Saving the blob to the manager as it is returned from the invocation

julianstirling · julianstirling · commit 26c112107a6c · 2025-07-17T00:44:26.000+01:00
diff --git a/src/labthings_fastapi/actions/__init__.py b/src/labthings_fastapi/actions/__init__.py
@@ -19,7 +19,7 @@
     InvocationCancelledError,
     invocation_logger,
 )
-from ..outputs.blob import BlobIOContextDep
+from ..outputs.blob import Blob, BlobDataManager
 
 if TYPE_CHECKING:
     # We only need these imports for type hints, so this avoids circular imports.
@@ -40,6 +40,7 @@ def __init__(
         self,
         action: ActionDescriptor,
         thing: Thing,
+        blob_data_manager: BlobDataManager,
         input: Optional[BaseModel] = None,
         dependencies: Optional[dict[str, Any]] = None,
         default_stop_timeout: float = 5,
@@ -56,6 +57,8 @@ def __init__(
         self.dependencies = dependencies if dependencies is not None else {}
         self.cancel_hook = cancel_hook
 
+        self._blob_data_manager = blob_data_manager
+
         # A UUID for the Invocation (not the same as the threading.Thread ident)
         self._ID = id if id is not None else uuid.uuid4()  # Task ID
 
@@ -181,6 +184,9 @@ def run(self):
             ret = action.__get__(thing)(**kwargs, **self.dependencies)
 
             with self._status_lock:
+                if isinstance(ret, Blob):
+                    blob_id = self._blob_data_manager.add_blob(ret.data)
+                    ret.href = f"/blob/{blob_id}"
                 self._return_value = ret
                 self._status = InvocationStatus.COMPLETED
                 self.action.emit_changed_event(self.thing, self._status)
@@ -241,7 +247,8 @@ def emit(self, record):
 class ActionManager:
     """A class to manage a collection of actions"""
 
-    def __init__(self):
+    def __init__(self, server):
+        self._server = server
         self._invocations = {}
         self._invocations_lock = Lock()
 
@@ -271,6 +278,7 @@ def invoke_action(
             dependencies=dependencies,
             id=id,
             cancel_hook=cancel_hook,
+            blob_data_manager=self._server.blob_data_manager,
         )
         self.append_invocation(thread)
         thread.start()
@@ -312,17 +320,15 @@ def attach_to_app(self, app: FastAPI):
         """Add /action_invocations and /action_invocation/{id} endpoints to FastAPI"""
 
         @app.get(ACTION_INVOCATIONS_PATH, response_model=list[InvocationModel])
-        def list_all_invocations(request: Request, _blob_manager: BlobIOContextDep):
+        def list_all_invocations(request: Request):
             return self.list_invocations(as_responses=True, request=request)
 
         @app.get(
             ACTION_INVOCATIONS_PATH + "/{id}",
             response_model=InvocationModel,
             responses={404: {"description": "Invocation ID not found"}},
         )
-        def action_invocation(
-            id: uuid.UUID, request: Request, _blob_manager: BlobIOContextDep
-        ):
+        def action_invocation(id: uuid.UUID, request: Request):
             try:
                 with self._invocations_lock:
                     return self._invocations[id].response(request=request)
@@ -346,7 +352,7 @@ def action_invocation(
                 503: {"description": "No result is available for this invocation"},
             },
         )
-        def action_invocation_output(id: uuid.UUID, _blob_manager: BlobIOContextDep):
+        def action_invocation_output(id: uuid.UUID):
             """Get the output of an action invocation
 
             This returns just the "output" component of the action invocation. If the
diff --git a/src/labthings_fastapi/descriptors/action.py b/src/labthings_fastapi/descriptors/action.py
@@ -23,7 +23,7 @@
     input_model_from_signature,
     return_type,
 )
-from ..outputs.blob import BlobIOContextDep
+
 from ..thing_description import type_to_dataschema
 from ..thing_description.model import ActionAffordance, ActionOp, Form, Union
 from ..utilities import labthings_data, get_blocking_portal
@@ -178,7 +178,6 @@ def add_to_fastapi(self, app: FastAPI, thing: Thing):
         # the function to the decorator.
         def start_action(
             action_manager: ActionManagerContextDep,
-            _blob_manager: BlobIOContextDep,
             request: Request,
             body,
             id: InvocationID,
diff --git a/src/labthings_fastapi/outputs/blob.py b/src/labthings_fastapi/outputs/blob.py
@@ -43,33 +43,24 @@ def get_image(self) -> MyImageBlob:
 """
 
 from __future__ import annotations
-from contextvars import ContextVar
 import io
 import os
-import re
 import shutil
 from typing import (
-    Annotated,
-    Callable,
     Literal,
     Mapping,
     Optional,
 )
 from weakref import WeakValueDictionary
-from typing_extensions import TypeAlias
 from tempfile import TemporaryDirectory
 import uuid
 
