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