posts/render.go

package main

import (
	"bytes"
	"crypto/sha256"
	"embed"
	"encoding/hex"
	"html/template"
	"io/fs"
	"log"
	"net/http"
	"strings"
	"time"

	"github.com/yuin/goldmark"
	"github.com/yuin/goldmark/extension"
	"github.com/yuin/goldmark/parser"
)

var (
	//go:embed templates/*.html
	templateFS embed.FS
	//go:embed static
	staticFS embed.FS
	//go:embed about.md
	aboutMarkdown []byte
)

// newMarkdown returns a CommonMark renderer with GitHub-style extensions.
// Raw HTML in posts is omitted (goldmark's default).
func newMarkdown() goldmark.Markdown {
	return goldmark.New(
		goldmark.WithExtensions(extension.GFM),
		goldmark.WithParserOptions(parser.WithAutoHeadingID()),
	)
}

// assetHashes returns a short content hash for each file in static/, keyed
// by its path under static/. Pages link to static files with ?v=<hash> so a
// changed file gets a new URL and browsers never use a stale cached copy.
func assetHashes() (map[string]string, error) {
	hashes := map[string]string{}
	err := fs.WalkDir(staticFS, "static", func(path string, d fs.DirEntry, err error) error {
		if err != nil || d.IsDir() {
			return err
		}
		b, err := staticFS.ReadFile(path)
		if err != nil {
			return err
		}
		sum := sha256.Sum256(b)
		hashes[strings.TrimPrefix(path, "static/")] = hex.EncodeToString(sum[:])[:10]
		return nil
	})
	return hashes, err
}

// pageData is passed to every template.
type pageData struct {
	Site         string
	CSS          string // stylesheet URL including its content hash
	Config       siteConfig
	Posts        []*Post
	Post         *Post
	Newer, Older *Post
	Status       int
	Message      string

	// About page only.
	Version, Commit string
	About           template.HTML

	// Release notes pages (and the About page's link to them).
	Releases []*Release
	Release  *Release
}

// loadTemplates parses each page template together with the shared layout.
func loadTemplates() (map[string]*template.Template, error) {
	funcs := template.FuncMap{
		"date":    func(t time.Time) string { return t.Format("2 January 2006") },
		"isodate": func(t time.Time) string { return t.Format(time.DateOnly) },
	}
	base, err := template.New("layout.html").Funcs(funcs).ParseFS(templateFS, "templates/layout.html")
	if err != nil {
		return nil, err
	}
	pages := map[string]*template.Template{}
	for _, name := range []string{"index", "post", "about", "releases", "release", "error"} {
		t, err := base.Clone()
		if err != nil {
			return nil, err
		}
		if pages[name], err = t.ParseFS(templateFS, "templates/"+name+".html"); err != nil {
			return nil, err
		}
	}
	return pages, nil
}

// render executes a page into a buffer first so a template error becomes a
// clean 500 instead of a half-written page.
func (a *app) render(w http.ResponseWriter, status int, page string, data pageData) {
	data.Site = a.siteName
	data.CSS = "/static/style.css?v=" + a.assets["style.css"]
	data.Config = a.config.Get()
	var buf bytes.Buffer
	if err := a.pages[page].ExecuteTemplate(&buf, "layout.html", data); err != nil {
		log.Printf("render %s: %v", page, err)
		http.Error(w, "internal server error", http.StatusInternalServerError)
		return
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.WriteHeader(status)
	buf.WriteTo(w)
}