1 // 2 // 3 // Copyright 2015 gRPC authors. 4 // 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 8 // 9 // http://www.apache.org/licenses/LICENSE-2.0 10 // 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. 16 // 17 // 18 19 #ifndef GRPCPP_SUPPORT_INTERCEPTOR_H 20 #define GRPCPP_SUPPORT_INTERCEPTOR_H 21 22 #include <map> 23 #include <memory> 24 #include <string> 25 26 #include <grpc/impl/grpc_types.h> 27 #include <grpcpp/impl/metadata_map.h> 28 #include <grpcpp/support/byte_buffer.h> 29 #include <grpcpp/support/config.h> 30 #include <grpcpp/support/string_ref.h> 31 32 namespace grpc { 33 34 class ChannelInterface; 35 class Status; 36 37 namespace experimental { 38 39 /// An enumeration of different possible points at which the \a Intercept 40 /// method of the \a Interceptor interface may be called. Any given call 41 /// to \a Intercept will include one or more of these hook points, and 42 /// each hook point makes certain types of information available to the 43 /// interceptor. 44 /// In these enumeration names, PRE_SEND means that an interception has taken 45 /// place between the time the application provided a certain type of data 46 /// (e.g., initial metadata, status) and the time that that data goes to the 47 /// other side. POST_SEND means that the data has been committed for going to 48 /// the other side (even if it has not yet been received at the other side). 49 /// PRE_RECV means an interception between the time that a certain 50 /// operation has been requested and it is available. POST_RECV means that a 51 /// result is available but has not yet been passed back to the application. 52 /// A batch of interception points will only contain either PRE or POST hooks 53 /// but not both types. For example, a batch with PRE_SEND hook points will not 54 /// contain POST_RECV or POST_SEND ops. Likewise, a batch with POST_* ops can 55 /// not contain PRE_* ops. 56 enum class InterceptionHookPoints { 57 /// The first three in this list are for clients and servers 58 PRE_SEND_INITIAL_METADATA, 59 PRE_SEND_MESSAGE, 60 POST_SEND_MESSAGE, 61 PRE_SEND_STATUS, // server only 62 PRE_SEND_CLOSE, // client only: WritesDone for stream; after write in unary 63 /// The following three are for hijacked clients only. A batch with PRE_RECV_* 64 /// hook points will never contain hook points of other types. 65 PRE_RECV_INITIAL_METADATA, 66 PRE_RECV_MESSAGE, 67 PRE_RECV_STATUS, 68 /// The following two are for all clients and servers 69 POST_RECV_INITIAL_METADATA, 70 POST_RECV_MESSAGE, 71 POST_RECV_STATUS, // client only 72 POST_RECV_CLOSE, // server only 73 /// This is a special hook point available to both clients and servers when 74 /// TryCancel() is performed. 75 /// - No other hook points will be present along with this. 76 /// - It is illegal for an interceptor to block/delay this operation. 77 /// - ALL interceptors see this hook point irrespective of whether the 78 /// RPC was hijacked or not. 79 PRE_SEND_CANCEL, 80 NUM_INTERCEPTION_HOOKS 81 }; 82 83 /// Class that is passed as an argument to the \a Intercept method 84 /// of the application's \a Interceptor interface implementation. It has five 85 /// purposes: 86 /// 1. Indicate which hook points are present at a specific interception 87 /// 2. Allow an interceptor to inform the library that an RPC should 88 /// continue to the next stage of its processing (which may be another 89 /// interceptor or the main path of the library) 90 /// 3. Allow an interceptor to hijack the processing of the RPC (only for 91 /// client-side RPCs with PRE_SEND_INITIAL_METADATA) so that it does not 92 /// proceed with normal processing beyond that stage 93 /// 4. Access the relevant fields of an RPC at each interception point 94 /// 5. Set some fields of an RPC at each interception point, when possible 95 class InterceptorBatchMethods { 96 public: ~InterceptorBatchMethods()97 virtual ~InterceptorBatchMethods() {} 98 /// Determine whether the current batch has an interception hook point 99 /// of type \a type 100 virtual bool QueryInterceptionHookPoint(InterceptionHookPoints type) = 0; 101 /// Signal that the interceptor is done intercepting the current batch of the 102 /// RPC. Every interceptor must either call Proceed or Hijack on each 103 /// interception. In most cases, only Proceed will be used. Explicit use of 104 /// Proceed is what enables interceptors to delay the processing of RPCs 105 /// while they perform other work. 106 /// Proceed is a no-op if the batch contains PRE_SEND_CANCEL. Simply returning 107 /// from the Intercept method does the job of continuing the RPC in this case. 108 /// This is because PRE_SEND_CANCEL is always in a separate batch and is not 109 /// allowed to be delayed. 110 virtual void Proceed() = 0; 111 /// Indicate that the interceptor has hijacked the RPC (only valid if the 112 /// batch contains send_initial_metadata on the client side). Later 113 /// interceptors in the interceptor list will not be called. Later batches 114 /// on the same RPC will go through interception, but only up to the point 115 /// of the hijacking interceptor. 