime::new()?;
-        rt.block_on(create_tokenizer_async(model_name_or_path))
+        rt.block_on(create_tokenizer_async_with_chat_template(
+            model_name_or_path,
+            chat_template_path,
+        ))
     }
 }
 

sgl-router/src/tokenizer/mod.rs

@@ -23,8 +23,9 @@ mod tests;
 
 // Re-exports
 pub use factory::{
-    create_tokenizer, create_tokenizer_async, create_tokenizer_from_file,
-    create_tokenizer_with_chat_template, TokenizerType,
+    create_tokenizer, create_tokenizer_async, create_tokenizer_async_with_chat_template,
+    create_tokenizer_from_file, create_tokenizer_with_chat_template,
+    create_tokenizer_with_chat_template_blocking, TokenizerType,
 };
 pub use sequence::Sequence;
 pub use stop::{SequenceDecoderOutput, StopSequenceConfig, StopSequenceDecoder};

sgl-router/tests/api_endpoints_test.rs

@@ -30,6 +30,7 @@ impl TestContext {
     async fn new(worker_configs: Vec<MockWorkerConfig>) -> Self {
         // Create default router config
         let config = RouterConfig {
+            chat_template: None,
             mode: RoutingMode::Regular {
                 worker_urls: vec![],
             },
@@ -1365,6 +1366,7 @@ mod error_tests {
     async fn test_payload_too_large() {
         // Create context with small payload limit
         let config = RouterConfig {
+            chat_template: None,
             mode: RoutingMode::Regular {
                 worker_urls: vec![],
             },
@@ -1723,6 +1725,7 @@ mod pd_mode_tests {
             .unwrap_or(9000);
 
         let config = RouterConfig {
+            chat_template: None,
             mode: RoutingMode::PrefillDecode {
                 prefill_urls: vec![(prefill_url, Some(prefill_port))],
                 decode_urls: vec![decode_url],
@@ -1888,6 +1891,7 @@ mod request_id_tests {
     async fn test_request_id_with_custom_headers() {
         // Create config with custom request ID headers
         let config = RouterConfig {
+            chat_template: None,
             mode: RoutingMode::Regular {
                 worker_urls: vec![],
             },

sgl-router/tests/request_formats_test.rs

@@ -18,6 +18,7 @@ struct TestContext {
 impl TestContext {
     async fn new(worker_configs: Vec<MockWorkerConfig>) -> Self {
         let mut config = RouterConfig {
+            chat_template: None,
             mode: RoutingMode::Regular {
                 worker_urls: vec![],
             },

sgl-router/tests/responses_api_test.rs

@@ -44,6 +44,7 @@ async fn test_non_streaming_mcp_minimal_e2e_with_persistence() {
 
     // Build router config (HTTP OpenAI mode)
     let router_cfg = RouterConfig {
+        chat_template: None,
         mode: RoutingMode::OpenAI {
             worker_urls: vec![worker_url],
         },
@@ -245,6 +246,7 @@ async fn test_non_streaming_mcp_minimal_e2e_with_persistence() {
 async fn test_conversations_crud_basic() {
     // Router in OpenAI mode (no actual upstream calls in these tests)
     let router_cfg = RouterConfig {
+        chat_template: None,
         mode: RoutingMode::OpenAI {
             worker_urls: vec!["http://localhost".to_string()],
         },
@@ -576,6 +578,7 @@ async fn test_multi_turn_loop_with_mcp() {
 
