Clean up wrong vanity rules

internal/server/server.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"html/template"
 	"io"
+	"io/fs"
 	"log/slog"
 	"net/http"
 	"strings"
@@ -32,6 +33,10 @@ type Server struct {
 	authLimiter *limiter
 	slots       chan struct{} // bounds uploads in flight
 
+	// favicon is the name of the embedded icon, or "" when this build has
+	// none. Resolved once: the assets cannot change while the process runs.
+	favicon string
+
 	now func() time.Time // swappable in tests
 }
 
@@ -50,6 +55,7 @@ func New(cfg *config.Config, st *store.Store, tokens *auth.File, log *slog.Logge
 		authLimiter: newLimiter(120, 20),
 		slots:       make(chan struct{}, cfg.MaxConcurrent),
 		now:         time.Now,
+		favicon:     faviconFor(web.Static()),
 	}
 	s.handler = s.routes()
 	return s, nil
@@ -70,6 +76,9 @@ func (s *Server) routes() http.Handler {
 	mux.HandleFunc("POST /login", s.handleLogin)
 	mux.HandleFunc("POST /logout", s.handleLogout)
 	mux.Handle("GET /static/", http.StripPrefix("/static/", s.staticHandler()))
+	if s.favicon != "" {
+		mux.HandleFunc("GET /favicon.ico", s.handleFavicon)
+	}
 	mux.HandleFunc("/", s.handleNotFound)
 
 	var h http.Handler = mux
@@ -92,6 +101,29 @@ func (s *Server) routes() http.Handler {
 
 // staticHandler serves the embedded assets with a long, immutable-ish cache
 // window kept short enough that an edit shows up without a cache-buster.
+// faviconFor names the icon to serve, or "" when the build has none. The file
+// is optional on purpose: none is committed, and dropping one into web/static
+// before building is the whole of the installation procedure.
+func faviconFor(fsys fs.FS) string {
+	// A .png is preferred where both exist; every browser in service reads it,
+	// and .ico survives only as the name the root request asks for.
+	for _, name := range []string{"favicon.png", "favicon.ico"} {
+		if f, err := fsys.Open(name); err == nil {
+			f.Close()
+			return name
+		}
+	}
+	return ""
+}
+
+// handleFavicon answers the root request browsers make on their own, whichever
+// of the two names the build supplied: a .png served here is still a .png, and
+// the Content-Type says so.
+func (s *Server) handleFavicon(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Cache-Control", "public, max-age=300")
+	http.ServeFileFS(w, r, web.Static(), s.favicon)
+}
+
 func (s *Server) staticHandler() http.Handler {
 	fileServer := http.FileServerFS(web.Static())
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -196,6 +228,10 @@ type page struct {
 	User  string
 	Admin bool
 
+	// Favicon is the icon's URL, empty when the build shipped none, in which
+	// case the markup carries no link rather than one that 404s.
+	Favicon string
+
 	// Wide widens the page for content that is a table rather than a form.
 	// The reading measure that suits the upload page is far too narrow for a
 	// listing, which otherwise ends up behind a horizontal scrollbar.
@@ -206,6 +242,9 @@ type page struct {
 // who is logged in and offer only the links they can use.
 func (s *Server) page(r *http.Request, title string, script bool) page {
 	p := page{Base: s.cfg.BasePath, Title: title, Script: script}
+	if s.favicon != "" {
+		p.Favicon = s.cfg.BasePath + "static/" + s.favicon
+	}
 	if lim, err := s.limitsFor(r, cookieCredential(r)); err == nil {
 		p.User, p.Admin = lim.Name, lim.Admin
 	}