116 virtual void Hijack() = 0; 117 118 /// Send Message Methods 119 /// GetSerializedSendMessage and GetSendMessage/ModifySendMessage are the 120 /// available methods to view and modify the request payload. An interceptor 121 /// can access the payload in either serialized form or non-serialized form 122 /// but not both at the same time. 123 /// gRPC performs serialization in a lazy manner, which means 124 /// that a call to GetSerializedSendMessage will result in a serialization 125 /// operation if the payload stored is not in the serialized form already; the 126 /// non-serialized form will be lost and GetSendMessage will no longer return 127 /// a valid pointer, and this will remain true for later interceptors too. 128 /// This can change however if ModifySendMessage is used to replace the 129 /// current payload. Note that ModifySendMessage requires a new payload 130 /// message in the non-serialized form. This will overwrite the existing 131 /// payload irrespective of whether it had been serialized earlier. Also note 132 /// that gRPC Async API requires early serialization of the payload which 133 /// means that the payload would be available in the serialized form only 134 /// unless an interceptor replaces the payload with ModifySendMessage. 135 136 /// Returns a modifable ByteBuffer holding the serialized form of the message 137 /// that is going to be sent. Valid for PRE_SEND_MESSAGE interceptions. 138 /// A return value of nullptr indicates that this ByteBuffer is not valid. 139 virtual ByteBuffer* GetSerializedSendMessage() = 0; 140 141 /// Returns a non-modifiable pointer to the non-serialized form of the message 142 /// to be sent. Valid for PRE_SEND_MESSAGE interceptions. A return value of 143 /// nullptr indicates that this field is not valid. 144 virtual const void* GetSendMessage() = 0; 145 146 /// Overwrites the message to be sent with \a message. \a message should be in 147 /// the non-serialized form expected by the method. Valid for PRE_SEND_MESSAGE 148 /// interceptions. Note that the interceptor is responsible for maintaining 149 /// the life of the message till it is serialized or it receives the 150 /// POST_SEND_MESSAGE interception point, whichever happens earlier. The 151 /// modifying interceptor may itself force early serialization by calling 152 /// GetSerializedSendMessage. 153 virtual void ModifySendMessage(const void* message) = 0; 154 155 /// Checks whether the SEND MESSAGE op succeeded. Valid for POST_SEND_MESSAGE 156 /// interceptions. 157 virtual bool GetSendMessageStatus() = 0; 158 159 /// Returns a modifiable multimap of the initial metadata to be sent. Valid 160 /// for PRE_SEND_INITIAL_METADATA interceptions. A value of nullptr indicates 161 /// that this field is not valid. 162 virtual std::multimap<std::string, std::string>* GetSendInitialMetadata() = 0; 163 164 /// Returns the status to be sent. Valid for PRE_SEND_STATUS interceptions. 165 virtual Status GetSendStatus() = 0; 166 167 /// Overwrites the status with \a status. Valid for PRE_SEND_STATUS 168 /// interceptions. 169 virtual void ModifySendStatus(const Status& status) = 0; 170 171 /// Returns a modifiable multimap of the trailing metadata to be sent. Valid 172 /// for PRE_SEND_STATUS interceptions. A value of nullptr indicates 173 /// that this field is not valid. 174 virtual std::multimap<std::string, std::string>* 175 GetSendTrailingMetadata() = 0; 176 177 /// Returns a pointer to the modifiable received message. Note that the 178 /// message is already deserialized but the type is not set; the interceptor 179 /// should static_cast to the appropriate type before using it. This is valid 180 /// for PRE_RECV_MESSAGE and POST_RECV_MESSAGE interceptions; nullptr for not 181 /// valid 182 virtual void* GetRecvMessage() = 0; 183 184 /// Returns a modifiable multimap of the received initial metadata. 185 /// Valid for PRE_RECV_INITIAL_METADATA and POST_RECV_INITIAL_METADATA 186 /// interceptions; nullptr if not valid 187 virtual std::multimap<grpc::string_ref, grpc::string_ref>* 188 GetRecvInitialMetadata() = 0; 189 190 /// Returns a modifiable view of the received status on PRE_RECV_STATUS and 191 /// POST_RECV_STATUS interceptions; nullptr if not valid. 192 virtual Status* GetRecvStatus() = 0; 193 194 /// Returns a modifiable multimap of the received trailing metadata on 195 /// PRE_RECV_STATUS and POST_RECV_STATUS interceptions; nullptr if not valid 196 virtual std::multimap<grpc::string_ref, grpc::string_ref>* 197 GetRecvTrailingMetadata() = 0; 198 199 /// Gets an intercepted channel. When a call is started on this interceptor, 200 /// only interceptors after the current interceptor are created from the 201 /// factory objects registered with the channel. This allows calls to be 202 /// started from interceptors without infinite regress through the interceptor 203 /// list. 204 virtual std::unique_ptr<ChannelInterface> GetInterceptedChannel() = 0; 205 206 /// On a hijacked RPC, an interceptor can decide to fail a PRE_RECV_MESSAGE 207 /// op. This would be a signal to the reader that there will be no more 208 /// messages, or the stream has failed or been cancelled. 209 virtual void FailHijackedRecvMessage() = 0; 210 211 /// On a hijacked RPC/ to-be hijacked RPC, this can be called to fail a SEND 212 /// MESSAGE op 213 virtual void FailHijackedSendMessage() = 0; 214 }; 215 216 /// Interface for an interceptor. Interceptor authors must create a class 217 /// that derives from this parent class. 218 class Interceptor { 219 public: ~Interceptor()220 virtual ~Interceptor() {} 221 222 /// The one public method of an Interceptor interface. Override this to 223 /// trigger the desired actions at the hook points described above. 224 virtual void Intercept(InterceptorBatchMethods* methods) = 0; 225 }; 226 227 } // namespace experimental 228 } // namespace grpc 229 230 #endif // GRPCPP_SUPPORT_INTERCEPTOR_H 231