3 * Copyright 2018 gRPC authors.
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
9 * http://www.apache.org/licenses/LICENSE-2.0
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
19 #ifndef GRPCPP_IMPL_CODEGEN_INTERCEPTOR_H
20 #define GRPCPP_IMPL_CODEGEN_INTERCEPTOR_H
22 #include <grpc/impl/codegen/grpc_types.h>
23 #include <grpcpp/impl/codegen/byte_buffer.h>
24 #include <grpcpp/impl/codegen/config.h>
25 #include <grpcpp/impl/codegen/core_codegen_interface.h>
26 #include <grpcpp/impl/codegen/metadata_map.h>
30 class ChannelInterface;
33 namespace experimental {
35 /// An enumeration of different possible points at which the \a Intercept
36 /// method of the \a Interceptor interface may be called. Any given call
37 /// to \a Intercept will include one or more of these hook points, and
38 /// each hook point makes certain types of information available to the
40 /// In these enumeration names, PRE_SEND means that an interception has taken
41 /// place between the time the application provided a certain type of data
42 /// (e.g., initial metadata, status) and the time that that data goes to the
43 /// other side. POST_SEND means that the data has been committed for going to
44 /// the other side (even if it has not yet been received at the other side).
45 /// PRE_RECV means an interception between the time that a certain
46 /// operation has been requested and it is available. POST_RECV means that a
47 /// result is available but has not yet been passed back to the application.
48 /// A batch of interception points will only contain either PRE or POST hooks
49 /// but not both types. For example, a batch with PRE_SEND hook points will not
50 /// contain POST_RECV or POST_SEND ops. Likewise, a batch with POST_* ops can
51 /// not contain PRE_* ops.
52 enum class InterceptionHookPoints {
53 /// The first three in this list are for clients and servers
54 PRE_SEND_INITIAL_METADATA,
57 PRE_SEND_STATUS, // server only
58 PRE_SEND_CLOSE, // client only: WritesDone for stream; after write in unary
59 /// The following three are for hijacked clients only. A batch with PRE_RECV_*
60 /// hook points will never contain hook points of other types.
61 PRE_RECV_INITIAL_METADATA,
64 /// The following two are for all clients and servers
65 POST_RECV_INITIAL_METADATA,
67 POST_RECV_STATUS, // client only
68 POST_RECV_CLOSE, // server only
69 /// This is a special hook point available to both clients and servers when
70 /// TryCancel() is performed.
71 /// - No other hook points will be present along with this.
72 /// - It is illegal for an interceptor to block/delay this operation.
73 /// - ALL interceptors see this hook point irrespective of whether the
74 /// RPC was hijacked or not.
76 NUM_INTERCEPTION_HOOKS
79 /// Class that is passed as an argument to the \a Intercept method
80 /// of the application's \a Interceptor interface implementation. It has five
82 /// 1. Indicate which hook points are present at a specific interception
83 /// 2. Allow an interceptor to inform the library that an RPC should
84 /// continue to the next stage of its processing (which may be another
85 /// interceptor or the main path of the library)
86 /// 3. Allow an interceptor to hijack the processing of the RPC (only for
87 /// client-side RPCs with PRE_SEND_INITIAL_METADATA) so that it does not
88 /// proceed with normal processing beyond that stage
89 /// 4. Access the relevant fields of an RPC at each interception point
90 /// 5. Set some fields of an RPC at each interception point, when possible
91 class InterceptorBatchMethods {
93 virtual ~InterceptorBatchMethods() {}
94 /// Determine whether the current batch has an interception hook point
96 virtual bool QueryInterceptionHookPoint(InterceptionHookPoints type) = 0;
97 /// Signal that the interceptor is done intercepting the current batch of the
98 /// RPC. Every interceptor must either call Proceed or Hijack on each
99 /// interception. In most cases, only Proceed will be used. Explicit use of
100 /// Proceed is what enables interceptors to delay the processing of RPCs
101 /// while they perform other work.
102 /// Proceed is a no-op if the batch contains PRE_SEND_CANCEL. Simply returning
103 /// from the Intercept method does the job of continuing the RPC in this case.
104 /// This is because PRE_SEND_CANCEL is always in a separate batch and is not
105 /// allowed to be delayed.
106 virtual void Proceed() = 0;
107 /// Indicate that the interceptor has hijacked the RPC (only valid if the
108 /// batch contains send_initial_metadata on the client side). Later
109 /// interceptors in the interceptor list will not be called. Later batches
110 /// on the same RPC will go through interception, but only up to the point
111 /// of the hijacking interceptor.
112 virtual void Hijack() = 0;
114 /// Send Message Methods
115 /// GetSerializedSendMessage and GetSendMessage/ModifySendMessage are the
116 /// available methods to view and modify the request payload. An interceptor
117 /// can access the payload in either serialized form or non-serialized form
118 /// but not both at the same time.
119 /// gRPC performs serialization in a lazy manner, which means
120 /// that a call to GetSerializedSendMessage will result in a serialization
121 /// operation if the payload stored is not in the serialized form already; the
122 /// non-serialized form will be lost and GetSendMessage will no longer return
123 /// a valid pointer, and this will remain true for later interceptors too.
