ref: replace usage of deprecated imp (#449)

* Use types instead of imp.new_module.

I can follow up with https://docs.python.org/3/library/importlib.html#importlib.util.module_from_spec if need be.

* use source loader from importlib

* Revert "use source loader from importlib"

This reverts commit 1f255704f7bf618fb7e0432e1fccef6ee22364d4.

* use inspect.getsource, but alas

* placate linter

* use find_spec to resolve a module spec to a file path

* better function naming

* remove outdated comment

sshuttle/assembler.py

 import sys
 import zlib
-import imp
+import types
 
 verbosity = verbosity  # noqa: F821 must be a previously defined global
 z = zlib.decompressobj()
@@ -15,7 +15,7 @@ while 1:
                              % (name, nbytes))
         content = z.decompress(sys.stdin.read(nbytes))
 
-        module = imp.new_module(name)
+        module = types.ModuleType(name)
         parents = name.rsplit(".", 1)
         if len(parents) == 2:
             parent, parent_name = parents

sshuttle/ssh.py

@@ -3,7 +3,7 @@ import os
 import re
 import socket
 import zlib
-import imp
+import importlib
 import subprocess as ssubprocess
 import shlex
 from shlex import quote
@@ -14,43 +14,15 @@ import sshuttle.helpers as helpers
 from sshuttle.helpers import debug2
 
 
-def readfile(name):
-    tokens = name.split(".")
-    f = None
-
-    token = tokens[0]
-    token_name = [token]
-    token_str = ".".join(token_name)
-
-    try:
-        f, pathname, description = imp.find_module(token_str)
-
-        for token in tokens[1:]:
-            module = imp.load_module(token_str, f, pathname, description)
-            if f is not None:
-                f.close()
-
-            token_name.append(token)
-            token_str = ".".join(token_name)
-
-            f, pathname, description = imp.find_module(
-                token, module.__path__)
-
-        if f is not None:
-            contents = f.read()
-        else:
-            contents = ""
-
-    finally:
-        if f is not None:
-            f.close()
-
-    return contents.encode("UTF8")
+def get_module_source(name):
+    spec = importlib.util.find_spec(name)
+    with open(spec.origin, "rt") as f:
+        return f.read().encode("utf-8")
 
 
 def empackage(z, name, data=None):
     if not data:
-        data = readfile(name)
+        data = get_module_source(name)
     content = z.compress(data)
     content += z.flush(zlib.Z_SYNC_FLUSH)
 
@@ -116,7 +88,7 @@ def connect(ssh_cmd, rhostport, python, stderr, options):
         rhost = host
 
     z = zlib.compressobj(1)
-    content = readfile('sshuttle.assembler')
+    content = get_module_source('sshuttle.assembler')
     optdata = ''.join("%s=%r\n" % (k, v) for (k, v) in list(options.items()))
     optdata = optdata.encode("UTF8")
     content2 = (empackage(z, 'sshuttle') +