Generic PATCH handler class.

A class-based approach is easier to extend than the function-based approach
used in the nodes. That one is still there, though -- might look at it
at a later time. This handler is primarily for Flamenco.

pillar/api/patch_handler.py

@@ -0,0 +1,90 @@
+"""Handler for PATCH requests.
+
+This supports PATCH request in the sense described by William Durand:
+http://williamdurand.fr/2014/02/14/please-do-not-patch-like-an-idiot/
+
+Each PATCH should be a JSON dict with at least a key 'op' with the
+name of the operation to perform.
+"""
+
+import logging
+
+import flask
+
+from pillar.api.utils import authorization
+
+log = logging.getLogger(__name__)
+
+
+class AbstractPatchHandler:
+    """Abstract PATCH handler supporting multiple operations.
+
+    Each operation, i.e. possible value of the 'op' key in the PATCH body,
+    should be matched to a similarly named "patch_xxx" function in a subclass.
+    For example, the operation "set-owner" is mapped to "patch_set_owner".
+
+    :cvar route: the Flask/Werkzeug route to attach this handler to.
+        For most handlers, the default will be fine.
+    :cvar item_name: the name of the things to patch, like "job", "task" etc.
+        Only used for logging.
+    """
+
+    route: str = '/<object_id>'
+    item_name: str = None
+
+    def __init_subclass__(cls, **kwargs):
+        if not cls.route:
+            raise ValueError('Subclass must set route')
+        if not cls.item_name:
+            raise ValueError('Subclass must set item_name')
+
+    def __init__(self, blueprint: flask.Blueprint):
+        self.log: logging.Logger = log.getChild(self.__class__.__name__)
+        self.patch_handlers = {
+            name[6:].replace('_', '-'): getattr(self, name)
+            for name in dir(self)
+            if name.startswith('patch_') and callable(getattr(self, name))
+        }
+
+        if self.log.isEnabledFor(logging.INFO):
+            self.log.info('Creating PATCH handler %s%s for operations: %s',
+                          blueprint.name, self.route,
+                          sorted(self.patch_handlers.keys()))
+
+        blueprint.add_url_rule(self.route,
+                               self.patch.__name__,
+                               self.patch,
+                               methods=['PATCH'])
+
+    @authorization.require_login()
+    def patch(self, object_id: str):
+        from flask import request
+        import werkzeug.exceptions as wz_exceptions
+        from pillar.api.utils import str2id, authentication
+
+        # Parse the request
+        real_object_id = str2id(object_id)
+        patch = request.get_json()
+        if not patch:
+            raise wz_exceptions.BadRequest('Patch must contain JSON')
+
+        try:
+            patch_op = patch['op']
+        except KeyError:
+            raise wz_exceptions.BadRequest("PATCH should contain 'op' key to denote operation.")
+
+        log.debug('User %s wants to PATCH "%s" %s %s',
+                  authentication.current_user_id(), patch_op, self.item_name, real_object_id)
+
+        # Find the PATCH handler for the operation.
+        try:
+            handler = self.patch_handlers[patch_op]
+        except KeyError:
+            log.warning('No %s PATCH handler for operation %r', self.item_name, patch_op)
+            raise wz_exceptions.BadRequest('Operation %r not supported' % patch_op)
+
+        # Let the PATCH handler do its thing.
+        response = handler(real_object_id, patch)
+        if response is None:
+            return '', 204
+        return response