124 /// This can change however if ModifySendMessage is used to replace the
125 /// current payload. Note that ModifySendMessage requires a new payload
126 /// message in the non-serialized form. This will overwrite the existing
127 /// payload irrespective of whether it had been serialized earlier. Also note
128 /// that gRPC Async API requires early serialization of the payload which
129 /// means that the payload would be available in the serialized form only
130 /// unless an interceptor replaces the payload with ModifySendMessage.
132 /// Returns a modifable ByteBuffer holding the serialized form of the message
133 /// that is going to be sent. Valid for PRE_SEND_MESSAGE interceptions.
134 /// A return value of nullptr indicates that this ByteBuffer is not valid.
135 virtual ByteBuffer* GetSerializedSendMessage() = 0;
137 /// Returns a non-modifiable pointer to the non-serialized form of the message
138 /// to be sent. Valid for PRE_SEND_MESSAGE interceptions. A return value of
139 /// nullptr indicates that this field is not valid.
140 virtual const void* GetSendMessage() = 0;
142 /// Overwrites the message to be sent with \a message. \a message should be in
143 /// the non-serialized form expected by the method. Valid for PRE_SEND_MESSAGE
144 /// interceptions. Note that the interceptor is responsible for maintaining
145 /// the life of the message till it is serialized or it receives the
146 /// POST_SEND_MESSAGE interception point, whichever happens earlier. The
147 /// modifying interceptor may itself force early serialization by calling
148 /// GetSerializedSendMessage.
149 virtual void ModifySendMessage(const void* message) = 0;
151 /// Checks whether the SEND MESSAGE op succeeded. Valid for POST_SEND_MESSAGE
153 virtual bool GetSendMessageStatus() = 0;
155 /// Returns a modifiable multimap of the initial metadata to be sent. Valid
156 /// for PRE_SEND_INITIAL_METADATA interceptions. A value of nullptr indicates
157 /// that this field is not valid.
158 virtual std::multimap<grpc::string, grpc::string>*
159 GetSendInitialMetadata() = 0;
161 /// Returns the status to be sent. Valid for PRE_SEND_STATUS interceptions.
162 virtual Status GetSendStatus() = 0;
164 /// Overwrites the status with \a status. Valid for PRE_SEND_STATUS
166 virtual void ModifySendStatus(const Status& status) = 0;
168 /// Returns a modifiable multimap of the trailing metadata to be sent. Valid
169 /// for PRE_SEND_STATUS interceptions. A value of nullptr indicates
170 /// that this field is not valid.
171 virtual std::multimap<grpc::string, grpc::string>*
172 GetSendTrailingMetadata() = 0;
174 /// Returns a pointer to the modifiable received message. Note that the
175 /// message is already deserialized but the type is not set; the interceptor
176 /// should static_cast to the appropriate type before using it. This is valid
177 /// for PRE_RECV_MESSAGE and POST_RECV_MESSAGE interceptions; nullptr for not
179 virtual void* GetRecvMessage() = 0;
181 /// Returns a modifiable multimap of the received initial metadata.
182 /// Valid for PRE_RECV_INITIAL_METADATA and POST_RECV_INITIAL_METADATA
183 /// interceptions; nullptr if not valid
184 virtual std::multimap<grpc::string_ref, grpc::string_ref>*
185 GetRecvInitialMetadata() = 0;
187 /// Returns a modifiable view of the received status on PRE_RECV_STATUS and
188 /// POST_RECV_STATUS interceptions; nullptr if not valid.
189 virtual Status* GetRecvStatus() = 0;
191 /// Returns a modifiable multimap of the received trailing metadata on
192 /// PRE_RECV_STATUS and POST_RECV_STATUS interceptions; nullptr if not valid
193 virtual std::multimap<grpc::string_ref, grpc::string_ref>*
194 GetRecvTrailingMetadata() = 0;
196 /// Gets an intercepted channel. When a call is started on this interceptor,
197 /// only interceptors after the current interceptor are created from the
198 /// factory objects registered with the channel. This allows calls to be
199 /// started from interceptors without infinite regress through the interceptor
201 virtual std::unique_ptr<ChannelInterface> GetInterceptedChannel() = 0;
203 /// On a hijacked RPC, an interceptor can decide to fail a PRE_RECV_MESSAGE
204 /// op. This would be a signal to the reader that there will be no more
205 /// messages, or the stream has failed or been cancelled.
206 virtual void FailHijackedRecvMessage() = 0;
208 /// On a hijacked RPC/ to-be hijacked RPC, this can be called to fail a SEND
210 virtual void FailHijackedSendMessage() = 0;
213 /// Interface for an interceptor. Interceptor authors must create a class
214 /// that derives from this parent class.
217 virtual ~Interceptor() {}
219 /// The one public method of an Interceptor interface. Override this to
220 /// trigger the desired actions at the hook points described above.
221 virtual void Intercept(InterceptorBatchMethods* methods) = 0;
224 } // namespace experimental
227 #endif // GRPCPP_IMPL_CODEGEN_INTERCEPTOR_H