Prefix-defined Kafka topics (#1254)

* Prefix-defined Kafka topics

* Fix current state server test

internal/config/config_kafka.go

@@ -0,0 +1,52 @@
+package config
+
+import "fmt"
+
+// Defined Kafka topics.
+const (
+	TopicOutputTypingEvent       = "OutputTypingEvent"
+	TopicOutputSendToDeviceEvent = "OutputSendToDeviceEvent"
+	TopicOutputKeyChangeEvent    = "OutputKeyChangeEvent"
+	TopicOutputRoomEvent         = "OutputRoomEvent"
+	TopicOutputClientData        = "OutputClientData"
+)
+
+type Kafka struct {
+	// A list of kafka addresses to connect to.
+	Addresses []string `yaml:"addresses"`
+	// Whether to use naffka instead of kafka.
+	// Naffka can only be used when running dendrite as a single monolithic server.
+	// Kafka can be used both with a monolithic server and when running the
+	// components as separate servers.
+	UseNaffka bool `yaml:"use_naffka"`
+	// The Naffka database is used internally by the naffka library, if used.
+	Database DatabaseOptions `yaml:"naffka_database"`
+	// The prefix to use for Kafka topic names for this homeserver - really only
+	// useful if running more than one Dendrite on the same Kafka deployment.
+	TopicPrefix string `yaml:"topic_prefix"`
+}
+
+func (k *Kafka) TopicFor(name string) string {
+	return fmt.Sprintf("%s%s", k.TopicPrefix, name)
+}
+
+func (c *Kafka) Defaults() {
+	c.UseNaffka = true
+	c.Database.Defaults()
+	c.Database.ConnectionString = DataSource("file:naffka.db")
+	c.TopicPrefix = "Dendrite"
+}
+
+func (c *Kafka) Verify(configErrs *ConfigErrors, isMonolith bool) {
+	if c.UseNaffka {
+		if !isMonolith {
+			configErrs.Add("naffka can only be used in a monolithic server")
+		}
+		checkNotEmpty(configErrs, "global.kafka.database.connection_string", string(c.Database.ConnectionString))
+	} else {
+		// If we aren't using naffka then we need to have at least one kafka
+		// server to talk to.
+		checkNotZero(configErrs, "global.kafka.addresses", int64(len(c.Addresses)))
+	}
+	checkNotEmpty(configErrs, "global.kafka.topic_prefix", string(c.TopicPrefix))
+}