facet_manager.cc | Explore in Territory

// Copyright 2015 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Note: Read the class comment of AffiliationService for the definition
// of the terms used below.
//
// On-demand fetching strategy
//
// A GetAffiliationsAndBranding() request concerning facet X will be served from
// the cache as long as the cache contains fresh affiliation information for
// facet X, that is, if there is an equivalence class in the cache that contains
// X and has been fetched less than |kCacheHardExpiryInHours| hours ago.
//
// Otherwise, a network request is issued against the Affiliation API as soon as
// possible, that is, immediately if there is no fetch in flight, or right after
// completion of the fetch in flight if there is one, provided that the required
// data is not incidentally returned by the first fetch.
//
//
// Proactive fetching strategy
//
// A Prefetch() request concerning facet Y can trigger an initial network fetch,
// or periodic refetches only when:
//   * The prefetch request is not already expired, i.e., its |keep_fresh_until|
//     threshold is strictly in the future (that is, prefetch intervals are open
//     from the right).
//   * Affiliation information in the cache pertaining to facet Y will get stale
//     strictly before the specified |keep_fresh_until| threshold.
//
// An initial fetch will be issued as soon as possible if, in addition to the
// two necessery conditions above, and at the time of the Prefetch() call, the
// cache contains no affiliation information regarding facet Y, or if the data
// in the cache for facet Y is near-stale, that is, it has been fetched more
// than |kCacheHardExpiryInHours| hours ago.
//
// A refetch will be issued every time the data in the cache regarding facet Y
// becomes near-stale, that is, exactly |kCacheSoftExpiry| hours after the last
// fetch, provided that the above two necessary conditions are also met.
//
// Fetches are triggered already when the data gets near-stale, as opposed to
// waiting until the data would get stale, in an effort to keep the data fresh
// even in face of temporary network errors lasting no more than the difference
// between soft and hard expiry times.
//
// The current fetch scheduling logic, however, can only deal with at most one
// such 'early' fetch between taking place between the prior fetch and the
// corresponding hard expiry time of the data, therefore it is assumed that:
//
//   kCacheSoftExpiryInHours < kCacheHardExpiryInHours, and
//   2 * kCacheSoftExpiryInHours > kCacheHardExpiryInHours.
//
//
// Cache freshness terminology
//
//
//      Fetch (t=0)              kCacheSoftExpiry        kCacheHardExpiry
//      /                        /                       /
//  ---o------------------------o-----------------------o-----------------> t
//     |                        |                       |
//     |                        [-- Cache near-stale --------------------- ..
//     [--------------- Cache is fresh ----------------)[-- Cache is stale ..
//

#include "components/affiliations/core/browser/facet_manager.h"

#include "base/functional/bind.h"
#include "base/location.h"
#include "base/task/task_runner.h"
#include "base/time/clock.h"
#include "base/time/time.h"
#include "components/affiliations/core/browser/facet_manager_host.h"

namespace affiliations {

// statics
const int FacetManager::kCacheSoftExpiryInHours = …;
const int FacetManager::kCacheHardExpiryInHours = …;

static_assert …;

static_assert …;

// Encapsulates the details of a pending GetAffiliationsAndBranding() request.
struct FacetManager::RequestInfo { … };

FacetManager::FacetManager(const FacetURI& facet_uri,
                           FacetManagerHost* backend,
                           base::Clock* clock)
    : … { … }

FacetManager::~FacetManager() { … }

void FacetManager::GetAffiliationsAndBranding(
    StrategyOnCacheMiss cache_miss_strategy,
    AffiliationService::ResultCallback callback,
    const scoped_refptr<base::TaskRunner>& callback_task_runner) { … }

void FacetManager::Prefetch(const base::Time& keep_fresh_until) { … }

void FacetManager::CancelPrefetch(const base::Time& keep_fresh_until) { … }

void FacetManager::OnFetchSucceeded(
    const AffiliatedFacetsWithUpdateTime& affiliation) { … }

void FacetManager::OnFetchFailed() { … }

void FacetManager::NotifyAtRequestedTime() { … }

bool FacetManager::CanBeDiscarded() const { … }

bool FacetManager::CanCachedDataBeDiscarded() const { … }

bool FacetManager::DoesRequireFetch() const { … }

bool FacetManager::IsCachedDataFresh() const { … }

bool FacetManager::IsCachedDataNearStale() const { … }

base::Time FacetManager::GetCacheSoftExpiryTime() const { … }

base::Time FacetManager::GetCacheHardExpiryTime() const { … }

base::Time FacetManager::GetMaximumKeepFreshUntilThreshold() const { … }

base::Time FacetManager::GetNextRequiredFetchTimeDueToPrefetch() const { … }

// static
void FacetManager::ServeRequestWithSuccess(
    RequestInfo request_info,
    const AffiliatedFacets& affiliation) { … }

// static
void FacetManager::ServeRequestWithFailure(RequestInfo request_info) { … }

}  // namespace affiliations
chromium/components/affiliations/core/browser/facet_manager.cc
