[Feature] integrate Structural Tag in xgrammar backend for function calling (#3566)

Co-authored-by: shuaills <shishuaiuoe@gmail.com>

python/sglang/srt/constrained/xgrammar_backend.py

@@ -13,6 +13,7 @@
 # ==============================================================================
 """Constrained decoding with xgrammar backend."""
 
+import json
 import logging
 from typing import List, Tuple
 
@@ -21,6 +22,7 @@ from xgrammar import (
     CompiledGrammar,
     GrammarCompiler,
     GrammarMatcher,
+    StructuralTagItem,
     TokenizerInfo,
     allocate_token_bitmask,
     apply_token_bitmask_inplace,
@@ -138,6 +140,23 @@ class XGrammarGrammarBackend(BaseGrammarBackend):
             except RuntimeError as e:
                 logging.warning(f"Skip invalid regex: regex={key_string}, {e=}")
                 return None
+        elif key_type == "structural_tag":
+            try:
+                structural_tag = json.loads(key_string)
+                tags = [
+                    StructuralTagItem(
+                        begin=structure["begin"],
+                        schema=json.dumps(structure["schema"]),
+                        end=structure["end"],
+                    )
+                    for structure in structural_tag["structures"]
+                ]
+                ctx = self.grammar_compiler.compile_structural_tag(
+                    tags, structural_tag["triggers"]
+                )
+            except RuntimeError as e:
+                logging.warning(f"Skip invalid regex: regex={key_string}, {e=}")
+                return None
         else:
             raise ValueError(f"Invalid key_type: {key_type}")
 

python/sglang/srt/managers/scheduler.py

@@ -710,6 +710,7 @@ class Scheduler:
             req.sampling_params.json_schema is not None
             or req.sampling_params.regex is not None
             or req.sampling_params.ebnf is not None
+            or req.sampling_params.structural_tag is not None
         ):
             assert self.grammar_backend is not None
             if req.sampling_params.json_schema is not None:
@@ -718,6 +719,8 @@ class Scheduler:
                 key = ("regex", req.sampling_params.regex)
             elif req.sampling_params.ebnf is not None:
                 key = ("ebnf", req.sampling_params.ebnf)
+            elif req.sampling_params.structural_tag:
+                key = ("structural_tag", req.sampling_params.structural_tag)
 
             req.grammar = self.grammar_backend.get_cached_value(key)
             if not req.grammar:

python/sglang/srt/openai_api/adapter.py

@@ -994,10 +994,17 @@ def v1_chat_generate_request(
             "ignore_eos": request.ignore_eos,
             "skip_special_tokens": request.skip_special_tokens,
         }
+
         if request.response_format and request.response_format.type == "json_schema":
             sampling_params["json_schema"] = convert_json_schema_to_str(
                 request.response_format.json_schema.schema_
             )
+        elif (
+            request.response_format and request.response_format.type == "structural_tag"
+        ):
+            sampling_params["structural_tag"] = convert_json_schema_to_str(
+                request.response_format.model_dump(by_alias=True)
+            )
         sampling_params_list.append(sampling_params)
 
         image_data_list.append(image_data)

python/sglang/srt/openai_api/protocol.py

@@ -258,6 +258,18 @@ class ResponseFormat(BaseModel):
     json_schema: Optional[JsonSchemaResponseFormat] = None
 
 
+class StructuresResponseFormat(BaseModel):
+    begin: str
+    schema_: Optional[Dict[str, object]] = Field(alias="schema", default=None)
+    end: str
+
+
+class StructuralTagResponseFormat(BaseModel):
+    type: Literal["structural_tag"]
+    structures: List[StructuresResponseFormat]
+    triggers: List[str]
+
+
 class Function(BaseModel):
     """Function descriptions."""
 
@@ -298,7 +310,7 @@ class ChatCompletionRequest(BaseModel):
     max_tokens: Optional[int] = None
     n: int = 1
     presence_penalty: float = 0.0
-    response_format: Optional[ResponseFormat] = None
+    response_format: Union[ResponseFormat, StructuralTagResponseFormat] = None
     seed: Optional[int] = None
     stop: Optional[Union[str, List[str]]] = None
     stream: bool = False

python/sglang/srt/sampling/sampling_params.py

@@ -45,6 +45,7 @@ class SamplingParams:
         json_schema: Optional[str] = None,
         regex: Optional[str] = None,
         ebnf: Optional[str] = None,
+        structural_tag: Optional[str] = None,
         no_stop_trim: bool = False,
         ignore_eos: bool = False,
         skip_special_tokens: bool = True,
@@ -72,6 +73,7 @@ class SamplingParams:
         self.n = n
         self.json_schema = json_schema
         self.ebnf = ebnf
+        self.structural_tag = structural_tag
         self.no_stop_trim = no_stop_trim
         self.return_hidden_states = return_hidden_states
         self.custom_params = custom_params