Exception handling when file-not-found

Added rudimentary exception handling for when yaml_fs encounters
a node/class for which no file exists.

Unfortunately, there is no way to properly communicate that to Ansible
when it invokes the adapter. Oh well.

Signed-off-by: martin f. krafft <madduck@madduck.net>
diff --git a/adapters/ansible b/adapters/ansible
index bb35e3f..2e485ec 100755
--- a/adapters/ansible
+++ b/adapters/ansible
@@ -8,12 +8,12 @@
 #
 import os, sys, posix, stat
 
-def usage_error(msg):
+def exit_error(msg, rc):
     print >>sys.stderr, msg
-    sys.exit(posix.EX_USAGE)
+    sys.exit(rc)
 
 if len(sys.argv) == 1:
-    usage_error('Need to specify --list or --host.')
+    exit_error('Need to specify --list or --host.', posix.EX_USAGE)
 
 ansible_dir = os.path.dirname(sys.argv[0])
 
@@ -22,7 +22,7 @@
 # symlinks are resolved.
 realpath = os.path.realpath(sys.argv[0] + '/../../')
 sys.path.insert(0, realpath)
-import reclass, config
+import reclass, config, errors
 
 # The adapter resides in the Ansible directory, so let's look there for an
 # optional configuration file called reclass-config.yml.
@@ -40,7 +40,7 @@
     if stat.S_ISDIR(os.stat(nodes_uri).st_mode):
         options['nodes_uri'] = nodes_uri
     else:
-        usage_error('nodes_uri not specified')
+        exit_error('nodes_uri not specified', posix.EX_USAGE)
 
 if 'classes_uri' not in options:
     classes_uri = os.path.join(ansible_dir, 'classes')
@@ -53,29 +53,35 @@
 # False instead, we print the inventory. Yeah for option abuse!
 if sys.argv[1] == '--list':
     if len(sys.argv) > 2:
-        usage_error('Unknown arguments: ' + ' '.join(sys.argv[2:]))
+        exit_error('Unknown arguments: ' + ' '.join(sys.argv[2:]),
+                    posix.EX_USAGE)
     options['node'] = False
 
 elif sys.argv[1] == '--host':
     if len(sys.argv) < 3:
-        usage_error('Missing hostname.')
+        exit_error('Missing hostname.', posix.EX_USAGE)
     elif len(sys.argv) > 3:
-        usage_error('Unknown arguments: ' + ' '.join(sys.argv[3:]))
+        exit_error('Unknown arguments: ' + ' '.join(sys.argv[3:]),
+                    posix.EX_USAGE)
     options['node'] = sys.argv[2]
 
 else:
-    usage_error('Unknown mode (--list or --host required).')
+    exit_error('Unknown mode (--list or --host required).', posix.EX_USAGE)
 
-data = reclass.get_data(options['storage_type'], options['nodes_uri'],
-                        options['classes_uri'], options['node'])
+try:
+    data = reclass.get_data(options['storage_type'], options['nodes_uri'],
+                            options['classes_uri'], options['node'])
 
-if options['node']:
-    # Massage and shift the data like Ansible wants it
-    data['parameters']['RECLASS'] = data['RECLASS']
-    for i in ('classes', 'applications'):
-        data['parameters']['RECLASS'][i] = data[i]
-    data = data['parameters']
+    if options['node']:
+        # Massage and shift the data like Ansible wants it
+        data['parameters']['RECLASS'] = data['RECLASS']
+        for i in ('classes', 'applications'):
+            data['parameters']['RECLASS'][i] = data[i]
+        data = data['parameters']
 
-print reclass.output(data, options['output'], options['pretty_print'])
+    print reclass.output(data, options['output'], options['pretty_print'])
 
