[Frontend] Fix request length check and add option to disallow auto truncation in scheduler (#2876)

python/sglang/srt/managers/utils.py

@@ -0,0 +1,41 @@
+import logging
+from typing import Optional
+
+from sglang.srt.managers.schedule_batch import FINISH_ABORT, Req
+
+logger = logging.getLogger(__name__)
+
+
+def validate_input_length(
+    req: Req, max_req_input_len: int, allow_auto_truncate: bool
+) -> Optional[str]:
+    """Validate and potentially truncate input length.
+
+    Args:
+        req: The request containing input_ids to validate
+        max_req_input_len: Maximum allowed input length
+        allow_auto_truncate: Whether to truncate long inputs
+
+    Returns:
+        Error message if validation fails, None if successful
+    """
+    if len(req.origin_input_ids) >= max_req_input_len:
+        if allow_auto_truncate:
+            logger.warning(
+                "Request length is longer than the KV cache pool size or "
+                "the max context length. Truncated. "
+                f"{len(req.origin_input_ids)=}, {max_req_input_len=}."
+            )
+            req.origin_input_ids = req.origin_input_ids[:max_req_input_len]
+            return None
+        else:
+            error_msg = (
+                f"Input length ({len(req.origin_input_ids)} tokens) exceeds "
+                f"the maximum allowed length ({max_req_input_len} tokens). "
+                f"Use a shorter input or enable --allow-auto-truncate."
+            )
+            logger.error(error_msg)
+            req.finished_reason = FINISH_ABORT(error_msg)
+            return error_msg
+
+    return None