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Forked from elithrar/server.go
Created Feb 10, 2017
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package main
import (
// appContext contains our local context; our database pool, session store, template
// registry and anything else our handlers need to access. We'll create an instance of it
// in our main() function and then explicitly pass a reference to it for our handlers to access.
type appContext struct {
db *sqlx.DB
store *sessions.CookieStore
templates map[string]*template.Template
decoder *schema.Decoder
// ... and the rest of our globals.
// We've turned our original appHandler into a struct with two fields:
// - A function type similar to our original handler type (but that now takes an *appContext)
// - An embedded field of type *appContext
type appHandler struct {
h func(*appContext, http.ResponseWriter, *http.Request) (int, error)
// Our ServeHTTP method is mostly the same, and also has the ability to
// access our *appContext's fields (templates, loggers, etc.) as well.
func (ah appHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// Updated to pass ah.appContext as a parameter to our handler type.
status, err := ah.h(ah.appContext, w, r)
if err != nil {
log.Printf("HTTP %d: %q", status, err)
switch status {
case http.StatusNotFound:
http.NotFound(w, r)
// And if we wanted a friendlier error page:
// err := ah.renderTemplate(w, "http_404.tmpl", nil)
case http.StatusInternalServerError:
http.Error(w, http.StatusText(status), status)
http.Error(w, http.StatusText(status), status)
func main() {
// These are 'nil' for our example, but we'd either assign
// the values as below or use a constructor function like
// (NewAppContext(conf config) *appContext) that initialises
// it for us based on our application's configuration file.
context := &appContext{db: nil, store: nil} // Simplified for this example
r := web.New()
// We pass an instance to our context pointer, and our handler.
r.Get("/", appHandler{context, IndexHandler})
graceful.ListenAndServe(":8000", r)
func IndexHandler(a *appContext, w http.ResponseWriter, r *http.Request) (int, error) {
// Our handlers now have access to the members of our context struct.
// e.g. we can call methods on our DB type via err := a.db.GetPosts()
fmt.Fprintf(w, "IndexHandler: db is %q and store is %q", a.db,
return 200, nil
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