diff --git a/ironic/api/args.py b/ironic/api/args.py
new file mode 100644
index 0000000000..4c721f7b19
--- /dev/null
+++ b/ironic/api/args.py
@@ -0,0 +1,387 @@
+# Copyright 2011-2019 the WSME authors and contributors
+# (See https://opendev.org/x/wsme/)
+#
+# This module is part of WSME and is also released under
+# the MIT License: http://www.opensource.org/licenses/mit-license.php
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+import cgi
+import datetime
+import decimal
+import json
+import logging
+
+from dateutil import parser as dateparser
+
+from ironic.api import types as atypes
+from ironic.common import exception
+
+LOG = logging.getLogger(__name__)
+
+
+CONTENT_TYPE = 'application/json'
+ACCEPT_CONTENT_TYPES = [
+    CONTENT_TYPE,
+    'text/javascript',
+    'application/javascript'
+]
+ENUM_TRUE = ('true', 't', 'yes', 'y', 'on', '1')
+ENUM_FALSE = ('false', 'f', 'no', 'n', 'off', '0')
+
+
+def fromjson_array(datatype, value):
+    if not isinstance(value, list):
+        raise ValueError("Value not a valid list: %s" % value)
+    return [fromjson(datatype.item_type, item) for item in value]
+
+
+def fromjson_dict(datatype, value):
+    if not isinstance(value, dict):
+        raise ValueError("Value not a valid dict: %s" % value)
+    return dict((
+        (fromjson(datatype.key_type, item[0]),
+            fromjson(datatype.value_type, item[1]))
+        for item in value.items()))
+
+
+def fromjson_bool(value):
+    if isinstance(value, (int, bool)):
+        return bool(value)
+    if value in ENUM_TRUE:
+        return True
+    if value in ENUM_FALSE:
+        return False
+    raise ValueError("Value not an unambiguous boolean: %s" % value)
+
+
+def fromjson(datatype, value):
+    """A generic converter from json base types to python datatype.
+
+    """
+    if value is None:
+        return None
+
+    if isinstance(datatype, atypes.ArrayType):
+        return fromjson_array(datatype, value)
+
+    if isinstance(datatype, atypes.DictType):
+        return fromjson_dict(datatype, value)
+
+    if datatype is bytes:
+        if isinstance(value, (str, int, float)):
+            return str(value).encode('utf8')
+        return value
+
+    if datatype is str:
+        if isinstance(value, bytes):
+            return value.decode('utf-8')
+        return value
+
+    if datatype in (int, float):
+        return datatype(value)
+
+    if datatype is bool:
+        return fromjson_bool(value)
+
+    if datatype is decimal.Decimal:
+        return decimal.Decimal(value)
+
+    if datatype is datetime.datetime:
+        return dateparser.parse(value)
+
+    if atypes.iscomplex(datatype):
+        return fromjson_complex(datatype, value)
+
+    if atypes.isusertype(datatype):
+        return datatype.frombasetype(fromjson(datatype.basetype, value))
+
+    return value
+
+
+def fromjson_complex(datatype, value):
+    obj = datatype()
+    attributes = atypes.list_attributes(datatype)
+
+    # Here we check that all the attributes in the value are also defined
+    # in our type definition, otherwise we raise an Error.
+    v_keys = set(value.keys())
+    a_keys = set(adef.name for adef in attributes)
+    if not v_keys <= a_keys:
+        raise exception.UnknownAttribute(None, v_keys - a_keys)
+
+    for attrdef in attributes:
+        if attrdef.name in value:
+            try:
+                val_fromjson = fromjson(attrdef.datatype,
+                                        value[attrdef.name])
+            except exception.UnknownAttribute as e:
+                e.add_fieldname(attrdef.name)
+                raise
+            if getattr(attrdef, 'readonly', False):
+                raise exception.InvalidInput(attrdef.name, val_fromjson,
+                                             "Cannot set read only field.")
+            setattr(obj, attrdef.key, val_fromjson)
+        elif attrdef.mandatory:
+            raise exception.InvalidInput(attrdef.name, None,
+                                         "Mandatory field missing.")
