20.23. "xmlrpclib" — XML-RPC client access
******************************************

Note: The "xmlrpclib" module has been renamed to "xmlrpc.client" in
  Python 3.  The *2to3* tool will automatically adapt imports when
  converting your sources to Python 3.

New in version 2.2.

**Source code:** Lib/xmlrpclib.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.

Warning: The "xmlrpclib" module is not secure against maliciously
  constructed data.  If you need to parse untrusted or unauthenticated
  data see XML vulnerabilities.

Changed in version 2.7.9: For HTTPS URIs, "xmlrpclib" now performs all
the necessary certificate and hostname checks by default.

class xmlrpclib.ServerProxy(uri[, transport[, encoding[, verbose[, allow_none[, use_datetime[, context]]]]]])

   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.

   The following parameters govern the use of the returned proxy
   instance. 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. If an HTTPS URL is provided,
   *context* may be "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):

   +------------------------+---------------------------------------------------------+
   | XML-RPC type           | Python type                                             |
   +========================+=========================================================+
   | "boolean"              | "bool"                                                  |
   +------------------------+---------------------------------------------------------+
   | "int" or "i4"          | "int" or "long" in range from -2147483648 to            |
   |                        | 2147483647.                                             |
   +------------------------+---------------------------------------------------------+
   | "double"               | "float"                                                 |
   +------------------------+---------------------------------------------------------+
   | "string"               | "str" or "unicode"                                      |
   +------------------------+---------------------------------------------------------+
   | "array"                | "list" or "tuple" containing conformable elements.      |
   |                        | Arrays are returned as "lists".                         |
   +------------------------+---------------------------------------------------------+
   | "struct"               | "dict".  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.                                            |
   +------------------------+---------------------------------------------------------+
   | "dateTime.iso8601"     | "DateTime" or "datetime.datetime". Returned type        |
   |                        | depends on values of the *use_datetime* flags.          |
   +------------------------+---------------------------------------------------------+
   | "base64"               | "Binary"                                                |
   +------------------------+---------------------------------------------------------+
   | "nil"                  | The "None" constant.  Passing is allowed only if        |
   |                        | *allow_none* is true.                                   |
   +------------------------+---------------------------------------------------------+

   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 even though
   starting with Python 2.2 you can subclass built-in types, the
   xmlrpclib module currently does not marshal instances of such
   subclasses.

   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".

   Changed in version 2.5: The *use_datetime* flag was added.

   Changed in version 2.6: Instances of *new-style class*es can be
   passed in if they have an *__dict__* attribute and don’t have a
   base class that is marshalled in a special way.

   Changed in version 2.7.9: Added the *context* argument.

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.”


20.23.1. 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.


20.23.2. 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))


20.23.3. DateTime Objects
=========================

class xmlrpclib.DateTime

   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)

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

   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
   "__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")


20.23.4. Binary Objects
=======================

class xmlrpclib.Binary

   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)

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

   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 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)


20.23.5. Fault Objects
======================

class xmlrpclib.Fault

   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


20.23.6. ProtocolError Objects
==============================

class xmlrpclib.ProtocolError

   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


20.23.7. MultiCall Objects
==========================

New in version 2.4.

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

class xmlrpclib.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 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)


20.23.8. 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]]]])

   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])

   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.


20.23.9. 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()


20.23.10. Example of Client and Server Usage
============================================

See SimpleXMLRPCServer Example.

-[ Footnotes ]-

[1] This approach has been first presented in a discussion on
    xmlrpc.com.
