Generate OpenAPI documentation for FromFiles and FromText parameters

[Copilot]

FromFiles and FromText parameters were not generating any request body documentation in OpenAPI/Swagger, making file upload endpoints invisible in the documentation UI.

Changes

blacksheep/server/openapi/v3.py

• Added _get_files_binder() to detect FilesBinder in handlers
• Updated get_request_body() to generate multipart/form-data schema when FilesBinder is present without a BodyBinder
• Schema generates type: array with format: binary items for file uploads

tests/test_openapi_v3.py

• Added test_handles_from_files_multipart_docs()
• Added test_handles_from_text_docs()

Example

Previously, this endpoint generated no request body documentation:

@app.router.post("/upload")
async def upload_file(files: FromFiles):
    return 'ok'

Now generates:

requestBody:
    content:
        multipart/form-data:
            schema:
                type: array
                items:
                    type: string
                    format: binary
    required: true

The file upload form now renders correctly in Swagger UI.

Original prompt

work on #546

Created from Copilot CLI via the copilot delegate command.

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[RobertoPrevato]

This is a great start! However, I would like something more.

I would like to support defining custom BodyBinder classes that describe complex structures, and have them generated accordingly. Example of what I was planning to do:

# In the framework:
class FromMultipart:
    ...


class MultipartBinder(BodyBinder):
    """This class allows to define complex objects to be received as multipart form data"""

    handle = FromMultipartFormData

    @property
    def content_type(self) -> str:
        return "multipart/form-data"
        
    ...  # binding logic


# User defined example:

class Address:
    street: str
    city: str

class ExampleClass:
    id: UUID
    addresses: list[Address]
    profile_image: bytes

@app.router.post("/upload")
async def create_item(data: FromMultipart[ExampleClass]):
    # data.value.id is UUID
    # data.value.addresses is a list of Address
    # data.value.profile_image is a bytes array containing the image
    return 'ok'

Would generate the following OpenAPI Specification:

requestBody:
  content:
    multipart/form-data: # Media type
      schema: # Request payload
        type: object
        properties: # Request parts
          id: # Part 1 (string value)
            type: string
            format: uuid
          address: # Part2 (object)
            type: object
            properties:
              street:
                type: string
              city:
                type: string
          profileImage: # Part 3 (an image)
            type: string
            format: binary