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1 | // Licensed to the Apache Software Foundation (ASF) under one |
2 | // or more contributor license agreements. See the NOTICE file | |
3 | // distributed with this work for additional information | |
4 | // regarding copyright ownership. The ASF licenses this file | |
5 | // to you under the Apache License, Version 2.0 (the | |
6 | // "License"); you may not use this file except in compliance | |
7 | // with the License. You may obtain a copy of the License at | |
8 | // | |
9 | // http://www.apache.org/licenses/LICENSE-2.0 | |
10 | // | |
11 | // Unless required by applicable law or agreed to in writing, | |
12 | // software distributed under the License is distributed on an | |
13 | // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY | |
14 | // KIND, either express or implied. See the License for the | |
15 | // specific language governing permissions and limitations | |
16 | // under the License. | |
17 | ||
18 | // Interfaces for defining middleware for Flight clients. Currently | |
19 | // experimental. | |
20 | ||
21 | #pragma once | |
22 | ||
23 | #include <memory> | |
24 | ||
25 | #include "arrow/flight/middleware.h" | |
26 | #include "arrow/flight/visibility.h" // IWYU pragma: keep | |
27 | #include "arrow/status.h" | |
28 | ||
29 | namespace arrow { | |
30 | namespace flight { | |
31 | ||
32 | /// \brief Client-side middleware for a call, instantiated per RPC. | |
33 | /// | |
34 | /// Middleware should be fast and must be infallible: there is no way | |
35 | /// to reject the call or report errors from the middleware instance. | |
36 | class ARROW_FLIGHT_EXPORT ClientMiddleware { | |
37 | public: | |
38 | virtual ~ClientMiddleware() = default; | |
39 | ||
40 | /// \brief A callback before headers are sent. Extra headers can be | |
41 | /// added, but existing ones cannot be read. | |
42 | virtual void SendingHeaders(AddCallHeaders* outgoing_headers) = 0; | |
43 | ||
44 | /// \brief A callback when headers are received from the server. | |
45 | virtual void ReceivedHeaders(const CallHeaders& incoming_headers) = 0; | |
46 | ||
47 | /// \brief A callback after the call has completed. | |
48 | virtual void CallCompleted(const Status& status) = 0; | |
49 | }; | |
50 | ||
51 | /// \brief A factory for new middleware instances. | |
52 | /// | |
53 | /// If added to a client, this will be called for each RPC (including | |
54 | /// Handshake) to give the opportunity to intercept the call. | |
55 | /// | |
56 | /// It is guaranteed that all client middleware methods are called | |
57 | /// from the same thread that calls the RPC method implementation. | |
58 | class ARROW_FLIGHT_EXPORT ClientMiddlewareFactory { | |
59 | public: | |
60 | virtual ~ClientMiddlewareFactory() = default; | |
61 | ||
62 | /// \brief A callback for the start of a new call. | |
63 | /// | |
64 | /// \param info Information about the call. | |
65 | /// \param[out] middleware The middleware instance for this call. If | |
66 | /// unset, will not add middleware to this call instance from | |
67 | /// this factory. | |
68 | virtual void StartCall(const CallInfo& info, | |
69 | std::unique_ptr<ClientMiddleware>* middleware) = 0; | |
70 | }; | |
71 | ||
72 | } // namespace flight | |
73 | } // namespace arrow |