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// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef COMPONENTS_CBOR_WRITER_H_
#define COMPONENTS_CBOR_WRITER_H_
#include <stddef.h>
#include <stdint.h>
#include <optional>
#include <vector>
#include "base/memory/raw_ptr.h"
#include "components/cbor/cbor_export.h"
#include "components/cbor/float_conversions.h"
#include "components/cbor/values.h"
// A basic Concise Binary Object Representation (CBOR) encoder as defined by
// https://tools.ietf.org/html/rfc7049. This is a generic encoder that supplies
// canonical, well-formed CBOR values but does not guarantee their validity
// (see https://tools.ietf.org/html/rfc7049#section-3.2).
// Supported:
// * Major types:
// * 0: Unsigned integers, up to INT64_MAX.
// * 1: Negative integers, to INT64_MIN.
// * 2: Byte strings.
// * 3: UTF-8 strings.
// * 4: Arrays, with the number of elements known at the start.
// * 5: Maps, with the number of elements known at the start
// of the container.
// * 7: Simple values.
//
// Unsupported:
// * Indefinite-length encodings.
// * Parsing.
//
// Requirements for canonical CBOR as suggested by RFC 7049 are:
// 1) All major data types for the CBOR values must be as short as possible.
// * Unsigned integer between 0 to 23 must be expressed in same byte as
// the major type.
// * 24 to 255 must be expressed only with an additional uint8_t.
// * 256 to 65535 must be expressed only with an additional uint16_t.
// * 65536 to 4294967295 must be expressed only with an additional
// uint32_t. * The rules for expression of length in major types
// 2 to 5 follow the above rule for integers.
// 2) Keys in every map must be sorted (first by major type, then by key
// length, then by value in byte-wise lexical order).
// 3) Indefinite length items must be converted to definite length items.
// 4) All maps must not have duplicate keys.
//
// Current implementation of Writer encoder meets all the requirements of
// canonical CBOR.
namespace cbor {
class CBOR_EXPORT Writer {
public:
// Default that should be sufficiently large for most use cases.
static constexpr size_t kDefaultMaxNestingDepth = 16;
struct CBOR_EXPORT Config {
// Controls the maximum depth of CBOR nesting that will be permitted in a
// Value. Nesting depth is defined as the number of arrays/maps that have to
// be traversed to reach the most nested contained Value. Primitive values
// and empty containers have nesting depths of 0.
int max_nesting_level = kDefaultMaxNestingDepth;
// Controls whether the Writer allows writing string values of type
// Value::Type::INVALID_UTF8. Regular CBOR strings must be valid UTF-8.
// Writers with this setting will produce invalid CBOR, so it may only be
// enabled in tests.
bool allow_invalid_utf8_for_testing = false;
};
Writer(const Writer&) = delete;
Writer& operator=(const Writer&) = delete;
~Writer();
// Returns the CBOR byte string representation of |node|, unless its nesting
// depth is greater than |max_nesting_level|, in which case an empty optional
// value is returned.
static std::optional<std::vector<uint8_t>> Write(
const Value& node,
size_t max_nesting_level = kDefaultMaxNestingDepth);
// A version of |Write| above that takes a Config.
static std::optional<std::vector<uint8_t>> Write(const Value& node,
const Config& config);
private:
explicit Writer(std::vector<uint8_t>* cbor);
// Called recursively to build the CBOR bytestring. When completed,
// |encoded_cbor_| will contain the CBOR.
bool EncodeCBOR(const Value& node,
int max_nesting_level,
bool allow_invalid_utf8);
// Encodes the type and size of the data being added.
void StartItem(Value::Type type, uint64_t size);
// Encodes the additional information for the data.
void SetAdditionalInformation(uint8_t additional_information);
// Encodes an unsigned integer value. This is used to both write
// unsigned integers and to encode the lengths of other major types.
void SetUint(uint64_t value);
// Returns the number of bytes needed to store the unsigned integer.
size_t GetNumUintBytes(uint64_t value);
// Holds the encoded CBOR data.
raw_ptr<std::vector<uint8_t>> encoded_cbor_;
};
} // namespace cbor
#endif // COMPONENTS_CBOR_WRITER_H_
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