posts/main.go

// posts serves a Markdown blog: each .md file in CONTENT_DIR is one post.
package main

import (
	"bytes"
	"html/template"
	"io/fs"
	"log"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"strings"
	"time"
)

type app struct {
	store    *Store
	config   *configFile
	pages    map[string]*template.Template
	assets   map[string]string // static file -> content hash
	about    template.HTML
	siteURL  string // absolute base URL, no trailing slash
	siteName string
	commit   string
}

func newApp(contentDir, siteURL string) (*app, error) {
	pages, err := loadTemplates()
	if err != nil {
		return nil, err
	}
	siteURL = strings.TrimRight(siteURL, "/")
	u, err := url.Parse(siteURL)
	if err != nil {
		return nil, err
	}
	assets, err := assetHashes()
	if err != nil {
		return nil, err
	}
	md := newMarkdown()
	var about bytes.Buffer
	if err := md.Convert(aboutMarkdown, &about); err != nil {
		return nil, err
	}
	return &app{
		store:    NewStore(contentDir, md),
		config:   newConfigFile(filepath.Join(contentDir, "site.json")),
		pages:    pages,
		assets:   assets,
		about:    template.HTML(about.String()),
		siteURL:  siteURL,
		siteName: u.Host,
		commit:   buildCommit(),
	}, nil
}

func (a *app) routes() http.Handler {
	static, err := fs.Sub(staticFS, "static")
	if err != nil {
		panic(err)
	}
	files := http.StripPrefix("/static/", http.FileServerFS(static))

	mux := http.NewServeMux()
	mux.HandleFunc("GET /{$}", a.index)
	mux.HandleFunc("GET /posts/{slug}", a.post)
	mux.HandleFunc("GET /about", a.aboutPage)
	mux.HandleFunc("GET /feed.xml", a.feed)
	mux.HandleFunc("GET /static/", func(w http.ResponseWriter, r *http.Request) {
		if strings.HasSuffix(r.URL.Path, "/") { // no directory listings
			a.notFound(w, r)
			return
		}
		// A URL carrying the file's current hash never changes content, so it
		// can be cached for a year; anything else gets an hour.
		cache := "public, max-age=3600"
		if v := r.URL.Query().Get("v"); v != "" && v == a.assets[strings.TrimPrefix(r.URL.Path, "/static/")] {
			cache = "public, max-age=31536000, immutable"
		}
		w.Header().Set("Cache-Control", cache)
		files.ServeHTTP(w, r)
	})
	mux.HandleFunc("/", a.notFound)
	return securityHeaders(mux)
}

func (a *app) index(w http.ResponseWriter, r *http.Request) {
	idx, err := a.store.Index()
	if err != nil {
		a.serverError(w, err)
		return
	}
	a.render(w, http.StatusOK, "index", pageData{Posts: idx.posts})
}

func (a *app) post(w http.ResponseWriter, r *http.Request) {
	idx, err := a.store.Index()
	if err != nil {
		a.serverError(w, err)
		return
	}
	i, ok := idx.bySlug[r.PathValue("slug")]
	if !ok {
		a.notFound(w, r)
		return
	}
	data := pageData{Post: idx.posts[i]}
	if i > 0 {
		data.Newer = idx.posts[i-1]
	}
	if i+1 < len(idx.posts) {
		data.Older = idx.posts[i+1]
	}
	a.render(w, http.StatusOK, "post", data)
}

func (a *app) aboutPage(w http.ResponseWriter, r *http.Request) {
	idx, err := a.store.Index()
	if err != nil {
		a.serverError(w, err)
		return
	}
	a.render(w, http.StatusOK, "about", pageData{
		Posts:   idx.posts,
		Version: version,
		Commit:  a.commit,
		About:   a.about,
	})
}

func (a *app) notFound(w http.ResponseWriter, r *http.Request) {
	a.render(w, http.StatusNotFound, "error", pageData{Status: 404, Message: "That page doesn't exist."})
}

func (a *app) serverError(w http.ResponseWriter, err error) {
	log.Printf("error: %v", err)
	a.render(w, http.StatusInternalServerError, "error", pageData{Status: 500, Message: "Something went wrong."})
}

// securityHeaders sets a strict policy: posts never contain scripts, and
// images may come from anywhere over HTTPS.
func securityHeaders(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		h := w.Header()
		h.Set("Content-Security-Policy", "default-src 'self'; img-src 'self' https: data:; script-src 'none'; object-src 'none'; base-uri 'none'; frame-ancestors 'none'")
		h.Set("X-Content-Type-Options", "nosniff")
		h.Set("Referrer-Policy", "strict-origin-when-cross-origin")
		next.ServeHTTP(w, r)
	})
}

func getenv(key, def string) string {
	if v := os.Getenv(key); v != "" {
		return v
	}
	return def
}

func main() {
	port := os.Getenv("PORT")
	if port == "" {
		log.Fatal("PORT not set")
	}
	a, err := newApp(getenv("CONTENT_DIR", "content"), getenv("SITE_URL", "https://posts.monoaf.com"))
	if err != nil {
		log.Fatal(err)
	}
	srv := &http.Server{
		Addr:              "127.0.0.1:" + port,
		Handler:           a.routes(),
		ReadHeaderTimeout: 5 * time.Second,
		ReadTimeout:       10 * time.Second,
		WriteTimeout:      30 * time.Second,
		IdleTimeout:       2 * time.Minute,
	}
	log.Printf("listening on %s", srv.Addr)
	log.Fatal(srv.ListenAndServe())
}