snapshot of https://github.com/ThreeDotsLabs/watermill.git (master, 2026-09-15; blobs > 131072B omitted)

docs/content/advanced/fanin.md

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+title = "FanIn (merging topics)"
+description = "Merging two topics into one with the FanIn component"
+date = 2023-01-21T12:47:30+01:00
+weight = -100
+draft = false
+bref = "Merging two topics into one with the FanIn component"
++++
+
+## FanIn component
+
+The FanIn component merges two topics into one.
+
+### Configuring
+
+{{% load-snippet-partial file="src-link/components/fanin/fanin.go" first_line_contains="type Config struct {" last_line_contains="CloseTimeout time.Duration" padding_after="1" %}}
+
+### Running
+
+You need to provide a Publisher and a Subscriber implementation for the FanIn component.
+
+You can find the list of supported Pub/Subs on [Supported Pub/Subs page](/pubsubs/).
+The Publisher and subscriber can be implemented by different message brokers (for example, you can merge a Kafka topic with a RabbitMQ topic).
+
+```go
+
+logger := watermill.NewStdLogger(false, false)
+
+// create Publisher and Subscriber
+pub, err := // ...
+sub, err := // ...
+
+fi, err := fanin.NewFanIn(
+    sub,
+    pub,
+    fanin.Config{
+        SourceTopics: upstreamTopics,
+        TargetTopic:  downstreamTopic,
+    },
+    logger,
+)
+if err != nil {
+    panic(err)
+}
+
+if err := fi.Run(context.Background()); err != nil {
+    panic(err)
+}
+```
+
+### Controlling FanIn component
+
+The FanIn component can be stopped by cancelling the context passed to the `Run` method or by calling the `Close` method.
+
+{{% load-snippet-partial file="src-link/components/fanin/fanin.go" first_line_contains="func (f *FanIn) Run" last_line_contains=" Close() error" padding_after="2" %}}