// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef NET_HTTP_HTTP_VARY_DATA_H_
#define NET_HTTP_HTTP_VARY_DATA_H_

#include <array>
#include <cstdint>
#include <string_view>
#include <variant>

#include "base/check.h"
#include "crypto/hash.h"
#include "crypto/obsolete/md5.h"
#include "net/base/net_export.h"

namespace base {
class Pickle;
class PickleIterator;
}  // namespace base

namespace net {

struct HttpRequestInfo;
class HttpResponseHeaders;

using Md5Hash = std::array<uint8_t, crypto::obsolete::Md5::kSize>;
using Sha256Hash = std::array<uint8_t, crypto::hash::kSha256Size>;

// Used to implement the HTTP/1.1 Vary header.  This class contains a
// cryptographic hash over the request headers indicated by a Vary header.
//
// While RFC 2616 requires strict request header comparisons, it is much
// cheaper to store a hash, which should be sufficient.  Storing a hash also
// avoids messy privacy issues as some of the request headers could hold
// sensitive data (e.g., cookies).
//
// This class supports both SHA-256 and the legacy MD5 hash algorithms. New
// entries use SHA-256.

// NOTE: This class does not hold onto the contents of the Vary header.
// Instead, it relies on the consumer to store that and to supply it again to
// the MatchesRequest function for comparing against future HTTP requests.
//
class NET_EXPORT_PRIVATE HttpVaryData {
 public:
  // The hash algorithm used for the digest. These values are persisted to disk
  // and should not be changed.
  enum class HashType {
    kMD5 = 0,
    kSHA256 = 1,
  };

  HttpVaryData();

  bool is_valid() const { return is_valid_; }

  // Initialize from a request and its corresponding response headers.
  //
  // Returns true if a Vary header was found in the response headers and that
  // Vary header was not empty. Upon success, the object is also marked as valid
  // such that is_valid() will return true.  Otherwise, false is returned to
  // indicate that this object is marked as invalid.
  // New entries are created with SHA256.
  bool Init(const HttpRequestInfo& request_info,
            const HttpResponseHeaders& response_headers,
            HashType hash_type = HashType::kSHA256);

  // Initialize from a pickle that contains data generated by a call to the
  // vary data's Persist method.
  //
  // Upon success, true is returned and the object is marked as valid such that
  // is_valid() will return true.  Otherwise, false is returned to indicate
  // that this object is marked as invalid.
  //
  bool InitFromPickle(base::PickleIterator* pickle_iter);
  // Call this method to persist the vary data. Illegal to call this on an
  // invalid object.
  void Persist(base::Pickle* pickle) const;

  // Call this method to test if the given request matches the previous request
  // with which this vary data corresponds.  The |cached_response_headers| must
  // be the same response headers used to generate this vary data.
  bool MatchesRequest(const HttpRequestInfo& request_info,
                      const HttpResponseHeaders& cached_response_headers) const;

  HashType hash_type() const {
    if (std::holds_alternative<Md5Hash>(hash_)) {
      return HashType::kMD5;
    }
    CHECK(std::holds_alternative<Sha256Hash>(hash_));
    return HashType::kSHA256;
  }

 private:
  // A variant to hold either a SHA-256 or MD5 hash of the request headers.
  std::variant<Md5Hash, Sha256Hash> hash_;
  // True when `hash_` contains meaningful data.
  bool is_valid_ = false;
};

}  // namespace net

#endif  // NET_HTTP_HTTP_VARY_DATA_H_