docs/daprdocs/content/en/developing-applications/develop-components/develop-middleware.md

type	title	linkTitle	weight	description	aliases
docs	How to: Author middleware components	Middleware components	200	Learn how to develop middleware components	/developing-applications/middleware/middleware-overview/ /concepts/middleware-concept/

Dapr allows custom processing pipelines to be defined by chaining a series of middleware components. In this guide, you'll learn how to create a middleware component. To learn how to configure an existing middleware component, see [Configure middleware components]({{< ref middleware.md >}})

Writing a custom middleware

Dapr uses FastHTTP to implement its HTTP server. Hence, your HTTP middleware needs to be written as a FastHTTP handler. Your middleware needs to implement a middleware interface, which defines a GetHandler method that returns fasthttp.RequestHandler and error:

type Middleware interface {
  GetHandler(metadata Metadata) (func(h fasthttp.RequestHandler) fasthttp.RequestHandler, error)
}

Your handler implementation can include any inbound logic, outbound logic, or both:

func (m *customMiddleware) GetHandler(metadata Metadata) (func(fasthttp.RequestHandler) fasthttp.RequestHandler, error) {
  var err error
  return func(h fasthttp.RequestHandler) fasthttp.RequestHandler {
    return func(ctx *fasthttp.RequestCtx) {
      // inbound logic
      h(ctx)  // call the downstream handler
      // outbound logic
    }
  }, err
}

Related links

• [Component schema]({{< ref component-schema.md >}})
• [Configuration overview]({{< ref configuration-overview.md >}})
• API middleware sample