feat: add batches API with OpenAI compatibility

Add complete batches API implementation with protocol, providers, and tests:

Core Infrastructure:
- Add batches API protocol using OpenAI Batch types directly
- Add Api.batches enum value and protocol mapping in resolver
- Add OpenAI "batch" file purpose support
- Include proper error handling (ConflictError, ResourceNotFoundError)

Reference Provider:
- Add ReferenceBatchesImpl with full CRUD operations (create, retrieve, cancel, list)
- Implement background batch processing with configurable concurrency
- Add SQLite KVStore backend for persistence
- Support /v1/chat/completions endpoint with request validation

Comprehensive Test Suite:
- Add unit tests for provider implementation with validation
- Add integration tests for end-to-end batch processing workflows
- Add error handling tests for validation, malformed inputs, and edge cases

Configuration:
- Add max_concurrent_batches and max_concurrent_requests_per_batch options
- Add provider documentation with sample configurations

Test with -

```
$ uv run llama stack build --image-type venv --providers inference=YOU_PICK,files=inline::localfs,batches=inline::reference --run &
$ LLAMA_STACK_CONFIG=http://localhost:8321 uv run pytest tests/unit/providers/batches tests/integration/batches --text-model YOU_PICK
```

llama_stack/providers/inline/batches/__init__.py

@@ -0,0 +1,5 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.

llama_stack/providers/inline/batches/reference/__init__.py

@@ -0,0 +1,36 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+from typing import Any
+
+from llama_stack.apis.files import Files
+from llama_stack.apis.inference import Inference
+from llama_stack.apis.models import Models
+from llama_stack.core.datatypes import AccessRule, Api
+from llama_stack.providers.utils.kvstore import kvstore_impl
+
+from .batches import ReferenceBatchesImpl
+from .config import ReferenceBatchesImplConfig
+
+__all__ = ["ReferenceBatchesImpl", "ReferenceBatchesImplConfig"]
+
+
+async def get_provider_impl(config: ReferenceBatchesImplConfig, deps: dict[Api, Any], policy: list[AccessRule]):
+    kvstore = await kvstore_impl(config.kvstore)
+    inference_api: Inference | None = deps.get(Api.inference)
+    files_api: Files | None = deps.get(Api.files)
+    models_api: Models | None = deps.get(Api.models)
+
+    if inference_api is None:
+        raise ValueError("Inference API is required but not provided in dependencies")
+    if files_api is None:
+        raise ValueError("Files API is required but not provided in dependencies")
+    if models_api is None:
+        raise ValueError("Models API is required but not provided in dependencies")
+
+    impl = ReferenceBatchesImpl(config, inference_api, files_api, models_api, kvstore)
+    await impl.initialize()
+    return impl

