mukesh agrawal | 9d2165f | 2016-09-21 11:35:29 -0700 | [diff] [blame] | 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 MESSAGE_BUFFER_H_ |
| 18 | #define MESSAGE_BUFFER_H_ |
| 19 | |
| 20 | #include <cstdint> |
| 21 | #include <memory> |
mukesh agrawal | 6d8e220 | 2016-09-21 14:23:21 -0700 | [diff] [blame] | 22 | #include <tuple> |
mukesh agrawal | 9d2165f | 2016-09-21 11:35:29 -0700 | [diff] [blame] | 23 | |
| 24 | #include "android-base/macros.h" |
| 25 | |
mukesh agrawal | fd65102 | 2016-09-21 13:27:07 -0700 | [diff] [blame] | 26 | #include "wifilogd/local_utils.h" |
| 27 | |
mukesh agrawal | 9d2165f | 2016-09-21 11:35:29 -0700 | [diff] [blame] | 28 | namespace android { |
| 29 | namespace wifilogd { |
| 30 | |
| 31 | // A fixed-size buffer, which provides FIFO access to read and write |
| 32 | // a sequence of messages. |
| 33 | class MessageBuffer { |
| 34 | public: |
mukesh agrawal | fd08064 | 2016-10-07 15:45:37 -0700 | [diff] [blame] | 35 | // A wrapper which guarantees that a MessageBuffer will be rewound, |
| 36 | // when the program exits the wrapper's scope. The user must ensure that |
| 37 | // |buffer| does not expire before the ScopedRewinder. |
| 38 | class ScopedRewinder { |
| 39 | public: |
| 40 | explicit ScopedRewinder(NONNULL MessageBuffer* buffer) : buffer_(buffer) {} |
| 41 | ~ScopedRewinder() { buffer_->Rewind(); } |
| 42 | |
| 43 | private: |
| 44 | MessageBuffer* const buffer_; |
| 45 | }; |
| 46 | |
mukesh agrawal | 9d2165f | 2016-09-21 11:35:29 -0700 | [diff] [blame] | 47 | // Constructs the buffer. |size| must be greater than GetHeaderSize(). |
| 48 | explicit MessageBuffer(size_t size); |
| 49 | |
mukesh agrawal | fd65102 | 2016-09-21 13:27:07 -0700 | [diff] [blame] | 50 | // Appends a single message to the buffer. |data_len| must be >=1. Returns |
| 51 | // true if the message was added to the buffer. |
| 52 | bool Append(NONNULL const uint8_t* data, uint16_t data_len); |
| 53 | |
mukesh agrawal | 0e465b4 | 2016-09-21 15:19:38 -0700 | [diff] [blame] | 54 | // Returns true if the buffer is large enough to hold |length| bytes of user |
| 55 | // data, when the buffer is empty. |
| 56 | bool CanFitEver(uint16_t length) const; |
| 57 | |
mukesh agrawal | fd65102 | 2016-09-21 13:27:07 -0700 | [diff] [blame] | 58 | // Returns true if the buffer currently has enough free space to hold |length| |
| 59 | // bytes of user data. |
| 60 | bool CanFitNow(uint16_t length) const; |
| 61 | |
mukesh agrawal | 6969007 | 2016-09-21 14:34:21 -0700 | [diff] [blame] | 62 | // Clears the buffer. An immediately following read operation will return an |
| 63 | // empty message. An immediately following write operation will write to the |
| 64 | // head of the buffer. Clearing may be lazy (i.e., underlying storage is not |
| 65 | // necessarily zeroed). |
| 66 | void Clear(); |
| 67 | |
mukesh agrawal | 6d8e220 | 2016-09-21 14:23:21 -0700 | [diff] [blame] | 68 | // Returns the first unread message in the buffer. If there is no such |
| 69 | // message, returns {nullptr, 0}. MessageBuffer retains ownership of the |
| 70 | // message's storage. |
| 71 | std::tuple<const uint8_t*, size_t> ConsumeNextMessage(); |
| 72 | |
mukesh agrawal | 9d2165f | 2016-09-21 11:35:29 -0700 | [diff] [blame] | 73 | // Returns the size of MessageBuffer's per-message header. |
| 74 | static constexpr size_t GetHeaderSize() { return sizeof(LengthHeader); } |
| 75 | |
mukesh agrawal | fd65102 | 2016-09-21 13:27:07 -0700 | [diff] [blame] | 76 | // Returns the total available free space in the buffer. This may be |
| 77 | // larger than the usable space, due to overheads. |
| 78 | size_t GetFreeSize() const { return capacity_ - write_pos_; } |
| 79 | |
mukesh agrawal | 5f88ee7 | 2016-09-21 15:04:09 -0700 | [diff] [blame] | 80 | // Resets the read pointer to the start of the buffer. An immediately |
| 81 | // following read will return the first message in the buffer. An immediately |
| 82 | // following write, however, will be placed at the same position as if |
| 83 | // Rewind() had not been called. |
| 84 | void Rewind(); |
| 85 | |
mukesh agrawal | 9d2165f | 2016-09-21 11:35:29 -0700 | [diff] [blame] | 86 | private: |
| 87 | struct LengthHeader { |
| 88 | uint16_t payload_len; |
| 89 | }; |
| 90 | |
mukesh agrawal | fd65102 | 2016-09-21 13:27:07 -0700 | [diff] [blame] | 91 | // Prepares a header, and writes that header into the buffer. |
| 92 | void AppendHeader(uint16_t message_len); |
| 93 | |
| 94 | // Writes arbitrary data into the buffer. |
| 95 | void AppendRawBytes(NONNULL const void* data_start, size_t data_len); |
| 96 | |
mukesh agrawal | b0ef315 | 2016-10-05 14:03:17 -0700 | [diff] [blame] | 97 | // Returns the total number of bytes available for reading. This number |
| 98 | // includes headers. |
| 99 | size_t GetReadableSize() const { return write_pos_ - read_pos_; } |
| 100 | |
mukesh agrawal | b1af012 | 2016-09-30 10:37:42 -0700 | [diff] [blame] | 101 | const std::unique_ptr<uint8_t[]> data_; |
| 102 | const size_t capacity_; |
mukesh agrawal | 6d8e220 | 2016-09-21 14:23:21 -0700 | [diff] [blame] | 103 | size_t read_pos_; |
mukesh agrawal | fd65102 | 2016-09-21 13:27:07 -0700 | [diff] [blame] | 104 | size_t write_pos_; |
mukesh agrawal | 9d2165f | 2016-09-21 11:35:29 -0700 | [diff] [blame] | 105 | |
| 106 | // MessageBuffer is a value type, so it would be semantically reasonable to |
| 107 | // support copy and assign. Performance-wise, though, we should avoid |
| 108 | // copies. Remove the copy constructor and the assignment operator, to |
| 109 | // ensure that we don't accidentally make copies. |
| 110 | DISALLOW_COPY_AND_ASSIGN(MessageBuffer); |
| 111 | }; |
| 112 | |
| 113 | } // namespace wifilogd |
| 114 | } // namespace android |
| 115 | |
| 116 | #endif // MESSAGE_BUFFER_H_ |