-from fastapi import FastAPI, Depends, Request
+from fastapi import FastAPI
 from fastapi.responses import FileResponse, Response
 from pydantic import (
     BaseModel,
-    create_model,
     model_serializer,
-    model_validator,
 )
-from labthings_fastapi.dependencies.thing_server import find_thing_server
-from starlette.exceptions import HTTPException
 from typing_extensions import Self, Protocol, runtime_checkable
 
 
@@ -203,88 +194,25 @@ class Blob(BaseModel):
     documentation.
     """
 
-    href: str
+    href: str = "blob://local"
     """The URL where the data may be retrieved. This will be `blob://local`
     if the data is stored locally."""
-    media_type: str = "*/*"
-    """The MIME type of the data. This should be overridden in subclasses."""
     rel: Literal["output"] = "output"
     description: str = (
         "The output from this action is not serialised to JSON, so it must be "
         "retrieved as a file. This link will return the file."
     )
+    media_type: str = "*/*"
+    """The MIME type of the data. This should be overridden in subclasses."""
 
-    _data: Optional[ServerSideBlobData] = None
-    """This object holds the data, either in memory or as a file.
-    
-    If `_data` is `None`, then the Blob has not been deserialised yet, and the
-    `href` should point to a valid address where the data may be downloaded.
-    """
-
-    @model_validator(mode="after")
-    def retrieve_data(self):
-        """Retrieve the data from the URL
-
-        When a [`Blob`](#labthings_fastapi.outputs.blob.Blob) is created
-        using its constructor, [`pydantic`](https://docs.pydantic.dev/latest/)
-        will attempt to deserialise it by retrieving the data from the URL
-        specified in `href`. Currently, this must be a URL pointing to a
-        [`Blob`](#labthings_fastapi.outputs.blob.Blob) that already exists on
-        this server.
-
-        This validator will only work if the function to resolve URLs to
-        [`BlobData`](#labthings_fastapi.outputs.blob.BlobData) objects
-        has been set in the context variable
-        [`url_to_blobdata_ctx`](#labthings_fastapi.outputs.blob.url_to_blobdata_ctx).
-        This is done when actions are being invoked over HTTP by the
-        [`BlobIOContextDep`](#labthings_fastapi.outputs.blob.BlobIOContextDep) dependency.
-        """
-        if self.href == "blob://local":
-            if self._data:
-                return self
-            raise ValueError("Blob objects must have data if the href is blob://local")
-        try:
-            url_to_blobdata = url_to_blobdata_ctx.get()
-            self._data = url_to_blobdata(self.href)
-            self.href = "blob://local"
-        except LookupError:
-            raise LookupError(
-                "Blobs may only be created from URLs passed in over HTTP."
-                f"The URL in question was {self.href}."
-            )
-        return self
+    _data: ServerSideBlobData
+    """This object holds the data, either in memory or as a file."""
 
     @model_serializer(mode="plain", when_used="always")
     def to_dict(self) -> Mapping[str, str]:
-        """Serialise the Blob to a dictionary and make it downloadable
-
-        When [`pydantic`](https://docs.pydantic.dev/latest/) serialises this object,
-        it will call this method to convert it to a dictionary. There is a
-        significant side-effect, which is that we will add the blob to the
-        [`BlobDataManager`](#labthings_fastapi.outputs.blob.BlobDataManager) so it
-        can be downloaded.
-
-        This serialiser will only work if the function to assign URLs to
-        [`BlobData`](#labthings_fastapi.outputs.blob.BlobData) objects
-        has been set in the context variable
-        [`blobdata_to_url_ctx`](#labthings_fastapi.outputs.blob.blobdata_to_url_ctx).
-        This is done when actions are being returned over HTTP by the
-        [`BlobIOContextDep`](#labthings_fastapi.outputs.blob.BlobIOContextDep) dependency.
-        """
-        if self.href == "blob://local":
-            try:
-                blobdata_to_url = blobdata_to_url_ctx.get()
-                # MyPy seems to miss that `self.data` is a property, hence the ignore
-                href = blobdata_to_url(self.data)  # type: ignore[arg-type]
-            except LookupError:
-                raise LookupError(
-                    "Blobs may only be serialised inside the "
-                    "context created by BlobIOContextDep."
-                )
-        else:
-            href = self.href
+        """Serialise the Blob to a dictionary and make it downloadable"""
         return {
-            "href": href,
+            "href": self.href,
             "media_type": self.media_type,
             "rel": self.rel,
             "description": self.description,
@@ -348,9 +276,8 @@ def open(self) -> io.IOBase:
     @classmethod
     def from_bytes(cls, data: bytes) -> Self:
         """Create a BlobOutput from a bytes object"""
-        return cls.model_construct(  # type: ignore[return-value]
-            href="blob://local",
-            _data=BlobBytes(data, media_type=cls.default_media_type()),
+        return cls.model_construct(
+            _data=BlobBytes(data, media_type=cls.default_media_type())
         )
 