llama_stack/providers/inline/batches/reference/batches.py

@@ -0,0 +1,553 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+import asyncio
+import itertools
+import json
+import time
+import uuid
+from io import BytesIO
+from typing import Any
+
+from openai.types.batch import BatchError, Errors
+from pydantic import BaseModel
+
+from llama_stack.apis.batches import Batches, BatchObject, ListBatchesResponse
+from llama_stack.apis.common.errors import ConflictError, ResourceNotFoundError
+from llama_stack.apis.files import Files, OpenAIFilePurpose
+from llama_stack.apis.inference import Inference
+from llama_stack.apis.models import Models
+from llama_stack.log import get_logger
+from llama_stack.providers.utils.kvstore import KVStore
+
+from .config import ReferenceBatchesImplConfig
+
+BATCH_PREFIX = "batch:"
+
+logger = get_logger(__name__)
+
+
+class AsyncBytesIO:
+    """
+    Async-compatible BytesIO wrapper to allow async file-like operations.
+
+    We use this when uploading files to the Files API, as it expects an
+    async file-like object.
+    """
+
+    def __init__(self, data: bytes):
+        self._buffer = BytesIO(data)
+
+    async def read(self, n=-1):
+        return self._buffer.read(n)
+
+    async def seek(self, pos, whence=0):
+        return self._buffer.seek(pos, whence)
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        self._buffer.close()
+
+    def __getattr__(self, name):
+        return getattr(self._buffer, name)
+
+
+class BatchRequest(BaseModel):
+    line_num: int
+    custom_id: str
+    method: str
+    url: str
+    body: dict[str, Any]
+
+
+class ReferenceBatchesImpl(Batches):
+    """Reference implementation of the Batches API.
+
+    This implementation processes batch files by making individual requests
+    to the inference API and generates output files with results.
+    """
+
+    def __init__(
+        self,
+        config: ReferenceBatchesImplConfig,
+        inference_api: Inference,
+        files_api: Files,
+        models_api: Models,
+        kvstore: KVStore,
+    ) -> None:
+        self.config = config
+        self.kvstore = kvstore
+        self.inference_api = inference_api
+        self.files_api = files_api
+        self.models_api = models_api
+        self._processing_tasks: dict[str, asyncio.Task] = {}
+        self._batch_semaphore = asyncio.Semaphore(config.max_concurrent_batches)
+        self._update_batch_lock = asyncio.Lock()
+
+        # this is to allow tests to disable background processing
+        self.process_batches = True
+
+    async def initialize(self) -> None:
+        # TODO: start background processing of existing tasks
+        pass
+
+    async def shutdown(self) -> None:
+        """Shutdown the batches provider."""
+        if self._processing_tasks:
+            # don't cancel tasks - just let them stop naturally on shutdown
+            # cancelling would mark batches as "cancelled" in the database
+            logger.info(f"Shutdown initiated with {len(self._processing_tasks)} active batch processing tasks")
+
+    # TODO (SECURITY): this currently works w/ configured api keys, not with x-llamastack-provider-data or with user policy restrictions
+    async def create_batch(
+        self,
+        input_file_id: str,
+        endpoint: str,
+        completion_window: str,
+        metadata: dict[str, str] | None = None,
+    ) -> BatchObject:
+        """
+        Create a new batch for processing multiple API requests.
+
+        Error handling by levels -
+         0. Input param handling, results in 40x errors before processing, e.g.
+           - Wrong completion_window
+           - Invalid metadata types
+           - Unknown endpoint
+          -> no batch created
+         1. Errors preventing processing, result in BatchErrors aggregated in process_batch, e.g.
+           - input_file_id missing
+           - invalid json in file
+           - missing custom_id, method, url, body
+           - invalid model
+           - streaming
+          -> batch created, validation sends to failed status
+         2. Processing errors, result in error_file_id entries, e.g.
+           - Any error returned from inference endpoint
+          -> batch created, goes to completed status
+        """
+
+        # TODO: set expiration time for garbage collection
+
+        if endpoint not in ["/v1/chat/completions"]:
+            raise ValueError(
+                f"Invalid endpoint: {endpoint}. Supported values: /v1/chat/completions. Code: invalid_value. Param: endpoint",
+            )
+
+        if completion_window != "24h":
+            raise ValueError(
+                f"Invalid completion_window: {completion_window}. Supported values are: 24h. Code: invalid_value. Param: completion_window",
+            )
+
+        batch_id = f"batch_{uuid.uuid4().hex[:16]}"
+        current_time = int(time.time())
+
+        batch = BatchObject(
+            id=batch_id,
+            object="batch",
+            endpoint=endpoint,
+            input_file_id=input_file_id,
+            completion_window=completion_window,
+            status="validating",
+            created_at=current_time,
+            metadata=metadata,
+        )
+
+        await self.kvstore.set(f"batch:{batch_id}", batch.to_json())
+
+        if self.process_batches:
+            task = asyncio.create_task(self._process_batch(batch_id))
+            self._processing_tasks[batch_id] = task
+
+        return batch
+
+    async def cancel_batch(self, batch_id: str) -> BatchObject:
+        """Cancel a batch that is in progress."""
+        batch = await self.retrieve_batch(batch_id)
+
+        if batch.status in ["cancelled", "cancelling"]:
+            return batch
+
+        if batch.status in ["completed", "failed", "expired"]:
