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python3.8.1 Doc library xmlrpc.client.rst

:mod:`xmlrpc.client` --- XML-RPC client access

.. module:: xmlrpc.client
 :synopsis: XML-RPC client access.

.. moduleauthor:: Fredrik Lundh <fredrik@pythonware.com>

.. sectionauthor:: Eric S. Raymond <esr@snark.thyrsus.com>

Source code: :source:`Lib/xmlrpc/client.py`

---

XML-RPC is a Remote Procedure Call method that uses XML passed via HTTP(S) as a transport. With it, a client can call methods with parameters on a remote server (the server is named by a URI) and get back structured data. This module supports writing XML-RPC client code; it handles all the details of translating between conformable Python objects and XML on the wire.

.. versionchanged:: 3.5

 For HTTPS URIs, :mod:`xmlrpc.client` now performs all the necessary
 certificate and hostname checks by default.

.. versionchanged:: 3.3
 The *use_builtin_types* flag was added.

.. versionchanged:: 3.8
 The *headers* parameter was added.

 Both the HTTP and HTTPS transports support the URL syntax extension for HTTP
 Basic Authentication: ``http://user:pass@host:port/path``. The ``user:pass``
 portion will be base64-encoded as an HTTP 'Authorization' header, and sent to
 the remote server as part of the connection process when invoking an XML-RPC
 method. You only need to use this if the remote server requires a Basic
 Authentication user and password. If an HTTPS URL is provided, *context* may
 be :class:`ssl.SSLContext` and configures the SSL settings of the underlying
 HTTPS connection.

 The returned instance is a proxy object with methods that can be used to invoke
 corresponding RPC calls on the remote server. If the remote server supports the
 introspection API, the proxy can also be used to query the remote server for the
 methods it supports (service discovery) and fetch other server-associated
 metadata.

 Types that are conformable (e.g. that can be marshalled through XML),
 include the following (and except where noted, they are unmarshalled
 as the same Python type):

 .. tabularcolumns:: |l|L|

 +----------------------+-------------------------------------------------------+
 | XML-RPC type | Python type |
 +======================+=======================================================+
 | ``boolean`` | :class:`bool` |
 +----------------------+-------------------------------------------------------+
 | ``int``, ``i1``, | :class:`int` in range from -2147483648 to 2147483647. |
 | ``i2``, ``i4``, | Values get the ``<int>`` tag. |
 | ``i8`` or | |
 | ``biginteger`` | |
 +----------------------+-------------------------------------------------------+
 | ``double`` or | :class:`float`. Values get the ``<double>`` tag. |
 | ``float`` | |
 +----------------------+-------------------------------------------------------+
 | ``string`` | :class:`str` |
 +----------------------+-------------------------------------------------------+
 | ``array`` | :class:`list` or :class:`tuple` containing |
 | | conformable elements. Arrays are returned as |
 | | :class:`lists <list>`. |
 +----------------------+-------------------------------------------------------+
 | ``struct`` | :class:`dict`. Keys must be strings, values may be |
 | | any conformable type. Objects of user-defined |
 | | classes can be passed in; only their |
 | | :attr:`~object.__dict__` attribute is transmitted. |
 +----------------------+-------------------------------------------------------+
 | ``dateTime.iso8601`` | :class:`DateTime` or :class:`datetime.datetime`. |
 | | Returned type depends on values of |
 | | *use_builtin_types* and *use_datetime* flags. |
 +----------------------+-------------------------------------------------------+
 | ``base64`` | :class:`Binary`, :class:`bytes` or |
 | | :class:`bytearray`. Returned type depends on the |
 | | value of the *use_builtin_types* flag. |
 +----------------------+-------------------------------------------------------+
 | ``nil`` | The ``None`` constant. Passing is allowed only if |
 | | *allow_none* is true. |
 +----------------------+-------------------------------------------------------+
 | ``bigdecimal`` | :class:`decimal.Decimal`. Returned type only. |
 +----------------------+-------------------------------------------------------+

 This is the full set of data types supported by XML-RPC. Method calls may also
 raise a special :exc:`Fault` instance, used to signal XML-RPC server errors, or
 :exc:`ProtocolError` used to signal an error in the HTTP/HTTPS transport layer.
 Both :exc:`Fault` and :exc:`ProtocolError` derive from a base class called
 :exc:`Error`. Note that the xmlrpc client module currently does not marshal
 instances of subclasses of built-in types.

 When passing strings, characters special to XML such as ``<``, ``>``, and ``&``
 will be automatically escaped. However, it's the caller's responsibility to
 ensure that the string is free of characters that aren't allowed in XML, such as
 the control characters with ASCII values between 0 and 31 (except, of course,
 tab, newline and carriage return); failing to do this will result in an XML-RPC
 request that isn't well-formed XML. If you have to pass arbitrary bytes
 via XML-RPC, use :class:`bytes` or :class:`bytearray` classes or the
 :class:`Binary` wrapper class described below.

 :class:`Server` is retained as an alias for :class:`ServerProxy` for backwards
 compatibility. New code should use :class:`ServerProxy`.

 .. versionchanged:: 3.5
 Added the *context* argument.

 .. versionchanged:: 3.6
 Added support of type tags with prefixes (e.g. ``ex:nil``).
 Added support of unmarshalling additional types used by Apache XML-RPC
 implementation for numerics: ``i1``, ``i2``, ``i8``, ``biginteger``,
 ``float`` and ``bigdecimal``.
 See http://ws.apache.org/xmlrpc/types.html for a description.

