✨ Raise early when using form data without installing python-multipart (#1851)

* Check if Form exists and multipart is in virtual environment

* Remove unused import

* Move BodyFieldInfo check to separate helper function

* Fix type UploadFile to File for BodyFieldInfo check

* Working solution. Kind of nasty though.

* Use better method of determing if correct package imported

* Use better method of determing if correct package imported

* Add raising exceptions, update error messages

* Check if Form exists and multipart is in virtual environment

* Move BodyFieldInfo check to separate helper function

* Fix type UploadFile to File for BodyFieldInfo check

* Use better method of determing if correct package imported

* Add raising exceptions, update error messages
* Removed unused import, added comments

Co-authored-by: Christopher Nguyen <chrisngyn99@gmail.com>

* Updated what kind of exception will be thrown

* Add type annotations

Adds annotations to is_form_data

* Fix import order

* Add basic tests

* Fixed Travis tests

* Replace logging with fastapi logger

* Change AttributeError to ImportError to fix exception handling

* Fixing tests

* Catch ModuleNotFoundError first

Fix code coverage

* Update fastapi/dependencies/utils.py

Remove error spaces when printing

Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com>

* Update fastapi/dependencies/utils.py

Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com>

* Removed spaces in error printing

* ♻️ Refactor form data detection

* ✅ Update/increase tests for incorrect multipart install

* 🔥 Remove deprecated Travis (moved to GitHub Actions)

Co-authored-by: yk396 <yk396@cornell.edu>
Co-authored-by: Christopher Nguyen <chrisngyn99@gmail.com>
Co-authored-by: Kai Chen <kaichen120@gmail.com>
Co-authored-by: Chris N <hello@chris-nguyen.me>
Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com>

fastapi/dependencies/utils.py

@@ -24,6 +24,7 @@ from fastapi.concurrency import (
     contextmanager_in_threadpool,
 )
 from fastapi.dependencies.models import Dependant, SecurityRequirement
+from fastapi.logger import logger
 from fastapi.security.base import SecurityBase
 from fastapi.security.oauth2 import OAuth2, SecurityScopes
 from fastapi.security.open_id_connect_url import OpenIdConnect
@@ -96,6 +97,42 @@ sequence_shape_to_type = {
 }
 
 
+multipart_not_installed_error = (
+    'Form data requires "python-multipart" to be installed. \n'
+    'You can install "python-multipart" with: \n\n'
+    "pip install python-multipart\n"
+)
+multipart_incorrect_install_error = (
+    'Form data requires "python-multipart" to be installed. '
+    'It seems you installed "multipart" instead. \n'
+    'You can remove "multipart" with: \n\n'
+    "pip uninstall multipart\n\n"
+    'And then install "python-multipart" with: \n\n'
+    "pip install python-multipart\n"
+)
+
+
+def check_file_field(field: ModelField) -> None:
+    field_info = get_field_info(field)
+    if isinstance(field_info, params.Form):
+        try:
+            # __version__ is available in both multiparts, and can be mocked
+            from multipart import __version__
+
+            assert __version__
+            try:
+                # parse_options_header is only available in the right multlipart
+                from multipart.multipart import parse_options_header
+
+                assert parse_options_header
+            except ImportError:
+                logger.error(multipart_incorrect_install_error)
+                raise RuntimeError(multipart_incorrect_install_error)
+        except ImportError:
+            logger.error(multipart_not_installed_error)
+            raise RuntimeError(multipart_not_installed_error)
+
+
 def get_param_sub_dependant(
     *, param: inspect.Parameter, path: str, security_scopes: Optional[List[str]] = None
 ) -> Dependant:
@@ -733,9 +770,8 @@ def get_schema_compatible_field(*, field: ModelField) -> ModelField:
             default=field.default,
             required=field.required,
             alias=field.alias,
-            field_info=field.field_info if PYDANTIC_1 else field.schema,  # type: ignore
+            field_info=get_field_info(field),
         )
-
     return out_field
 
