[router] fix chat template loading and tokenizer path (#10999)

sgl-router/src/tokenizer/hub.rs

@@ -40,6 +40,13 @@ fn is_tokenizer_file(filename: &str) -> bool {
         || filename.ends_with("merges.txt")
         || filename.ends_with(".model")  // SentencePiece models
         || filename.ends_with(".tiktoken")
+        || is_chat_template_file(filename) // Include chat template files
+}
+
+/// Checks if a file is a chat template file
+fn is_chat_template_file(filename: &str) -> bool {
+    filename.ends_with(".jinja")  // Direct Jinja files
+        || filename == "chat_template.json" // JSON file containing Jinja template
 }
 
 /// Attempt to download tokenizer files from Hugging Face
@@ -123,7 +130,13 @@ pub async fn download_tokenizer_from_hf(model_id: impl AsRef<Path>) -> anyhow::R
     }
 
     match cache_dir {
-        Some(dir) => Ok(dir),
+        Some(dir) => {
+            // Ensure we return the correct model directory, not a subfolder
+            // Some models have an "original" subfolder for PyTorch weights
+            // We want the main model directory that contains tokenizer files
+            let final_dir = resolve_model_cache_dir(&dir, &model_name);
+            Ok(final_dir)
+        }
         None => Err(anyhow::anyhow!(
             "Invalid HF cache path for model '{}'",
             model_name
@@ -206,11 +219,76 @@ pub async fn from_hf(name: impl AsRef<Path>, ignore_weights: bool) -> anyhow::Re
     }
 
     match p.parent() {
-        Some(p) => Ok(p.to_path_buf()),
+        Some(p) => {
+            let final_dir = resolve_model_cache_dir(p, &model_name);
+            Ok(final_dir)
+        }
         None => Err(anyhow::anyhow!("Invalid HF cache path: {}", p.display())),
     }
 }
 
+/// Resolve the correct model cache directory
+/// Handles cases where files might be in subfolders (e.g., "original" folder)
+fn resolve_model_cache_dir(path: &Path, model_name: &str) -> PathBuf {
+    // Check if we're in a subfolder like "original"
+    if let Some(parent) = path.parent() {
+        if let Some(folder_name) = path.file_name() {
+            if folder_name == "original" {
+                // We're in the "original" subfolder, go up one level
+                return parent.to_path_buf();
+            }
+        }
+    }
+
+    // Check if the current path contains the model name components
+    // This helps ensure we're at the right directory level
+    let model_parts: Vec<&str> = model_name.split('/').collect();
+    if model_parts.len() >= 2 {
+        let expected_pattern = format!(
+            "models--{}--{}",
+            model_parts[0].replace("-", "--"),
+            model_parts[1].replace("-", "--")
+        );
+
+        if path.to_string_lossy().contains(&expected_pattern) {
+            // We're already at the correct level
+            return path.to_path_buf();
+        }
+
+        let mut current = path.to_path_buf();
+
+        // First check if current path already contains tokenizer files
+        if current.join("tokenizer.json").exists() || current.join("tokenizer_config.json").exists()
+        {
+            return current;
+        }
+
+        // If not, traverse up to find the model root, then look in snapshots
+        while let Some(parent) = current.parent() {
+            if parent.to_string_lossy().contains(&expected_pattern) {
+                let snapshots_dir = parent.join("snapshots");
+                if snapshots_dir.exists() && snapshots_dir.is_dir() {
+                    if let Ok(entries) = std::fs::read_dir(&snapshots_dir) {
+                        for entry in entries.flatten() {
+                            let snapshot_path = entry.path();
+                            if snapshot_path.is_dir()
+                                && (snapshot_path.join("tokenizer.json").exists()
+                                    || snapshot_path.join("tokenizer_config.json").exists())
+                            {
+                                return snapshot_path;
+                            }
+                        }
+                    }
+                }
+                return parent.to_path_buf();
+            }
+            current = parent.to_path_buf();
+        }
+    }
+
+    path.to_path_buf()
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -223,10 +301,24 @@ mod tests {
         assert!(is_tokenizer_file("vocab.json"));
         assert!(is_tokenizer_file("merges.txt"));
         assert!(is_tokenizer_file("spiece.model"));
+        assert!(is_tokenizer_file("chat_template.jinja"));
+        assert!(is_tokenizer_file("template.jinja"));
         assert!(!is_tokenizer_file("model.bin"));
         assert!(!is_tokenizer_file("README.md"));
     }
 
+    #[test]
+    fn test_is_chat_template_file() {
+        assert!(is_chat_template_file("chat_template.jinja"));
+        assert!(is_chat_template_file("template.jinja"));
+        assert!(is_chat_template_file("any_file.jinja"));
+        assert!(is_chat_template_file("chat_template.json"));
+        assert!(!is_chat_template_file("tokenizer.json"));
+        assert!(!is_chat_template_file("other_file.json"));
+        assert!(!is_chat_template_file("chat_template"));
+        assert!(!is_chat_template_file("README.md"));
+    }
+
     #[test]
     fn test_is_weight_file() {
         assert!(is_weight_file("model.bin"));