1 /* 2 * Copyright (C) 2017 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef SRC_IPC_BUFFERED_FRAME_DESERIALIZER_H_ 18 #define SRC_IPC_BUFFERED_FRAME_DESERIALIZER_H_ 19 20 #include <stddef.h> 21 22 #include <list> 23 #include <memory> 24 25 #include <sys/mman.h> 26 27 #include "perfetto/base/paged_memory.h" 28 #include "perfetto/base/utils.h" 29 #include "perfetto/ipc/basic_types.h" 30 31 namespace perfetto { 32 namespace ipc { 33 34 class Frame; // Defined in the protobuf autogenerated wire_protocol.pb.h. 35 36 // Deserializes incoming frames, taking care of buffering and tokenization. 37 // Used by both host and client to decode incoming frames. 38 // 39 // Which problem does it solve? 40 // ---------------------------- 41 // The wire protocol is as follows: 42 // [32-bit frame size][proto-encoded Frame], e.g: 43 // [06 00 00 00][00 11 22 33 44 55 66] 44 // [02 00 00 00][AA BB] 45 // [04 00 00 00][CC DD EE FF] 46 // However, given that the socket works in SOCK_STREAM mode, the recv() calls 47 // might see the following: 48 // 06 00 00 49 // 00 00 11 22 33 44 55 50 // 66 02 00 00 00 ... 51 // This class takes care of buffering efficiently the data received, without 52 // making any assumption on how the incoming data will be chunked by the socket. 53 // For instance, it is possible that a recv() doesn't produce any frame (because 54 // it received only a part of the frame) or produces more than one frame. 55 // 56 // Usage 57 // ----- 58 // Both host and client use this as follows: 59 // 60 // auto buf = rpc_frame_decoder.BeginReceive(); 61 // size_t rsize = socket.recv(buf.first, buf.second); 62 // rpc_frame_decoder.EndReceive(rsize); 63 // while (Frame frame = rpc_frame_decoder.PopNextFrame()) { 64 // ... process |frame| 65 // } 66 // 67 // Design goals: 68 // ------------- 69 // - Optimize for the realistic case of each recv() receiving one or more 70 // whole frames. In this case no memmove is performed. 71 // - Guarantee that frames lay in a virtually contiguous memory area. 72 // This allows to use the protobuf-lite deserialization API (scattered 73 // deserialization is supported only by libprotobuf-full). 74 // - Put a hard boundary to the size of the incoming buffer. This is to prevent 75 // that a malicious sends an abnormally large frame and OOMs us. 76 // - Simplicity: just use a linear mmap region. No reallocations or scattering. 77 // Takes care of madvise()-ing unused memory. 78 79 class BufferedFrameDeserializer { 80 public: 81 struct ReceiveBuffer { 82 char* data; 83 size_t size; 84 }; 85 86 // |max_capacity| is overridable only for tests. 87 explicit BufferedFrameDeserializer(size_t max_capacity = kIPCBufferSize); 88 ~BufferedFrameDeserializer(); 89 90 // This function doesn't really belong here as it does Serialization, unlike 91 // the rest of this class. However it is so small and has so many dependencies 92 // in common that doesn't justify having its own class. 93 static std::string Serialize(const Frame&); 94 95 // Returns a buffer that can be passed to recv(). The buffer is deliberately 96 // not initialized. 97 ReceiveBuffer BeginReceive(); 98 99 // Must be called soon after BeginReceive(). 100 // |recv_size| is the number of valid bytes that have been written into the 101 // buffer previously returned by BeginReceive() (the return value of recv()). 102 // Returns false if a header > |max_capacity| is received, in which case the 103 // caller is expected to shutdown the socket and terminate the ipc. 104 bool EndReceive(size_t recv_size) PERFETTO_WARN_UNUSED_RESULT; 105 106 // Decodes and returns the next decoded frame in the buffer if any, nullptr 107 // if no further frames have been decoded. 108 std::unique_ptr<Frame> PopNextFrame(); 109 capacity()110 size_t capacity() const { return capacity_; } size()111 size_t size() const { return size_; } 112 113 private: 114 BufferedFrameDeserializer(const BufferedFrameDeserializer&) = delete; 115 BufferedFrameDeserializer& operator=(const BufferedFrameDeserializer&) = 116 delete; 117 118 // If a valid frame is decoded it is added to |decoded_frames_|. 119 void DecodeFrame(const char*, size_t); 120 buf()121 char* buf() { return reinterpret_cast<char*>(buf_.Get()); } 122 123 base::PagedMemory buf_; 124 const size_t capacity_ = 0; // sizeof(|buf_|). 125 126 // THe number of bytes in |buf_| that contain valid data (as a result of 127 // EndReceive()). This is always <= |capacity_|. 128 size_t size_ = 0; 129 130 std::list<std::unique_ptr<Frame>> decoded_frames_; 131 }; 132 133 } // namespace ipc 134 } // namespace perfetto 135 136 #endif // SRC_IPC_BUFFERED_FRAME_DESERIALIZER_H_ 137