+            raise ConflictError(f"Cannot cancel batch '{batch_id}' with status '{batch.status}'")
+
+        await self._update_batch(batch_id, status="cancelling", cancelling_at=int(time.time()))
+
+        if batch_id in self._processing_tasks:
+            self._processing_tasks[batch_id].cancel()
+            # note: task removal and status="cancelled" handled in finally block of _process_batch
+
+        return await self.retrieve_batch(batch_id)
+
+    async def list_batches(
+        self,
+        after: str | None = None,
+        limit: int = 20,
+    ) -> ListBatchesResponse:
+        """
+        List all batches, eventually only for the current user.
+
+        With no notion of user, we return all batches.
+        """
+        batch_values = await self.kvstore.values_in_range("batch:", "batch:\xff")
+
+        batches = []
+        for batch_data in batch_values:
+            if batch_data:
+                batches.append(BatchObject.model_validate_json(batch_data))
+
+        batches.sort(key=lambda b: b.created_at, reverse=True)
+
+        start_idx = 0
+        if after:
+            for i, batch in enumerate(batches):
+                if batch.id == after:
+                    start_idx = i + 1
+                    break
+
+        page_batches = batches[start_idx : start_idx + limit]
+        has_more = (start_idx + limit) < len(batches)
+
+        first_id = page_batches[0].id if page_batches else None
+        last_id = page_batches[-1].id if page_batches else None
+
+        return ListBatchesResponse(
+            data=page_batches,
+            first_id=first_id,
+            last_id=last_id,
+            has_more=has_more,
+        )
+
+    async def retrieve_batch(self, batch_id: str) -> BatchObject:
+        """Retrieve information about a specific batch."""
+        batch_data = await self.kvstore.get(f"batch:{batch_id}")
+        if not batch_data:
+            raise ResourceNotFoundError(batch_id, "Batch", "batches.list()")
+
+        return BatchObject.model_validate_json(batch_data)
+
+    async def _update_batch(self, batch_id: str, **updates) -> None:
+        """Update batch fields in kvstore."""
+        async with self._update_batch_lock:
+            try:
+                batch = await self.retrieve_batch(batch_id)
+
+                # batch processing is async. once cancelling, only allow "cancelled" status updates
+                if batch.status == "cancelling" and updates.get("status") != "cancelled":
+                    logger.info(
+                        f"Skipping status update for cancelled batch {batch_id}: attempted {updates.get('status')}"
+                    )
+                    return
+
+                if "errors" in updates:
+                    updates["errors"] = updates["errors"].model_dump()
+
+                batch_dict = batch.model_dump()
+                batch_dict.update(updates)
+
+                await self.kvstore.set(f"batch:{batch_id}", json.dumps(batch_dict))
+            except Exception as e:
+                logger.error(f"Failed to update batch {batch_id}: {e}")
+
+    async def _validate_input(self, batch: BatchObject) -> tuple[list[BatchError], list[BatchRequest]]:
+        """
+        Read & validate input, return errors and valid input.
+
+        Validation of
+        - input_file_id existance
+        - valid json
+        - custom_id, method, url, body presence and valid
+        - no streaming
+        """
+        requests: list[BatchRequest] = []
+        errors: list[BatchError] = []
+        try:
+            await self.files_api.openai_retrieve_file(batch.input_file_id)
+        except Exception:
+            errors.append(
+                BatchError(
+                    code="invalid_request",
+                    line=None,
+                    message=f"Cannot find file {batch.input_file_id}.",
+                    param="input_file_id",
+                )
+            )
+            return errors, requests
+
+        # TODO(SECURITY): do something about large files
+        file_content_response = await self.files_api.openai_retrieve_file_content(batch.input_file_id)
+        file_content = file_content_response.body.decode("utf-8")
+        for line_num, line in enumerate(file_content.strip().split("\n"), 1):
+            if line.strip():  # skip empty lines
+                try:
+                    request = json.loads(line)
+
+                    if not isinstance(request, dict):
+                        errors.append(
+                            BatchError(
+                                code="invalid_request",
+                                line=line_num,
+                                message="Each line must be a JSON dictionary object",
+                            )
+                        )
+                        continue
+
+                    valid = True
+
+                    for param, expected_type, type_string in [
+                        ("custom_id", str, "string"),
+                        ("method", str, "string"),
+                        ("url", str, "string"),
+                        ("body", dict, "JSON dictionary object"),
+                    ]:
+                        if param not in request:
+                            errors.append(
+                                BatchError(
+                                    code="missing_required_parameter",
+                                    line=line_num,
+                                    message=f"Missing required parameter: {param}",
+                                    param=param,
+                                )
+                            )
+                            valid = False
+                        elif not isinstance(request[param], expected_type):