+
+    return atypes.validate_value(datatype, obj)
+
+
+def parse(s, datatypes, bodyarg, encoding='utf8'):
+    jload = json.load
+    if not hasattr(s, 'read'):
+        if isinstance(s, bytes):
+            s = s.decode(encoding)
+        jload = json.loads
+    try:
+        jdata = jload(s)
+    except ValueError:
+        raise exception.ClientSideError("Request is not in valid JSON format")
+    if bodyarg:
+        argname = list(datatypes.keys())[0]
+        try:
+            kw = {argname: fromjson(datatypes[argname], jdata)}
+        except ValueError as e:
+            raise exception.InvalidInput(argname, jdata, e.args[0])
+        except exception.UnknownAttribute as e:
+            # We only know the fieldname at this level, not in the
+            # called function. We fill in this information here.
+            e.add_fieldname(argname)
+            raise
+    else:
+        kw = {}
+        extra_args = []
+        if not isinstance(jdata, dict):
+            raise exception.ClientSideError("Request must be a JSON dict")
+        for key in jdata:
+            if key not in datatypes:
+                extra_args.append(key)
+            else:
+                try:
+                    kw[key] = fromjson(datatypes[key], jdata[key])
+                except ValueError as e:
+                    raise exception.InvalidInput(key, jdata[key], e.args[0])
+                except exception.UnknownAttribute as e:
+                    # We only know the fieldname at this level, not in the
+                    # called function. We fill in this information here.
+                    e.add_fieldname(key)
+                    raise
+        if extra_args:
+            raise exception.UnknownArgument(', '.join(extra_args))
+    return kw
+
+
+def from_param(datatype, value):
+    if datatype is datetime.datetime:
+        return dateparser.parse(value) if value else None
+
+    if datatype is atypes.File:
+        if isinstance(value, cgi.FieldStorage):
+            return atypes.File(fieldstorage=value)
+        return atypes.File(content=value)
+
+    if isinstance(datatype, atypes.UserType):
+        return datatype.frombasetype(
+            from_param(datatype.basetype, value))
+
+    if isinstance(datatype, atypes.ArrayType):
+        if value is None:
+            return value
+        return [
+            from_param(datatype.item_type, item)
+            for item in value
+        ]
+
+    return datatype(value) if value is not None else None
+
+
+def from_params(datatype, params, path, hit_paths):
+    if isinstance(datatype, atypes.ArrayType):
+        return array_from_params(datatype, params, path, hit_paths)
+
+    if isinstance(datatype, atypes.UserType):
+        return usertype_from_params(datatype, params, path, hit_paths)
+
+    if path in params:
+        assert not isinstance(datatype, atypes.DictType), \
+            'DictType unsupported'
+        assert not atypes.iscomplex(datatype) or datatype is atypes.File, \
+            'complex type unsupported'
+        hit_paths.add(path)
+        return from_param(datatype, params[path])
+    return atypes.Unset
+
+
+def array_from_params(datatype, params, path, hit_paths):
+    if hasattr(params, 'getall'):
+        # webob multidict
+        def getall(params, path):
+            return params.getall(path)
+    elif hasattr(params, 'getlist'):
+        # werkzeug multidict
+        def getall(params, path):  # noqa
+            return params.getlist(path)
+    if path in params:
+        hit_paths.add(path)
+        return [
+            from_param(datatype.item_type, value)
+            for value in getall(params, path)]
+
+    return atypes.Unset
+
+
+def usertype_from_params(datatype, params, path, hit_paths):
+    if path in params:
+        hit_paths.add(path)
+        value = from_param(datatype.basetype, params[path])
+        if value is not atypes.Unset:
+            return datatype.frombasetype(value)
+    return atypes.Unset
+
+
+def args_from_args(funcdef, args, kwargs):
+    newargs = []
+    for argdef, arg in zip(funcdef.arguments[:len(args)], args):
+        try:
+            newargs.append(from_param(argdef.datatype, arg))
+        except Exception as e:
+            if isinstance(argdef.datatype, atypes.UserType):
+                datatype_name = argdef.datatype.name
+            elif isinstance(argdef.datatype, type):
+                datatype_name = argdef.datatype.__name__
+            else:
+                datatype_name = argdef.datatype.__class__.__name__
+            raise exception.InvalidInput(
+                argdef.name,
+                arg,
+                "unable to convert to %(datatype)s. Error: %(error)s" % {
+                    'datatype': datatype_name, 'error': e})
+    newkwargs = {}
+    for argname, value in kwargs.items():
+        newkwargs[argname] = from_param(
+            funcdef.get_arg(argname).datatype, value
+        )
+    return newargs, newkwargs
+
+
+def args_from_params(funcdef, params):
+    kw = {}
+    hit_paths = set()
+    for argdef in funcdef.arguments:
+        value = from_params(
+            argdef.datatype, params, argdef.name, hit_paths)
+        if value is not atypes.Unset:
+            kw[argdef.name] = value
+    paths = set(params.keys())
+    unknown_paths = paths - hit_paths
+    if '__body__' in unknown_paths:
+        unknown_paths.remove('__body__')
+    if not funcdef.ignore_extra_args and unknown_paths:
+        raise exception.UnknownArgument(', '.join(unknown_paths))
+    return [], kw
+
+
+def args_from_body(funcdef, body, mimetype):
+    if funcdef.body_type is not None:
+        datatypes = {funcdef.arguments[-1].name: funcdef.body_type}
+    else:
+        datatypes = dict(((a.name, a.datatype) for a in funcdef.arguments))
+
+    if not body:
+        return (), {}
+
+    if mimetype == "application/x-www-form-urlencoded":
+        # the parameters should have been parsed in params
+        return (), {}
+    elif mimetype not in ACCEPT_CONTENT_TYPES:
+        raise exception.ClientSideError("Unknown mimetype: %s" % mimetype,
+                                        status_code=415)
+
+    try:
+        kw = parse(
+            body, datatypes, bodyarg=funcdef.body_type is not None
+        )
+    except exception.UnknownArgument:
+        if not funcdef.ignore_extra_args:
+            raise
+        kw = {}
+
+    return (), kw
+
+
+def combine_args(funcdef, akw, allow_override=False):
+    newargs, newkwargs = [], {}
+    for args, kwargs in akw:
+        for i, arg in enumerate(args):
+            n = funcdef.arguments[i].name
+            if not allow_override and n in newkwargs:
+                raise exception.ClientSideError(
+                    "Parameter %s was given several times" % n)
+            newkwargs[n] = arg
+        for name, value in kwargs.items():
+            n = str(name)
+            if not allow_override and n in newkwargs:
+                raise exception.ClientSideError(
+                    "Parameter %s was given several times" % n)
+            newkwargs[n] = value
+    return newargs, newkwargs
+
+
+def get_args(funcdef, args, kwargs, params, body, mimetype):
+    """Combine arguments from multiple sources
+
+    Combine arguments from :
+    * the host framework args and kwargs
+    * the request params
+    * the request body
+
+    Note that the host framework args and kwargs can be overridden
+    by arguments from params of body
+
+    """
+    # get the body from params if not given directly
+    if not body and '__body__' in params:
+        body = params['__body__']
+
+    # extract args from the host args and kwargs
+    from_args = args_from_args(funcdef, args, kwargs)
+
+    # extract args from the request parameters
+    from_params = args_from_params(funcdef, params)
+
+    # extract args from the request body
+    from_body = args_from_body(funcdef, body, mimetype)
+
+    # combine params and body arguments
+    from_params_and_body = combine_args(
+        funcdef,
+        (from_params, from_body)
+    )
+
+    args, kwargs = combine_args(
+        funcdef,
+        (from_args, from_params_and_body),
+        allow_override=True
+    )
+    check_arguments(funcdef, args, kwargs)
+    return args, kwargs
+
+
+def check_arguments(funcdef, args, kw):
+    """Check if some arguments are missing"""
+    assert len(args) == 0
+    for arg in funcdef.arguments:
+        if arg.mandatory and arg.name not in kw:
+            raise exception.MissingArgument(arg.name)
diff --git a/ironic/api/expose.py b/ironic/api/expose.py
index 71bfa15005..94bfb3b5a1 100644
--- a/ironic/api/expose.py
+++ b/ironic/api/expose.py
@@ -25,8 +25,8 @@ import traceback
 from oslo_config import cfg
 from oslo_log import log
 import pecan
-import wsme.rest.args
 
+from ironic.api import args as api_args
 from ironic.api import functions
 from ironic.api import types as atypes
 
@@ -70,8 +70,8 @@ def expose(*args, **kwargs):
             return_type = funcdef.return_type
 
             try:
-                args, kwargs = wsme.rest.args.get_args(
-                    funcdef, args, kwargs, pecan.request.params, None,
+                args, kwargs = api_args.get_args(
+                    funcdef, args, kwargs, pecan.request.params,
                     pecan.request.body, pecan.request.content_type
                 )
                 result = f(self, *args, **kwargs)
diff --git a/ironic/api/types.py b/ironic/api/types.py
index 0da12360b3..ae9efa55d4 100644
--- a/ironic/api/types.py
+++ b/ironic/api/types.py
@@ -22,6 +22,7 @@ from wsme.types import Enum  # noqa
 from wsme.types import File  # noqa
 from wsme.types import IntegerType  # noqa
 from wsme.types import iscomplex  # noqa
+from wsme.types import isusertype  # noqa
 from wsme.types import list_attributes  # noqa
 from wsme.types import registry  # noqa
 from wsme.types import StringType  # noqa
@@ -29,6 +30,7 @@ from wsme.types import text  # noqa
 from wsme.types import Unset  # noqa
 from wsme.types import UnsetType  # noqa
 from wsme.types import UserType  # noqa
+from wsme.types import validate_value  # noqa
 from wsme.types import wsattr  # noqa
 from wsme.types import wsproperty  # noqa
 
diff --git a/ironic/common/exception.py b/ironic/common/exception.py
index a314e75e01..7ce8ba8e7a 100644
--- a/ironic/common/exception.py
+++ b/ironic/common/exception.py
@@ -725,3 +725,75 @@ class NodeIsRetired(Invalid):
 class NoFreeIPMITerminalPorts(TemporaryFailure):
     _msg_fmt = _("Unable to allocate a free port on host %(host)s for IPMI "
                  "terminal, not enough free ports.")
+
+
+class InvalidInput(ClientSideError):
+    def __init__(self, fieldname, value, msg=''):
+        self.fieldname = fieldname
+        self.value = value
+        super(InvalidInput, self).__init__(msg)
+
+    @property
+    def faultstring(self):
+        return _(
+            "Invalid input for field/attribute %(fieldname)s. "
+            "Value: '%(value)s'. %(msg)s"
+        ) % {
+            'fieldname': self.fieldname,
+            'value': self.value,
+            'msg': self.msg
+        }
+
+
+class UnknownArgument(ClientSideError):
+    def __init__(self, argname, msg=''):
+        self.argname = argname
+        super(UnknownArgument, self).__init__(msg)
+
+    @property
+    def faultstring(self):
+        return _('Unknown argument: "%(argname)s"%(msg)s') % {
+            'argname': self.argname,
+            'msg': self.msg and ": " + self.msg or ""
+        }
+
+
+class MissingArgument(ClientSideError):
+    def __init__(self, argname, msg=''):
+        self.argname = argname
+        super(MissingArgument, self).__init__(msg)
+
+    @property
+    def faultstring(self):
+        return _('Missing argument: "%(argname)s"%(msg)s') % {
+            'argname': self.argname,
+            'msg': self.msg and ": " + self.msg or ""
+        }
+
+
+class UnknownAttribute(ClientSideError):
+    def __init__(self, fieldname, attributes, msg=''):
+        self.fieldname = fieldname
+        self.attributes = attributes
+        self.msg = msg
+        super(UnknownAttribute, self).__init__(self.msg)
+
+    @property
+    def faultstring(self):
+        error = _("Unknown attribute for argument %(argn)s: %(attrs)s")
+        if len(self.attributes) > 1:
+            error = _("Unknown attributes for argument %(argn)s: %(attrs)s")
+        str_attrs = ", ".join(self.attributes)
+        return error % {'argn': self.fieldname, 'attrs': str_attrs}
+
+    def add_fieldname(self, name):
+        """Add a fieldname to concatenate the full name.
+
+        Add a fieldname so that the whole hierarchy is displayed. Successive
+        calls to this method will prepend ``name`` to the hierarchy of names.
+        """
+        if self.fieldname is not None:
+            self.fieldname = "{}.{}".format(name, self.fieldname)
+        else:
+            self.fieldname = name
+        super(UnknownAttribute, self).__init__(self.msg)
diff --git a/ironic/common/utils.py b/ironic/common/utils.py
index 2d389af593..4141973e13 100644
--- a/ironic/common/utils.py
+++ b/ironic/common/utils.py
@@ -42,6 +42,15 @@ from ironic.conf import CONF
 
 LOG = logging.getLogger(__name__)
 
+DATE_RE = r'(?P<year>-?\d{4,})-(?P<month>\d{2})-(?P<day>\d{2})'
+TIME_RE = r'(?P<hour>\d{2}):(?P<min>\d{2}):(?P<sec>\d{2})' + \
+          r'(\.(?P<sec_frac>\d+))?'
+TZ_RE = r'((?P<tz_sign>[+-])(?P<tz_hour>\d{2}):(?P<tz_min>\d{2}))' + \
+        r'|(?P<tz_z>Z)'
+
+DATETIME_RE = re.compile(
+    '%sT%s(%s)?' % (DATE_RE, TIME_RE, TZ_RE))
+
 warn_deprecated_extra_vif_port_id = False
 
 
diff --git a/ironic/tests/unit/api/test_args.py b/ironic/tests/unit/api/test_args.py
new file mode 100644
index 0000000000..57c4f5feac
--- /dev/null
+++ b/ironic/tests/unit/api/test_args.py
@@ -0,0 +1,512 @@
+# Copyright 2020 Red Hat, Inc.
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import datetime
+import decimal
+import io
+
+from webob import multidict
+
+from ironic.api import args
+from ironic.api.controllers.v1 import types
+from ironic.api import functions
+from ironic.api import types as atypes
+from ironic.common import exception
+from ironic.tests import base as test_base
+
+
+class Obj(atypes.Base):
+
+    id = atypes.wsattr(int, mandatory=True)
+    name = str
+    readonly_field = atypes.wsattr(str, readonly=True)
+    default_field = atypes.wsattr(str, default='foo')
+    unset_me = str
+
+
+class NestedObj(atypes.Base):
+    o = Obj
+
+
+class TestArgs(test_base.TestCase):
+
+    def test_fromjson_array(self):
+        atype = atypes.ArrayType(int)
+        self.assertEqual(
+            [0, 1, 1234, None],
+            args.fromjson_array(atype, [0, '1', '1_234', None])
+        )
+        self.assertRaises(ValueError, args.fromjson_array,
+                          atype, ['one', 'two', 'three'])
+        self.assertRaises(ValueError, args.fromjson_array,
+                          atype, 'one')
+
+    def test_fromjson_dict(self):
+        dtype = atypes.DictType(str, int)
+        self.assertEqual({
+            'zero': 0,
+            'one': 1,
+            'etc': 1234,
+            'none': None
+        }, args.fromjson_dict(dtype, {
+            'zero': 0,
+            'one': '1',
+            'etc': '1_234',
+            'none': None
+        }))
+
+        self.assertRaises(ValueError, args.fromjson_dict,
+                          dtype, [])
+        self.assertRaises(ValueError, args.fromjson_dict,
+                          dtype, {'one': 'one'})
+
+    def test_fromjson_bool(self):
+        for b in (1, 2, True, 'true', 't', 'yes', 'y', 'on', '1'):
+            self.assertTrue(args.fromjson_bool(b))
+        for b in (0, False, 'false', 'f', 'no', 'n', 'off', '0'):
+            self.assertFalse(args.fromjson_bool(b))
+        for b in ('yup', 'yeet', 'NOPE', 3.14):
+            self.assertRaises(ValueError, args.fromjson_bool, b)
+
+    def test_fromjson(self):
+        # parse None
+        self.assertIsNone(args.fromjson(None, None))
+
+        # parse array
+        atype = atypes.ArrayType(int)
+        self.assertEqual(
+            [0, 1, 1234, None],
+            args.fromjson(atype, [0, '1', '1_234', None])
+        )
+
+        # parse dict
+        dtype = atypes.DictType(str, int)
+        self.assertEqual({
+            'zero': 0,
+            'one': 1,
+            'etc': 1234,
+            'none': None
+        }, args.fromjson(dtype, {
+            'zero': 0,
+            'one': '1',
+            'etc': '1_234',
+            'none': None
+        }))
+
+        # parse bytes
+        self.assertEqual(
+            b'asdf',
+            args.fromjson(bytes, b'asdf')
+        )
+        self.assertEqual(
+            b'asdf',
+            args.fromjson(bytes, 'asdf')
+        )
+        self.assertEqual(
+            b'33',
+            args.fromjson(bytes, 33)
+        )
+        self.assertEqual(
+            b'3.14',
+            args.fromjson(bytes, 3.14)
+        )
+
+        # parse str
+        self.assertEqual(
+            'asdf',
+            args.fromjson(str, b'asdf')
+        )
+        self.assertEqual(
+            'asdf',
+            args.fromjson(str, 'asdf')
+        )
+
+        # parse int/float
+        self.assertEqual(
+            3,
+            args.fromjson(int, '3')
+        )
+        self.assertEqual(
+            3,
+            args.fromjson(int, 3)
+        )
+        self.assertEqual(
+            3.14,
+            args.fromjson(float, 3.14)
+        )
+
+        # parse bool
+        self.assertFalse(args.fromjson(bool, 'no'))
+        self.assertTrue(args.fromjson(bool, 'yes'))
+
+        # parse decimal
+        self.assertEqual(
+            decimal.Decimal(3.14),
+            args.fromjson(decimal.Decimal, 3.14)
+        )
+
+        # parse datetime
+        expected = datetime.datetime(2015, 8, 13, 11, 38, 9, 496475)
+        self.assertEqual(
+            expected,
+            args.fromjson(datetime.datetime, '2015-08-13T11:38:09.496475')
+        )
+
+        # parse complex
+        n = args.fromjson(NestedObj, {'o': {
+            'id': 1234,
+            'name': 'an object'
+        }})
+        self.assertIsInstance(n.o, Obj)
+        self.assertEqual(1234, n.o.id)
+        self.assertEqual('an object', n.o.name)
+        self.assertEqual('foo', n.o.default_field)
+
+        # parse usertype
+        self.assertEqual(
+            ['0', '1', '2', 'three'],
+            args.fromjson(types.listtype, '0,1, 2, three')
+        )
+
+    def test_fromjson_complex(self):
+        n = args.fromjson_complex(NestedObj, {'o': {
+            'id': 1234,
+            'name': 'an object'
+        }})
+        self.assertIsInstance(n.o, Obj)
+        self.assertEqual(1234, n.o.id)
+        self.assertEqual('an object', n.o.name)
+        self.assertEqual('foo', n.o.default_field)
+
+        e = self.assertRaises(exception.UnknownAttribute,
+                              args.fromjson_complex,
+                              Obj, {'ooo': {}})
+        self.assertEqual({'ooo'}, e.attributes)
+
+        e = self.assertRaises(exception.InvalidInput, args.fromjson_complex,
+                              Obj,
+                              {'name': 'an object'})
+        self.assertEqual('id', e.fieldname)
+        self.assertEqual('Mandatory field missing.', e.msg)
+
+        e = self.assertRaises(exception.InvalidInput, args.fromjson_complex,
+                              Obj,
+                              {'id': 1234, 'readonly_field': 'foo'})
+        self.assertEqual('readonly_field', e.fieldname)
+        self.assertEqual('Cannot set read only field.', e.msg)
+
+    def test_parse(self):
+        # source as bytes
+        s = b'{"o": {"id": 1234, "name": "an object"}}'
+
+        # test bodyarg=True
+        n = args.parse(s, {"o": NestedObj}, True)['o']
+        self.assertEqual(1234, n.o.id)
+        self.assertEqual('an object', n.o.name)
+
+        # source as file
+        s = io.StringIO('{"o": {"id": 1234, "name": "an object"}}')
+
+        # test bodyarg=False
+        n = args.parse(s, {"o": Obj}, False)['o']
+        self.assertEqual(1234, n.id)
+        self.assertEqual('an object', n.name)
+
+        # fromjson ValueError
+        s = '{"o": ["id", "name"]}'
+        self.assertRaises(exception.InvalidInput, args.parse,
+                          s, {"o": atypes.DictType(str, str)}, False)
+        s = '["id", "name"]'
+        self.assertRaises(exception.InvalidInput, args.parse,
+                          s, {"o": atypes.DictType(str, str)}, True)
+
+        # fromjson UnknownAttribute
+        s = '{"o": {"foo": "bar", "id": 1234, "name": "an object"}}'
+        self.assertRaises(exception.UnknownAttribute, args.parse,
+                          s, {"o": NestedObj}, True)
+        self.assertRaises(exception.UnknownAttribute, args.parse,
+                          s, {"o": Obj}, False)
+
+        # invalid json
+        s = '{Sunn O)))}'
+        self.assertRaises(exception.ClientSideError, args.parse,
+                          s, {"o": Obj}, False)
+
+        # extra args
+        s = '{"foo": "bar", "o": {"id": 1234, "name": "an object"}}'
+        self.assertRaises(exception.UnknownArgument, args.parse,
+                          s, {"o": Obj}, False)
+
+    def test_from_param(self):
+        # datetime param
+        expected = datetime.datetime(2015, 8, 13, 11, 38, 9, 496475)
+        self.assertEqual(
+            expected,
+            args.from_param(datetime.datetime, '2015-08-13T11:38:09.496475')
+        )
+        self.assertIsNone(args.from_param(datetime.datetime, None))
+
+        # file param
+        self.assertEqual(
+            b'foo',
+            args.from_param(atypes.File, b'foo').content
+        )
+
+        # usertype param
+        self.assertEqual(
+            ['0', '1', '2', 'three'],
+            args.from_param(types.listtype, '0,1, 2, three')
+        )
+
+        # array param
+        atype = atypes.ArrayType(int)
+        self.assertEqual(
+            [0, 1, 1234, None],
+            args.from_param(atype, [0, '1', '1_234', None])
+        )
+        self.assertIsNone(args.from_param(atype, None))
+
+        # string param
+        self.assertEqual('foo', args.from_param(str, 'foo'))
+        self.assertIsNone(args.from_param(str, None))
+
+        # string param with from_params
+        hit_paths = set()
+        params = multidict.MultiDict(
+            foo='bar',
+        )
+        self.assertEqual(
+            'bar',
+            args.from_params(str, params, 'foo', hit_paths)
+        )
+        self.assertEqual({'foo'}, hit_paths)
+
+    def test_array_from_params(self):
+        hit_paths = set()
+        datatype = atypes.ArrayType(str)
+        params = multidict.MultiDict(
+            foo='bar',
+            one='two'
+        )
+        self.assertEqual(
+            ['bar'],
+            args.from_params(datatype, params, 'foo', hit_paths)
+        )
+        self.assertEqual({'foo'}, hit_paths)
+        self.assertEqual(
+            ['two'],
+            args.array_from_params(datatype, params, 'one', hit_paths)
+        )
+        self.assertEqual({'foo', 'one'}, hit_paths)
+
+    def test_usertype_from_params(self):
+        hit_paths = set()
+        datatype = types.listtype
+        params = multidict.MultiDict(
+            foo='0,1, 2, three',
+        )
+        self.assertEqual(
+            ['0', '1', '2', 'three'],
+            args.usertype_from_params(datatype, params, 'foo', hit_paths)
+        )
+        self.assertEqual(
+            ['0', '1', '2', 'three'],
+            args.from_params(datatype, params, 'foo', hit_paths)
+        )
+        self.assertEqual(
+            atypes.Unset,
+            args.usertype_from_params(datatype, params, 'bar', hit_paths)
+        )
+
+    def test_args_from_args(self):
+
+        fromargs = ['one', 2, [0, '1', '2_34']]
+        fromkwargs = {'foo': '1, 2, 3'}
+
+        @functions.signature(str, str, int, atypes.ArrayType(int),
+                             types.listtype)
+        def myfunc(self, first, second, third, foo):
+            pass
+        funcdef = functions.FunctionDefinition.get(myfunc)
+
+        newargs, newkwargs = args.args_from_args(funcdef, fromargs, fromkwargs)
+        self.assertEqual(['one', 2, [0, 1, 234]], newargs)
+        self.assertEqual({'foo': ['1', '2', '3']}, newkwargs)
+
+    def test_args_from_params(self):
+
+        @functions.signature(str, str, int, atypes.ArrayType(int),
+                             types.listtype)
+        def myfunc(self, first, second, third, foo):
+            pass
+        funcdef = functions.FunctionDefinition.get(myfunc)
+        params = multidict.MultiDict(
+            foo='0,1, 2, three',
+            third='1',
+            second='2'
+        )
+        self.assertEqual(
+            ([], {'foo': ['0', '1', '2', 'three'], 'second': 2, 'third': [1]}),
+            args.args_from_params(funcdef, params)
+        )
+
+        # unexpected param
+        params = multidict.MultiDict(bar='baz')
+        self.assertRaises(exception.UnknownArgument, args.args_from_params,
+                          funcdef, params)
+
+        # no params plus a body
+        params = multidict.MultiDict(__body__='')
+        self.assertEqual(
+            ([], {}),
+            args.args_from_params(funcdef, params)
+        )
+
+    def test_args_from_body(self):
+        @functions.signature(str, body=NestedObj)
+        def myfunc(self, nested):
+            pass
+        funcdef = functions.FunctionDefinition.get(myfunc)
+        mimetype = 'application/json'
+        body = b'{"o": {"id": 1234, "name": "an object"}}'
+        newargs, newkwargs = args.args_from_body(funcdef, body, mimetype)
+
+        self.assertEqual(1234, newkwargs['nested'].o.id)
+        self.assertEqual('an object', newkwargs['nested'].o.name)
+
+        self.assertEqual(
+            ((), {}),
+            args.args_from_body(funcdef, None, mimetype)
+        )
+
+        self.assertRaises(exception.ClientSideError, args.args_from_body,
+                          funcdef, body, 'application/x-corba')
+
+        self.assertEqual(
+            ((), {}),
+            args.args_from_body(funcdef, body,
+                                'application/x-www-form-urlencoded')
+        )
+
+    def test_combine_args(self):
+
+        @functions.signature(str, str, int)
+        def myfunc(self, first, second,):
+            pass
+        funcdef = functions.FunctionDefinition.get(myfunc)
+
+        # empty
+        self.assertEqual(
+            ([], {}),
+            args.combine_args(
+                funcdef, (
+                    ([], {}),
+                    ([], {}),
+                )
+            )
+        )
+
+        # combine kwargs
+        self.assertEqual(
+            ([], {'first': 'one', 'second': 'two'}),
+            args.combine_args(
+                funcdef, (
+                    ([], {}),
+                    ([], {'first': 'one', 'second': 'two'}),
+                )
+            )
+        )
+
+        # combine mixed args
+        self.assertEqual(
+            ([], {'first': 'one', 'second': 'two'}),
+            args.combine_args(
+                funcdef, (
+                    (['one'], {}),
+                    ([], {'second': 'two'}),
+                )
+            )
+        )
+
+        # override kwargs
+        self.assertEqual(
+            ([], {'first': 'two'}),
+            args.combine_args(
+                funcdef, (
+                    ([], {'first': 'one'}),
+                    ([], {'first': 'two'}),
+                ),
+                allow_override=True
+            )
+        )
+
+        # override args
+        self.assertEqual(
+            ([], {'first': 'two', 'second': 'three'}),
+            args.combine_args(
+                funcdef, (
+                    (['one', 'three'], {}),
+                    (['two'], {}),
+                ),
+                allow_override=True
+            )
+        )
+
+        # can't override args
+        self.assertRaises(exception.ClientSideError, args.combine_args,
+                          funcdef,
+                          ((['one'], {}), (['two'], {})))
+
+        # can't override kwargs
+        self.assertRaises(exception.ClientSideError, args.combine_args,
+                          funcdef,
+                          (([], {'first': 'one'}), ([], {'first': 'two'})))
+
+    def test_get_args(self):
+        @functions.signature(str, str, int, atypes.ArrayType(int),
+                             types.listtype, body=NestedObj)
+        def myfunc(self, first, second, third, foo, nested):
+            pass
+        funcdef = functions.FunctionDefinition.get(myfunc)
+        params = multidict.MultiDict(
+            foo='0,1, 2, three',
+            second='2'
+        )
+        mimetype = 'application/json'
+        body = b'{"o": {"id": 1234, "name": "an object"}}'
+        fromargs = ['one']
+        fromkwargs = {'third': '1'}
+
+        newargs, newkwargs = args.get_args(funcdef, fromargs, fromkwargs,
+                                           params, body, mimetype)
+        self.assertEqual([], newargs)
+        n = newkwargs.pop('nested')
+        self.assertEqual({
+            'first': 'one',
+            'foo': ['0', '1', '2', 'three'],
+            'second': 2,
+            'third': [1]},
+            newkwargs
+        )
+        self.assertEqual(1234, n.o.id)
+        self.assertEqual('an object', n.o.name)
+
+        # check_arguments missing mandatory argument 'second'
+        params = multidict.MultiDict(
+            foo='0,1, 2, three',
+        )
+        self.assertRaises(exception.MissingArgument, args.get_args,
+                          funcdef, fromargs, fromkwargs,
+                          params, body, mimetype)