pw_protobuf/public/pw_protobuf/serialized_size.h

// 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.
#pragma once

#include <cstdint>

#include "pw_protobuf/wire_format.h"
#include "pw_varint/varint.h"

namespace pw::protobuf {

// Field types that directly map to fixed wire types:
inline constexpr size_t kMaxSizeBytesFixed32 = 4;
inline constexpr size_t kMaxSizeBytesFixed64 = 8;
inline constexpr size_t kMaxSizeBytesSfixed32 = 4;
inline constexpr size_t kMaxSizeBytesSfixed64 = 8;
inline constexpr size_t kMaxSizeBytesFloat = kMaxSizeBytesFixed32;
inline constexpr size_t kMaxSizeBytesDouble = kMaxSizeBytesFixed64;

// Field types that map to varint:
inline constexpr size_t kMaxSizeBytesUint32 = varint::kMaxVarint32SizeBytes;
inline constexpr size_t kMaxSizeBytesUint64 = varint::kMaxVarint64SizeBytes;
inline constexpr size_t kMaxSizeBytesSint32 = varint::kMaxVarint32SizeBytes;
inline constexpr size_t kMaxSizeBytesSint64 = varint::kMaxVarint64SizeBytes;
// The int32 field type does not use zigzag encoding, ergo negative values
// can result in the worst case varint size.
inline constexpr size_t kMaxSizeBytesInt32 = varint::kMaxVarint64SizeBytes;
inline constexpr size_t kMaxSizeBytesInt64 = varint::kMaxVarint64SizeBytes;
// The bool field type is backed by a varint, but has a limited value range.
inline constexpr size_t kMaxSizeBytesBool = 1;

inline constexpr size_t kMaxSizeBytesEnum = kMaxSizeBytesInt32;

inline constexpr size_t kMaxSizeOfFieldNumber = varint::kMaxVarint32SizeBytes;

inline constexpr size_t kMaxSizeOfLength = varint::kMaxVarint32SizeBytes;

// Calculate the serialized size of a proto tag (field number + wire type).
//
// Args:
//   field_number: The field number for the field.
//
// Returns:
//   The size of the field's encoded tag.
//
// Precondition: The field_number must be a ValidFieldNumber.
template <typename T>
constexpr size_t TagSizeBytes(T field_number) {
  static_assert((std::is_enum<T>() || std::is_integral<T>()) &&
                    sizeof(T) <= sizeof(uint32_t),
                "Field numbers must be 32-bit enums or integers");
  // The wiretype does not impact the serialized size, so use kVarint (0), which
  // will be optimized out by the compiler.
  return varint::EncodedSize(
      FieldKey(static_cast<uint32_t>(field_number), WireType::kVarint));
}

// Calculates the size of a varint field (uint32/64, int32/64, sint32/64, enum).
template <typename T, typename U>
constexpr size_t SizeOfVarintField(T field_number, U value) {
  return TagSizeBytes(field_number) + varint::EncodedSize(value);
}

// Calculates the size of a delimited field (string, bytes, nested message,
// packed repeated), excluding the data itself. This accounts for the field
// tag and length varint only. The default value for length_bytes assumes
// the length is kMaxSizeOfLength bytes long.
template <typename T>
constexpr size_t SizeOfDelimitedFieldWithoutValue(
    T field_number,
    uint32_t length_bytes = std::numeric_limits<uint32_t>::max()) {
  return TagSizeBytes(field_number) + varint::EncodedSize(length_bytes);
}

// Calculates the total size of a delimited field (string, bytes, nested
// message, packed repeated), including the data itself.
template <typename T>
constexpr size_t SizeOfDelimitedField(T field_number, uint32_t length_bytes) {
  return SizeOfDelimitedFieldWithoutValue(field_number, length_bytes) +
         length_bytes;
}

