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