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// Copyright 2019 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "platform/impl/tls_write_buffer.h"
#include <algorithm>
#include <cstring>
#include "platform/api/tls_connection.h"
#include "util/osp_logging.h"
namespace openscreen {
TlsWriteBuffer::TlsWriteBuffer() = default;
TlsWriteBuffer::~TlsWriteBuffer() = default;
bool TlsWriteBuffer::Push(const void* data, size_t len) {
const size_t currently_written_bytes =
bytes_written_so_far_.load(std::memory_order_relaxed);
const size_t current_read_bytes =
bytes_read_so_far_.load(std::memory_order_acquire);
// Calculates the current size of the buffer.
const size_t bytes_currently_used =
currently_written_bytes - current_read_bytes;
OSP_DCHECK_LE(bytes_currently_used, kBufferSizeBytes);
if ((kBufferSizeBytes - bytes_currently_used) < len) {
return false;
}
// Calculates the number of bytes out of |len| to write in the first memcpy
// operation, which is either all of |len| or the number that can be written
// before wrapping around to the beginning of the underlying array.
const size_t current_write_index = currently_written_bytes % kBufferSizeBytes;
const size_t first_write_len =
std::min(len, kBufferSizeBytes - current_write_index);
memcpy(&buffer_[current_write_index], data, first_write_len);
// If fewer than |len| bytes were transferred in the previous memcpy, copy any
// remaining bytes to the array, starting at 0 (since the last write must have
// finished at the end of the array).
if (first_write_len != len) {
const uint8_t* new_start =
static_cast<const uint8_t*>(data) + first_write_len;
memcpy(buffer_, new_start, len - first_write_len);
}
// Store and return updated values.
const size_t new_write_size = currently_written_bytes + len;
bytes_written_so_far_.store(new_write_size, std::memory_order_release);
return true;
}
absl::Span<const uint8_t> TlsWriteBuffer::GetReadableRegion() {
const size_t current_read_bytes =
bytes_read_so_far_.load(std::memory_order_relaxed);
const size_t currently_written_bytes =
bytes_written_so_far_.load(std::memory_order_acquire);
// Stop reading at either the end of the array or the current write index,
// whichever is sooner. While there may be more data wrapped around after the
// end of the array, the API for GetReadableRegion() only guarantees to return
// a subset of all available read data, so there is no reason to introduce
// this additional level of complexity.
const size_t avail = currently_written_bytes - current_read_bytes;
const size_t begin = current_read_bytes % kBufferSizeBytes;
const size_t end = std::min(begin + avail, kBufferSizeBytes);
return absl::Span<const uint8_t>(&buffer_[begin], end - begin);
}
void TlsWriteBuffer::Consume(size_t byte_count) {
const size_t current_read_bytes =
bytes_read_so_far_.load(std::memory_order_relaxed);
const size_t currently_written_bytes =
bytes_written_so_far_.load(std::memory_order_acquire);
OSP_DCHECK_GE(currently_written_bytes - current_read_bytes, byte_count);
const size_t new_read_index = current_read_bytes + byte_count;
bytes_read_so_far_.store(new_read_index, std::memory_order_release);
}
// static
constexpr size_t TlsWriteBuffer::kBufferSizeBytes;
} // namespace openscreen
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