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Context
Request handling

Context

At the heart of every Buffalo request handler is the Context. This context gives handlers a simple, and clean, function definition, while being immensely powerful.

The Context Interface

The buffalo.Context interface supports context.Context so it can be passed around and used as a “standard” Go Context.

Since buffalo.Context is an interface it is possible to create an application specific implementation that is tailored to the needs of the application being built.

Since 0.12.0 
type Context interface {
  context.Context
  Response() http.ResponseWriter
  Request() *http.Request
  Session() *Session
  Cookies() *Cookies
  Params() ParamValues
  Param(string) string
  Set(string, interface{})
  LogField(string, interface{})
  LogFields(map[string]interface{})
  Logger() Logger
  Bind(interface{}) error
  Render(int, render.Renderer) error
  Error(int, error) error
  Redirect(int, string, ...interface{}) error
  Data() map[string]interface{}
  Flash() *Flash
  File(string) (binding.File, error)
}

The Websocket() (*websocket.Conn, error) function was removed from buffalo.Context in version v0.12.0. Use the http://www.gorillatoolkit.org/pkg/websocket package directly instead

Context and Rendering

As part of the context interface, there is a Render function that takes a type of render.Renderer. See rendering for more information.

Any values that are “set” on the context will automatically be available to the render.Renderer that is passed into the Render function.

func Hello(c buffalo.Context) error {
  c.Set("name", "Mark")
  return c.Render(200, render.String("Hi <%= name %>"))
}

Implementing the Interface

The buffalo.Context is never meant to be “fully” implemented. Instead it is recommended that you use composition and implement only the functions that you want to provide custom implementations of.

Below is an example of changing the Error function to log the error and kill application:

// actions/context.go
type MyContext struct {
  buffalo.Context
}

func (my MyContext) Error(status int, err error) error {
  my.Logger().Fatal(err)
  return err
}

// actions/app.go
// ...
func App() *buffalo.App {
  if app != nil {
    // ...
    app.Use(func (next buffalo.Handler) buffalo.Handler {
      return func(c buffalo.Context) error {
      // change the context to MyContext
      return next(MyContext{c})
      }
    })
    // ...
  }
  return app
}
// ...

Ranging Over Parameters

The buffalo.Context#Params method returns buffalo.ParamValues which is an interface around url.Values. You can cast to this type in a handler to range over the parameter values.

import "net/url"

func HomeHandler(c buffalo.Context) error {
  if m, ok := c.Params().(url.Values); ok {
    for k, v := range m {
      fmt.Println(k, v)
    }
  }
  return c.Render(200, r.HTML("index.html"))
}

What’s in the Context

Buffalo stuffs the context of each request with a lot of information that could be useful in your application, such as the current_route or the session. Below is a list of what Buffalo adds to the context on each request that you can access from in your actions or templates.

Key Type Usage
app *buffalo.App The current Buffalo application that’s running.
env string The current environment the app is running in. Example: test, development, production
routes buffalo.RouteList A list of all of the routes mapped on the application.
current_route buffalo.RouteInfo The current route that is being accessed.
current_path string The current path being requested. Example: /users/1/edit
*Path RouteHelperFunc Helpers to create paths based off of mapped routes. Example: editUserPath. Run buffalo task routes to see a full list for your app.
params map[string]string Query parameters for the requested page.
flash map[string][]string A map of messages set using buffalo.Context#Flash.
session *buffalo.Session The current user’s session.
request *http.Request The current request.
tx *pop.Connection Only set if using the github.com/gobuffalo/buffalo/middleware.PopTransaction middleware (on by default).

See Helpers for a list of built-in helper functions available inside of templates.