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// Copyright 2023 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
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// 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.
// Definitions for the static and dynamic versions of the pw_rpc encoding
// buffer. Both version are compiled rot, but only one is instantiated,
// depending on the PW_RPC_DYNAMIC_ALLOCATION config option.
#pragma once
#include <array>
#include "pw_assert/assert.h"
#include "pw_bytes/span.h"
#include "pw_rpc/internal/config.h"
#include "pw_rpc/internal/lock.h"
#include "pw_rpc/internal/packet.h"
#include "pw_status/status_with_size.h"
#if PW_RPC_DYNAMIC_ALLOCATION
#include PW_RPC_DYNAMIC_CONTAINER_INCLUDE
#endif // PW_RPC_DYNAMIC_ALLOCATION
namespace pw::rpc::internal {
constexpr ByteSpan ResizeForPayload(ByteSpan buffer) {
return buffer.subspan(Packet::kMinEncodedSizeWithoutPayload);
}
// Wraps a statically allocated encoding buffer.
class StaticEncodingBuffer {
public:
constexpr StaticEncodingBuffer() : buffer_{} {}
ByteSpan AllocatePayloadBuffer() { return ResizeForPayload(buffer_); }
ByteSpan GetPacketBuffer(size_t /* payload_size */) { return buffer_; }
void Release() {}
void ReleaseIfAllocated() {}
private:
static_assert(MaxSafePayloadSize() > 0,
"pw_rpc's encode buffer is too small to fit any data");
std::array<std::byte, cfg::kEncodingBufferSizeBytes> buffer_;
};
#if PW_RPC_DYNAMIC_ALLOCATION
// Wraps a dynamically allocated encoding buffer.
class DynamicEncodingBuffer {
public:
DynamicEncodingBuffer() = default;
~DynamicEncodingBuffer() { PW_DASSERT(buffer_.empty()); }
// Allocates a new buffer and returns a portion to use to encode the payload.
ByteSpan AllocatePayloadBuffer(size_t payload_size) {
Allocate(payload_size);
return ResizeForPayload(buffer_);
}
// Returns the buffer into which to encode the packet, allocating a new buffer
// if necessary.
ByteSpan GetPacketBuffer(size_t payload_size) {
if (buffer_.empty()) {
Allocate(payload_size);
}
return buffer_;
}
// Frees the payload buffer, which MUST have been allocated previously.
void Release() {
PW_DASSERT(!buffer_.empty());
buffer_.clear();
}
// Frees the payload buffer, if one was allocated.
void ReleaseIfAllocated() {
if (!buffer_.empty()) {
Release();
}
}
private:
void Allocate(size_t payload_size) {
const size_t buffer_size =
payload_size + Packet::kMinEncodedSizeWithoutPayload;
PW_DASSERT(buffer_.empty());
buffer_.resize(buffer_size);
}
PW_RPC_DYNAMIC_CONTAINER(std::byte) buffer_;
};
using EncodingBuffer = DynamicEncodingBuffer;
#else
using EncodingBuffer = StaticEncodingBuffer;
#endif // PW_RPC_DYNAMIC_ALLOCATION
// Instantiate the global encoding buffer variable, depending on whether dynamic
// allocation is enabled or not.
inline EncodingBuffer encoding_buffer PW_GUARDED_BY(rpc_lock());
// Successful calls to EncodeToPayloadBuffer MUST send the returned buffer,
// without releasing the RPC lock.
template <typename Proto, typename Encoder>
static Result<ByteSpan> EncodeToPayloadBuffer(Proto& payload,
const Encoder& encoder)
PW_EXCLUSIVE_LOCKS_REQUIRED(rpc_lock()) {
// If dynamic allocation is enabled, calculate the size of the encoded
// protobuf and allocate a buffer for it.
#if PW_RPC_DYNAMIC_ALLOCATION
StatusWithSize payload_size = encoder.EncodedSizeBytes(payload);
if (!payload_size.ok()) {
return Status::Internal();
}
ByteSpan buffer = encoding_buffer.AllocatePayloadBuffer(payload_size.size());
#else
ByteSpan buffer = encoding_buffer.AllocatePayloadBuffer();
#endif // PW_RPC_DYNAMIC_ALLOCATION
StatusWithSize result = encoder.Encode(payload, buffer);
if (!result.ok()) {
encoding_buffer.ReleaseIfAllocated();
return result.status();
}
return buffer.first(result.size());
}
} // namespace pw::rpc::internal
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