// Calculates the size of a proto field in the wire format. This is the size of
// a final serialized protobuf entry, including the key (field number + wire
// type), encoded payload size (for length-delimited types), and data.
//
// Args:
//   field_number: The field number for the field.
//   type: The wire type of the field
//   data_size: The size of the payload.
//
// Returns:
//   The size of the field.
//
// Precondition: The field_number must be a ValidFieldNumber.
// Precondition: `data_size_bytes` must be smaller than
//   std::numeric_limits<uint32_t>::max()
template <typename T>
constexpr size_t SizeOfField(T field_number,
                             WireType type,
                             size_t data_size_bytes) {
  if (type == WireType::kDelimited) {
    return SizeOfDelimitedField(field_number, data_size_bytes);
  }
  return TagSizeBytes(field_number) + data_size_bytes;
}

// Functions for calculating the size of each type of protobuf field. Varint
// fields (int32, uint64, etc.) accept a value argument that defaults to the
// largest-to-encode value for the type.
template <typename T>
constexpr size_t SizeOfFieldFloat(T field_number) {
  return TagSizeBytes(field_number) + sizeof(float);
}
template <typename T>
constexpr size_t SizeOfFieldDouble(T field_number) {
  return TagSizeBytes(field_number) + sizeof(double);
}
template <typename T>
constexpr size_t SizeOfFieldInt32(T field_number, int32_t value = -1) {
  return SizeOfVarintField(field_number, value);
}
template <typename T>
constexpr size_t SizeOfFieldInt64(T field_number, int64_t value = -1) {
  return SizeOfVarintField(field_number, value);
}
template <typename T>
constexpr size_t SizeOfFieldSint32(
    T field_number, int32_t value = std::numeric_limits<int32_t>::min()) {
  return SizeOfVarintField(field_number, varint::ZigZagEncode(value));
}
template <typename T>
constexpr size_t SizeOfFieldSint64(
    T field_number, int64_t value = std::numeric_limits<int64_t>::min()) {
  return SizeOfVarintField(field_number, varint::ZigZagEncode(value));
}
template <typename T>
constexpr size_t SizeOfFieldUint32(
    T field_number, uint32_t value = std::numeric_limits<uint32_t>::max()) {
  return SizeOfVarintField(field_number, value);
}
template <typename T>
constexpr size_t SizeOfFieldUint64(
    T field_number, uint64_t value = std::numeric_limits<uint64_t>::max()) {
  return SizeOfVarintField(field_number, value);
}
template <typename T>
constexpr size_t SizeOfFieldFixed32(T field_number) {
  return TagSizeBytes(field_number) + sizeof(uint32_t);
}
template <typename T>
constexpr size_t SizeOfFieldFixed64(T field_number) {
  return TagSizeBytes(field_number) + sizeof(uint64_t);
}
template <typename T>
constexpr size_t SizeOfFieldSfixed32(T field_number) {
  return TagSizeBytes(field_number) + sizeof(uint32_t);
}
template <typename T>
constexpr size_t SizeOfFieldSfixed64(T field_number) {
  return TagSizeBytes(field_number) + sizeof(uint64_t);
}
template <typename T>
constexpr size_t SizeOfFieldBool(T field_number) {
  return TagSizeBytes(field_number) + 1;
}
template <typename T>
constexpr size_t SizeOfFieldString(T field_number, uint32_t length_bytes) {
  return SizeOfDelimitedField(field_number, length_bytes);
}
template <typename T>
constexpr size_t SizeOfFieldBytes(T field_number, uint32_t length_bytes) {
  return SizeOfDelimitedField(field_number, length_bytes);
}
template <typename T, typename U = int32_t>
constexpr size_t SizeOfFieldEnum(T field_number, U value = static_cast<U>(-1)) {
  static_assert((std::is_enum<U>() || std::is_integral<U>()) &&
                    sizeof(U) <= sizeof(uint32_t),
                "Enum values must be 32-bit enums or integers");
  return SizeOfFieldInt32(field_number, static_cast<int32_t>(value));
}

}  // namespace pw::protobuf