Add gRPC Python Example: Metadata

examples/python/metadata/README.md

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+An example showing how to add custom HTTP2 headers (or [metadata](https://grpc.io/grpc/python/glossary.html) in gRPC glossary)
+
+HTTP2 supports initial headers and trailing headers, which gRPC utilizes both of them ([learn more](https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md)).
+
+More complete documentation lives at [grpc.io](https://grpc.io/docs/tutorials/basic/python.html).
+For API reference please see [API](https://grpc.io/grpc/python/grpc.html).

examples/python/metadata/helloworld_pb2.py

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+# Generated by the protocol buffer compiler.  DO NOT EDIT!
+# source: helloworld.proto
+
+import sys
+_b=sys.version_info[0]<3 and (lambda x:x) or (lambda x:x.encode('latin1'))
+from google.protobuf import descriptor as _descriptor
+from google.protobuf import message as _message
+from google.protobuf import reflection as _reflection
+from google.protobuf import symbol_database as _symbol_database
+from google.protobuf import descriptor_pb2
+# @@protoc_insertion_point(imports)
+
+_sym_db = _symbol_database.Default()
+
+
+
+
+DESCRIPTOR = _descriptor.FileDescriptor(
+  name='helloworld.proto',
+  package='helloworld',
+  syntax='proto3',
+  serialized_pb=_b('\n\x10helloworld.proto\x12\nhelloworld\"\x1c\n\x0cHelloRequest\x12\x0c\n\x04name\x18\x01 \x01(\t\"\x1d\n\nHelloReply\x12\x0f\n\x07message\x18\x01 \x01(\t2I\n\x07Greeter\x12>\n\x08SayHello\x12\x18.helloworld.HelloRequest\x1a\x16.helloworld.HelloReply\"\x00\x42\x36\n\x1bio.grpc.examples.helloworldB\x0fHelloWorldProtoP\x01\xa2\x02\x03HLWb\x06proto3')
+)
+
+
+
+
+_HELLOREQUEST = _descriptor.Descriptor(
+  name='HelloRequest',
+  full_name='helloworld.HelloRequest',
+  filename=None,
+  file=DESCRIPTOR,
+  containing_type=None,
+  fields=[
+    _descriptor.FieldDescriptor(
+      name='name', full_name='helloworld.HelloRequest.name', index=0,
+      number=1, type=9, cpp_type=9, label=1,
+      has_default_value=False, default_value=_b("").decode('utf-8'),
+      message_type=None, enum_type=None, containing_type=None,
+      is_extension=False, extension_scope=None,
+      options=None),
+  ],
+  extensions=[
+  ],
+  nested_types=[],
+  enum_types=[
+  ],
+  options=None,
+  is_extendable=False,
+  syntax='proto3',
+  extension_ranges=[],
+  oneofs=[
+  ],
+  serialized_start=32,
+  serialized_end=60,
+)
+
+
+_HELLOREPLY = _descriptor.Descriptor(
+  name='HelloReply',
+  full_name='helloworld.HelloReply',
+  filename=None,
+  file=DESCRIPTOR,
+  containing_type=None,
+  fields=[
+    _descriptor.FieldDescriptor(
+      name='message', full_name='helloworld.HelloReply.message', index=0,
+      number=1, type=9, cpp_type=9, label=1,
+      has_default_value=False, default_value=_b("").decode('utf-8'),
+      message_type=None, enum_type=None, containing_type=None,
+      is_extension=False, extension_scope=None,
+      options=None),
+  ],
+  extensions=[
+  ],
+  nested_types=[],
+  enum_types=[
+  ],
+  options=None,
+  is_extendable=False,
+  syntax='proto3',
+  extension_ranges=[],
+  oneofs=[
+  ],
+  serialized_start=62,
+  serialized_end=91,
+)
+
+DESCRIPTOR.message_types_by_name['HelloRequest'] = _HELLOREQUEST
+DESCRIPTOR.message_types_by_name['HelloReply'] = _HELLOREPLY
+_sym_db.RegisterFileDescriptor(DESCRIPTOR)
+
+HelloRequest = _reflection.GeneratedProtocolMessageType('HelloRequest', (_message.Message,), dict(
+  DESCRIPTOR = _HELLOREQUEST,
+  __module__ = 'helloworld_pb2'
+  # @@protoc_insertion_point(class_scope:helloworld.HelloRequest)
+  ))
+_sym_db.RegisterMessage(HelloRequest)
+
+HelloReply = _reflection.GeneratedProtocolMessageType('HelloReply', (_message.Message,), dict(
+  DESCRIPTOR = _HELLOREPLY,
+  __module__ = 'helloworld_pb2'
+  # @@protoc_insertion_point(class_scope:helloworld.HelloReply)
+  ))
+_sym_db.RegisterMessage(HelloReply)
+
+
+DESCRIPTOR.has_options = True
+DESCRIPTOR._options = _descriptor._ParseOptions(descriptor_pb2.FileOptions(), _b('\n\033io.grpc.examples.helloworldB\017HelloWorldProtoP\001\242\002\003HLW'))
+
+_GREETER = _descriptor.ServiceDescriptor(
+  name='Greeter',
+  full_name='helloworld.Greeter',
+  file=DESCRIPTOR,
+  index=0,
+  options=None,
+  serialized_start=93,
+  serialized_end=166,
+  methods=[
+  _descriptor.MethodDescriptor(
+    name='SayHello',
+    full_name='helloworld.Greeter.SayHello',
+    index=0,
+    containing_service=None,
+    input_type=_HELLOREQUEST,
+    output_type=_HELLOREPLY,
+    options=None,
+  ),
+])
+_sym_db.RegisterServiceDescriptor(_GREETER)
+
+DESCRIPTOR.services_by_name['Greeter'] = _GREETER
+
+# @@protoc_insertion_point(module_scope)

