Move caching out of MultiThreadedCertVerifier

net/cert/caching_cert_verifier.cc

+// Copyright 2016 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.
+
+#include "net/cert/caching_cert_verifier.h"
+
+#include "base/time/time.h"
+#include "net/base/net_errors.h"
+#include "net/cert/cert_trust_anchor_provider.h"
+
+namespace net {
+
+namespace {
+
+// The maximum number of cache entries to use for the ExpiringCache.
+const unsigned kMaxCacheEntries = 256;
+
+// The number of seconds to cache entries.
+const unsigned kTTLSecs = 1800;  // 30 minutes.
+
+}  // namespace
+
+CachingCertVerifier::CachingCertVerifier(std::unique_ptr<CertVerifier> verifier)
+    : verifier_(std::move(verifier)),
+      trust_anchor_provider_(nullptr),
+      cache_(kMaxCacheEntries),
+      requests_(0u),
+      cache_hits_(0u) {
+  CertDatabase::GetInstance()->AddObserver(this);
+}
+
+CachingCertVerifier::~CachingCertVerifier() {
+  CertDatabase::GetInstance()->RemoveObserver(this);
+}
+
+void CachingCertVerifier::SetCertTrustAnchorProvider(
+    CertTrustAnchorProvider* trust_anchor_provider) {
+  DCHECK(!trust_anchor_provider_);
+  trust_anchor_provider_ = trust_anchor_provider;
+}
+
+int CachingCertVerifier::Verify(const CertVerifier::RequestParams& params,
+                                CRLSet* crl_set,
+                                CertVerifyResult* verify_result,
+                                const CompletionCallback& callback,
+                                std::unique_ptr<Request>* out_req,
+                                const BoundNetLog& net_log) {
+  out_req->reset();
+
+  requests_++;
+
+  CertificateList additional_trust_anchors(params.additional_trust_anchors());
+  if (trust_anchor_provider_) {
+    const CertificateList& trust_anchors =
+        trust_anchor_provider_->GetAdditionalTrustAnchors();
+    additional_trust_anchors.insert(additional_trust_anchors.begin(),
+                                    trust_anchors.begin(), trust_anchors.end());
+  }
+
+  const CertVerifier::RequestParams new_params(
+      params.certificate(), params.hostname(), params.flags(),
+      params.ocsp_response(), additional_trust_anchors);
+  const CertVerificationCache::value_type* cached_entry =
+      cache_.Get(new_params, CacheValidityPeriod(base::Time::Now()));
+  if (cached_entry) {
+    ++cache_hits_;
+    *verify_result = cached_entry->result;
+    return cached_entry->error;
+  }
+
+  base::Time start_time = base::Time::Now();
+  CompletionCallback caching_callback = base::Bind(
+      &CachingCertVerifier::OnRequestFinished, base::Unretained(this),
+      new_params, start_time, callback, verify_result);

[Ryan Sleevi, 2016/05/20 03:24:13]

I'm not sure how obvious this callback trick is, nor if it's entirely the right
behaviour that we want.

Namely, because I don't interject an explicit CertVerifier::Request overload, if
the caller cancels this request, we won't end up caching the result (where
previously, in MTCV, we'd cache the result, but just not notify any jobs). I
opted for this because I thought it 'simple' and 'obvious', and we had no code
relying on the 'canceled async requests still go to the cache', but I could be
convinced that I should be subclassing a CertVerifier::Request that could handle
'caching even after cancellation'.

[eroman, 2016/06/10 01:26:38]

This approach seems fine.

If we really cared about caching even on cancellation I would actually suggest a
different approach. Namely composing caching directly into
MultiThreadedCertVerifier -- similar to how HostResolverImpl embeds a HostCache
member. Trying to subclass CertVerifier::Request to handle this case seems worse
IMO.

[Ryan Sleevi, 2016/06/10 07:51:20]

Well, it's a good thing we don't care, because I think I disagree on that
layering approach :)

A significant motivation for this is to extract the caching from having any
relationship to threading. That would be a step back :)

I'm not sure why you say it's worse, but I suppose that's mostly moot for now.