+                            param_name = "URL" if param == "url" else param.capitalize()
+                            errors.append(
+                                BatchError(
+                                    code="invalid_request",
+                                    line=line_num,
+                                    message=f"{param_name} must be a {type_string}",
+                                    param=param,
+                                )
+                            )
+                            valid = False
+
+                    if (url := request.get("url")) and isinstance(url, str) and url != batch.endpoint:
+                        errors.append(
+                            BatchError(
+                                code="invalid_url",
+                                line=line_num,
+                                message="URL provided for this request does not match the batch endpoint",
+                                param="url",
+                            )
+                        )
+                        valid = False
+
+                    if (body := request.get("body")) and isinstance(body, dict):
+                        if body.get("stream", False):
+                            errors.append(
+                                BatchError(
+                                    code="streaming_unsupported",
+                                    line=line_num,
+                                    message="Streaming is not supported in batch processing",
+                                    param="body.stream",
+                                )
+                            )
+                            valid = False
+
+                        for param, expected_type, type_string in [
+                            ("model", str, "a string"),
+                            # messages is specific to /v1/chat/completions
+                            # we could skip validating messages here and let inference fail. however,
+                            # that would be a very expensive way to find out messages is wrong.
+                            ("messages", list, "an array"),  # TODO: allow messages to be a string?
+                        ]:
+                            if param not in body:
+                                errors.append(
+                                    BatchError(
+                                        code="invalid_request",
+                                        line=line_num,
+                                        message=f"{param.capitalize()} parameter is required",
+                                        param=f"body.{param}",
+                                    )
+                                )
+                                valid = False
+                            elif not isinstance(body[param], expected_type):
+                                errors.append(
+                                    BatchError(
+                                        code="invalid_request",
+                                        line=line_num,
+                                        message=f"{param.capitalize()} must be {type_string}",
+                                        param=f"body.{param}",
+                                    )
+                                )
+                                valid = False
+
+                        if "model" in body and isinstance(body["model"], str):
+                            try:
+                                await self.models_api.get_model(body["model"])
+                            except Exception:
+                                errors.append(
+                                    BatchError(
+                                        code="model_not_found",
+                                        line=line_num,
+                                        message=f"Model '{body['model']}' does not exist or is not supported",
+                                        param="body.model",
+                                    )
+                                )
+                                valid = False
+
+                    if valid:
+                        assert isinstance(url, str), "URL must be a string"  # for mypy
+                        assert isinstance(body, dict), "Body must be a dictionary"  # for mypy
+                        requests.append(
+                            BatchRequest(
+                                line_num=line_num,
+                                url=url,
+                                method=request["method"],
+                                custom_id=request["custom_id"],
+                                body=body,
+                            ),
+                        )
+                except json.JSONDecodeError:
+                    errors.append(
+                        BatchError(
+                            code="invalid_json_line",
+                            line=line_num,
+                            message="This line is not parseable as valid JSON.",
+                        )
+                    )
+
+        return errors, requests
+
+    async def _process_batch(self, batch_id: str) -> None:
+        """Background task to process a batch of requests."""
+        try:
+            logger.info(f"Starting batch processing for {batch_id}")
+            async with self._batch_semaphore:  # semaphore to limit concurrency
+                logger.info(f"Acquired semaphore for batch {batch_id}")
+                await self._process_batch_impl(batch_id)
+        except asyncio.CancelledError:
+            logger.info(f"Batch processing cancelled for {batch_id}")
+            await self._update_batch(batch_id, status="cancelled", cancelled_at=int(time.time()))
+        except Exception as e:
+            logger.error(f"Batch processing failed for {batch_id}: {e}")
