feat: Support "stop" parameter in remote:vLLM (#1715)

# What does this PR do?

This adds support for "stop" parameter:
https://platform.openai.com/docs/api-reference/completions/create#completions-create-stop

## Test Plan

```
tests/integration/inference/test_text_inference.py::test_text_completion_non_streaming[txt=8B-inference:completion:sanity] PASSED                                  [  5%]
tests/integration/inference/test_text_inference.py::test_text_completion_streaming[txt=8B-inference:completion:sanity] PASSED                                      [ 11%]
tests/integration/inference/test_text_inference.py::test_text_completion_stop_sequence[txt=8B-inference:completion:stop_sequence] PASSED                           [ 16%]
tests/integration/inference/test_text_inference.py::test_text_completion_log_probs_non_streaming[txt=8B-inference:completion:log_probs] PASSED                     [ 22%]
tests/integration/inference/test_text_inference.py::test_text_completion_log_probs_streaming[txt=8B-inference:completion:log_probs] PASSED                         [ 27%]
tests/integration/inference/test_text_inference.py::test_text_completion_structured_output[txt=8B-inference:completion:structured_output] PASSED                   [ 33%]
tests/integration/inference/test_text_inference.py::test_text_chat_completion_non_streaming[txt=8B-inference:chat_completion:non_streaming_01] PASSED              [ 38%]
tests/integration/inference/test_text_inference.py::test_text_chat_completion_non_streaming[txt=8B-inference:chat_completion:non_streaming_02] PASSED              [ 44%]
tests/integration/inference/test_text_inference.py::test_text_chat_completion_first_token_profiling[txt=8B-inference:chat_completion:ttft] ^TPASSED                  [ 50%]
tests/integration/inference/test_text_inference.py::test_text_chat_completion_streaming[txt=8B-inference:chat_completion:streaming_01] PASSED                      [ 55%]
tests/integration/inference/test_text_inference.py::test_text_chat_completion_streaming[txt=8B-inference:chat_completion:streaming_02] PASSED                      [ 61%]
tests/integration/inference/test_text_inference.py::test_text_chat_completion_with_tool_calling_and_non_streaming[txt=8B-inference:chat_completion:tool_calling] PASSED [ 66%]
tests/integration/inference/test_text_inference.py::test_text_chat_completion_with_tool_calling_and_streaming[txt=8B-inference:chat_completion:tool_calling] PASSED [ 72%]
tests/integration/inference/test_text_inference.py::test_text_chat_completion_with_tool_choice_required[txt=8B-inference:chat_completion:tool_calling] PASSED      [ 77%]
tests/integration/inference/test_text_inference.py::test_text_chat_completion_with_tool_choice_none[txt=8B-inference:chat_completion:tool_calling] PASSED          [ 83%]
tests/integration/inference/test_text_inference.py::test_text_chat_completion_structured_output[txt=8B-inference:chat_completion:structured_output] PASSED         [ 88%]
tests/integration/inference/test_text_inference.py::test_text_chat_completion_tool_calling_tools_not_in_request[txt=8B-inference:chat_completion:tool_calling_tools_absent-True] PASSED [ 94%]
tests/integration/inference/test_text_inference.py::test_text_chat_completion_tool_calling_tools_not_in_request[txt=8B-inference:chat_completion:tool_calling_tools_absent-False] PASSED [100%]

=============================================================== 18 passed, 3 warnings in 755.79s (0:12:35) ===============================================================
```

---------

Signed-off-by: Yuan Tang <terrytangyuan@gmail.com>

docs/_static/llama-stack-spec.html

@@ -4053,22 +4053,33 @@
                 "type": "object",
                 "properties": {
                     "strategy": {
-                        "$ref": "#/components/schemas/SamplingStrategy"
+                        "$ref": "#/components/schemas/SamplingStrategy",
+                        "description": "The sampling strategy."
                     },
                     "max_tokens": {
                         "type": "integer",
-                        "default": 0
+                        "default": 0,
+                        "description": "The maximum number of tokens that can be generated in the completion. The token count of your prompt plus max_tokens cannot exceed the model's context length."
                     },
                     "repetition_penalty": {
                         "type": "number",
-                        "default": 1.0
+                        "default": 1.0,
+                        "description": "Number between -2.0 and 2.0. Positive values penalize new tokens based on whether they appear in the text so far, increasing the model's likelihood to talk about new topics."
+                    },
+                    "stop": {
+                        "type": "array",
+                        "items": {
+                            "type": "string"
+                        },
+                        "description": "Up to 4 sequences where the API will stop generating further tokens. The returned text will not contain the stop sequence."
                     }
                 },
                 "additionalProperties": false,
                 "required": [
                     "strategy"
                 ],
-                "title": "SamplingParams"
+                "title": "SamplingParams",
+                "description": "Sampling parameters."
             },
             "SamplingStrategy": {
                 "oneOf": [

