1 /* 2 * Copyright (C) 2016 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 MEMORY_READER_H_ 18 #define MEMORY_READER_H_ 19 20 #include <cstdint> 21 #include <tuple> 22 23 #include "wifilogd/local_utils.h" 24 25 namespace android { 26 namespace wifilogd { 27 28 // A non-owning adapter, which helps with reading protocol messages out 29 // of a buffer. This is, essentially, the inverse of ByteBuffer. 30 // 31 // The user is responsible for ensuring that a MemoryReader does not 32 // outlive the underlying buffer. 33 class MemoryReader { 34 public: MemoryReader(const void * buf,size_t buflen)35 MemoryReader(const void* buf, size_t buflen) 36 : head_(static_cast<const uint8_t*>(buf)), n_bytes_avail_(buflen) {} 37 MemoryReader(std::tuple<const uint8_t *,size_t> buf)38 explicit MemoryReader(std::tuple<const uint8_t*, size_t> buf) 39 : head_(std::get<0>(buf)), n_bytes_avail_(std::get<1>(buf)) {} 40 41 // Copies a |T| out of our referenced memory, aborting if sizeof(T) exceeds 42 // the number of bytes available. On success, updates the read position, and 43 // the number of bytes available. 44 template <typename T> CopyOutOrDie()45 T CopyOutOrDie() { 46 CHECK(head_); 47 const T out{local_utils::CopyFromBufferOrDie<T>(head_, n_bytes_avail_)}; 48 head_ += sizeof(T); 49 n_bytes_avail_ -= sizeof(T); 50 return out; 51 } 52 53 // Returns a pointer to the next bytes available for reading. Aborts if 54 // the number of available bytes is less than |n_bytes|. On success, updates 55 // the read position, and the number of bytes available. 56 RETURNS_NONNULL const uint8_t* GetBytesOrDie(size_t n_bytes); 57 58 // Returns true if the referenced memory is non-NULL, and has at least 59 // one byte available for reading. 60 explicit operator bool() const { return head_ && n_bytes_avail_; } 61 62 // Returns the number of bytes available for reading. size()63 size_t size() const { return (head_ ? n_bytes_avail_ : 0); } 64 65 private: 66 const uint8_t* head_; // non-owned 67 size_t n_bytes_avail_; 68 }; 69 70 } // namespace wifilogd 71 } // namespace android 72 73 #endif // MEMORY_READER_H_ 74