+            await self._update_batch(
+                batch_id,
+                status="failed",
+                failed_at=int(time.time()),
+                errors=Errors(data=[BatchError(code="internal_error", message=str(e))]),
+            )
+        finally:
+            self._processing_tasks.pop(batch_id, None)
+
+    async def _process_batch_impl(self, batch_id: str) -> None:
+        """Implementation of batch processing logic."""
+        errors: list[BatchError] = []
+        batch = await self.retrieve_batch(batch_id)
+
+        errors, requests = await self._validate_input(batch)
+        if errors:
+            await self._update_batch(batch_id, status="failed", failed_at=int(time.time()), errors=Errors(data=errors))
+            logger.info(f"Batch validation failed for {batch_id} with {len(errors)} errors")
+            return
+
+        logger.info(f"Processing {len(requests)} requests for batch {batch_id}")
+
+        total_requests = len(requests)
+        await self._update_batch(
+            batch_id,
+            status="in_progress",
+            request_counts={"total": total_requests, "completed": 0, "failed": 0},
+        )
+
+        error_results = []
+        success_results = []
+        completed_count = 0
+        failed_count = 0
+
+        for chunk in itertools.batched(requests, self.config.max_concurrent_requests_per_batch):
+            # we use a TaskGroup to ensure all process-single-request tasks are canceled when process-batch is cancelled
+            async with asyncio.TaskGroup() as tg:
+                chunk_tasks = [tg.create_task(self._process_single_request(batch_id, request)) for request in chunk]
+
+                chunk_results = await asyncio.gather(*chunk_tasks, return_exceptions=True)
+
+            for result in chunk_results:
+                if isinstance(result, dict) and result.get("error") is not None:  # error response from inference
+                    failed_count += 1
+                    error_results.append(result)
+                elif isinstance(result, dict) and result.get("response") is not None:  # successful inference
+                    completed_count += 1
+                    success_results.append(result)
+                else:  # unexpected result
+                    failed_count += 1
+                    errors.append(BatchError(code="internal_error", message=f"Unexpected result: {result}"))
+
+            await self._update_batch(
+                batch_id,
+                request_counts={"total": total_requests, "completed": completed_count, "failed": failed_count},
+            )
+
+            if errors:
+                await self._update_batch(
+                    batch_id, status="failed", failed_at=int(time.time()), errors=Errors(data=errors)
+                )
+                return
+
+        try:
+            output_file_id = await self._create_output_file(batch_id, success_results, "success")
+            await self._update_batch(batch_id, output_file_id=output_file_id)
+
+            error_file_id = await self._create_output_file(batch_id, error_results, "error")
+            await self._update_batch(batch_id, error_file_id=error_file_id)
+
+            await self._update_batch(batch_id, status="completed", completed_at=int(time.time()))
+
+            logger.info(
+                f"Batch processing completed for {batch_id}: {completed_count} completed, {failed_count} failed"
+            )
+        except Exception as e:
+            # note: errors is empty at this point, so we don't lose anything by ignoring it
+            await self._update_batch(
+                batch_id,
+                status="failed",
+                failed_at=int(time.time()),
+                errors=Errors(data=[BatchError(code="output_failed", message=str(e))]),
+            )
+
+    async def _process_single_request(self, batch_id: str, request: BatchRequest) -> dict:
+        """Process a single request from the batch."""
+        request_id = f"batch_req_{batch_id}_{request.line_num}"
+
+        try:
+            # TODO(SECURITY): review body for security issues
+            chat_response = await self.inference_api.openai_chat_completion(**request.body)
+
+            # this is for mypy, we don't allow streaming so we'll get the right type
+            assert hasattr(chat_response, "model_dump_json"), "Chat response must have model_dump_json method"
+            return {
+                "id": request_id,
+                "custom_id": request.custom_id,
+                "response": {
+                    "status_code": 200,
+                    "request_id": request_id,  # TODO: should this be different?
+                    "body": chat_response.model_dump_json(),
+                },
+            }
+        except Exception as e:
+            logger.info(f"Error processing request {request.custom_id} in batch {batch_id}: {e}")
+            return {
+                "id": request_id,
+                "custom_id": request.custom_id,
+                "error": {"type": "request_failed", "message": str(e)},
+            }
+
+    async def _create_output_file(self, batch_id: str, results: list[dict], file_type: str) -> str:
+        """
+        Create an output file with batch results.
+
+        This function filters results based on the specified file_type
+        and uploads the file to the Files API.
+        """
+        output_lines = [json.dumps(result) for result in results]
+
+        with AsyncBytesIO("\n".join(output_lines).encode("utf-8")) as file_buffer:
+            file_buffer.filename = f"{batch_id}_{file_type}.jsonl"
+            uploaded_file = await self.files_api.openai_upload_file(file=file_buffer, purpose=OpenAIFilePurpose.BATCH)
+            return uploaded_file.id

