Creating global middleware for net/http servers in Go
When you're writing pure net/http HTTP services with Go, you may want to wrap them in a middleware, for instance to ensure that authentication is provided, or to provide logging.
Having largely just used gorilla/mux, I found it was a little bit awkward to do so, but with thanks to Gregor Best for the help with this on the Gopher Slack, we got to the following solution.
package main
import (
"log"
"net/http"
)
func use(r *http.ServeMux, middlewares ...func(next http.Handler) http.Handler) http.Handler {
var s http.Handler
s = r
for _, mw := range middlewares {
s = mw(s)
}
return s
}
func loggingMiddleware(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
log.Printf("Before %s", r.URL.String())
next.ServeHTTP(w, r)
log.Printf("Before %s", r.URL.String())
})
}
func acceptHeaderMiddleware(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
log.Printf("Accept: %v", r.Header.Get("Accept"))
next.ServeHTTP(w, r)
})
}
func path1(w http.ResponseWriter, r *http.Request) {
w.Write([]byte("OK"))
}
func path2(w http.ResponseWriter, r *http.Request) {
w.Write([]byte("also-ok"))
}
func main() {
r := http.NewServeMux()
r.HandleFunc("/path1", path1)
r.HandleFunc("/path2", path2)
wrapped := use(r, loggingMiddleware, acceptHeaderMiddleware)
log.Fatal(http.ListenAndServe(":3000", wrapped))
}