+  int result = verifier_->Verify(new_params, crl_set, verify_result,
+                                 caching_callback, out_req, net_log);
+  if (result != ERR_IO_PENDING) {
+    // Synchronous completion; add directly to cache.
+    AddResultToCache(new_params, start_time, *verify_result, result);
+  }
+
+  return result;
+}
+
+bool CachingCertVerifier::SupportsOCSPStapling() {
+  return verifier_->SupportsOCSPStapling();
+}
+
+CachingCertVerifier::CachedResult::CachedResult() : error(ERR_FAILED) {}
+
+CachingCertVerifier::CachedResult::~CachedResult() {}
+
+CachingCertVerifier::CacheValidityPeriod::CacheValidityPeriod(base::Time now)
+    : verification_time(now), expiration_time(now) {}
+
+CachingCertVerifier::CacheValidityPeriod::CacheValidityPeriod(
+    base::Time now,
+    base::Time expiration)
+    : verification_time(now), expiration_time(expiration) {}
+
+bool CachingCertVerifier::CacheExpirationFunctor::operator()(
+    const CacheValidityPeriod& now,
+    const CacheValidityPeriod& expiration) const {
+  // Ensure this functor is being used for expiration only, and not strict
+  // weak ordering/sorting. |now| should only ever contain a single
+  // base::Time.
+  // Note: DCHECK_EQ is not used due to operator<< overloading requirements.
+  DCHECK(now.verification_time == now.expiration_time);
+
+  // |now| contains only a single time (verification_time), while |expiration|
+  // contains the validity range - both when the certificate was verified and
+  // when the verification result should expire.
+  //
+  // If the user receives a "not yet valid" message, and adjusts their clock
+  // foward to the correct time, this will (typically) cause
+  // now.verification_time to advance past expiration.expiration_time, thus
+  // treating the cached result as an expired entry and re-verifying.
+  // If the user receives a "expired" message, and adjusts their clock
+  // backwards to the correct time, this will cause now.verification_time to
+  // be less than expiration_verification_time, thus treating the cached
+  // result as an expired entry and re-verifying.
+  // If the user receives either of those messages, and does not adjust their
+  // clock, then the result will be (typically) be cached until the expiration
+  // TTL.
+  //
+  // This algorithm is only problematic if the user consistently keeps
+  // adjusting their clock backwards in increments smaller than the expiration
+  // TTL, in which case, cached elements continue to be added. However,
+  // because the cache has a fixed upper bound, if no entries are expired, a
+  // 'random' entry will be, thus keeping the memory constraints bounded over
+  // time.
+  return now.verification_time >= expiration.verification_time &&
+         now.verification_time < expiration.expiration_time;
+};
+
+void CachingCertVerifier::OnRequestFinished(const RequestParams& params,
+                                            base::Time start_time,
+                                            const CompletionCallback& callback,
+                                            CertVerifyResult* verify_result,
+                                            int error) {
+  AddResultToCache(params, start_time, *verify_result, error);
+
+  // Now chain to the user's callback, which may delete |this|.
+  callback.Run(error);
+}
+
+void CachingCertVerifier::AddResultToCache(
+    const RequestParams& params,
+    base::Time start_time,
+    const CertVerifyResult& verify_result,
+    int error) {
+  // When caching, this uses the time that validation started as the
+  // beginning of the validity, rather than the time that it ended (aka
+  // base::Time::Now()), to account for the fact that during validation,
+  // the clock may have changed.
+  //
+  // If the clock has changed significantly, then this result will ideally
+  // be evicted and the next time the certificate is encountered, it will
+  // be revalidated.
+  //
+  // Because of this, it's possible for situations to arise where the
+  // clock was correct at the start of validation, changed to an
+  // incorrect time during validation (such as too far in the past or
+  // future), and then was reset to the correct time. If this happens,
+  // it's likely that the result will not be a valid/correct result,
+  // but will still be used from the cache because the clock was reset
+  // to the correct time after the (bad) validation result completed.
+  //
+  // However, this solution optimizes for the case where the clock is
+  // bad at the start of validation, and subsequently is corrected. In
+  // that situation, the result is also incorrect, but because the clock
+  // was corrected after validation, if the cache validity period was
+  // computed at the end of validation, it would continue to serve an
+  // invalid result for kTTLSecs.
+  CachedResult cached_result;
+  cached_result.error = error;
+  cached_result.result = verify_result;
+  cache_.Put(
+      params, cached_result, CacheValidityPeriod(start_time),
+      CacheValidityPeriod(start_time,
+                          start_time + base::TimeDelta::FromSeconds(kTTLSecs)));
+}
+
+void CachingCertVerifier::OnCACertChanged(const X509Certificate* cert) {
+  ClearCache();
+}
+
+void CachingCertVerifier::ClearCache() {
+  cache_.Clear();
+}
+
+size_t CachingCertVerifier::GetCacheSize() const {
+  return cache_.size();
+}
+
+}  // namespace net