correct errors from running mypy and black

Makefile

@@ -28,7 +28,7 @@ safety: ## Runs `safety check` to check python dependencies for vulnerabilities
 		done
 
 .PHONY: lint
-lint: isort black ## Run isort, black and flake8
+lint: isort-check black-check ## Run isort, black and flake8
 	@flake8 securedrop_proxy tests
 
 .PHONY: mypy
@@ -37,11 +37,19 @@ mypy: ## Run mypy static type checker
 
 .PHONY: black
 black: ## Run black for file formatting
-	@black --config ./blackconfig/pyproject.toml --check securedrop_proxy tests
+	@black securedrop_proxy tests
+
+.PHONY: black-check
+black-check: ## Check Python source code formatting with black
+	@black --check --diff securedrop_proxy tests
 
 .PHONY: isort
 isort: ## Run isort for file formatting
-	@isort -c -w 100 securedrop_proxy/*.py tests/*.py --diff
+	@isort securedrop_proxy/*.py tests/*.py
+
+.PHONY: isort-check
+isort-check: ## Check isort for file formatting
+	@isort --check-only --diff securedrop_proxy/*.py tests/*.py
 
 .PHONY: update-pip-requirements
 update-pip-requirements: ## Updates all Python requirements files via pip-compile.

pyproject.toml

@@ -0,0 +1,5 @@
+[tool.black]
+line-length = 100
+
+[tool.isort]
+line_length = 100

securedrop_proxy/proxy.py

@@ -9,7 +9,7 @@
 from tempfile import _TemporaryFileWrapper  # type: ignore
 from typing import Dict, Optional
 
-import furl
+import furl  # type: ignore
 import requests
 import werkzeug
 import yaml
@@ -32,14 +32,14 @@ def __init__(self) -> None:
         self.method = ""
         self.path_query = ""
         self.body = ""
-        self.headers: Dict[str, str] = {}
+        self.headers = {}  # type: Dict[str, str]
 
 
 class Response:
     def __init__(self, status: int) -> None:
         self.status = status
         self.body = ""
-        self.headers: Dict[str, str] = {}
+        self.headers = {}  # type: Dict[str, str]
         self.version = version.version
 
 
@@ -48,10 +48,10 @@ def __init__(self, conf_path: str, req: Req = Req(), timeout: float = 10.0) -> N
         self.read_conf(conf_path)
 
         self.req = req
-        self.res: Optional[Response] = None
+        self.res = None  # type: Optional[Response]
         self.timeout = float(timeout)
 
-        self._prepared_request: Optional[Req] = None
+        self._prepared_request = None  # type: Optional[requests.PreparedRequest]
 
     def on_done(self) -> None:
         print(json.dumps(self.res.__dict__))
@@ -79,12 +79,14 @@ def read_conf(self, conf_path: str) -> None:
                 conf_in = yaml.safe_load(fh)
         except yaml.YAMLError:
             self.simple_error(
-                500, "YAML syntax error while reading configuration file {}".format(conf_path),
+                500,
+                "YAML syntax error while reading configuration file {}".format(conf_path),
             )
             self.err_on_done()
         except Exception:
             self.simple_error(
-                500, "Error while opening or reading configuration file {}".format(conf_path),
+                500,
+                "Error while opening or reading configuration file {}".format(conf_path),
             )
             self.err_on_done()
 
@@ -186,7 +188,7 @@ def handle_json_response(self) -> None:
 
         res = Response(self._presp.status_code)
 
-        res.headers = self._presp.headers
+        res.headers = dict(self._presp.headers)
         res.body = self._presp.content.decode()
 
         self.res = res
@@ -204,7 +206,7 @@ def handle_non_json_response(self) -> None:
 
         fh.close()
 
-        res.headers = self._presp.headers
+        res.headers = dict(self._presp.headers)
 
         self.on_save(fh, res)
 
@@ -259,7 +261,8 @@ def proxy(self) -> None:
             logger.error(e)
             try:
                 self.simple_error(
-                    e.response.status_code, http.HTTPStatus(e.response.status_code).phrase.lower(),
+                    e.response.status_code,
+                    http.HTTPStatus(e.response.status_code).phrase.lower(),
                 )
             except ValueError:
                 # Return a generic error message when the response