 
@@ -748,7 +784,9 @@ def get_body_field(*, dependant: Dependant, name: str) -> Optional[ModelField]:
     embed = getattr(field_info, "embed", None)
     body_param_names_set = {param.name for param in flat_dependant.body_params}
     if len(body_param_names_set) == 1 and not embed:
-        return get_schema_compatible_field(field=first_param)
+        final_field = get_schema_compatible_field(field=first_param)
+        check_file_field(final_field)
+        return final_field
     # If one field requires to embed, all have to be embedded
     # in case a sub-dependency is evaluated with a single unique body field
     # That is combined (embedded) with other body fields
@@ -779,10 +817,12 @@ def get_body_field(*, dependant: Dependant, name: str) -> Optional[ModelField]:
         ]
         if len(set(body_param_media_types)) == 1:
             BodyFieldInfo_kwargs["media_type"] = body_param_media_types[0]
-    return create_response_field(
+    final_field = create_response_field(
         name="body",
         type_=BodyModel,
         required=required,
         alias="body",
         field_info=BodyFieldInfo(**BodyFieldInfo_kwargs),
     )
+    check_file_field(final_field)
+    return final_field

tests/test_multipart_installation.py

@@ -0,0 +1,106 @@
+import pytest
+from fastapi import FastAPI, File, Form, UploadFile
+from fastapi.dependencies.utils import (
+    multipart_incorrect_install_error,
+    multipart_not_installed_error,
+)
+
+
+def test_incorrect_multipart_installed_form(monkeypatch):
+    monkeypatch.delattr("multipart.multipart.parse_options_header", raising=False)
+    with pytest.raises(RuntimeError, match=multipart_incorrect_install_error):
+        app = FastAPI()
+
+        @app.post("/")
+        async def root(username: str = Form(...)):
+            return username  # pragma: nocover
+
+
+def test_incorrect_multipart_installed_file_upload(monkeypatch):
+    monkeypatch.delattr("multipart.multipart.parse_options_header", raising=False)
+    with pytest.raises(RuntimeError, match=multipart_incorrect_install_error):
+        app = FastAPI()
+
+        @app.post("/")
+        async def root(f: UploadFile = File(...)):
+            return f  # pragma: nocover
+
+
+def test_incorrect_multipart_installed_file_bytes(monkeypatch):
+    monkeypatch.delattr("multipart.multipart.parse_options_header", raising=False)
+    with pytest.raises(RuntimeError, match=multipart_incorrect_install_error):
+        app = FastAPI()
+
+        @app.post("/")
+        async def root(f: bytes = File(...)):
+            return f  # pragma: nocover
+
+
+def test_incorrect_multipart_installed_multi_form(monkeypatch):
+    monkeypatch.delattr("multipart.multipart.parse_options_header", raising=False)
+    with pytest.raises(RuntimeError, match=multipart_incorrect_install_error):
+        app = FastAPI()
+
+        @app.post("/")
+        async def root(username: str = Form(...), pasword: str = Form(...)):
+            return username  # pragma: nocover
+
+
+def test_incorrect_multipart_installed_form_file(monkeypatch):
+    monkeypatch.delattr("multipart.multipart.parse_options_header", raising=False)
+    with pytest.raises(RuntimeError, match=multipart_incorrect_install_error):
+        app = FastAPI()
+
+        @app.post("/")
+        async def root(username: str = Form(...), f: UploadFile = File(...)):
+            return username  # pragma: nocover
+
+
+def test_no_multipart_installed(monkeypatch):
+    monkeypatch.delattr("multipart.__version__", raising=False)
+    with pytest.raises(RuntimeError, match=multipart_not_installed_error):
+        app = FastAPI()
+
+        @app.post("/")
+        async def root(username: str = Form(...)):
+            return username  # pragma: nocover
+
+
+def test_no_multipart_installed_file(monkeypatch):
+    monkeypatch.delattr("multipart.__version__", raising=False)
+    with pytest.raises(RuntimeError, match=multipart_not_installed_error):
+        app = FastAPI()
+
+        @app.post("/")
+        async def root(f: UploadFile = File(...)):
+            return f  # pragma: nocover
+
+
+def test_no_multipart_installed_file_bytes(monkeypatch):
+    monkeypatch.delattr("multipart.__version__", raising=False)
+    with pytest.raises(RuntimeError, match=multipart_not_installed_error):
+        app = FastAPI()
+
+        @app.post("/")
+        async def root(f: bytes = File(...)):
+            return f  # pragma: nocover
+
+
+def test_no_multipart_installed_multi_form(monkeypatch):
+    monkeypatch.delattr("multipart.__version__", raising=False)
+    with pytest.raises(RuntimeError, match=multipart_not_installed_error):
+        app = FastAPI()
+
+        @app.post("/")
+        async def root(username: str = Form(...), password: str = Form(...)):
+            return username  # pragma: nocover
+
+
+def test_no_multipart_installed_form_file(monkeypatch):
+    monkeypatch.delattr("multipart.__version__", raising=False)
+    with pytest.raises(RuntimeError, match=multipart_not_installed_error):
+        app = FastAPI()
+
+        @app.post("/")
+        async def root(username: str = Form(...), f: UploadFile = File(...)):
+            return username  # pragma: nocover