76 lines
2.5 KiB
Go
76 lines
2.5 KiB
Go
package main
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import (
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"crypto/sha256"
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"encoding/hex"
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"fmt"
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"html/template"
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"io/fs"
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"net/http"
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"strings"
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)
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// assetVersions maps each embedded asset (path relative to assets/, e.g.
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// "page/toc.js") to a short hash of its content. Templates reference assets
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// through assetURL, which appends the hash as ?v=…, so a versioned URL names
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// one exact file content and can be cached forever; a rebuilt asset gets a
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// new URL.
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var assetVersions = hashAssets()
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func hashAssets() map[string]string {
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versions := map[string]string{}
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_ = fs.WalkDir(assets, "assets", func(p string, d fs.DirEntry, err error) error {
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if err != nil || d.IsDir() {
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return err
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}
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b, err := assets.ReadFile(p)
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if err != nil {
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return err
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}
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sum := sha256.Sum256(b)
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versions[strings.TrimPrefix(p, "assets/")] = hex.EncodeToString(sum[:])[:12]
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return nil
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})
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return versions
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}
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// assetURL is the "asset" template func: {{asset "style.css"}} renders
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// /_/style.css?v=<hash>. An unknown name fails the template so a typo or a
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// removed file surfaces as a render error instead of a silent 404.
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func assetURL(name string) (string, error) {
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v, ok := assetVersions[name]
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if !ok {
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return "", fmt.Errorf("unknown asset %q", name)
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}
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return "/_/" + name + "?v=" + v, nil
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}
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// assetFuncs is for the standalone fragment templates that do not take the
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// full tmplFuncs.
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var assetFuncs = template.FuncMap{"asset": assetURL}
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// serveStatic serves the embedded assets under /_/. Embedded files carry no
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// modtime, so http.FileServer alone sends no validators and browsers refetch
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// every asset on every page. Instead:
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// - a URL carrying the current ?v= hash is immutable;
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// - fonts are immutable too (referenced unversioned from style.css, never
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// change);
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// - anything else (unversioned or stale ?v=, e.g. icons from CSS) gets the
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// content hash as ETag and revalidates, answered with 304 when unchanged.
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func serveStatic() http.Handler {
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staticFS, _ := fs.Sub(assets, "assets")
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static := http.StripPrefix("/_/", http.FileServer(http.FS(staticFS)))
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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name := strings.TrimPrefix(r.URL.Path, "/_/")
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v, ok := assetVersions[name]
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switch {
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case ok && r.URL.Query().Get("v") == v, strings.HasPrefix(name, "fonts/"):
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w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
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case ok:
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w.Header().Set("Cache-Control", "no-cache")
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w.Header().Set("ETag", `"`+v+`"`)
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}
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static.ServeHTTP(w, r)
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})
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}
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