canonical.go

Documentation: github.com/gorilla/handlers

     1  package handlers
     2  
     3  import (
     4  	"net/http"
     5  	"net/url"
     6  	"strings"
     7  )
     8  
     9  type 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  //
    30  func 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  
    38  func (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.
    69  func cleanHost(in string) string {
    70  	if i := strings.IndexAny(in, " /"); i != -1 {
    71  		return in[:i]
    72  	}
    73  	return in
    74  }
    75
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