     // Build router config
     let router_cfg = RouterConfig {
+        chat_template: None,
         mode: RoutingMode::OpenAI {
             worker_urls: vec![worker_url],
         },
@@ -753,6 +756,7 @@ async fn test_max_tool_calls_limit() {
     let worker_url = worker.start().await.expect("start worker");
 
     let router_cfg = RouterConfig {
+        chat_template: None,
         mode: RoutingMode::OpenAI {
             worker_urls: vec![worker_url],
         },
@@ -896,6 +900,7 @@ async fn setup_streaming_mcp_test() -> (
     let worker_url = worker.start().await.expect("start worker");
 
     let router_cfg = RouterConfig {
+        chat_template: None,
         mode: RoutingMode::OpenAI {
             worker_urls: vec![worker_url],
         },
@@ -1338,6 +1343,7 @@ async fn test_streaming_multi_turn_with_mcp() {
 async fn test_conversation_items_create_and_get() {
     // Test creating items and getting a specific item
     let router_cfg = RouterConfig {
+        chat_template: None,
         mode: RoutingMode::OpenAI {
             worker_urls: vec!["http://localhost".to_string()],
         },
@@ -1440,6 +1446,7 @@ async fn test_conversation_items_create_and_get() {
 async fn test_conversation_items_delete() {
     // Test deleting an item from a conversation
     let router_cfg = RouterConfig {
+        chat_template: None,
         mode: RoutingMode::OpenAI {
             worker_urls: vec!["http://localhost".to_string()],
         },
@@ -1548,6 +1555,7 @@ async fn test_conversation_items_delete() {
 async fn test_conversation_items_max_limit() {
     // Test that creating > 20 items returns error
     let router_cfg = RouterConfig {
+        chat_template: None,
         mode: RoutingMode::OpenAI {
             worker_urls: vec!["http://localhost".to_string()],
         },
@@ -1626,6 +1634,7 @@ async fn test_conversation_items_max_limit() {
 async fn test_conversation_items_unsupported_type() {
     // Test that unsupported item types return error
     let router_cfg = RouterConfig {
+        chat_template: None,
         mode: RoutingMode::OpenAI {
             worker_urls: vec!["http://localhost".to_string()],
         },
@@ -1703,6 +1712,7 @@ async fn test_conversation_items_unsupported_type() {
 async fn test_conversation_items_multi_conversation_sharing() {
     // Test that items can be shared across conversations via soft delete
     let router_cfg = RouterConfig {
+        chat_template: None,
         mode: RoutingMode::OpenAI {
             worker_urls: vec!["http://localhost".to_string()],
         },

sgl-router/tests/streaming_tests.rs

@@ -19,6 +19,7 @@ struct TestContext {
 impl TestContext {
     async fn new(worker_configs: Vec<MockWorkerConfig>) -> Self {
         let mut config = RouterConfig {
+            chat_template: None,
             mode: RoutingMode::Regular {
                 worker_urls: vec![],
             },

sgl-router/tests/test_openai_routing.rs

@@ -867,6 +867,7 @@ async fn test_openai_router_models_auth_forwarding() {
 #[test]
 fn oracle_config_validation_requires_config_when_enabled() {
     let config = RouterConfig {
+        chat_template: None,
         mode: RoutingMode::OpenAI {
             worker_urls: vec!["https://api.openai.com".to_string()],
         },
@@ -891,6 +892,7 @@ fn oracle_config_validation_requires_config_when_enabled() {
 #[test]
 fn oracle_config_validation_accepts_dsn_only() {
     let config = RouterConfig {
+        chat_template: None,
         mode: RoutingMode::OpenAI {
             worker_urls: vec!["https://api.openai.com".to_string()],
         },
@@ -913,6 +915,7 @@ fn oracle_config_validation_accepts_dsn_only() {
 #[test]
 fn oracle_config_validation_accepts_wallet_alias() {
     let config = RouterConfig {
+        chat_template: None,
         mode: RoutingMode::OpenAI {
             worker_urls: vec!["https://api.openai.com".to_string()],
         },

sgl-router/tests/test_pd_routing.rs

@@ -164,6 +164,7 @@ mod test_pd_routing {
 
         for (mode, policy) in test_cases {
             let config = RouterConfig {
+                chat_template: None,
                 mode,
                 policy,
                 host: "127.0.0.1".to_string(),