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Middleware functions are key component of the Buffalo framework, in Buffalo a Middleware facilitates tasks that need to be done across multiple actions or the entire application. Examples for middleware use case include:

  • Logging
  • Authentication
  • Authorization
  • Caching
  • Rate limiting
  • Loading common data

And in general, middleware functions are used to perform tasks that need to be done before or after an action is executed.

Middleware Anatomy#

Middleware function must have the buffalo.Middleware type which receives a handler and returns another one.

type Middleware func(handler buffalo.Handler) buffalo.Handler

As an example you can see next a middleware function that adds a request ID to the context, so it can later be used by the logger for debugging purposes.

// SetRequestID sets a unique request ID in the context,// this is just an example but could be used for logging.func SetRequestID(h buffalo.Handler) buffalo.Handler {    // Returns the original handler wrapped within a Handler function    // which logs something before calling the original handler.    return func (c buffalo.Context) error {        c.Set("requestID", uuid.NewV4().String())        return h(c)    }}

To use a middleware Buffalo applications (and Groups) have the the Use method which takes one or more middleware functions and applies it to the application.

Ox default Middleware#

Ox generated applications ship with default middleware for common things in Buffalo applications, these middleware are defined in the middleware folder and used in app/routes.go.

// in routes.go// SetRoutes for the applicationfunc setRoutes(root *buffalo.App) {    root.Use(middleware.Transaction)    root.Use(middleware.ParameterLogger)    root.Use(middleware.CSRF)    ...

There are 3 default middleware functions that are used by the application. Lets explain what these are:

  • middleware.Transaction: Takes care of setting up a tx field in the context for each request, so handlers can use it to access the database.
  • middleware.ParameterLogger: Logs the parameters of the request.
  • middleware.CSRF: Adds a CSRF token to the context for use in forms.

For more info on Middleware see Middleware.