Multiple domains

Routing by host is a small http.Handler in front of your routers: look up the host, then hand the request to that host’s router. Each router stays independent, with its own routes, middleware and 404.

examples/multidomain/main.go

// Command multidomain serves a different router for each host name.
package main

import (
  "fmt"
  "log"
  "net"
  "net/http"
  "time"

  "github.com/vardius/gorouter/v5"
)

// hostSwitch picks the handler for a request by its host name, ignoring the port.
type hostSwitch map[string]http.Handler

func (hs hostSwitch) ServeHTTP(w http.ResponseWriter, r *http.Request) {
  host, _, err := net.SplitHostPort(r.Host)
  if err != nil {
    host = r.Host // no port
  }

  if h, ok := hs[host]; ok {
    h.ServeHTTP(w, r)
    return
  }
  http.Error(w, "unknown host", http.StatusMisdirectedRequest)
}

func newHandler() http.Handler {
  site := gorouter.New()
  site.GET("/", func(w http.ResponseWriter, _ *http.Request) {
    fmt.Fprintln(w, "the website")
  })

  api := gorouter.New()
  api.GET("/users/{id}", func(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintf(w, "api user %s\n", r.PathValue("id"))
  })

  return hostSwitch{
    "example.com":     site,
    "www.example.com": site,
    "api.example.com": api,
  }
}

func main() {
  srv := &http.Server{Addr: ":8080", Handler: newHandler(), ReadHeaderTimeout: 5 * time.Second}
  log.Fatal(srv.ListenAndServe())
}

The host switch strips the port, so example.com:8080 finds the example.com router. A host it doesn’t know gets 421 Misdirected Request.