.. seealso::

 `XML-RPC HOWTO <http://www.tldp.org/HOWTO/XML-RPC-HOWTO/index.html>`_
 A good description of XML-RPC operation and client software in several languages.
 Contains pretty much everything an XML-RPC client developer needs to know.

 `XML-RPC Introspection <http://xmlrpc-c.sourceforge.net/introspection.html>`_
 Describes the XML-RPC protocol extension for introspection.

 `XML-RPC Specification <http://xmlrpc.scripting.com/spec.html>`_
 The official specification.

 `Unofficial XML-RPC Errata <http://effbot.org/zone/xmlrpc-errata.htm>`_
 Fredrik Lundh's "unofficial errata, intended to clarify certain
 details in the XML-RPC specification, as well as hint at
 'best practices' to use when designing your own XML-RPC
 implementations."

ServerProxy Objects

A :class:`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 :class:`Fault` or :class:`ProtocolError` object indicating an error.

Servers that support the XML introspection API support some common methods grouped under the reserved :attr:`~ServerProxy.system` attribute:

.. method:: ServerProxy.system.listMethods()

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

.. method:: 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.

.. method:: 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.

.. versionchanged:: 3.5

 Instances of :class:`ServerProxy` support the :term:`context manager` protocol
 for closing the underlying transport.

A working example follows. The server code:

from xmlrpc.server 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 xmlrpc.client

with xmlrpc.client.ServerProxy("http://localhost:8000/") as proxy:
 print("3 is even: %s" % str(proxy.is_even(3)))
 print("100 is even: %s" % str(proxy.is_even(100)))

DateTime Objects

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

.. method:: decode(string)

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

.. method:: encode(out)

 Write the XML-RPC encoding of this :class:`DateTime` item to the *out* stream
 object.

It also supports certain of Python's built-in operators through rich comparison and :meth:`__repr__` methods.

A working example follows. The server code:

import datetime
from xmlrpc.server import SimpleXMLRPCServer
import xmlrpc.client

def today():
 today = datetime.datetime.today()
 return xmlrpc.client.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 xmlrpc.client
import datetime

proxy = xmlrpc.client.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"))

Binary Objects

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

.. attribute:: data

 The binary data encapsulated by the :class:`Binary` instance. The data is
 provided as a :class:`bytes` object.

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

.. method:: decode(bytes)

 Accept a base64 :class:`bytes` object and decode it as the instance's new data.

.. method:: encode(out)

 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:`RFC 2045 section 6.8 <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 :meth:`__eq__` and :meth:`__ne__` methods.

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

from xmlrpc.server import SimpleXMLRPCServer
import xmlrpc.client

def python_logo():
 with open("python_logo.jpg", "rb") as handle:
 return xmlrpc.client.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 xmlrpc.client

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

Fault Objects

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

.. attribute:: faultCode

 A string indicating the fault type.

.. attribute:: faultString

 A string containing a diagnostic message associated with the fault.

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

from xmlrpc.server 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 xmlrpc.client

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

ProtocolError Objects

A :class:`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:

.. attribute:: url

 The URI or URL that triggered the error.

.. attribute:: errcode

 The error code.

.. attribute:: errmsg

 The error message or diagnostic string.

.. attribute:: headers

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

In the following example we're going to intentionally cause a :exc:`ProtocolError` by providing an invalid URI:

import xmlrpc.client

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

try:
 proxy.some_method()
except xmlrpc.client.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)

MultiCall Objects

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

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 :class:`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 :term:`generator`; iterating over this generator yields the individual results.

A usage example of this class follows. The server code:

from xmlrpc.server 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 xmlrpc.client

proxy = xmlrpc.client.ServerProxy("http://localhost:8000/")
multicall = xmlrpc.client.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))

Convenience Functions

.. function:: dumps(params, methodname=None, methodresponse=None, encoding=None, allow_none=False)

 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
 :exc:`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 :const:`None` value cannot be used in standard XML-RPC; to allow using
 it via an extension, provide a true value for *allow_none*.

.. function:: loads(data, use_datetime=False, use_builtin_types=False)

 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 :exc:`Fault` exception.
 The *use_builtin_types* flag can be used to cause date/time values to be
 presented as :class:`datetime.datetime` objects and binary data to be
 presented as :class:`bytes` objects; this flag is false by default.

 The obsolete *use_datetime* flag is similar to *use_builtin_types* but it
 applies only to date/time values.

 .. versionchanged:: 3.3
 The *use_builtin_types* flag was added.

Example of Client Usage

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

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

 print(proxy)

 try:
 print(proxy.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 http.client
import xmlrpc.client

class ProxiedTransport(xmlrpc.client.Transport):

 def set_proxy(self, host, port=None, headers=None):
 self.proxy = host, port
 self.proxy_headers = headers

 def make_connection(self, host):
 connection = http.client.HTTPConnection(*self.proxy)
 connection.set_tunnel(host, headers=self.proxy_headers)
 self._connection = host, connection
 return connection

transport = ProxiedTransport()
transport.set_proxy('proxy-server', 8080)
server = xmlrpc.client.ServerProxy('http://betty.userland.com', transport=transport)
print(server.examples.getStateName(41))

Example of Client and Server Usage

See :ref:`simplexmlrpcserver-example`.

Footnotes

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