components/autofill/core/browser/randomized_encoder.h

// Copyright 2018 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.

#ifndef COMPONENTS_AUTOFILL_CORE_BROWSER_RANDOMIZED_ENCODER_H_
#define COMPONENTS_AUTOFILL_CORE_BROWSER_RANDOMIZED_ENCODER_H_

#include <memory>
#include <string>

#include "base/strings/string_piece.h"
#include "components/autofill/core/browser/proto/server.pb.h"
#include "components/autofill/core/common/signatures_util.h"

class PrefService;

namespace autofill {

// Encodes string values using the differential-privacy scheme as described
// in go/autofill-metadata-upload (Google internal link).
class RandomizedEncoder {
 public:
  struct EncodingInfo {
    AutofillRandomizedValue_EncodingType encoding_type;
    size_t final_size;
    size_t bit_offset;
    size_t bit_stride;
  };

  // Form-level data-type identifiers.
  static const char FORM_ID[];
  static const char FORM_NAME[];
  static const char FORM_ACTION[];
  static const char FORM_CSS_CLASS[];

  // Field-level data-type identifiers.
  static const char FIELD_ID[];
  static const char FIELD_NAME[];
  static const char FIELD_CONTROL_TYPE[];
  static const char FIELD_LABEL[];
  static const char FIELD_ARIA_LABEL[];
  static const char FIELD_ARIA_DESCRIPTION[];
  static const char FIELD_CSS_CLASS[];
  static const char FIELD_PLACEHOLDER[];
  static const char FIELD_INITIAL_VALUE_HASH[];

  // Factory Function
  static std::unique_ptr<RandomizedEncoder> Create(PrefService* pref_service);

  RandomizedEncoder(std::string seed,
                    AutofillRandomizedValue_EncodingType encoding_type);

  // Encode |data_value| using this instance's |encoding_type_|.
  std::string Encode(FormSignature form_signature,
                     FieldSignature field_signature,
                     base::StringPiece data_type,
                     base::StringPiece data_value) const;

  // Encode |data_value| using this instance's |encoding_type_|.
  std::string Encode(FormSignature form_signature,
                     FieldSignature field_signature,
                     base::StringPiece data_type,
                     base::StringPiece16 data_value) const;

  AutofillRandomizedValue_EncodingType encoding_type() const {
    DCHECK(encoding_info_);
    return encoding_info_
               ? encoding_info_->encoding_type
               : AutofillRandomizedValue_EncodingType_UNSPECIFIED_ENCODING_TYPE;
  }

 protected:
  // Get the pseudo-random string to use at the coin bit-field. This function
  // is internal, but exposed here to facilitate testing.
  std::string GetCoins(FormSignature form_signature,
                       FieldSignature field_signature,
                       base::StringPiece data_type) const;

  // Get the pseudo-random string to use at the noise bit-field. This function
  // is internal, but exposed here to facilitate testing.
  std::string GetNoise(FormSignature form_signature,
                       FieldSignature field_signature,
                       base::StringPiece data_type) const;

 private:
  const std::string seed_;
  const EncodingInfo* const encoding_info_;
};
}  // namespace autofill

#endif  // COMPONENTS_AUTOFILL_CORE_BROWSER_RANDOMIZED_ENCODER_H_