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Navigate HTTP resources using WADL files as guides.

Project description

Copyright (C) 2008-2013 Canonical Ltd.

This file is part of wadllib.

wadllib is free software: you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License as published by the
Free Software Foundation, version 3 of the License.

wadllib is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for
more details.

You should have received a copy of the GNU Lesser General Public License
along with wadllib. If not, see <>.


An Application object represents a web service described by a WADL

>>> import os
>>> import sys
>>> import pkg_resources
>>> from wadllib.application import Application

The first argument to the Application constructor is the URL at which
the WADL file was found. The second argument may be raw WADL markup.

>>> wadl_string = pkg_resources.resource_string(
... '', 'launchpad-wadl.xml')
>>> wadl = Application("", wadl_string)

Or the second argument may be an open filehandle containing the markup.

>>> cleanups = []
>>> def application_for(filename, url=""):
... wadl_stream = pkg_resources.resource_stream(
... '', filename)
... cleanups.append(wadl_stream)
... return Application(url, wadl_stream)
>>> wadl = application_for("launchpad-wadl.xml",
... "")

Link navigation

The preferred technique for finding a resource is to start at one of
the resources defined in the WADL file, and follow links. This code
retrieves the definition of the root resource.

>>> service_root = wadl.get_resource_by_path('')
>>> service_root.url
>>> service_root.type_url

The service root resource supports GET.

>>> get_method = service_root.get_method('get')

>>> get_method = service_root.get_method('GET')

If we want to invoke this method, we send a GET request to the service
root URL.

>>> get_method.build_request_url()

The WADL description of a resource knows which representations are
available for that resource. In this case, the server root resource
has a a JSON representation, and it defines parameters like
'people_collection_link', a link to a list of people in Launchpad. We
should be able to use the get_parameter() method to get the WADL
definition of the 'people_collection_link' parameter and find out more
about it--for instance, is it a link to another resource?

>>> def test_raises(exc_class, method, *args, **kwargs):
... try:
... method(*args, **kwargs)
... except Exception:
... # Contortion to support Python < 2.6 and >= 3 simultaneously.
... e = sys.exc_info()[1]
... if isinstance(e, exc_class):
... print(e)
... return
... raise
... raise Exception("Expected exception %s not raised" % exc_class)

>>> from wadllib.application import NoBoundRepresentationError
>>> link_name = 'people_collection_link'
>>> test_raises(
... NoBoundRepresentationError, service_root.get_parameter, link_name)
Resource is not bound to any representation, and no media media type was specified.

Oops. The code has no way to know whether 'people_collection_link' is
a parameter of the JSON representation or some other kind of
representation. We can pass a media type to get_parameter and let it
know which representation the parameter lives in.

>>> link_parameter = service_root.get_parameter(
... link_name, 'application/json')
>>> test_raises(NoBoundRepresentationError, link_parameter.get_value)
Resource is not bound to any representation.

Oops again. The parameter is available, but it has no value, because
there's no actual data associated with the resource. The browser can
look up the description of the GET method to make an actual GET
request to the service root, and bind the resulting representation to
the WADL description of the service root.

You can't bind just any representation to a WADL resource description.
It has to be of a media type understood by the WADL description.

>>> from wadllib.application import UnsupportedMediaTypeError
>>> test_raises(
... UnsupportedMediaTypeError, service_root.bind,
... '<html>Some HTML</html>', 'text/html')
This resource doesn't define a representation for media type text/html

The WADL description of the service root resource has a JSON
representation. Here it is.

>>> json_representation = service_root.get_representation_definition(
... 'application/json')
>>> json_representation.media_type

We already have a WADL representation of the service root resource, so
let's try binding it to that JSON representation. We use test JSON
data from a file to simulate the result of a GET request to the
service root.

>>> def get_testdata(filename):
... return pkg_resources.resource_string(
... '', filename + '.json')

>>> def bind_to_testdata(resource, filename):
... return resource.bind(get_testdata(filename), 'application/json')

The return value is a new Resource object that's "bound" to that JSON
test data.

