Start Kafka connections for each component that needs them (#1527)

* Start Kafka connection for each component that needs one

* Fix roomserver unit tests

* Rename to naffkaInstance (@Kegsay review comment)

* Fix import cycle

internal/setup/kafka/kafka.go

@@ -0,0 +1,53 @@
+package kafka
+
+import (
+	"github.com/Shopify/sarama"
+	"github.com/matrix-org/dendrite/internal/config"
+	"github.com/matrix-org/naffka"
+	naffkaStorage "github.com/matrix-org/naffka/storage"
+	"github.com/sirupsen/logrus"
+)
+
+func SetupConsumerProducer(cfg *config.Kafka) (sarama.Consumer, sarama.SyncProducer) {
+	if cfg.UseNaffka {
+		return setupNaffka(cfg)
+	}
+	return setupKafka(cfg)
+}
+
+// setupKafka creates kafka consumer/producer pair from the config.
+func setupKafka(cfg *config.Kafka) (sarama.Consumer, sarama.SyncProducer) {
+	consumer, err := sarama.NewConsumer(cfg.Addresses, nil)
+	if err != nil {
+		logrus.WithError(err).Panic("failed to start kafka consumer")
+	}
+
+	producer, err := sarama.NewSyncProducer(cfg.Addresses, nil)
+	if err != nil {
+		logrus.WithError(err).Panic("failed to setup kafka producers")
+	}
+
+	return consumer, producer
+}
+
+// In monolith mode with Naffka, we don't have the same constraints about
+// consuming the same topic from more than one place like we do with Kafka.
+// Therefore, we will only open one Naffka connection in case Naffka is
+// running on SQLite.
+var naffkaInstance *naffka.Naffka
+
+// setupNaffka creates kafka consumer/producer pair from the config.
+func setupNaffka(cfg *config.Kafka) (sarama.Consumer, sarama.SyncProducer) {
+	if naffkaInstance != nil {
+		return naffkaInstance, naffkaInstance
+	}
+	naffkaDB, err := naffkaStorage.NewDatabase(string(cfg.Database.ConnectionString))
+	if err != nil {
+		logrus.WithError(err).Panic("Failed to setup naffka database")
+	}
+	naffkaInstance, err = naffka.New(naffkaDB)
+	if err != nil {
+		logrus.WithError(err).Panic("Failed to setup naffka")
+	}
+	return naffkaInstance, naffkaInstance
+}