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// Copyright 2013 The Go Authors. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd.
package httputil
import (
"io"
"io/ioutil"
"net/http"
"net/url"
"strings"
"sync"
)
type busterWriter struct {
headerMap http.Header
status int
io.Writer
}
func (bw *busterWriter) Header() http.Header {
return bw.headerMap
}
func (bw *busterWriter) WriteHeader(status int) {
bw.status = status
}
// CacheBusters maintains a cache of cache busting tokens for static resources served by Handler.
type CacheBusters struct {
Handler http.Handler
mu sync.Mutex
tokens map[string]string
}
func sanitizeTokenRune(r rune) rune {
if r <= ' ' || r >= 127 {
return -1
}
// Convert percent encoding reserved characters to '-'.
if strings.ContainsRune("!#$&'()*+,/:;=?@[]", r) {
return '-'
}
return r
}
// Get returns the cache busting token for path. If the token is not already
// cached, Get issues a HEAD request on handler and uses the response ETag and
// Last-Modified headers to compute a token.
func (cb *CacheBusters) Get(path string) string {
cb.mu.Lock()
if cb.tokens == nil {
cb.tokens = make(map[string]string)
}
token, ok := cb.tokens[path]
cb.mu.Unlock()
if ok {
return token
}
w := busterWriter{
Writer: ioutil.Discard,
headerMap: make(http.Header),
}
r := &http.Request{URL: &url.URL{Path: path}, Method: "HEAD"}
cb.Handler.ServeHTTP(&w, r)
if w.status == 200 {
token = w.headerMap.Get("Etag")
if token == "" {
token = w.headerMap.Get("Last-Modified")
}
token = strings.Trim(token, `" `)
token = strings.Map(sanitizeTokenRune, token)
}
cb.mu.Lock()
cb.tokens[path] = token
cb.mu.Unlock()
return token
}
// AppendQueryParam appends the token as a query parameter to path.
func (cb *CacheBusters) AppendQueryParam(path string, name string) string {
token := cb.Get(path)
if token == "" {
return path
}
return path + "?" + name + "=" + token
}
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