components/variations/variations_associated_data.h

// Copyright 2013 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_VARIATIONS_VARIATIONS_ASSOCIATED_DATA_H_
#define COMPONENTS_VARIATIONS_VARIATIONS_ASSOCIATED_DATA_H_

#include <map>
#include <string>

#include "base/metrics/field_trial.h"

// This file provides various helpers that extend the functionality around
// base::FieldTrial.
//
// This includes several simple APIs to handle getting and setting additional
// data related to Chrome variations, such as parameters and Google variation
// IDs. These APIs are meant to extend the base::FieldTrial APIs to offer extra
// functionality that is not offered by the simpler base::FieldTrial APIs.
//
// The AssociateGoogleVariationID and AssociateVariationParams functions are
// generally meant to be called by the VariationsService based on server-side
// variation configs, but may also be used for client-only field trials by
// invoking them directly after appending all the groups to a FieldTrial.
//
// Experiment code can then use the getter APIs to retrieve variation parameters
// or IDs:
//
//  std::map<std::string, std::string> params;
//  if (GetVariationParams("trial", &params)) {
//    // use |params|
//  }
//
//  std::string value = GetVariationParamValue("trial", "param_x");
//  // use |value|, which will be "" if it does not exist
//
// VariationID id = GetGoogleVariationID(GOOGLE_WEB_PROPERTIES, "trial",
//                                       "group1");
// if (id != chrome_variations::kEmptyID) {
//   // use |id|
// }

namespace chrome_variations {

typedef int VariationID;

const VariationID EMPTY_ID = 0;

// The Unique ID of a trial and its active group, where the name and group
// identifiers are hashes of the trial and group name strings.
struct ActiveGroupId {
  uint32 name;
  uint32 group;
};

// Returns an ActiveGroupId struct for the given trial and group names.
ActiveGroupId MakeActiveGroupId(const std::string& trial_name,
                                const std::string& group_name);

// We need to supply a Compare class for templates since ActiveGroupId is a
// user-defined type.
struct ActiveGroupIdCompare {
  bool operator() (const ActiveGroupId& lhs, const ActiveGroupId& rhs) const {
    // The group and name fields are just SHA-1 Hashes, so we just need to treat
    // them as IDs and do a less-than comparison. We test group first, since
    // name is more likely to collide.
    if (lhs.group != rhs.group)
      return lhs.group < rhs.group;
    return lhs.name < rhs.name;
  }
};

// A key into the Associate/Get methods for VariationIDs. This is used to create
// separate ID associations for separate parties interested in VariationIDs.
enum IDCollectionKey {
  // This collection is used by Google web properties, transmitted through the
  // X-Chrome-Variations header.
  GOOGLE_WEB_PROPERTIES,
  // This collection is used by Google update services, transmitted through the
  // Google Update experiment labels.
  GOOGLE_UPDATE_SERVICE,
  // The total count of collections.
  ID_COLLECTION_COUNT,
};

// Associate a chrome_variations::VariationID value with a FieldTrial group for
// collection |key|. If an id was previously set for |trial_name| and
// |group_name|, this does nothing. The group is denoted by |trial_name| and
// |group_name|. This must be called whenever a FieldTrial is prepared (create
// the trial and append groups) and needs to have a
// chrome_variations::VariationID associated with it so Google servers can
// recognize the FieldTrial. Thread safe.
void AssociateGoogleVariationID(IDCollectionKey key,
                                const std::string& trial_name,
                                const std::string& group_name,
                                VariationID id);

// As above, but overwrites any previously set id. Thread safe.
void AssociateGoogleVariationIDForce(IDCollectionKey key,
                                     const std::string& trial_name,
                                     const std::string& group_name,
                                     VariationID id);

// Retrieve the chrome_variations::VariationID associated with a FieldTrial
// group for collection |key|. The group is denoted by |trial_name| and
// |group_name|. This will return chrome_variations::kEmptyID if there is
// currently no associated ID for the named group. This API can be nicely
// combined with FieldTrial::GetActiveFieldTrialGroups() to enumerate the
// variation IDs for all active FieldTrial groups. Thread safe.
VariationID GetGoogleVariationID(IDCollectionKey key,
                                 const std::string& trial_name,
                                 const std::string& group_name);

// Associates the specified set of key-value |params| with the variation
// specified by |trial_name| and |group_name|. Fails and returns false if the
// specified variation already has params associated with it or the field trial
// is already active (group() has been called on it). Thread safe.
bool AssociateVariationParams(const std::string& trial_name,
                              const std::string& group_name,
                              const std::map<std::string, std::string>& params);

// Retrieves the set of key-value |params| for the variation associated with
// the specified field trial, based on its selected group. If the field trial
// does not exist or its selected group does not have any parameters associated
// with it, returns false and does not modify |params|. Calling this function
// will result in the field trial being marked as active if found (i.e. group()
// will be called on it), if it wasn't already. Currently, this information is
// only available from the browser process. Thread safe.
bool GetVariationParams(const std::string& trial_name,
                        std::map<std::string, std::string>* params);

// Retrieves a specific parameter value corresponding to |param_name| for the
// variation associated with the specified field trial, based on its selected
// group. If the field trial does not exist or the specified parameter does not
// exist, returns an empty string. Calling this function will result in the
// field trial being marked as active if found (i.e. group() will be called on
// it), if it wasn't already. Currently, this information is only available from
// the browser process. Thread safe.
std::string GetVariationParamValue(const std::string& trial_name,
                                   const std::string& param_name);

// Expose some functions for testing.
namespace testing {

// Clears all of the mapped associations.
void ClearAllVariationIDs();

// Clears all of the associated params.
void ClearAllVariationParams();

}  // namespace testing

}  // namespace chrome_variations

#endif  // COMPONENTS_VARIATIONS_VARIATIONS_ASSOCIATED_DATA_H_