Fix/expose only supported methods

[AndreasBBS]

Expose only implemented methods

Make this Plugin list only implemented methods instead of all possible methods

Example:

For the path defined by the class:

import falcon
from schemas.Pet import PetSchema

from app import app, spec

from random import randint, choices
from string import ascii_uppercase, digits

class RandomPetResource:
    async def on_get(self, req, resp):
        """A cute furry animal endpoint.
        ---
        description: Get a random pet
        responses:
            200:
                description: A pet to be returned
                schema: PetSchema
        """
        pet = {
            "id": randint(1, 100),
            "name": ''.join(
                choices(ascii_uppercase + digits, k=10)
            )
        }
        resp.media = PetSchema().dump(pet)
        resp.status = falcon.HTTP_200

# Register Pet Resource
pets = RandomPetResource()
app.add_route('/pet', pets)
spec.path(resource=pets)

Before the fix, the resulting swagger.json looks like:

{
  "paths": {
    "/pet": {
      "get": {
        "description": "Get a random pet",
        "responses": {
          "200": {
            "description": "A pet to be returned",
            "schema": {
              "$ref": "#/components/schemas/Pet"
            }
          }
        }
      },
      "options": {},
      "delete": {},
      "head": {},
      "patch": {},
      "post": {},
      "put": {},
      "trace": {}
    }
  },
  "info": {
    "title": "TenScores API",
    "version": "0.0.1"
  },
  "openapi": "3.0.2",
  "components": {
    "schemas": {
      "Pet": {
        "type": "object",
        "properties": {
          "id": {
            "type": "integer"
          },
          "name": {
            "type": "string"
          }
        },
        "required": [
          "name"
        ]
      }
    }
  }
}

After the fix, the resulting swagger.json looks like:

{
  "paths": {
    "/pet": {
      "get": {
        "description": "Get a random pet",
        "responses": {
          "200": {
            "description": "A pet to be returned",
            "schema": {
              "$ref": "#/components/schemas/Pet"
            }
          }
        }
      }
    }
  },
  "info": {
    "title": "TenScores API",
    "version": "0.0.1"
  },
  "openapi": "3.0.2",
  "components": {
    "schemas": {
      "Pet": {
        "type": "object",
        "properties": {
          "name": {
            "type": "string"
          },
          "id": {
            "type": "integer"
          }
        },
        "required": [
          "name"
        ]
      }
    }
  }
}

It's also more efficient because, instead of going through all the routes and creating a mapping for each resource every time spec.path gets called, it filters for the route with the passed resource.

Feel free to try my changes by using pip install git+https://github.com/AndreasBBS/falcon-apispec.git@fix/expose_only_supported_methods#egg=falcon-apispec

NOTE: I'm also including the changes in this PR #32 that's taking ages to get merged cause I couldn't be bothered to change falcon to a version prior to 3.0

[AndreasBBS]

@alysivji @aslantar @Javlopez Forgot to put you as reviewrs and can't do it now. Please set yourselves. I'd love to hear back if you think this is useful too.