Add support metadata in policy.json

* if there is a policy.json in the course dir, read it
* file format is a dict with keys {category}/{url_name}, and values metadata dictionaries
* apply the policy, overwriting keys that are in the xml
* then do metadata inheritance, inheriting any overwritten keys.

* also a management cmd to generate a policy.json from a course dir.

common/lib/xmodule/xmodule/modulestore/xml.py

+import json
 import logging
 import os
 import re
@@ -149,7 +150,7 @@ class XMLModuleStore(ModuleStoreBase):
         for course_dir in course_dirs:
             self.try_load_course(course_dir)
 
-    def try_load_course(self,course_dir):
+    def try_load_course(self, course_dir):
         '''
         Load a course, keeping track of errors as we go along.
         '''
@@ -170,7 +171,27 @@ class XMLModuleStore(ModuleStoreBase):
         '''
         String representation - for debugging
         '''
-        return '<XMLModuleStore>data_dir=%s, %d courses, %d modules' % (self.data_dir,len(self.courses),len(self.modules))
+        return '<XMLModuleStore>data_dir=%s, %d courses, %d modules' % (
+            self.data_dir, len(self.courses), len(self.modules))
+
+    def load_policy(self, policy_path, tracker):
+        """
+        Attempt to read a course policy from policy_path.  If the file
+        exists, but is invalid, log an error and return {}.
+
+        If the policy loads correctly, returns the deserialized version.
+        """
+        if not os.path.exists(policy_path):
+            return {}
+        try:
+            with open(policy_path) as f:
+                return json.load(f)
+        except (IOError, ValueError) as err:
+            msg = "Error loading course policy from {}".format(policy_path)
+            tracker(msg)
+            log.warning(msg + " " + str(err))
+        return {}
+
 
     def load_course(self, course_dir, tracker):
         """
@@ -214,6 +235,11 @@ class XMLModuleStore(ModuleStoreBase):
             system = ImportSystem(self, org, course, course_dir, tracker)
 
             course_descriptor = system.process_xml(etree.tostring(course_data))
+            policy_path = self.data_dir / course_dir / 'policy.json'
+
+            policy = self.load_policy(policy_path, tracker)
+            XModuleDescriptor.apply_policy(course_descriptor, policy)
+
             # NOTE: The descriptors end up loading somewhat bottom up, which
             # breaks metadata inheritance via get_children().  Instead
             # (actually, in addition to, for now), we do a final inheritance pass

common/lib/xmodule/xmodule/x_module.py

@@ -298,6 +298,14 @@ class XModule(HTMLSnippet):
         return ""
 
 
+def policy_key(location):
+    """
+    Get the key for a location in a policy file.  (Since the policy file is
+    specific to a course, it doesn't need the full location url).
+    """
+    return '{cat}/{name}'.format(cat=location.category, name=location.name)
+
+
 class XModuleDescriptor(Plugin, HTMLSnippet):
     """
     An XModuleDescriptor is a specification for an element of a course. This
@@ -416,6 +424,24 @@ class XModuleDescriptor(Plugin, HTMLSnippet):
         return dict((k,v) for k,v in self.metadata.items()
                     if k not in self._inherited_metadata)
 
+
+    @staticmethod
+    def apply_policy(node, policy):
+        """
+        Given a descriptor, traverse all its descendants and update its metadata
+        with the policy.
+
+        Notes:
+          - this does not propagate inherited metadata.  The caller should
+            call compute_inherited_metadata after applying the policy.
+          - metadata specified in the policy overrides metadata in the xml
+        """
+        k = policy_key(node.location)
+        if k in policy:
+            node.metadata.update(policy[k])
+        for c in node.get_children():
+            XModuleDescriptor.apply_policy(c, policy)
+
     @staticmethod
     def compute_inherited_metadata(node):
         """Given a descriptor, traverse all of its descendants and do metadata

lms/djangoapps/courseware/management/commands/metadata_to_json.py

+"""
+A script to walk a course xml tree, generate a dictionary of all the metadata,
+and print it out as a json dict.
+"""
+import os
+import sys
+import json
+
+from collections import OrderedDict
+from path import path
+
+from django.core.management.base import BaseCommand
+
+from xmodule.modulestore.xml import XMLModuleStore
+from xmodule.x_module import policy_key
+
+def import_course(course_dir, verbose=True):
+    course_dir = path(course_dir)
+    data_dir = course_dir.dirname()
+    course_dirs = [course_dir.basename()]
+
+    # No default class--want to complain if it doesn't find plugins for any
+    # module.
+    modulestore = XMLModuleStore(data_dir,
+                   default_class=None,
+                   eager=True,
+                   course_dirs=course_dirs)
+
+    def str_of_err(tpl):
+        (msg, exc_str) = tpl
+        return '{msg}\n{exc}'.format(msg=msg, exc=exc_str)
+
+    courses = modulestore.get_courses()
+
+    n = len(courses)
+    if n != 1:
+        sys.stderr.write('ERROR: Expect exactly 1 course.  Loaded {n}: {lst}\n'.format(
+            n=n, lst=courses))
+        return None
+
+    course = courses[0]
+    errors = modulestore.get_item_errors(course.location)
+    if len(errors) != 0:
+        sys.stderr.write('ERRORs during import: {}\n'.format('\n'.join(map(str_of_err, errors))))
+
+    return course
+
+def node_metadata(node):
+    # make a copy
+    to_export = ('format', 'display_name',
+                 'graceperiod', 'showanswer', 'rerandomize',
+                 'start', 'due', 'graded', 'hide_from_toc',
+                 'ispublic', 'xqa_key')
+
+    orig = node.own_metadata
+    d = {k: orig[k] for k in to_export if k in orig}
+    return d
+
+def get_metadata(course):
+    d = OrderedDict({})
+    queue = [course]
+    while len(queue) > 0:
+        node = queue.pop()
+        d[policy_key(node.location)] = node_metadata(node)
+        # want to print first children first, so put them at the end
+        # (we're popping from the end)
+        queue.extend(reversed(node.get_children()))
+    return d
+
+
+def print_metadata(course_dir, output):
+    course = import_course(course_dir)
+    if course:
+        meta = get_metadata(course)
+        result = json.dumps(meta, indent=4)
+        if output:
+            with file(output, 'w') as f:
+                f.write(result)
+        else:
+            print result
+
+
+class Command(BaseCommand):
+    help = """Imports specified course.xml and prints its
+metadata as a json dict.
+
+Usage: metadata_to_json PATH-TO-COURSE-DIR OUTPUT-PATH
+
+if OUTPUT-PATH isn't given, print to stdout.
+"""
+    def handle(self, *args, **options):
+        n = len(args)
+        if n < 1 or n > 2:
+            print Command.help
+            return
+
+        output_path = args[1] if n > 1 else None
+        print_metadata(args[0], output_path)