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package handlers
import (
"net/http"
"net/url"
"strings"
)
type canonical struct {
h http.Handler
domain string
code int
}
// CanonicalHost is HTTP middleware that re-directs requests to the canonical
// domain. It accepts a domain and a status code (e.g. 301 or 302) and
// re-directs clients to this domain. The existing request path is maintained.
//
// Note: If the provided domain is considered invalid by url.Parse or otherwise
// returns an empty scheme or host, clients are not re-directed.
//
// Example:
//
// r := mux.NewRouter()
// canonical := handlers.CanonicalHost("http://www.gorillatoolkit.org", 302)
// r.HandleFunc("/route", YourHandler)
//
// log.Fatal(http.ListenAndServe(":7000", canonical(r)))
//
func CanonicalHost(domain string, code int) func(h http.Handler) http.Handler {
fn := func(h http.Handler) http.Handler {
return canonical{h, domain, code}
}
return fn
}
func (c canonical) ServeHTTP(w http.ResponseWriter, r *http.Request) {
dest, err := url.Parse(c.domain)
if err != nil {
// Call the next handler if the provided domain fails to parse.
c.h.ServeHTTP(w, r)
return
}
if dest.Scheme == "" || dest.Host == "" {
// Call the next handler if the scheme or host are empty.
// Note that url.Parse won't fail on in this case.
c.h.ServeHTTP(w, r)
return
}
if !strings.EqualFold(cleanHost(r.Host), dest.Host) {
// Re-build the destination URL
dest := dest.Scheme + "://" + dest.Host + r.URL.Path
if r.URL.RawQuery != "" {
dest += "?" + r.URL.RawQuery
}
http.Redirect(w, r, dest, c.code)
return
}
c.h.ServeHTTP(w, r)
}
// cleanHost cleans invalid Host headers by stripping anything after '/' or ' '.
// This is backported from Go 1.5 (in response to issue #11206) and attempts to
// mitigate malformed Host headers that do not match the format in RFC7230.
func cleanHost(in string) string {
if i := strings.IndexAny(in, " /"); i != -1 {
return in[:i]
}
return in
}