>>> bound_service_root = bind_to_testdata(service_root, 'root')
>>> sorted([ for param in bound_service_root.parameters()])
['bugs_collection_link', 'people_collection_link']
>>> sorted(bound_service_root.parameter_names())
['bugs_collection_link', 'people_collection_link']
>>> [ for method in bound_service_root.method_iter]

Now the bound resource object has a JSON representation, and now
'people_collection_link' makes sense. We can follow the
'people_collection_link' to a new Resource object.

>>> link_parameter = bound_service_root.get_parameter(link_name)
>>> print(link_parameter.get_value())
>>> personset_resource = link_parameter.linked_resource
>>> personset_resource.__class__
<class 'wadllib.application.Resource'>
>>> print(personset_resource.url)
>>> personset_resource.type_url

This new resource is a collection of people.


The "collection of people" resource supports a standard GET request as
well as a special GET and an overloaded POST. The get_method() method
is used to retrieve WADL definitions of the possible HTTP requests you
might make. Here's how to get the WADL definition of the standard GET

>>> get_method = personset_resource.get_method('get')

The method name passed into get_method() is treated case-insensitively.

>>> personset_resource.get_method('GET').id

To invoke the special GET request, the client sets the 'ws.op' query
parameter to the fixed string 'findPerson'.

>>> find_method = personset_resource.get_method(
... query_params={'ws.op' : 'findPerson'})

Given an end-user's values for the non-fixed parameters, it's possible
to get the URL that should be used to invoke the method.

>>> print(find_method.build_request_url(text='foo'))

>>> print(find_method.build_request_url(
... {'ws.op' : 'findPerson', 'text' : 'bar'}))

An error occurs if the end-user gives an incorrect value for a fixed
parameter value, or omits a required parameter.

>>> find_method.build_request_url()
Traceback (most recent call last):
ValueError: No value for required parameter 'text'

>>> find_method.build_request_url(
... {'ws.op' : 'findAPerson', 'text' : 'foo'})
Traceback (most recent call last):
ValueError: Value 'findAPerson' for parameter 'ws.op' conflicts
with fixed value 'findPerson'

To invoke the overloaded POST request, the client sets the 'ws.op'
query variable to the fixed string 'newTeam':

>>> create_team_method = personset_resource.get_method(
... 'post', representation_params={'ws.op' : 'newTeam'})

findMethod() returns None when there's no WADL method matching the
name or the fixed parameters.

>>> print(personset_resource.get_method('nosuchmethod'))

>>> print(personset_resource.get_method(
... 'post', query_params={'ws_op' : 'nosuchparam'}))

Let's say the browser makes a GET request to the person set resource
and gets back a representation. We can bind that representation to our
description of the person set resource.

>>> bound_personset = bind_to_testdata(personset_resource, 'personset')
>>> bound_personset.get_parameter("start").get_value()
>>> bound_personset.get_parameter("total_size").get_value()

We can keep following links indefinitely, so long as we bind to a
representation to each resource as we get it, and use the
representation to find the next link.

>>> next_page_link = bound_personset.get_parameter("next_collection_link")
>>> print(next_page_link.get_value())
>>> page_two = next_page_link.linked_resource
>>> bound_page_two = bind_to_testdata(page_two, 'personset-page2')
>>> print(bound_page_two.url)
>>> bound_page_two.get_parameter("start").get_value()
>>> print(bound_page_two.get_parameter("next_collection_link").get_value())

Let's say the browser makes a POST request that invokes the 'newTeam'
named operation. The response will include a number of HTTP headers,
including 'Location', which points the way to the newly created team.

>>> headers = { 'Location' : '' }
>>> response = create_team_method.response.bind(headers)
>>> location_parameter = response.get_parameter('Location')
>>> location_parameter.get_value()
>>> new_team = location_parameter.linked_resource
>>> new_team.url
>>> new_team.type_url

Examining links

The 'linked_resource' property of a parameter lets you follow a link
to another object. The 'link' property of a parameter lets you examine
links before following them.

