10. xmlrpclib — XML-RPC client access¶

10.1. ServerProxy Objects¶

A ServerProxy instance has a method corresponding to each remote procedure call accepted by the XML-RPC server. Calling the method performs an RPC, dispatched by both name and argument signature (e.g. the same method name can be overloaded with multiple argument signatures). The RPC finishes by returning a value, which may be either returned data in a conformant type or a Fault or ProtocolError object indicating an error.

Servers that support the XML introspection API support some common methods grouped under the reserved system attribute:

ServerProxy.system.listMethods()¶

This method returns a list of strings, one for each (non-system) method supported by the XML-RPC server.

ServerProxy.system.methodSignature(name)¶

This method takes one parameter, the name of a method implemented by the XML-RPC server. It returns an array of possible signatures for this method. A signature is an array of types. The first of these types is the return type of the method, the rest are parameters.

Because multiple signatures (ie. overloading) is permitted, this method returns a list of signatures rather than a singleton.

Signatures themselves are restricted to the top level parameters expected by a method. For instance if a method expects one array of structs as a parameter, and it returns a string, its signature is simply “string, array”. If it expects three integers and returns a string, its signature is “string, int, int, int”.

If no signature is defined for the method, a non-array value is returned. In Python this means that the type of the returned value will be something other than list.

ServerProxy.system.methodHelp(name)¶

This method takes one parameter, the name of a method implemented by the XML-RPC server. It returns a documentation string describing the use of that method. If no such string is available, an empty string is returned. The documentation string may contain HTML markup.

10.2. Boolean Objects¶

This class may be initialized from any Python value; the instance returned depends only on its truth value. It supports various Python operators through __cmp__(), __repr__(), __int__(), and __nonzero__() methods, all implemented in the obvious ways.

It also has the following method, supported mainly for internal use by the unmarshalling code:

Boolean.encode(out)¶

Write the XML-RPC encoding of this Boolean item to the out stream object.

A working example follows. The server code:

import xmlrpclib
from SimpleXMLRPCServer import SimpleXMLRPCServer

def is_even(n):
    return n % 2 == 0

server = SimpleXMLRPCServer(("localhost", 8000))
print "Listening on port 8000..."
server.register_function(is_even, "is_even")
server.serve_forever()

The client code for the preceding server:

import xmlrpclib

proxy = xmlrpclib.ServerProxy("http://localhost:8000/")
print "3 is even: %s" % str(proxy.is_even(3))
print "100 is even: %s" % str(proxy.is_even(100))

10.3. DateTime Objects¶

class xmlrpclib.DateTime[source]¶

This class may be initialized with seconds since the epoch, a time tuple, an ISO 8601 time/date string, or a datetime.datetime instance. It has the following methods, supported mainly for internal use by the marshalling/unmarshalling code:

decode(string)[source]¶

Accept a string as the instance’s new time value.

encode(out)[source]¶

Write the XML-RPC encoding of this DateTime item to the out stream object.

It also supports certain of Python’s built-in operators through __cmp__() and __repr__() methods.

A working example follows. The server code:

import datetime
from SimpleXMLRPCServer import SimpleXMLRPCServer
import xmlrpclib

def today():
    today = datetime.datetime.today()
    return xmlrpclib.DateTime(today)

server = SimpleXMLRPCServer(("localhost", 8000))
print "Listening on port 8000..."
server.register_function(today, "today")
server.serve_forever()

The client code for the preceding server:

import xmlrpclib
import datetime

proxy = xmlrpclib.ServerProxy("http://localhost:8000/")

today = proxy.today()
# convert the ISO8601 string to a datetime object
converted = datetime.datetime.strptime(today.value, "%Y%m%dT%H:%M:%S")
print "Today: %s" % converted.strftime("%d.%m.%Y, %H:%M")

10.4. Binary Objects¶

class xmlrpclib.Binary[source]¶

This class may be initialized from string data (which may include NULs). The primary access to the content of a Binary object is provided by an attribute:

data¶

The binary data encapsulated by the Binary instance. The data is provided as an 8-bit string.

Binary objects have the following methods, supported mainly for internal use by the marshalling/unmarshalling code:

decode(string)[source]¶

Accept a base64 string and decode it as the instance’s new data.

encode(out)[source]¶

Write the XML-RPC base 64 encoding of this binary item to the out stream object.

The encoded data will have newlines every 76 characters as per RFC 2045 section 6.8, which was the de facto standard base64 specification when the XML-RPC spec was written.

It also supports certain of Python’s built-in operators through a __cmp__() method.

Example usage of the binary objects. We’re going to transfer an image over XMLRPC:

from SimpleXMLRPCServer import SimpleXMLRPCServer
import xmlrpclib

def python_logo():
     with open("python_logo.jpg", "rb") as handle:
         return xmlrpclib.Binary(handle.read())

server = SimpleXMLRPCServer(("localhost", 8000))
print "Listening on port 8000..."
server.register_function(python_logo, 'python_logo')

server.serve_forever()

The client gets the image and saves it to a file:

import xmlrpclib

proxy = xmlrpclib.ServerProxy("http://localhost:8000/")
with open("fetched_python_logo.jpg", "wb") as handle:
    handle.write(proxy.python_logo().data)

10.5. Fault Objects¶

class xmlrpclib.Fault[source]¶

A Fault object encapsulates the content of an XML-RPC fault tag. Fault objects have the following attributes:

faultCode¶

A string indicating the fault type.

faultString¶

A string containing a diagnostic message associated with the fault.

