_OBS_Precheck and OBS_MetadataValidator

New functions to perform a precheck for the user data and metadata
parameters that are going to be used to execute a OBS_GetData operation.

Doing this before the OBD_GetData we are able to check if we're going to
have problems with the current request. Is useful because right now
we're using the *_Exception_Safe functions which return NULL in case we
have an exception, this leads to execute the whole request even if we
know beforehand that it's going to fail.

server/extension/sql/110_data_observatory_augmentation.sql

@@ -737,3 +737,49 @@ RETURNS JSON AS $$
         logger.error('Error trying to OBS_GetMeta', sys.exc_info(), data={"username": username, "orgname": orgname})
         raise Exception('Error trying to OBS_GetMeta')
 $$ LANGUAGE plpythonu;
+
+CREATE OR REPLACE FUNCTION cdb_dataservices_server._OBS_MetadataValidation(
+  username TEXT,
+  orgname TEXT,
+  geometry_extent Geometry(Geometry, 4326),
+  geometry_type text,
+  params JSON,
+  target_geoms INTEGER DEFAULT NULL)
+RETURNS TABLE(valid boolean, errors text[]) AS $$
+  CONNECT cdb_dataservices_server._obs_server_conn_str(username, orgname);
+  SELECT * FROM cdb_observatory.OBS_MetadataValidation(geometry_extent, geometry_type, params, target_geoms);
+$$ LANGUAGE plproxy;
+
+CREATE OR REPLACE FUNCTION cdb_dataservices_server.OBS_MetadataValidation(
+  username TEXT,
+  orgname TEXT,
+  geometry_extent Geometry(Geometry, 4326),
+  geometry_type text,
+  params JSON,
+  target_geoms INTEGER DEFAULT NULL)
+RETURNS TABLE(valid boolean, errors text[]) AS $$
+  from cartodb_services.metrics import metrics
+  from cartodb_services.tools import Logger,LoggerConfig
+
+  plpy.execute("SELECT cdb_dataservices_server._connect_to_redis('{0}')".format(username))
+  redis_conn = GD["redis_connection_{0}".format(username)]['redis_metrics_connection']
+  plpy.execute("SELECT cdb_dataservices_server._get_obs_config({0}, {1})".format(plpy.quote_nullable(username), plpy.quote_nullable(orgname)))
+  user_obs_config = GD["user_obs_config_{0}".format(username)]
+
+  plpy.execute("SELECT cdb_dataservices_server._get_logger_config()")
+  logger_config = GD["logger_config"]
+  logger = Logger(logger_config)
+
+  with metrics('obs_metadatavalidation', user_obs_config, logger):
+    try:
+        obs_plan = plpy.prepare("SELECT * FROM cdb_dataservices_server._OBS_MetadataValidation($1, $2, $3, $4, $5, $6);", ["text", "text", "Geometry (Geometry, 4326)",  "text", "json", "integer"])
+        result = plpy.execute(obs_plan, [username, orgname, geometry_extent, geometry_type, params, target_geoms])
+        if result:
+          return result
+        else:
+          return []
+    except BaseException as e:
+        import sys
+        logger.error('Error trying to OBS_MetadataValidation', sys.exc_info(), data={"username": username, "orgname": orgname})
+        raise Exception('Error trying to OBS_MetadataValidation')
+$$ LANGUAGE plpythonu;