>>> try:
... import simplejson as json
... except ImportError:
... import json
>>> links_wadl = application_for('links-wadl.xml')
>>> service_root = links_wadl.get_resource_by_path('')
>>> representation = json.dumps(
... {'scalar_value': 'foo',
... 'known_link': 'http://known/',
... 'unknown_link': 'http://unknown/'})
>>> bound_root = service_root.bind(representation)

>>> print(bound_root.get_parameter("scalar_value").link)

>>> known_resource = bound_root.get_parameter("known_link")
>>> unknown_resource = bound_root.get_parameter("unknown_link")

>>> print(
>>> print(

A link whose type is unknown is a link to a resource not described by
WADL. Following this link using .linked_resource or .link.follow will
cause a wadllib error. You'll need to follow the link using a general
HTTP library or some other tool.

<wadllib.application.Resource object ...>
>>> known_resource.linked_resource
<wadllib.application.Resource object ...>

>>> from wadllib.application import WADLError
>>> test_raises(WADLError, getattr,, 'follow')
Cannot follow a link when the target has no WADL
description. Try using a general HTTP client instead.

>>> test_raises(WADLError, getattr, unknown_resource, 'linked_resource')
Cannot follow a link when the target has no WADL
description. Try using a general HTTP client instead.

Creating a Resource from a representation definition

Although every representation is a representation of some HTTP
resource, an HTTP resource doesn't necessarily correspond directly to
a WADL <resource> or <resource_type> tag. Sometimes a representation
is defined within a WADL <method> tag.

>>> find_method = personset_resource.get_method(
... query_params={'ws.op' : 'find'})

>>> representation_definition = (
... find_method.response.get_representation_definition(
... 'application/json'))

There may be no WADL <resource> or <resource_type> tag for the
representation defined here. That's why wadllib makes it possible to
instantiate an anonymous Resource object using only the representation

>>> from wadllib.application import Resource
>>> anonymous_resource = Resource(
... wadl, "http://foo/", representation_definition.tag)

We can bind this resource to a representation, as long as we
explicitly pass in the representation definition.

>>> anonymous_resource = anonymous_resource.bind(
... get_testdata('personset'), 'application/json',
... representation_definition=representation_definition)

Once the resource is bound to a representation, we can get its
parameter values.

>>> print(anonymous_resource.get_parameter(
... 'total_size', 'application/json').get_value())

Resource instantiation

If you happen to have the URL to an object lying around, and you know
its type, you can construct a Resource object directly instead of
by following links.

>>> from wadllib.application import Resource
>>> limi_person = Resource(wadl, "",
... "")
>>> sorted([ for method in limi_person.method_iter])[:3]
['person-acceptInvitationToBeMemberOf', 'person-addMember', 'person-declineInvitationToBeMemberOf']

>>> bound_limi = bind_to_testdata(limi_person, 'person-limi')
>>> sorted(bound_limi.parameter_names())[:3]
['admins_collection_link', 'confirmed_email_addresses_collection_link',
>>> languages_link = bound_limi.get_parameter("languages_collection_link")
>>> print(languages_link.get_value())

You can bind a Resource to a representation when you create it.

>>> limi_data = get_testdata('person-limi')
>>> bound_limi = Resource(
... wadl, "",
... "", limi_data,
... "application/json")
>>> print(bound_limi.get_parameter(
... "languages_collection_link").get_value())

By default the representation is treated as a string and processed
according to the media type you pass into the Resource constructor. If
you've already processed the representation, pass in False for the
'representation_needs_processing' argument.

>>> from wadllib import _make_unicode
>>> processed_limi_data = json.loads(_make_unicode(limi_data))
>>> bound_limi = Resource(wadl, "",
... "", processed_limi_data,
... "application/json", False)
>>> print(bound_limi.get_parameter(
... "languages_collection_link").get_value())

Most of the time, the representation of a resource is of the type
you'd get by sending a standard GET to that resource. If that's not
the case, you can specify a RepresentationDefinition as the
'representation_definition' argument to bind() or the Resource
constructor, to show what the representation really looks like. Here's
an example.

There's a method on a person resource such as bound_limi that's
identified by a distinctive query argument: ws.op=getMembersByStatus.

>>> method = bound_limi.get_method(
... query_params={'ws.op' : 'findPathToTeam'})

Invoke this method with a GET request and you'll get back a page from
a list of people.

