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 BYTE_BUFFER_H_
18 #define BYTE_BUFFER_H_
19 
20 #include <array>
21 #include <cstring>
22 
23 #include "android-base/logging.h"
24 
25 #include "wifilogd/local_utils.h"
26 
27 namespace android {
28 namespace wifilogd {
29 
30 // A fixed-size buffer, which provides the ability to accumulate bytes.
31 // The buffer tracks its (populated) size, and does not require dynamic
32 // memory allocation.
33 //
34 // Usage could be as follows:
35 //     const auto& buffer = ByteBuffer<1024>()
36 //         .AppendOrDie(header.data(), header.size())
37 //         .AppendOrDie(body.data(), body.size());
38 //     write(fd, buffer.data(), buffer.size());
39 template <size_t SizeBytes>
40 class ByteBuffer {
41  public:
ByteBuffer()42   ByteBuffer() : write_pos_(0) {}
43 
44   // Appends data to the end of this buffer. Aborts if the available
45   // space in the buffer is less than |data_len|. Returns a reference to
46   // the ByteBuffer, to support chaining.
AppendOrDie(NONNULL const void * data,size_t data_len)47   ByteBuffer<SizeBytes>& AppendOrDie(NONNULL const void* data,
48                                      size_t data_len) {
49     CHECK(data_len <= raw_buffer_.size() - write_pos_);
50     std::memcpy(raw_buffer_.data() + write_pos_, data, data_len);
51     write_pos_ += data_len;
52     return *this;
53   }
54 
55   // Returns a pointer to the head of this buffer.
data()56   RETURNS_NONNULL const uint8_t* data() const { return raw_buffer_.data(); }
57 
58   // Returns the number of bytes written to this buffer.
size()59   size_t size() const { return write_pos_; }
60 
61  private:
62   std::array<uint8_t, SizeBytes> raw_buffer_;
63   size_t write_pos_;
64 };
65 
66 }  // namespace wifilogd
67 }  // namespace android
68 #endif  // BYTE_BUFFER_H_
69