21.26. xmlrpc.client
— XML-RPC client access¶
Source code: 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.
Advertencia
The xmlrpc.client
module is not secure against maliciously
constructed data. If you need to parse untrusted or unauthenticated data see
XML vulnerabilities.
Distinto en la versión 3.5: For HTTPS URIs, xmlrpc.client
now performs all the necessary
certificate and hostname checks by default.
-
class
xmlrpc.client.
ServerProxy
(uri, transport=None, encoding=None, verbose=False, allow_none=False, use_datetime=False, use_builtin_types=False, *, context=None)¶ Distinto en la versión 3.3: The use_builtin_types flag was added.
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 internalSafeTransport
instance for https: URLs and an internal HTTPTransport
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 forNone
to raise aTypeError
. 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_builtin_types flag can be used to cause date/time values to be presented asdatetime.datetime
objects and binary data to be presented asbytes
objects; this flag is false by default.datetime.datetime
,bytes
andbytearray
objects may be passed to calls. The obsolete use_datetime flag is similar to use_builtin_types but it applies only to date/time values.Both the HTTP and HTTPS transports support the URL syntax extension for HTTP Basic Authentication:
http://user:pass@host:port/path
. Theuser: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 bessl.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
ori4
int
in range from -2147483648 to 2147483647.double
float
string
str
array
list
ortuple
containing conformable elements. Arrays are returned aslists
.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
ordatetime.datetime
. Returned type depends on values of use_builtin_types and use_datetime flags.base64
Binary
,bytes
orbytearray
. 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.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, orProtocolError
used to signal an error in the HTTP/HTTPS transport layer. BothFault
andProtocolError
derive from a base class calledError
. 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, usebytes
orbytearray
classes or theBinary
wrapper class described below.Server
is retained as an alias forServerProxy
for backwards compatibility. New code should useServerProxy
.Distinto en la versión 3.5: Added the context argument.
Ver también
- 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.»
21.26.1. 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.
Distinto en la versión 3.5: Instances of ServerProxy
support the 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)))
21.26.2. DateTime Objects¶
-
class
xmlrpc.client.
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.
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"))
21.26.3. Binary Objects¶
-
class
xmlrpc.client.
Binary
¶ This class may be initialized from bytes data (which may include NULs). The primary access to the content of a
Binary
object is provided by an attribute:Binary
objects have the following methods, supported mainly for internal use by the marshalling/unmarshalling code:-
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():
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)
21.26.4. Fault Objects¶
-
class
xmlrpc.client.
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 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)
21.26.5. ProtocolError Objects¶
-
class
xmlrpc.client.
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 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 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)
21.26.6. MultiCall Objects¶
The MultiCall
object provides a way to encapsulate multiple calls to a
remote server into a single request [1].
-
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 theMultiCall
object. Calling the object itself causes all stored calls to be transmitted as a singlesystem.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))
21.26.7. Convenience Functions¶
-
xmlrpc.client.
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
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’sNone
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=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, orNone
if no method name is present in the packet. If the XML-RPC packet represents a fault condition, this function will raise aFault
exception. The use_builtin_types flag can be used to cause date/time values to be presented asdatetime.datetime
objects and binary data to be presented asbytes
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.
Distinto en la versión 3.3: The use_builtin_types flag was added.
21.26.8. 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))
21.26.9. Example of Client and Server Usage¶
See SimpleXMLRPCServer Example.
Footnotes
[1] | This approach has been first presented in a discussion on xmlrpc.com. |