>>> people_page_repr_definition = (
... method.response.get_representation_definition('application/json'))
>>> people_page_repr_definition.tag.attrib['href']

As it happens, we have a page from a list of people to use as test data.

>>> people_page_repr = get_testdata('personset')

If we bind the resource to the result of the method invocation as
happened above, we don't be able to access any of the parameters we'd
expect. wadllib will think the representation is of type
'person-full', the default GET type for bound_limi.

>>> bad_people_page = bound_limi.bind(people_page_repr)
>>> print(bad_people_page.get_parameter('total_size'))

Since we don't actually have a 'person-full' representation, we won't
be able to get values for the parameters of that kind of

>>> bad_people_page.get_parameter('name').get_value()
Traceback (most recent call last):
KeyError: 'name'

So that's a dead end. *But*, if we pass the correct representation
type into bind(), we can access the parameters associated with a
'person-page' representation.

>>> people_page = bound_limi.bind(
... people_page_repr,
... representation_definition=people_page_repr_definition)
>>> people_page.get_parameter('total_size').get_value()

If you invoke the method and ask for a media type other than JSON, you
won't get anything.

>>> print(method.response.get_representation_definition('text/html'))

Data type conversion

The values of date and dateTime parameters are automatically converted to
Python datetime objects.

>>> data_type_wadl = application_for('data-types-wadl.xml')
>>> service_root = data_type_wadl.get_resource_by_path('')

>>> representation = json.dumps(
... {'a_date': '2007-10-20',
... 'a_datetime': '2005-06-06T08:59:51.619713+00:00'})
>>> bound_root = service_root.bind(representation, 'application/json')

>>> bound_root.get_parameter('a_date').get_value()
datetime.datetime(2007, 10, 20, 0, 0)
>>> bound_root.get_parameter('a_datetime').get_value()
datetime.datetime(2005, 6, 6, 8, ...)

A 'date' field can include a timestamp, and a 'datetime' field can
omit one. wadllib will turn both into datetime objects.

>>> representation = json.dumps(
... {'a_date': '2005-06-06T08:59:51.619713+00:00',
... 'a_datetime': '2007-10-20'})
>>> bound_root = service_root.bind(representation, 'application/json')

>>> bound_root.get_parameter('a_datetime').get_value()
datetime.datetime(2007, 10, 20, 0, 0)
>>> bound_root.get_parameter('a_date').get_value()
datetime.datetime(2005, 6, 6, 8, ...)

If a date or dateTime parameter has a null value, you get None. If the
value is a string that can't be parsed to a datetime object, you get a

>>> representation = json.dumps(
... {'a_date': 'foo', 'a_datetime': None})
>>> bound_root = service_root.bind(representation, 'application/json')
>>> bound_root.get_parameter('a_date').get_value()
Traceback (most recent call last):
ValueError: foo
>>> print(bound_root.get_parameter('a_datetime').get_value())

Representation creation

You must provide a representation when invoking certain methods. The
representation() method helps you build one without knowing the
details of how a representation is put together.

>>> create_team_method.build_representation(
... display_name='Joe Bloggs', name='joebloggs')
('application/x-www-form-urlencoded', 'display_name=Joe+Bloggs&name=joebloggs&ws.op=newTeam')

The return value of build_representation is a 2-tuple containing the
media type of the built representation, and the string representation
itself. Along with the resource's URL, this is all you need to send
the representation to a web server.

>>> bound_limi.get_method('patch').build_representation(name='limi2')
('application/json', '{"name": "limi2"}')

Representations may require values for certain parameters.

>>> create_team_method.build_representation()
Traceback (most recent call last):
ValueError: No value for required parameter 'display_name'

>>> bound_limi.get_method('put').build_representation(name='limi2')
Traceback (most recent call last):
ValueError: No value for required parameter 'mugshot_link'

Some representations may safely include binary data.

