Add a "contents" function that returns the content of the cert chain. (#116)

* Add a "what" function that returns the content of the cert chain.

* Use read_text because it makes more sense.

* Oh, and specify encoding.

* Add a workaround for pre-3.7 version of Python.

This workaround won't work in PyOxidizer but it allows those to
keep working while allowing 3.7+ usage in PyOxidizer.

* Rename "what()" to "contents()".

* Fix __main__ after the change from what() to contents().

* Update docstring.

* Add a comment describing when the fallback is used.

* Black keeps nagging me.

* Missed this after the what->contents change.

* Use a with statement to make sure things get dealt with properly.

Author: jeamland

certifi/__init__.py

@@ -1,3 +1,3 @@
-from .core import where
+from .core import contents, where
 
 __version__ = "2019.11.28"

certifi/__main__.py

@@ -1,2 +1,12 @@
-from certifi import where
-print(where())
+import argparse
+
+from certifi import contents, where
+
+parser = argparse.ArgumentParser()
+parser.add_argument("-c", "--contents", action="store_true")
+args = parser.parse_args()
+
+if args.contents:
+    print(contents())
+else:
+    print(where())

certifi/core.py

@@ -4,12 +4,27 @@
 certifi.py
 ~~~~~~~~~~
 
-This module returns the installation location of cacert.pem.
+This module returns the installation location of cacert.pem or its contents.
 """
 import os
 
+try:
+    from importlib.resources import read_text
+except ImportError:
+    # This fallback will work for Python versions prior to 3.7 that lack the
+    # importlib.resources module but relies on the existing `where` function
+    # so won't address issues with environments like PyOxidizer that don't set
+    # __file__ on modules.
+    def read_text(_module, _path, encoding="ascii"):
+        with open(where(), "r", encoding=encoding) as data:
+            return data.read()
+
 
 def where():
     f = os.path.dirname(__file__)
 
-    return os.path.join(f, 'cacert.pem')
+    return os.path.join(f, "cacert.pem")
+
+
+def contents():
+    return read_text("certifi", "cacert.pem", encoding="ascii")