Stop using pkg_resources (#158)

* stop using pkg_resources

* make mypy happy

* add str comment

* specify min version

* remove setuptools dep

* link to source

pyproject.toml

@@ -42,9 +42,6 @@ python = "^3.7"
 cryptography = ">=1.5"
 # Connection.set_tlsext_host_name (>=0.13)
 pyopenssl = ">=0.13"
-# For pkg_resources. >=1.0 so pip resolves it to a version cryptography
-# will tolerate; see #2599:
-setuptools = ">=1.0"
 # >=4.3.0 is needed for Python 3.10 support
 sphinx = {version = ">=4.3.0", optional = true}
 sphinx-rtd-theme = {version = ">=1.0", optional = true}
@@ -56,6 +53,10 @@ coverage = {version = ">=4.0", extras = ["toml"]}
 # https://github.com/PyCQA/flake8/issues/1701.
 flake8 = ">=4.0"
 flake8-assertive = "*"
+# importlib_resources 1.3 was the version included in Python 3.9 which
+# introduced the functionality we are using. See
+# https://github.com/python/importlib_resources/tree/7f4fbb5ee026d7610636d5ece18b09c64aa0c893#compatibility.
+importlib_resources = {version = ">=1.3", python = "<3.9"}
 isort = "*"
 mypy = "*"
 types-pyOpenSSL = "*"

tests/test_util.py

@@ -1,8 +1,10 @@
 """Test utilities."""
+import atexit
+import contextlib
 import os
+import sys
 from typing import Any
 
-import pkg_resources
 from cryptography.hazmat.backends import default_backend
 from cryptography.hazmat.primitives import serialization
 from OpenSSL import crypto
@@ -11,17 +13,31 @@
 from josepy import ComparableRSAKey, ComparableX509
 from josepy.util import ComparableECKey
 
+# This approach is based on the recommendation at
+# https://github.com/python/mypy/issues/1153#issuecomment-1207333806.
+if sys.version_info >= (3, 9):
+    import importlib.resources as importlib_resources
+else:
+    import importlib_resources
+
+TESTDATA = importlib_resources.files('testdata')
+
 
 def vector_path(*names: str) -> str:
     """Path to a test vector."""
-    return pkg_resources.resource_filename(
-        __name__, os.path.join('testdata', *names))
+    # This code is based on the recommendation at
+    # https://web.archive.org/web/20230131043552/https://importlib-resources.readthedocs.io/en/latest/migration.html#pkg-resources-resource-filename.
+    file_manager = contextlib.ExitStack()
+    atexit.register(file_manager.close)
+    ref = TESTDATA.joinpath(*names)
+    # We convert the value to str here because some of the calling code doesn't
+    # work with pathlib objects.
+    return str(file_manager.enter_context(importlib_resources.as_file(ref)))
 
 
 def load_vector(*names: str) -> bytes:
     """Load contents of a test vector."""
-    # luckily, resource_string opens file in binary mode
-    return pkg_resources.resource_string(__name__, os.path.join('testdata', *names))
+    return TESTDATA.joinpath(*names).read_bytes()
 
 
 def _guess_loader(filename: str, loader_pem: Any, loader_der: Any) -> Any: