Helper function that supports XPath style selectors to traverse an object tree e.g.

inst = {'fixed_ip': {'floating_ips': [{'address': '1.2.3.4'}], 'address': '192.168.0.3'}, 'hostname': ''}

private_ips = get_from_path(inst, 'fixed_ip/address')
public_ips = get_from_path(inst, 'fixed_ip/floating_ips/address')

Avoids messy [.get() / if / for]* nested code

3 files changed, 229 insertions, 11 deletions

diff --git a/nova/api/openstack/servers.py b/nova/api/openstack/servers.py
index 53eb9fcf1..63e047b39 100644
--- a/nova/api/openstack/servers.py
+++ b/nova/api/openstack/servers.py
@@ -63,19 +63,12 @@ def _translate_detail_keys(inst):
     inst_dict['addresses'] = dict(public=[], private=[])
 
     # grab single private fixed ip
-    try:
-        private_ip = inst['fixed_ip']['address']
-        if private_ip:
-            inst_dict['addresses']['private'].append(private_ip)
-    except KeyError:
-        LOG.debug(_("Failed to read private ip"))
+    private_ips = utils.get_from_path(inst, 'fixed_ip/address')
+    inst_dict['addresses']['private'] = private_ips
 
     # grab all public floating ips
-    try:
-        for floating in inst['fixed_ip']['floating_ips']:
-            inst_dict['addresses']['public'].append(floating['address'])
-    except KeyError:
-        LOG.debug(_("Failed to read public ip(s)"))
+    public_ips = utils.get_from_path(inst, 'fixed_ip/floating_ips/address')
+    inst_dict['addresses']['public'] = public_ips
 
     inst_dict['hostId'] = ''
 
diff --git a/nova/tests/test_utils.py b/nova/tests/test_utils.py
new file mode 100644
index 000000000..34a407f1a
--- /dev/null
+++ b/nova/tests/test_utils.py
@@ -0,0 +1,174 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+#    Copyright 2011 Justin Santa Barbara
+#
+#    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.
+
+from nova import test
+from nova import utils
+from nova import exception
+
+
+class GetFromPathTestCase(test.TestCase):
+    def test_tolerates_nones(self):
+        f = utils.get_from_path
+
+        input = []
+        self.assertEquals([], f(input, "a"))
+        self.assertEquals([], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+        input = [None]
+        self.assertEquals([], f(input, "a"))
+        self.assertEquals([], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+        input = [{'a': None}]
+        self.assertEquals([], f(input, "a"))
+        self.assertEquals([], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+        input = [{'a': {'b': None}}]
+        self.assertEquals([{'b': None}], f(input, "a"))
+        self.assertEquals([], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+        input = [{'a': {'b': {'c': None}}}]
+        self.assertEquals([{'b': {'c': None}}], f(input, "a"))
+        self.assertEquals([{'c': None}], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+        input = [{'a': {'b': {'c': None}}}, {'a': None}]
+        self.assertEquals([{'b': {'c': None}}], f(input, "a"))
+        self.assertEquals([{'c': None}], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+        input = [{'a': {'b': {'c': None}}}, {'a': {'b': None}}]
+        self.assertEquals([{'b': {'c': None}}, {'b': None}], f(input, "a"))
+        self.assertEquals([{'c': None}], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+    def test_does_select(self):
+        f = utils.get_from_path
+
+        input = [{'a': 'a_1'}]
+        self.assertEquals(['a_1'], f(input, "a"))
+        self.assertEquals([], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+        input = [{'a': {'b': 'b_1'}}]
+        self.assertEquals([{'b': 'b_1'}], f(input, "a"))
+        self.assertEquals(['b_1'], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+        input = [{'a': {'b': {'c': 'c_1'}}}]
+        self.assertEquals([{'b': {'c': 'c_1'}}], f(input, "a"))
+        self.assertEquals([{'c': 'c_1'}], f(input, "a/b"))
+        self.assertEquals(['c_1'], f(input, "a/b/c"))
+
+        input = [{'a': {'b': {'c': 'c_1'}}}, {'a': None}]
+        self.assertEquals([{'b': {'c': 'c_1'}}], f(input, "a"))
+        self.assertEquals([{'c': 'c_1'}], f(input, "a/b"))
+        self.assertEquals(['c_1'], f(input, "a/b/c"))
+
+        input = [{'a': {'b': {'c': 'c_1'}}},
+                 {'a': {'b': None}}]
+        self.assertEquals([{'b': {'c': 'c_1'}}, {'b': None}], f(input, "a"))
+        self.assertEquals([{'c': 'c_1'}], f(input, "a/b"))
+        self.assertEquals(['c_1'], f(input, "a/b/c"))
+
+        input = [{'a': {'b': {'c': 'c_1'}}},
+                 {'a': {'b': {'c': 'c_2'}}}]
+        self.assertEquals([{'b': {'c': 'c_1'}}, {'b': {'c': 'c_2'}}],
+                          f(input, "a"))
+        self.assertEquals([{'c': 'c_1'}, {'c': 'c_2'}], f(input, "a/b"))
+        self.assertEquals(['c_1', 'c_2'], f(input, "a/b/c"))
+
+        self.assertEquals([], f(input, "a/b/c/d"))
+        self.assertEquals([], f(input, "c/a/b/d"))
+        self.assertEquals([], f(input, "i/r/t"))
+
+    def test_flattens_lists(self):
+        f = utils.get_from_path
+
+        input = [{'a': [1, 2, 3]}]
+        self.assertEquals([1, 2, 3], f(input, "a"))
+        self.assertEquals([], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+        input = [{'a': {'b': [1, 2, 3]}}]
+        self.assertEquals([{'b': [1, 2, 3]}], f(input, "a"))
+        self.assertEquals([1, 2, 3], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+        input = [{'a': {'b': [1, 2, 3]}}, {'a': {'b': [4, 5, 6]}}]
+        self.assertEquals([1, 2, 3, 4, 5, 6], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+        input = [{'a': [{'b': [1, 2, 3]}, {'b': [4, 5, 6]}]}]
+        self.assertEquals([1, 2, 3, 4, 5, 6], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+        input = [{'a': [1, 2, {'b': 'b_1'}]}]
+        self.assertEquals([1, 2, {'b': 'b_1'}], f(input, "a"))
+        self.assertEquals(['b_1'], f(input, "a/b"))
+
+    def test_bad_xpath(self):
+        f = utils.get_from_path
+
+        self.assertRaises(exception.Error, f, [], None)
+        self.assertRaises(exception.Error, f, [], "")
+        self.assertRaises(exception.Error, f, [], "/")
+        self.assertRaises(exception.Error, f, [], "/a")
+        self.assertRaises(exception.Error, f, [], "/a/")
+        self.assertRaises(exception.Error, f, [], "//")
+        self.assertRaises(exception.Error, f, [], "//a")
+        self.assertRaises(exception.Error, f, [], "a//a")
+        self.assertRaises(exception.Error, f, [], "a//a/")
+        self.assertRaises(exception.Error, f, [], "a/a/")
+
+    def test_real_failure1(self):
+        # Real world failure case...
+        #  We weren't coping when the input was a Dictionary instead of a List
+        # This led to test_accepts_dictionaries
+        f = utils.get_from_path
+
+        inst = {'fixed_ip': {'floating_ips': [{'address': '1.2.3.4'}],
+                             'address': '192.168.0.3'},
+                'hostname': ''}
+
+        private_ips = f(inst, 'fixed_ip/address')
+        public_ips = f(inst, 'fixed_ip/floating_ips/address')
+        self.assertEquals(['192.168.0.3'], private_ips)
+        self.assertEquals(['1.2.3.4'], public_ips)
+
+    def test_accepts_dictionaries(self):
+        f = utils.get_from_path
+
+        input = {'a': [1, 2, 3]}
+        self.assertEquals([1, 2, 3], f(input, "a"))
+        self.assertEquals([], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+        input = {'a': {'b': [1, 2, 3]}}
+        self.assertEquals([{'b': [1, 2, 3]}], f(input, "a"))
+        self.assertEquals([1, 2, 3], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+        input = {'a': [{'b': [1, 2, 3]}, {'b': [4, 5, 6]}]}
+        self.assertEquals([1, 2, 3, 4, 5, 6], f(input, "a/b"))
+        self.assertEquals([], f(input, "a/b/c"))
+
+        input = {'a': [1, 2, {'b': 'b_1'}]}
+        self.assertEquals([1, 2, {'b': 'b_1'}], f(input, "a"))
+        self.assertEquals(['b_1'], f(input, "a/b"))
diff --git a/nova/utils.py b/nova/utils.py
index 2a3acf042..0cf91e0cc 100644
--- a/nova/utils.py
+++ b/nova/utils.py
@@ -2,6 +2,7 @@
 
 # Copyright 2010 United States Government as represented by the
 # Administrator of the National Aeronautics and Space Administration.
+# Copyright 2011 Justin Santa Barbara
 # All Rights Reserved.
 #
 #    Licensed under the Apache License, Version 2.0 (the "License"); you may
@@ -31,6 +32,7 @@ import string
 import struct
 import sys
 import time
+import types
 from xml.sax import saxutils
 import re
 import netaddr
@@ -499,3 +501,52 @@ def ensure_b64_encoding(val):
         return val
     except TypeError:
         return base64.b64encode(val)
+
+
+def get_from_path(items, path):
+    """ Returns a list of items matching the specified path.  Takes an
+    XPath-like expression e.g. prop1/prop2/prop3, and for each item in items,
+    looks up items[prop1][prop2][prop3].  Like XPath, if any of the
+    intermediate results are lists it will treat each list item individually.
+    A 'None' in items or any child expressions will be ignored, this function
+    will not throw because of None (anywhere) in items.  The returned list
+    will contain no None values."""
+
+    if path is None:
+        raise exception.Error("Invalid mini_xpath")
+
+    (first_token, sep, remainder) = path.partition("/")
+
+    if first_token == "":
+        raise exception.Error("Invalid mini_xpath")
+
+    results = []
+
+    if items is None:
+        return results
+
+    if not isinstance(items, types.ListType):
+        # Wrap single objects in a list
+        items = [items]
+
+    for item in items:
+        if item is None:
+            continue
+        get_method = getattr(item, "get", None)
+        if get_method is None:
+            continue
+        child = get_method(first_token)
+        if child is None:
+            continue
+        if isinstance(child, types.ListType):
+            # Flatten intermediate lists
+            for x in child:
+                results.append(x)
+        else:
+            results.append(child)
+
+    if not sep:
+        # No more tokens
+        return results
+    else:
+        return get_from_path(results, remainder)