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chaff.go
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chaff.go
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// Copyright 2020 the Exposure Notifications Verification Server authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package middleware
import (
"context"
"fmt"
"net/http"
"time"
"github.com/google/exposure-notifications-server/pkg/cache"
"github.com/google/exposure-notifications-server/pkg/logging"
"github.com/google/exposure-notifications-server/pkg/timeutils"
"github.com/google/exposure-notifications-verification-server/pkg/controller"
"github.com/google/exposure-notifications-verification-server/pkg/database"
"github.com/gorilla/mux"
"github.com/mikehelmick/go-chaff"
)
// ChaffHeader is the chaff header key.
const ChaffHeader = "X-Chaff"
// ChaffHeaderDetector returns a chaff header detector.
func ChaffHeaderDetector() chaff.Detector {
return chaff.HeaderDetector(ChaffHeader)
}
// localChaffCache is a local, in-memory cache of realms that have incremented
// chaff on the given UTC day. Values are stored as "<utc_day>:<realm_id>" and
// the cache purges after 48 hours. This exists to alleviate pressure on the
// database.
//
// cache.New only returns an error if the duration is negative, so we ignore the
// error here.
var localChaffCache, _ = cache.New(48 * time.Hour)
// ProcessChaff injects the chaff processing middleware. If chaff requests send
// a value of "daily" (case-insensitive), they will be counted toward the
// realm's total active users and return a chaff response. Any other values will
// only return a chaff response.
//
// This must come after RequireAPIKey.
func ProcessChaff(db *database.Database, t *chaff.Tracker, det chaff.Detector) mux.MiddlewareFunc {
return func(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
ctx := r.Context()
if v := r.Header.Get(ChaffHeader); v != "" {
now := timeutils.UTCMidnight(time.Now().UTC())
go recordChaffEvent(ctx, now, controller.RealmFromContext(ctx), db)
}
// Process normal chaff tracking
t.HandleTrack(det, next).ServeHTTP(w, r)
})
}
}
// recordChaff event annotates that the realm received a chaff request on the
// provided date.
func recordChaffEvent(ctx context.Context, t time.Time, realm *database.Realm, db *database.Database) {
if realm == nil || db == nil {
return
}
key := fmt.Sprintf("%s:%d", t.Format("2006-01-02"), realm.ID)
if _, err := localChaffCache.WriteThruLookup(key, func() (interface{}, error) {
if err := realm.RecordChaffEvent(db, t); err != nil {
return nil, err
}
return &struct{}{}, nil
}); err != nil {
logger := logging.FromContext(ctx).Named("chaff.recordChaffEvent")
logger.Errorw("failed to record chaff event", "realm", realm.ID, "error", err)
}
}