-sys.exit(posix.EX_OK)
+    sys.exit(posix.EX_OK)
+
+except errors.ReclassException, e:
+    exit_error(e.message, e.rc)
diff --git a/errors.py b/errors.py
new file mode 100644
index 0000000..dfb07b3
--- /dev/null
+++ b/errors.py
@@ -0,0 +1,53 @@
+#
+# -*- coding: utf-8 -*-
+#
+# This file is part of reclass (http://github.com/madduck/reclass)
+#
+# Copyright © 2007–13 martin f. krafft <madduck@madduck.net>
+# Released under the terms of the Artistic Licence 2.0
+#
+
+import posix
+
+class ReclassException(Exception):
+
+    def __init__(self, rc=posix.EX_SOFTWARE, *args):
+        super(ReclassException, self).__init__(*args)
+        self._rc = rc
+
+    def __str__(self):
+        return "reclass encountered an exception, sorry!"
+
+    message = property(lambda self: self.__str__())
+    rc = property(lambda self: self._rc)
+
+
+class NotFoundError(ReclassException):
+
+    def __init__(self, rc=posix.EX_IOERR):
+        super(NotFoundError, self).__init__(rc)
+
+
+class NodeNotFound(NotFoundError):
+
+    def __init__(self, storage, classname, uri):
+        super(NodeNotFound, self).__init__()
+        self._storage = storage
+        self._name = classname
+        self._uri = uri
+
+    def __str__(self):
+        return "Node '{0}' not found under {1}://{2}".format(self._name,
+                                                             self._storage,
+                                                             self._uri)
+
+
+class ClassNotFound(NodeNotFound):
+
+    def __init__(self, storage, classname, uri, nodename):
+        super(ClassNotFound, self).__init__(storage, classname, uri)
+        self._nodename = nodename
+
+    def __str__(self):
+        return "Class '{0}' (in ancestry of node {1}) not found under {2}://{3}" \
+                .format(self._name, self._nodename, self._storage, self._uri)
diff --git a/reclass.py b/reclass.py
index f0c24ce..cd44652 100755
--- a/reclass.py
+++ b/reclass.py
@@ -17,6 +17,7 @@
 import config
 from output import OutputLoader
 from storage import StorageBackendLoader
+import errors
 
 def get_options(config_file=None):
     return config.get_options(__name__, __version__, __description__, config_file)
@@ -38,6 +39,10 @@
     outputter = output_class()
     return outputter.dump(data, pretty_print=pretty_print)
 
+def _error(msg, rc):
+    print >>sys.stderr, msg
+    sys.exit(rc)
+
 if __name__ == '__main__':
     __name__ = __prog__
     config_file = None
@@ -46,8 +51,12 @@
         if os.access(f, os.R_OK):
             config_file = f
             break
-    options = get_options(config_file)
-    data = get_data(options.storage_type, options.nodes_uri,
-                    options.classes_uri, options.node)
-    print output(data, options.output, options.pretty_print)
-    sys.exit(posix.EX_OK)
+    try:
+        options = get_options(config_file)
+        data = get_data(options.storage_type, options.nodes_uri,
+                        options.classes_uri, options.node)
+        print output(data, options.output, options.pretty_print)
+        sys.exit(posix.EX_OK)
+
+    except errors.ReclassException, e:
+        _error(e.message, e.rc)
diff --git a/storage/yaml_fs/__init__.py b/storage/yaml_fs/__init__.py
index 0eff9ed..f53048f 100644
--- a/storage/yaml_fs/__init__.py
+++ b/storage/yaml_fs/__init__.py
@@ -10,6 +10,7 @@
 from storage import NodeStorageBase
 from yamlfile import YamlFile
 from directory import Directory
+import errors
 
 FILE_EXTENSION = '.yml'
 
@@ -18,16 +19,23 @@
     def __init__(self, nodes_uri, classes_uri):
         super(ExternalNodeStorage, self).__init__(nodes_uri, classes_uri)
 
-    def _read_nodeinfo(self, name, base_uri, seen):
+    def _read_nodeinfo(self, name, base_uri, seen, nodename=None):
         path = os.path.join(base_uri, name + FILE_EXTENSION)
-        entity = YamlFile(path).entity
-        seen[name] = True
-        for klass in entity.classes:
-            if klass not in seen:
-                ret = self._read_nodeinfo(klass, self.classes_uri, seen)[0]
-                ret.merge(entity)
-                entity = ret
-        return entity, path
+        try:
+            entity = YamlFile(path).entity
+            seen[name] = True
+            for klass in entity.classes:
+                if klass not in seen:
+                    ret = self._read_nodeinfo(klass, self.classes_uri, seen,
+                                              name if nodename is None else nodename)[0]
+                    ret.merge(entity)
+                    entity = ret
+            return entity, path
+        except IOError:
+            if base_uri == self.classes_uri:
+                raise errors.ClassNotFound('yaml_fs', name, base_uri, nodename)
+            else:
+                raise errors.NodeNotFound('yaml_fs', name, base_uri)
 
     def _list_inventory(self):
         d = Directory(self.nodes_uri)