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