docs/_static/llama-stack-spec.yaml

@@ -2787,16 +2787,33 @@ components:
       properties:
         strategy:
           $ref: '#/components/schemas/SamplingStrategy'
+          description: The sampling strategy.
         max_tokens:
           type: integer
           default: 0
+          description: >-
+            The maximum number of tokens that can be generated in the completion.
+            The token count of your prompt plus max_tokens cannot exceed the model's
+            context length.
         repetition_penalty:
           type: number
           default: 1.0
+          description: >-
+            Number between -2.0 and 2.0. Positive values penalize new tokens based
+            on whether they appear in the text so far, increasing the model's likelihood
+            to talk about new topics.
+        stop:
+          type: array
+          items:
+            type: string
+          description: >-
+            Up to 4 sequences where the API will stop generating further tokens. The
+            returned text will not contain the stop sequence.
       additionalProperties: false
       required:
         - strategy
       title: SamplingParams
+      description: Sampling parameters.
     SamplingStrategy:
       oneOf:
         - $ref: '#/components/schemas/GreedySamplingStrategy'

llama_stack/models/llama/datatypes.py

@@ -195,10 +195,22 @@ register_schema(SamplingStrategy, name="SamplingStrategy")
 
 @json_schema_type
 class SamplingParams(BaseModel):
+    """Sampling parameters.
+
+    :param strategy: The sampling strategy.
+    :param max_tokens: The maximum number of tokens that can be generated in the completion. The token count of
+        your prompt plus max_tokens cannot exceed the model's context length.
+    :param repetition_penalty: Number between -2.0 and 2.0. Positive values penalize new tokens
+        based on whether they appear in the text so far, increasing the model's likelihood to talk about new topics.
+    :param stop: Up to 4 sequences where the API will stop generating further tokens.
+        The returned text will not contain the stop sequence.
+    """
+
     strategy: SamplingStrategy = Field(default_factory=GreedySamplingStrategy)
 
     max_tokens: Optional[int] = 0
     repetition_penalty: Optional[float] = 1.0
+    stop: Optional[List[str]] = None
 
 
 class CheckpointQuantizationFormat(Enum):

llama_stack/providers/utils/inference/openai_compat.py

@@ -147,6 +147,9 @@ def get_sampling_options(params: SamplingParams) -> dict:
         if params.repetition_penalty is not None and params.repetition_penalty != 1.0:
             options["repeat_penalty"] = params.repetition_penalty
 
+        if params.stop is not None:
+            options["stop"] = params.stop
+
     return options
 
 

tests/integration/inference/test_text_inference.py

@@ -99,6 +99,33 @@ def test_text_completion_streaming(client_with_models, text_model_id, test_case)
     assert len(content_str) > 10
 
 
+@pytest.mark.parametrize(
+    "test_case",
+    [
+        "inference:completion:stop_sequence",
+    ],
+)
+def test_text_completion_stop_sequence(client_with_models, text_model_id, inference_provider_type, test_case):
+    skip_if_model_doesnt_support_completion(client_with_models, text_model_id)
+    # This is only supported/tested for remote vLLM: https://github.com/meta-llama/llama-stack/issues/1771
+    if inference_provider_type != "remote::vllm":
+        pytest.xfail(f"{inference_provider_type} doesn't support 'stop' parameter yet")
+    tc = TestCase(test_case)
+
+    response = client_with_models.inference.completion(
+        content=tc["content"],
+        stream=True,
+        model_id=text_model_id,
+        sampling_params={
+            "max_tokens": 50,
+            "stop": ["1963"],
+        },
+    )
+    streamed_content = [chunk.delta for chunk in response]
+    content_str = "".join(streamed_content).lower().strip()
+    assert "1963" not in content_str
+
+
 @pytest.mark.parametrize(
     "test_case",
     [

tests/integration/test_cases/inference/completion.json

@@ -10,6 +10,11 @@
             "expected": "1963"
         }
     },
+    "stop_sequence": {
+        "data": {
+            "content": "Return the exact same sentence and don't add additional words): Michael Jordan was born in the year of 1963"
+        }
+    },
     "streaming": {
         "data": {
             "content": "Roses are red,"