     @classmethod
@@ -362,8 +289,7 @@ def from_temporary_directory(cls, folder: TemporaryDirectory, file: str) -> Self
         collected.
         """
         file_path = os.path.join(folder.name, file)
-        return cls.model_construct(  # type: ignore[return-value]
-            href="blob://local",
+        return cls.model_construct(
             _data=BlobFile(
                 file_path,
                 media_type=cls.default_media_type(),
@@ -381,36 +307,15 @@ def from_file(cls, file: str) -> Self:
         temporary. If you are using temporary files, consider creating your
         Blob with `from_temporary_directory` instead.
         """
-        return cls.model_construct(  # type: ignore[return-value]
-            href="blob://local",
-            _data=BlobFile(file, media_type=cls.default_media_type()),
+        return cls.model_construct(
+            _data=BlobFile(file, media_type=cls.default_media_type())
         )
 
     def response(self):
         """ "Return a suitable response for serving the output"""
         return self.data.response()
 
 
-def blob_type(media_type: str) -> type[Blob]:
-    """Create a BlobOutput subclass for a given media type
-
-    This convenience function may confuse static type checkers, so it is usually
-    clearer to make a subclass instead, e.g.:
-
-    ```python
-    class MyImageBlob(Blob):
-        media_type = "image/png"
-    ```
-    """
-    if "'" in media_type or "\\" in media_type:
-        raise ValueError("media_type must not contain single quotes or backslashes")
-    return create_model(
-        f"{media_type.replace('/', '_')}_blob",
-        __base__=Blob,
-        media_type=(eval(f"Literal[r'{media_type}']"), media_type),
-    )
-
-
 class BlobDataManager:
     """A class to manage BlobData objects
 
@@ -452,59 +357,3 @@ def download_blob(self, blob_id: uuid.UUID):
     def attach_to_app(self, app: FastAPI):
         """Attach the BlobDataManager to a FastAPI app"""
         app.get("/blob/{blob_id}")(self.download_blob)
-
-
-blobdata_to_url_ctx = ContextVar[Callable[[ServerSideBlobData], str]]("blobdata_to_url")
-"""This context variable gives access to a function that makes BlobData objects
-downloadable, by assigning a URL and adding them to the 
-[`BlobDataManager`](#labthings_fastapi.outputs.blob.BlobDataManager).
-
-It is only available within a 
-[`blob_serialisation_context_manager`](#labthings_fastapi.outputs.blob.blob_serialisation_context_manager)
-because it requires access to the `BlobDataManager` and the `url_for` function
-from the FastAPI app.
-"""
-
-url_to_blobdata_ctx = ContextVar[Callable[[str], BlobData]]("url_to_blobdata")
-"""This context variable gives access to a function that makes BlobData objects
-from a URL, by retrieving them from the
-[`BlobDataManager`](#labthings_fastapi.outputs.blob.BlobDataManager).
-
-It is only available within a 
-[`blob_serialisation_context_manager`](#labthings_fastapi.outputs.blob.blob_serialisation_context_manager)
-because it requires access to the `BlobDataManager`.
-"""
-
-
-async def blob_serialisation_context_manager(request: Request):
-    """Set context variables to allow blobs to be [de]serialised"""
-    thing_server = find_thing_server(request.app)
-    blob_manager: BlobDataManager = thing_server.blob_data_manager
-    url_for = request.url_for
-
-    def blobdata_to_url(blob: ServerSideBlobData) -> str:
-        blob_id = blob_manager.add_blob(blob)
-        return str(url_for("download_blob", blob_id=blob_id))
-
-    def url_to_blobdata(url: str) -> BlobData:
-        m = re.search(r"blob/([0-9a-z\-]+)", url)
-        if not m:
-            raise HTTPException(
-                status_code=404, detail="Could not find blob ID in href"
-            )
-        invocation_id = uuid.UUID(m.group(1))
-        return blob_manager.get_blob(invocation_id)
-
-    t1 = blobdata_to_url_ctx.set(blobdata_to_url)
-    t2 = url_to_blobdata_ctx.set(url_to_blobdata)
-    try:
-        yield blob_manager
-    finally:
-        blobdata_to_url_ctx.reset(t1)
-        url_to_blobdata_ctx.reset(t2)
-
-
-BlobIOContextDep: TypeAlias = Annotated[
-    BlobDataManager, Depends(blob_serialisation_context_manager)
-]
-"""A dependency that enables `Blob`s to be serialised and deserialised."""
diff --git a/src/labthings_fastapi/server/__init__.py b/src/labthings_fastapi/server/__init__.py
@@ -30,7 +30,7 @@ def __init__(self, settings_folder: Optional[str] = None):
         self.app = FastAPI(lifespan=self.lifespan)
         self.set_cors_middleware()
         self.settings_folder = settings_folder or "./settings"
-        self.action_manager = ActionManager()
+        self.action_manager = ActionManager(self)
         self.action_manager.attach_to_app(self.app)
         self.blob_data_manager = BlobDataManager()
         self.blob_data_manager.attach_to_app(self.app)