>>> binary_stream = pkg_resources.resource_stream(
... '', 'multipart-binary-wadl.xml')
>>> cleanups.append(binary_stream)
>>> binary_wadl = Application(
... "", binary_stream)
>>> service_root = binary_wadl.get_resource_by_path('')

>>> method = service_root.get_method('post', 'multipart/form-data')
>>> media_type, doc = method.build_representation(
... text_field="text", binary_field="\x01\x02")
>>> print(media_type)
multipart/form-data; boundary=...
>>> print(doc)
MIME-Version: 1.0
Content-Type: multipart/form-data; boundary="..."
Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Content-Disposition: form-data; name="text_field"
Content-Type: application/octet-stream
MIME-Version: 1.0
Content-Disposition: form-data; name="binary_field"
>>> '\x01\x02' in doc

>>> method = service_root.get_method('post', 'text/unknown')
>>> method.build_representation(field="value")
Traceback (most recent call last):
ValueError: Unsupported media type: 'text/unknown'


Some parameters take values from a predefined list of options.

>>> option_wadl = application_for('options-wadl.xml')
>>> definitions = option_wadl.representation_definitions
>>> service_root = option_wadl.get_resource_by_path('')
>>> definition = definitions['service-root-json']
>>> param = definition.params(service_root)[0]
>>> print(
>>> sorted([option.value for option in param.options])
['Value 1', 'Value 2']

Such parameters cannot take values that are not in the list.

>>> definition.validate_param_values(
... [param], {'has_options': 'Value 1'})
{'has_options': 'Value 1'}

>>> definition.validate_param_values(
... [param], {'has_options': 'Invalid value'})
Traceback (most recent call last):
ValueError: Invalid value 'Invalid value' for parameter
'has_options': valid values are: "Value 1", "Value 2"

Error conditions

You'll get None if you try to look up a nonexistent resource.

>>> print(wadl.get_resource_by_path('nosuchresource'))

You'll get an exception if you try to look up a nonexistent resource

>>> print(wadl.get_resource_type('#nosuchtype'))
Traceback (most recent call last):
KeyError: 'No such XML ID: "#nosuchtype"'

You'll get None if you try to look up a method whose parameters don't
match any defined method.

>>> print(bound_limi.get_method(
... 'post', representation_params={ 'foo' : 'bar' }))

.. cleanup
>>> for stream in cleanups:
... stream.close()

.. toctree::


NEWS for wadllib

1.3.2 (2013-02-25)

- Impose sort order to avoid test failures due to hash randomization.
LP: #1132125
- Be sure to close streams opened by pkg_resources.resource_stream() to avoid
test suite complaints.

1.3.1 (2012-03-22)

- Correct the double pass through _from_string causing datetime issues

1.3.0 (2012-01-27)

- Add Python 3 compatibility

- Add the ability to inspect links before following them.

- Ensure that the sample data is packaged.

1.2.0 (2011-02-03)

- It's now possible to examine a link before following it, to see
whether it has a WADL description or whether it needs to be fetched
with a general HTTP client.

- It's now possible to iterate over a resource's Parameter objects
with the .parameters() method.

1.1.8 (2010-10-27)

- This revision contains no code changes, but the build system was
changed (yet again). This time to include the version.txt file
used by

1.1.7 (2010-10-26)

- This revision contains no code changes, but the build system was
changed (again) to include the sample data used in tests.

1.1.6 (2010-10-21)

- This revision contains no code changes, but the build system was
changed to include the sample data used in tests.

1.1.5 (2010-05-04)

- Fixed a bug (Launchpad bug 274074) that prevented the lookup of
parameter values in resources associated directly with a
representation definition (rather than a resource type with a
representation definition). Bug fix provided by James Westby.

1.1.4 (2009-09-15)

- Fixed a bug that crashed wadllib unless all parameters of a
multipart representation were provided.

1.1.3 (2009-08-26)

- Remove unnecessary build dependencies.

- Add missing dependencies to setup file.

- Remove sys.path hack from

1.1.2 (2009-08-20)

- Consistently handle different versions of simplejson.

1.1.1 (2009-07-14)

- Make wadllib aware of the <option> tags that go beneath <param> tags.

1.1 (2009-07-09)

- Make wadllib capable of recognizing and generating
multipart/form-data representations, including representations that
incorporate binary parameters.

1.0 (2009-03-23)

- Initial release on PyPI

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