examples/python/metadata/helloworld_pb2_grpc.py

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+# Generated by the gRPC Python protocol compiler plugin. DO NOT EDIT!
+import grpc
+
+import helloworld_pb2 as helloworld__pb2
+
+
+class GreeterStub(object):
+  """The greeting service definition.
+  """
+
+  def __init__(self, channel):
+    """Constructor.
+
+    Args:
+      channel: A grpc.Channel.
+    """
+    self.SayHello = channel.unary_unary(
+        '/helloworld.Greeter/SayHello',
+        request_serializer=helloworld__pb2.HelloRequest.SerializeToString,
+        response_deserializer=helloworld__pb2.HelloReply.FromString,
+        )
+
+
+class GreeterServicer(object):
+  """The greeting service definition.
+  """
+
+  def SayHello(self, request, context):
+    """Sends a greeting
+    """
+    context.set_code(grpc.StatusCode.UNIMPLEMENTED)
+    context.set_details('Method not implemented!')
+    raise NotImplementedError('Method not implemented!')
+
+
+def add_GreeterServicer_to_server(servicer, server):
+  rpc_method_handlers = {
+      'SayHello': grpc.unary_unary_rpc_method_handler(
+          servicer.SayHello,
+          request_deserializer=helloworld__pb2.HelloRequest.FromString,
+          response_serializer=helloworld__pb2.HelloReply.SerializeToString,
+      ),
+  }
+  generic_handler = grpc.method_handlers_generic_handler(
+      'helloworld.Greeter', rpc_method_handlers)
+  server.add_generic_rpc_handlers((generic_handler,))

examples/python/metadata/metadata_client.py

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+# Copyright 2018 The gRPC Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Example gRPC client that gets/sets metadata (HTTP2 headers)"""
+
+from __future__ import print_function
+import logging
+
+import grpc
+
+import helloworld_pb2
+import helloworld_pb2_grpc
+
+
+def run():
+    # NOTE(gRPC Python Team): .close() is possible on a channel and should be
+    # used in circumstances in which the with statement does not fit the needs
+    # of the code.
+    with grpc.insecure_channel('localhost:50051') as channel:
+        stub = helloworld_pb2_grpc.GreeterStub(channel)
+        response, call = stub.SayHello.with_call(
+            helloworld_pb2.HelloRequest(name='you'),
+            metadata=(
+                ('initial-metadata-1', 'The value should be str'),
+                ('binary-metadata-bin',
+                 b'With -bin surffix, the value can be bytes'),
+                ('accesstoken', 'gRPC Python is great'),
+            ))
+
+    print("Greeter client received: " + response.message)
+    for key, value in call.trailing_metadata():
+        print('Greeter client received trailing metadata: key=%s value=%s' %
+              (key, value))
+
+
+if __name__ == '__main__':
+    logging.basicConfig()
+    run()

examples/python/metadata/metadata_server.py

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+# Copyright 2018 The gRPC Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Example gRPC server that gets/sets metadata (HTTP2 headers)"""
+
+from __future__ import print_function
+from concurrent import futures
+import time
+import logging
+
+import grpc
+
+import helloworld_pb2
+import helloworld_pb2_grpc
+
+_ONE_DAY_IN_SECONDS = 60 * 60 * 24
+
+
+class Greeter(helloworld_pb2_grpc.GreeterServicer):
+
+    def SayHello(self, request, context):
+        for key, value in context.invocation_metadata():
+            print('Received initial metadata: key=%s value=%s' % (key, value))
+
+        context.set_trailing_metadata((
+            ('checksum-bin', b'I agree'),
+            ('retry', 'false'),
+        ))
+        return helloworld_pb2.HelloReply(message='Hello, %s!' % request.name)
+
+
+def serve():
+    server = grpc.server(futures.ThreadPoolExecutor(max_workers=10))
+    helloworld_pb2_grpc.add_GreeterServicer_to_server(Greeter(), server)
+    server.add_insecure_port('[::]:50051')
+    server.start()
+    try:
+        while True:
+            time.sleep(_ONE_DAY_IN_SECONDS)
+    except KeyboardInterrupt:
+        server.stop(0)
+
+
+if __name__ == '__main__':
+    logging.basicConfig()
+    serve()