
``xmlrpc.client`` --- XML-RPC client access
*******************************************

XML-RPC is a Remote Procedure Call method that uses XML passed via
HTTP 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.

class class xmlrpc.client.ServerProxy(uri[, transport[, encoding[, verbose[, allow_none[, use_datetime]]]]])

   A ``ServerProxy`` instance is an object that manages communication
   with a remote XML-RPC server.  The required first argument is a URI
   (Uniform Resource Indicator), and will normally be the URL of the
   server.  The optional second argument is a transport factory
   instance; by default it is an internal ``SafeTransport`` instance
   for https: URLs and an internal HTTP ``Transport`` instance
   otherwise.  The optional third argument is an encoding, by default
   UTF-8. The optional fourth argument is a debugging flag. If
   *allow_none* is true,  the Python constant ``None`` will be
   translated into XML; the default behaviour is for ``None`` to raise
   a ``TypeError``. This is a commonly-used extension to the XML-RPC
   specification, but isn't supported by all clients and servers; see
   http://ontosys.com/xml-rpc/extensions.php for a description.  The
   *use_datetime* flag can be used to cause date/time values to be
   presented as ``datetime.datetime`` objects; this is false by
   default. ``datetime.datetime`` objects may be passed to calls.

   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.

   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.

   ``ServerProxy`` instance methods take Python basic types and
   objects as arguments and return Python basic types and classes.
   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):

   +-----------------------------------+-----------------------------------------------+
   | Name                              | Meaning                                       |
   +===================================+===============================================+
   | ``boolean``                       | The ``True`` and ``False`` constants          |
   +-----------------------------------+-----------------------------------------------+
   | ``integers``                      | Pass in directly                              |
   +-----------------------------------+-----------------------------------------------+
   | ``floating-point numbers``        | Pass in directly                              |
   +-----------------------------------+-----------------------------------------------+
   | ``strings``                       | Pass in directly                              |
   +-----------------------------------+-----------------------------------------------+
   | ``arrays``                        | Any Python sequence type containing           |
   |                                   | conformable elements. Arrays are returned as  |
   |                                   | lists                                         |
   +-----------------------------------+-----------------------------------------------+
   | ``structures``                    | A Python dictionary. Keys must be strings,    |
   |                                   | values may be any conformable type. Objects   |
   |                                   | of user-defined classes can be passed in;     |
   |                                   | only their *__dict__* attribute is            |
   |                                   | transmitted.                                  |
   +-----------------------------------+-----------------------------------------------+
   | ``dates``                         | in seconds since the epoch (pass in an        |
   |                                   | instance of the ``DateTime`` class) or a      |
   |                                   | ``datetime.datetime`` instance.               |
   +-----------------------------------+-----------------------------------------------+
   | ``binary data``                   | pass in an instance of the ``Binary`` wrapper |
   |                                   | class                                         |
   +-----------------------------------+-----------------------------------------------+

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

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

See also:

   XML-RPC HOWTO
      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
      Describes the XML-RPC protocol extension for introspection.

   XML-RPC Specification
      The official specification.

   Unofficial XML-RPC Errata
      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 ``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`` member:

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.

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

   proxy = xmlrpc.client.ServerProxy("http://localhost:8000/")
   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 ``datetime.datetime``
instance.  It has the following methods, supported mainly for internal
use by the marshalling/unmarshalling code:

DateTime.decode(string)

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

DateTime.encode(out)

   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 rich
comparison and ``__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 string data (which may include
NULs). The primary access to the content of a ``Binary`` object is
provided by an attribute:

Binary.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:

Binary.decode(string)

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

Binary.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
   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
``__eq__()`` and ``__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():
        handle = open("python_logo.jpg")
        return xmlrpc.client.Binary(handle.read())
        handle.close()

   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/")
   handle = open("fetched_python_logo.jpg", "w")
   handle.write(proxy.python_logo().data)
   handle.close()


Fault Objects
=============

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

Fault.faultCode

   A string indicating the fault type.

Fault.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 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, err:
       print("A fault occurred")
       print("Fault code: %d" % err.faultCode)
       print("Fault string: %s" % err.faultString)


ProtocolError Objects
=====================

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
members:

ProtocolError.url

   The URI or URL that triggered the error.

ProtocolError.errcode

   The error code.

ProtocolError.errmsg

   The error message or diagnostic string.

ProtocolError.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
``ProtocolError`` by providing an invalid URI:

   import xmlrpc.client

   # create a ServerProxy with an invalid URI
   proxy = xmlrpc.client.ServerProxy("http://invalidaddress/")

   try:
       proxy.some_method()
   except xmlrpc.client.ProtocolError, 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
=================

In http://www.xmlrpc.com/discuss/msgReader%241208, an approach is
presented to encapsulate multiple calls to a remote server into a
single request.

class class xmlrpc.client.MultiCall(server)

   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 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
=====================

xmlrpc.client.dumps(params[, methodname[, methodresponse[, encoding[, allow_none]]]])

   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*.

xmlrpc.client.loads(data[, use_datetime])

   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.


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
   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 proxy, you need to define  a
custom transport.  The following example shows how:

   import xmlrpc.client, http.client

   class ProxiedTransport(xmlrpc.client.Transport):
       def set_proxy(self, proxy):
           self.proxy = proxy
       def make_connection(self, host):
           self.realhost = host
           h = http.client.HTTP(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 = xmlrpc.client.Server('http://time.xmlrpc.com/RPC2', transport=p)
   print(server.currentTime.getCurrentTime())


Example of Client and Server Usage
==================================

See *SimpleXMLRPCServer Example*.
