keyserver: produce key change events (#1218)

* Produce kafka events when keys are added

* Consume key changes in syncapi with TODO markers for handling them and catching up

* unbreak tests

* Linting

keyserver/producers/keychange.go

@@ -0,0 +1,57 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// 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 producers
+
+import (
+	"encoding/json"
+
+	"github.com/Shopify/sarama"
+	"github.com/matrix-org/dendrite/keyserver/api"
+	"github.com/sirupsen/logrus"
+)
+
+// KeyChange produces key change events for the sync API and federation sender to consume
+type KeyChange struct {
+	Topic    string
+	Producer sarama.SyncProducer
+}
+
+// ProduceKeyChanges creates new change events for each key
+func (p *KeyChange) ProduceKeyChanges(keys []api.DeviceKeys) error {
+	for _, key := range keys {
+		var m sarama.ProducerMessage
+
+		value, err := json.Marshal(key)
+		if err != nil {
+			return err
+		}
+
+		m.Topic = string(p.Topic)
+		m.Key = sarama.StringEncoder(key.UserID)
+		m.Value = sarama.ByteEncoder(value)
+
+		partition, offset, err := p.Producer.SendMessage(&m)
+		if err != nil {
+			return err
+		}
+		logrus.WithFields(logrus.Fields{
+			"user_id":   key.UserID,
+			"device_id": key.DeviceID,
+			"partition": partition,
+			"offset":    offset,
+		}).Infof("Produced to key change topic '%s'", p.Topic)
+	}
+	return nil
+}