In the following example we’re going to intentionally cause a Fault by returning a complex type object. The server code:

from SimpleXMLRPCServer import SimpleXMLRPCServer

# A marshalling error is going to occur because we're returning a
# complex number
def add(x, y):
    return x+y+0j

server = SimpleXMLRPCServer(("localhost", 8000))
print "Listening on port 8000..."
server.register_function(add, 'add')

server.serve_forever()

The client code for the preceding server:

import xmlrpclib

proxy = xmlrpclib.ServerProxy("http://localhost:8000/")
try:
    proxy.add(2, 5)
except xmlrpclib.Fault as err:
    print "A fault occurred"
    print "Fault code: %d" % err.faultCode
    print "Fault string: %s" % err.faultString

10.6. ProtocolError Objects¶

class xmlrpclib.ProtocolError[source]¶

A ProtocolError object describes a protocol error in the underlying transport layer (such as a 404 ‘not found’ error if the server named by the URI does not exist). It has the following attributes:

url¶

The URI or URL that triggered the error.

errcode¶

The error code.

errmsg¶

The error message or diagnostic string.

headers¶

A string containing the headers of the HTTP/HTTPS request that triggered the error.

In the following example we’re going to intentionally cause a ProtocolError by providing a URI that doesn’t point to an XMLRPC server:

import xmlrpclib

# create a ServerProxy with a URI that doesn't respond to XMLRPC requests
proxy = xmlrpclib.ServerProxy("http://www.google.com/")

try:
    proxy.some_method()
except xmlrpclib.ProtocolError as err:
    print "A protocol error occurred"
    print "URL: %s" % err.url
    print "HTTP/HTTPS headers: %s" % err.headers
    print "Error code: %d" % err.errcode
    print "Error message: %s" % err.errmsg

10.7. MultiCall Objects¶

The MultiCall object provides a way to encapsulate multiple calls to a remote server into a single request [1].

class xmlrpclib.MultiCall(server)[source]¶

Create an object used to boxcar method calls. server is the eventual target of the call. Calls can be made to the result object, but they will immediately return None, and only store the call name and parameters in the MultiCall object. Calling the object itself causes all stored calls to be transmitted as a single system.multicall request. The result of this call is a generator; iterating over this generator yields the individual results.

A usage example of this class follows. The server code

from SimpleXMLRPCServer import SimpleXMLRPCServer

def add(x,y):
    return x+y

def subtract(x, y):
    return x-y

def multiply(x, y):
    return x*y

def divide(x, y):
    return x/y

# A simple server with simple arithmetic functions
server = SimpleXMLRPCServer(("localhost", 8000))
print "Listening on port 8000..."
server.register_multicall_functions()
server.register_function(add, 'add')
server.register_function(subtract, 'subtract')
server.register_function(multiply, 'multiply')
server.register_function(divide, 'divide')
server.serve_forever()

The client code for the preceding server:

import xmlrpclib

proxy = xmlrpclib.ServerProxy("http://localhost:8000/")
multicall = xmlrpclib.MultiCall(proxy)
multicall.add(7,3)
multicall.subtract(7,3)
multicall.multiply(7,3)
multicall.divide(7,3)
result = multicall()

print "7+3=%d, 7-3=%d, 7*3=%d, 7/3=%d" % tuple(result)

10.8. Convenience Functions¶

xmlrpclib.boolean(value)¶

Convert any Python value to one of the XML-RPC Boolean constants, True or False.

xmlrpclib.dumps(params[, methodname[, methodresponse[, encoding[, allow_none]]]])[source]¶

Convert params into an XML-RPC request. or into a response if methodresponse is true. params can be either a tuple of arguments or an instance of the Fault exception class. If methodresponse is true, only a single value can be returned, meaning that params must be of length 1. encoding, if supplied, is the encoding to use in the generated XML; the default is UTF-8. Python’s None value cannot be used in standard XML-RPC; to allow using it via an extension, provide a true value for allow_none.

xmlrpclib.loads(data[, use_datetime])[source]¶

Convert an XML-RPC request or response into Python objects, a (params, methodname). params is a tuple of argument; methodname is a string, or None if no method name is present in the packet. If the XML-RPC packet represents a fault condition, this function will raise a Fault exception. The use_datetime flag can be used to cause date/time values to be presented as datetime.datetime objects; this is false by default.

Changed in version 2.5: The use_datetime flag was added.

10.9. Example of Client Usage¶

# simple test program (from the XML-RPC specification)
from xmlrpclib import ServerProxy, Error

# server = ServerProxy("http://localhost:8000") # local server
server = ServerProxy("http://betty.userland.com")

print server

try:
    print server.examples.getStateName(41)
except Error as v:
    print "ERROR", v

To access an XML-RPC server through a HTTP proxy, you need to define a custom transport. The following example shows how:

import xmlrpclib, httplib

class ProxiedTransport(xmlrpclib.Transport):
    def set_proxy(self, proxy):
        self.proxy = proxy

    def make_connection(self, host):
        self.realhost = host
        h = httplib.HTTPConnection(self.proxy)
        return h

    def send_request(self, connection, handler, request_body):
        connection.putrequest("POST", 'http://%s%s' % (self.realhost, handler))

    def send_host(self, connection, host):
        connection.putheader('Host', self.realhost)

p = ProxiedTransport()
p.set_proxy('proxy-server:8080')
server = xmlrpclib.ServerProxy('http://time.xmlrpc.com/RPC2', transport=p)
print server.currentTime.getCurrentTime()

10.10. Example of Client and Server Usage¶

See SimpleXMLRPCServer Example.

Footnotes