Fix python2 server compatibility

Fixes  sshuttle#469. We replace python3 exclusive code with a check for python3 and a compatibility fix. Note that the switch from os.set_nonblocking to fcntl.fcntl in 98d052d (fixing sshuttle#503) also fixes python2 compatibility.

sshuttle/assembler.py

@@ -7,8 +7,11 @@
 while 1:
     name = sys.stdin.readline().strip()
     if name:
-        name = name.decode("ASCII")
-
+        # python2 compat: in python2 sys.stdin.readline().strip() -> str
+        #                 in python3 sys.stdin.readline().strip() -> bytes
+        # (see #481)
+        if sys.version_info >= (3, 0):
+            name = name.decode("ASCII")
         nbytes = int(sys.stdin.readline())
         if verbosity >= 2:
             sys.stderr.write('server: assembling %r (%d bytes)\n'

sshuttle/server.py

@@ -6,7 +6,24 @@
 import sys
 import os
 import platform
-from shutil import which
+
+if sys.version_info >= (3, 0):
+    from shutil import which
+else:
+    # python2 compat: shutil.which is not available so we provide our own which command
+    def which(file, mode=os.F_OK | os.X_OK, path=None):
+        if path is not None:
+            search_paths = [path]
+        elif "PATH" in os.environ:
+            search_paths = os.environ["PATH"].split(os.pathsep)
+        else:
+            search_paths = os.defpath.split(os.pathsep)
+
+        for path in search_paths:
+            filepath = os.path.join(path, file)
+            if os.path.exists(filepath) and os.access(filepath, mode):
+                return filepath
+        return None
 
 import sshuttle.ssnet as ssnet
 import sshuttle.helpers as helpers