Getting error "cannot marshal None" in spite of adding allow_none=True while using XMLRPC in Python

Question

I've tried to create a simple download and upload system using XMLRPC in Python

Here is the code for client (name this file as client.py)

import sys
import xmlrpclib
import os

def return_pause():
    """Used for creating a pause during input"""

    raw_input("\n\tPress enter to continue")

def mod_file_download(file_name, local_port, remote_proxy, local_proxy):
    """Sending details to remote node which will send file to local node"""

    #print "till here"

    #print "{%s}\t{%s}" % (file_name,local_proxy)

    remote_proxy.mod_file_transfer(file_name, local_proxy)

def mod_file_upload(file_path, file_name, remote_proxy):
    """Used for sending files to a receiver. Sent file will always have the name file_1.txt"""

    new_file_name = "file_1.txt"
    with open(file_path, "rb") as handle:
        bin_data = xmlrpclib.Binary(handle.read())

    remote_proxy.mod_file_receive(bin_data, new_file_name)

    return True

##MAIN MODULE STARTS HERE##

# Connection details of remote node
local_port = sys.argv[1]

# Getting details of remote node
remote_port = raw_input("\n\tEnter remote port ID : ")

# Creating connection details of remote node
remote_proxy = xmlrpclib.ServerProxy("http://localhost:" + remote_port + "/")

# Creating connection details of local node
local_proxy = xmlrpclib.ServerProxy("http://localhost:" + local_port + "/")

while True:
    os.system('clear')

    print "\t. : Collab Menu for %s : .\n" % local_port
    print "\tSearch & download ...[1]"
    print "\tUpload            ...[2]"
    print "\tExit              ...[0]"

    input_val = raw_input("\n\n\tEnter option : ")

    if input_val == "1":
        file_name = raw_input("\n\tEnter name of file to be downloaded : ")

        mod_file_download(file_name, local_port, remote_proxy, local_proxy)

        return_pause()

    elif input_val == "2":
        file_name = raw_input("\n\tEnter name of file to be uploaded : ")

        file_path = "./" + file_name

        mod_file_upload(file_path, file_name, remote_proxy, local_proxy)

        return_pause()

    elif input_val == "0":
        print "\tExiting"
        break

    else:
        print "\tIncorrect option value"
        print "\tTry again..."
        return_pause()

os.system('clear')

And here is the code for the listener (name this file as listener.py)

import sys
import xmlrpclib
from SimpleXMLRPCServer import SimpleXMLRPCServer

def mod_file_transfer(file_name, requestor_proxy):
    """Initiating the file transfer"""

    print "[mod_file_transfer fired]"

    file_path = "./" + file_name

    print requestor_proxy

    with open(file_path, "rb") as handle:
        bin_data = xmlrpclib.Binary(handle.read())

    # Connecting to requestor's server
    requestor_proxy.mod_file_download_receive(bin_data, file_name)

    return True

def mod_file_receive(bin_data, file_name):
    """Used to receive a file upon a request of an upload"""

    print "[mod_file_receive fired]"

    new_file_name = "./" + file_name
    with open(new_file_name, "wb") as handle:
        handle.write(bin_data.data)
        return True

def mod_file_download_receive(bin_data, file_name):
    """Used to receive a file upon request of a download"""

    print "[mod_file_download_receive fired]"

    new_file_name = "./" + file_name + str(1)
    with open(new_file_name, "wb") as handle:
        handle.write(bin_data.data)
        return True

##MAIN MODULE STARTS HERE##

local_port = sys.argv[1]

# Declared an XMLRPC server
node = SimpleXMLRPCServer(("localhost", int(local_port)), logRequests=True, allow_none=True)
print "Listening on port %s..." % local_port

# Registered a list of functions
node.register_function(mod_file_transfer, 'mod_file_transfer')
node.register_function(mod_file_receive, 'mod_file_receive')
node.register_function(mod_file_download_receive, 'mod_file_download_receive')

# Initialized the XMLRPC server
node.serve_forever()

How to start the system?

1. Place both the files in the same directory
2. Execute the following commands
3. python listener 9000
4. python listener 9500
5. python client 9000 (then give remote client port as 9500 as input)
6. python client 9500 (then give remote client port as 9000 as input)

File upload is working fine

But file downloading is not working

It's giving me the following error

Traceback (most recent call last):
  File "collab_client.py", line 57, in <module>
    mod_file_download(file_name, local_port, remote_proxy, local_proxy)
  File "collab_client.py", line 17, in mod_file_download
    remote_proxy.mod_file_transfer(file_name, local_proxy)
  File "/usr/lib/python2.7/xmlrpclib.py", line 1240, in __call__
    return self.__send(self.__name, args)
  File "/usr/lib/python2.7/xmlrpclib.py", line 1593, in __request
    allow_none=self.__allow_none)
  File "/usr/lib/python2.7/xmlrpclib.py", line 1091, in dumps
    data = m.dumps(params)
  File "/usr/lib/python2.7/xmlrpclib.py", line 638, in dumps
    dump(v, write)
  File "/usr/lib/python2.7/xmlrpclib.py", line 660, in __dump
    f(self, value, write)
  File "/usr/lib/python2.7/xmlrpclib.py", line 762, in dump_instance
    self.dump_struct(value.__dict__, write)
  File "/usr/lib/python2.7/xmlrpclib.py", line 741, in dump_struct
    dump(v, write)
  File "/usr/lib/python2.7/xmlrpclib.py", line 660, in __dump
    f(self, value, write)
  File "/usr/lib/python2.7/xmlrpclib.py", line 762, in dump_instance
    self.dump_struct(value.__dict__, write)
  File "/usr/lib/python2.7/xmlrpclib.py", line 741, in dump_struct
    dump(v, write)
  File "/usr/lib/python2.7/xmlrpclib.py", line 660, in __dump
    f(self, value, write)
  File "/usr/lib/python2.7/xmlrpclib.py", line 720, in dump_array
    dump(v, write)
  File "/usr/lib/python2.7/xmlrpclib.py", line 660, in __dump
    f(self, value, write)
  File "/usr/lib/python2.7/xmlrpclib.py", line 664, in dump_nil
    raise TypeError, "cannot marshal None unless allow_none is enabled"
TypeError: cannot marshal None unless allow_none is enabled

But I already gave the option allow_none=True in the listener file.

Where am I going wrong?

Answer 1

I found it after much headache. It seems that connection details cannot be sent or marshall'ed. In the function mod_file_transfer I tried to send the client connection details as an object (so that server knows to whom it has to send the file), which was causing the error.

I simply sent the client connection details as a string and it worked. Thanks to me!