Add admin interface

internal/server/server.go

@@ -59,6 +59,7 @@ func (s *Server) routes() http.Handler {
 	mux.HandleFunc("GET /{$}", s.handleIndex)
 	mux.HandleFunc("POST /api/upload", s.handleUpload)
 	mux.HandleFunc("GET /api/limits", s.handleLimits)
+	mux.HandleFunc("GET /admin", s.handleAdmin)
 	mux.HandleFunc("GET /d/{id}", s.handleDownload)
 	mux.HandleFunc("GET /i/{id}", s.handleInfo)
 	mux.HandleFunc("POST /api/d/{id}/delete", s.handleDelete)
@@ -150,7 +151,7 @@ func bearer(r *http.Request) string {
 
 // --- rendering -----------------------------------------------------------
 
-var pageNames = []string{"index.html", "result.html", "info.html", "error.html"}
+var pageNames = []string{"index.html", "result.html", "info.html", "error.html", "admin.html"}
 
 // parsePages pairs each page with the shared layout. They cannot all be parsed
 // into one template set because every page defines "content".
@@ -172,10 +173,17 @@ type page struct {
 	Base   string
 	Title  string
 	Script bool
+	Admin  bool // show the administration link in the header
 }
 
-func (s *Server) page(title string, script bool) page {
-	return page{Base: s.cfg.BasePath, Title: title, Script: script}
+// page builds the common fields, resolving whether the caller is an admin so
+// the header can offer the link only to someone who can use it.
+func (s *Server) page(r *http.Request, title string, script bool) page {
+	admin := false
+	if lim, err := s.limitsFor(credential(r)); err == nil {
+		admin = lim.Admin
+	}
+	return page{Base: s.cfg.BasePath, Title: title, Script: script, Admin: admin}
 }
 
 func (s *Server) render(w http.ResponseWriter, status int, name string, data any) {
@@ -222,7 +230,7 @@ func (s *Server) fail(w http.ResponseWriter, r *http.Request, status int, msg st
 		return
 	}
 	s.render(w, status, "error.html", errorPage{
-		page:    s.page(http.StatusText(status), false),
+		page:    s.page(r, http.StatusText(status), false),
 		Status:  fmt.Sprintf("%d %s", status, http.StatusText(status)),
 		Message: msg,
 	})