1package handlers
2
3import (
4	"net/http"
5	"net/url"
6	"strings"
7)
8
9type canonical struct {
10	h      http.Handler
11	domain string
12	code   int
13}
14
15// CanonicalHost is HTTP middleware that re-directs requests to the canonical
16// domain. It accepts a domain and a status code (e.g. 301 or 302) and
17// re-directs clients to this domain. The existing request path is maintained.
18//
19// Note: If the provided domain is considered invalid by url.Parse or otherwise
20// returns an empty scheme or host, clients are not re-directed.
21//
22// Example:
23//
24//  r := mux.NewRouter()
25//  canonical := handlers.CanonicalHost("http://www.gorillatoolkit.org", 302)
26//  r.HandleFunc("/route", YourHandler)
27//
28//  log.Fatal(http.ListenAndServe(":7000", canonical(r)))
29//
30func CanonicalHost(domain string, code int) func(h http.Handler) http.Handler {
31	fn := func(h http.Handler) http.Handler {
32		return canonical{h, domain, code}
33	}
34
35	return fn
36}
37
38func (c canonical) ServeHTTP(w http.ResponseWriter, r *http.Request) {
39	dest, err := url.Parse(c.domain)
40	if err != nil {
41		// Call the next handler if the provided domain fails to parse.
42		c.h.ServeHTTP(w, r)
43		return
44	}
45
46	if dest.Scheme == "" || dest.Host == "" {
47		// Call the next handler if the scheme or host are empty.
48		// Note that url.Parse won't fail on in this case.
49		c.h.ServeHTTP(w, r)
50		return
51	}
52
53	if !strings.EqualFold(cleanHost(r.Host), dest.Host) {
54		// Re-build the destination URL
55		dest := dest.Scheme + "://" + dest.Host + r.URL.Path
56		if r.URL.RawQuery != "" {
57			dest += "?" + r.URL.RawQuery
58		}
59		http.Redirect(w, r, dest, c.code)
60		return
61	}
62
63	c.h.ServeHTTP(w, r)
64}
65
66// cleanHost cleans invalid Host headers by stripping anything after '/' or ' '.
67// This is backported from Go 1.5 (in response to issue #11206) and attempts to
68// mitigate malformed Host headers that do not match the format in RFC7230.
69func cleanHost(in string) string {
70	if i := strings.IndexAny(in, " /"); i != -1 {
71		return in[:i]
72	}
73	return in
74}
75