Customizable receive timeout for SMB Connection (#285)

* Added customizable receive timeout for SMB Connection

* Refactored customizable receive timeout as experimental environment variable

src/smbprotocol/connection.py

@@ -749,6 +749,9 @@ def __init__(self, guid, server_name, port=445, require_signing=True):
         self.port = port
         self.transport = None  # Instanciated in .connect()
 
+        # Experimental customizable value. Might be removed in the future
+        self._receive_timeout = int(os.environ.get("SMB_EXPERIMENTAL_TRANSPORT_RECEIVE_TIMEOUT", 600))
+
         # Table of Session entries, the order is important for smbclient.
         self.session_table = OrderedDict()
 
@@ -1306,7 +1309,7 @@ def _process_message_thread(self):
                 # safe choice.
                 # https://github.com/jborean93/smbprotocol/issues/31
                 try:
-                    b_msg = self.transport.recv(600)
+                    b_msg = self.transport.recv(self._receive_timeout)
                 except TimeoutError as ex:
                     # Check if the connection has unanswered keepalive echo requests with the reserved field set.
                     # When unanswered keep alive echo exists, the server did not respond withing two times the timeout.