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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
//
// 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.
#include "pw_hdlc/encoder.h"
#include <algorithm>
#include <array>
#include <cstddef>
#include <cstring>
#include <span>
#include "pw_bytes/endian.h"
#include "pw_hdlc/internal/encoder.h"
#include "pw_varint/varint.h"
using std::byte;
namespace pw::hdlc {
namespace internal {
Status EscapeAndWrite(const byte b, stream::Writer& writer) {
if (b == kFlag) {
return writer.Write(kEscapedFlag);
}
if (b == kEscape) {
return writer.Write(kEscapedEscape);
}
return writer.Write(b);
}
Status Encoder::WriteData(ConstByteSpan data) {
auto begin = data.begin();
while (true) {
auto end = std::find_if(begin, data.end(), NeedsEscaping);
if (Status status = writer_.Write(std::span(begin, end)); !status.ok()) {
return status;
}
if (end == data.end()) {
fcs_.Update(data);
return OkStatus();
}
if (Status status = EscapeAndWrite(*end, writer_); !status.ok()) {
return status;
}
begin = end + 1;
}
}
Status Encoder::FinishFrame() {
if (Status status =
WriteData(bytes::CopyInOrder(std::endian::little, fcs_.value()));
!status.ok()) {
return status;
}
return writer_.Write(kFlag);
}
size_t Encoder::MaxEncodedSize(uint64_t address, ConstByteSpan payload) {
constexpr size_t kFcsMaxSize = 8; // Worst case FCS: 0x7e7e7e7e.
size_t max_encoded_address_size = varint::EncodedSize(address) * 2;
size_t encoded_payload_size =
payload.size() +
std::count_if(payload.begin(), payload.end(), NeedsEscaping);
return max_encoded_address_size + sizeof(kUnusedControl) +
encoded_payload_size + kFcsMaxSize;
}
Status Encoder::StartFrame(uint64_t address, std::byte control) {
fcs_.clear();
if (Status status = writer_.Write(kFlag); !status.ok()) {
return status;
}
std::array<std::byte, 16> metadata_buffer;
size_t metadata_size =
varint::Encode(address, metadata_buffer, kAddressFormat);
if (metadata_size == 0) {
return Status::InvalidArgument();
}
metadata_buffer[metadata_size++] = control;
return WriteData(std::span(metadata_buffer).first(metadata_size));
}
} // namespace internal
Status WriteUIFrame(uint64_t address,
ConstByteSpan payload,
stream::Writer& writer) {
if (internal::Encoder::MaxEncodedSize(address, payload) >
writer.ConservativeWriteLimit()) {
return Status::ResourceExhausted();
}
internal::Encoder encoder(writer);
if (Status status = encoder.StartUnnumberedFrame(address); !status.ok()) {
return status;
}
if (Status status = encoder.WriteData(payload); !status.ok()) {
return status;
}
return encoder.FinishFrame();
}
} // namespace pw::hdlc