llama_stack/providers/inline/batches/reference/config.py

@@ -0,0 +1,40 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+from pydantic import BaseModel, Field
+
+from llama_stack.providers.utils.kvstore.config import KVStoreConfig, SqliteKVStoreConfig
+
+
+class ReferenceBatchesImplConfig(BaseModel):
+    """Configuration for the Reference Batches implementation."""
+
+    kvstore: KVStoreConfig = Field(
+        description="Configuration for the key-value store backend.",
+    )
+
+    max_concurrent_batches: int = Field(
+        default=1,
+        description="Maximum number of concurrent batches to process simultaneously.",
+        ge=1,
+    )
+
+    max_concurrent_requests_per_batch: int = Field(
+        default=10,
+        description="Maximum number of concurrent requests to process per batch.",
+        ge=1,
+    )
+
+    # TODO: add a max requests per second rate limiter
+
+    @classmethod
+    def sample_run_config(cls, __distro_dir__: str) -> dict:
+        return {
+            "kvstore": SqliteKVStoreConfig.sample_run_config(
+                __distro_dir__=__distro_dir__,
+                db_name="batches.db",
+            ),
+        }

llama_stack/providers/registry/batches.py

@@ -0,0 +1,26 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+
+from llama_stack.providers.datatypes import Api, InlineProviderSpec, ProviderSpec
+
+
+def available_providers() -> list[ProviderSpec]:
+    return [
+        InlineProviderSpec(
+            api=Api.batches,
+            provider_type="inline::reference",
+            pip_packages=["openai"],
+            module="llama_stack.providers.inline.batches.reference",
+            config_class="llama_stack.providers.inline.batches.reference.config.ReferenceBatchesImplConfig",
+            api_dependencies=[
+                Api.inference,
+                Api.files,
+                Api.models,
+            ],
+            description="Reference implementation of batches API with KVStore persistence.",
+        ),
+    ]