server: add read only mode (#92)

In read only mode the endpoint to save new effects or add new versions
is deactivated. Also in the gallery the create button is deactivated and
there is a notice that says:

    The server is in maintenance mode. You can not create or modify effects.

The button to save effects in the editor is not deactivated as it will
take a bit more time and wanted to have the page up as soon as possible.

server/assets/gallery.html

@@ -123,7 +123,13 @@ <h1><a href="/" style="text-transform:uppercase">GLSL Sandbox</a> <a href="https
 <a href="https://twitter.com/mrdoob">@mrdoob</a><br/>
 editor by <a href="https://twitter.com/mrdoob">@mrdoob</a>, <a href="https://twitter.com/mrkishi">@mrkishi</a>, <a href="https://twitter.com/p01">@p01</a>, <a href="https://twitter.com/alteredq">@alteredq</a>, <a href="https://twitter.com/kusmabite">@kusmabite</a> and <a href="https://twitter.com/emackey">@emackey</a>
 <br/><br/>
+
+{{ if .ReadOnly }}
+<h2 style="color:#ff6961">The server is in maintenance mode. You can not create or modify effects.</h2>
+{{ else }}
 <a href="/e"><button>new shader</button></a>
+{{ end }}
+
 <div id="gallery">
 
 {{ if .Admin }}

server/cmd/glslsandbox/main.go

@@ -25,6 +25,7 @@ type Config struct {
 	TLSAddr    string `envconfig:"TLS_ADDR"`
 	Domains    string `envconfig:"DOMAINS" default:"www.glslsandbox.com,glslsandbox.com"`
 	Dev        bool   `envconfig:"DEV" default:"true"`
+	ReadOnly   bool   `envconfig:"READ_ONLY" default:"false"`
 }
 
 func main() {
@@ -82,6 +83,7 @@ func start() error {
 		auth,
 		cfg.DataPath,
 		cfg.Dev,
+		cfg.ReadOnly,
 	)
 	if err != nil {
 		return fmt.Errorf("could not create server: %w", err)

server/server.go

@@ -27,9 +27,7 @@ const (
 	perPage     = 50
 )
 
-var (
-	ErrInvalidData = fmt.Errorf("invalid data")
-)
+var ErrInvalidData = fmt.Errorf("invalid data")
 
 type Template struct {
 	templates *template.Template
@@ -80,6 +78,7 @@ type Server struct {
 	effects  *store.Effects
 	auth     *Auth
 	dataPath string
+	readOnly bool
 }
 
 func New(
@@ -90,6 +89,7 @@ func New(
 	auth *Auth,
 	dataPath string,
 	dev bool,
+	readOnly bool,
 ) (*Server, error) {
 	var tpl *template.Template
 	if !dev {
@@ -115,6 +115,7 @@ func New(
 		effects:  e,
 		auth:     auth,
 		dataPath: dataPath,
+		readOnly: readOnly,
 	}, nil
 }
 
@@ -163,7 +164,10 @@ func (s *Server) routes() {
 	s.echo.GET("/", s.indexHandler)
 	s.echo.GET("/e", s.effectHandler)
 	s.echo.GET("/e_", s.effectHandler_)
-	s.echo.POST("/e", s.saveHandler)
+
+	if !s.readOnly {
+		s.echo.POST("/e", s.saveHandler)
+	}
 
 	cors := middleware.CORSWithConfig(middleware.CORSConfig{
 		Skipper:      middleware.DefaultSkipper,
@@ -228,6 +232,8 @@ type galleryData struct {
 	NextPage string
 	// Admin is true when accessing "/admin" path.
 	Admin bool
+	// ReadOnly tells the server is in read only mode.
+	ReadOnly bool
 }
 
 func (s *Server) indexRender(c echo.Context, admin bool) error {
@@ -290,6 +296,7 @@ func (s *Server) indexRender(c echo.Context, admin bool) error {
 		IsPrevious:   page > 0,
 		PreviousPage: previousPage,
 		Admin:        admin,
+		ReadOnly:     s.readOnly,
 	}
 
 	return c.Render(http.StatusOK, "gallery", d)