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// Copyright 2020 The Pigweed Authors
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
#pragma once
#include <algorithm>
#include <cstddef>
#include <cstring>
#include <initializer_list>
#include <utility>
#include "pw_bytes/span.h"
#include "pw_kvs/io.h"
#include "pw_span/span.h"
#include "pw_status/status_with_size.h"
namespace pw {
// Returns the value rounded down to the nearest multiple of alignment.
constexpr size_t AlignDown(size_t value, size_t alignment) {
return (value / alignment) * alignment;
// Returns the value rounded up to the nearest multiple of alignment.
constexpr size_t AlignUp(size_t value, size_t alignment) {
return (value + alignment - 1) / alignment * alignment;
// Returns the number of padding bytes required to align the provided length.
constexpr size_t Padding(size_t length, size_t alignment) {
return AlignUp(length, alignment) - length;
// Class for managing aligned writes. Stores data in an intermediate buffer and
// calls an output function with aligned data as the buffer becomes full. Any
// bytes remaining in the buffer are written to the output when Flush() is
// called or the AlignedWriter goes out of scope.
class AlignedWriter {
AlignedWriter(span<std::byte> buffer, size_t alignment_bytes, Output& writer)
: buffer_(,
write_size_(AlignDown(buffer.size(), alignment_bytes)),
bytes_in_buffer_(0) {
// TODO(hepler): Add DCHECK to ensure that buffer.size() >= alignment_bytes.
AlignedWriter(const AlignedWriter&) = delete;
AlignedWriter& operator=(const AlignedWriter&) = delete;
~AlignedWriter() {
Flush().IgnoreError(); // TODO(b/242598609): Handle Status properly
// Writes bytes to the AlignedWriter. The output may be called if the internal
// buffer is filled.
// The size in the return value is the total number of bytes for which a write
// has been attempted since Flush or Reset. The size is set for both
// successful and failed Write calls. On a failed write call, knowing the
// bytes attempted may be important when working with flash memory, since it
// can only be written once between erases.
StatusWithSize Write(span<const std::byte> data);
StatusWithSize Write(const void* data, size_t size) {
return Write(
span<const std::byte>(static_cast<const std::byte*>(data), size));
// Reads size bytes from the input and writes them to the output.
StatusWithSize Write(Input& input, size_t size);
// Flush and reset the AlignedWriter. Any remaining bytes in the buffer are
// zero-padded to an alignment boundary and written to the output. Flush is
// automatically called when the AlignedWriter goes out of scope.
StatusWithSize Flush();
static constexpr std::byte kPadByte = static_cast<std::byte>(0);
StatusWithSize AddBytesToBuffer(size_t bytes_added);
std::byte* const buffer_;
const size_t write_size_;
const size_t alignment_bytes_;
Output& output_;
size_t bytes_written_;
size_t bytes_in_buffer_;
// Declares an AlignedWriter with a built-in buffer.
template <size_t kBufferSize>
class AlignedWriterBuffer : public AlignedWriter {
template <typename... Args>
AlignedWriterBuffer(Args&&... aligned_writer_args)
: AlignedWriter(buffer_, std::forward<Args>(aligned_writer_args)...) {}
std::byte buffer_[kBufferSize];
// Writes data from multiple buffers using an AlignedWriter.
template <size_t kBufferSize>
StatusWithSize AlignedWrite(Output& output,
size_t alignment_bytes,
span<const span<const std::byte>> data) {
// TODO: This should convert to PW_CHECK once that is available for use in
// host tests.
if (alignment_bytes > kBufferSize) {
return StatusWithSize::Internal();
AlignedWriterBuffer<kBufferSize> buffer(alignment_bytes, output);
for (const span<const std::byte>& chunk : data) {
StatusWithSize result = buffer.Write(chunk);
if (!result.ok()) {
return result;
return buffer.Flush();
// Calls AlignedWrite with an initializer list.
template <size_t kBufferSize>
StatusWithSize AlignedWrite(Output& output,
size_t alignment_bytes,
std::initializer_list<span<const std::byte>> data) {
return AlignedWrite<kBufferSize>(
span<const ConstByteSpan>(data.begin(), data.size()));
} // namespace pw