amol- commented on a change in pull request #84:
URL: https://github.com/apache/arrow-cookbook/pull/84#discussion_r726940551
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File path: python/source/flight.rst
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+============
+Arrow Flight
+============
+
+Recipes related to leveraging Arrow Flight protocol
+
+.. contents::
+
+Using an Arrow Flight RPC server
+================================
+
+Suppose you want to implement a service that can store, send and receive
+parquet files using the Arrow Flight protocol,
+``pyarrow`` provides an implementation framework in :mod:`pyarrow.flight`
+and particularly through the :class:`pyarrow.flight.FlightServerBase` class.
+
+.. testcode::
+
+ import pathlib
+ import threading
+
+ import pyarrow as pa
+ import pyarrow.flight
+ import pyarrow.parquet
+
+
+ class FlightServer(pa.flight.FlightServerBase):
+
+ def __init__(self, location="grpc://0.0.0.0:8815",
+ repo=pathlib.Path("./datasets"), **kwargs):
+ super(FlightServer, self).__init__(location, **kwargs)
+ self._location = location
+ self._repo = repo
+
+ def _make_flight_info(self, dataset):
+ dataset_path = self._repo / dataset
+ schema = pa.parquet.read_schema(dataset_path)
+ metadata = pa.parquet.read_metadata(dataset_path)
+ descriptor = pa.flight.FlightDescriptor.for_path(
+ dataset.encode('utf-8')
+ )
+ endpoints = [pa.flight.FlightEndpoint(dataset, [self._location])]
+ return pyarrow.flight.FlightInfo(schema,
+ descriptor,
+ endpoints,
+ metadata.num_rows,
+ metadata.serialized_size)
+
+ def list_flights(self, context, criteria):
+ for dataset in self._repo.iterdir():
+ yield self._make_flight_info(dataset.name)
+
+ def get_flight_info(self, context, descriptor):
+ return self._make_flight_info(descriptor.path[0].decode('utf-8'))
+
+ def do_put(self, context, descriptor, reader, writer):
+ dataset = descriptor.path[0].decode('utf-8')
+ dataset_path = self._repo / dataset
+ data_table = reader.read_all()
+ pa.parquet.write_table(data_table, dataset_path)
+
+ def do_get(self, context, ticket):
+ dataset = ticket.ticket.decode('utf-8')
+ dataset_path = self._repo / dataset
+ return
pa.flight.RecordBatchStream(pa.parquet.read_table(dataset_path))
+
+ def list_actions(self, context):
+ return [
+ ("drop_dataset", "Delete a dataset."),
+ ]
+
+ def do_action(self, context, action):
+ if action.type == "drop_dataset":
+ self.do_drop_dataset(action.body.to_pybytes().decode('utf-8'))
+ else:
+ raise NotImplementedError
+
+ def do_drop_dataset(self, dataset):
+ dataset_path = self._repo / dataset
+ dataset_path.unlink()
+
+The example server exposes :meth:`pyarrow.flight.FlightServerBase.list_flights`
+which is the method in charge of returning the list of data streams available
+for fetching.
+
+Likewise, :meth:`pyarrow.flight.FlightServerBase.get_flight_info` provides
+the information regarding a single specific data stream.
+
+Then we expose :meth:`pyarrow.flight.FlightServerBase.do_get` which is in
charge
+of actually fetching the exposed data streams and sending them to the client.
+
+Allowing to list and dowload data streams would be pretty useless if we didn't
+expose a way to create them, this is the responsability of
+:meth:`pyarrow.flight.FlightServerBase.do_put` which is in charge of receiving
+new data from the client and dealing with it (in this case saving it
+into a parquet file)
+
+This are the most common Arrow Flight requests, if we need to add more
+functionalities, we can do so using custom actions.
+
+In the previous example a `drop_dataset` custom action is added.
+All custom actions are executed through the
+:meth:`pyarrow.flight.FlightServerBase.do_action` method, thus it's up to
+the server subclass to dispatch them properly. In this case we invoke
+the `do_drop_dataset` method when the `action.type` is the one we expect.
+
+Our server can then be started with
+:meth:`pyarrow.flight.FlightServerBase.serve`
+
+.. code-block::
+
+ if __name__ == '__main__':
+ server = FlightServer()
+ server._repo.mkdir(exist_ok=True)
+ server.serve()
+
+.. testcode::
+ :hide:
+
+ # Code block to start for real a server in background
+ # and wait for it to be available.
+ # Previous code block is just to show to user how to start it.
Review comment:
Good catch, I originally added it because I implemented a `shutdown`
action, but realised it wasn't necessary as I could just directly invoke
`server.shutdown` but forgot to remove the import
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