add response_format support for completion API (#9665)

python/sglang/srt/entrypoints/openai/protocol.py

@@ -108,6 +108,23 @@ class JsonSchemaResponseFormat(BaseModel):
     strict: Optional[bool] = False
 
 
+class ResponseFormat(BaseModel):
+    type: Literal["text", "json_object", "json_schema"]
+    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 FileRequest(BaseModel):
     # https://platform.openai.com/docs/api-reference/files/create
     file: bytes  # The File object (not file name) to be uploaded
@@ -200,6 +217,7 @@ class CompletionRequest(BaseModel):
     skip_special_tokens: bool = True
     lora_path: Optional[Union[List[Optional[str]], Optional[str]]] = None
     session_params: Optional[Dict] = None
+    response_format: Optional[Union[ResponseFormat, StructuralTagResponseFormat]] = None
 
     # For PD disaggregation
     bootstrap_host: Optional[Union[List[str], str]] = None
@@ -359,23 +377,6 @@ ChatCompletionMessageParam = Union[
 ]
 
 
-class ResponseFormat(BaseModel):
-    type: Literal["text", "json_object", "json_schema"]
-    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."""
 

python/sglang/srt/entrypoints/openai/serving_completions.py

@@ -23,6 +23,7 @@ from sglang.srt.entrypoints.openai.utils import (
 from sglang.srt.managers.io_struct import GenerateReqInput
 from sglang.srt.managers.template_manager import TemplateManager
 from sglang.srt.managers.tokenizer_manager import TokenizerManager
+from sglang.utils import convert_json_schema_to_str
 
 logger = logging.getLogger(__name__)
 
@@ -125,6 +126,20 @@ class OpenAIServingCompletion(OpenAIServingBase):
             "logit_bias": request.logit_bias,
         }
 
+        # Handle response_format constraints
+        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 == "json_object":
+            sampling_params["json_schema"] = '{"type": "object"}'
+        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)
+            )
+
         return sampling_params
 
     async def _handle_streaming_request(