Make canonical URL configurable

Author: Bios-Marcel

internal/config/config.go

@@ -54,6 +54,9 @@ type Config struct {
 	// domain. So it could be https://painting.com. This is required for some
 	// non critical functionality, such as metadata tags.
 	RootURL string `env:"ROOT_URL"`
+	// CanonicalURL specifies the original domain, in case we are accessing the
+	// site via some other domain, such as scribblers.fly.dev
+	CanonicalURL string `env:"CANONICAL_URL"`
 	// ServeDirectories is a map of `path` to `directory`. All directories are
 	// served under the given path.
 	ServeDirectories map[string]string `env:"SERVE_DIRECTORIES"`
@@ -148,6 +151,9 @@ func Load() (*Config, error) {
 
 	// Prevent user error and let the code decide when we need slashes.
 	config.RootURL = strings.TrimSuffix(config.RootURL, "/")
+	if config.CanonicalURL == "" {
+		config.CanonicalURL = config.RootURL
+	}
 	config.RootPath = strings.Trim(config.RootPath, "/")
 
 	return &config, nil

internal/frontend/http.go

@@ -51,6 +51,9 @@ type BasePageConfig struct {
 	// domain. So it could be https://painting.com. This is required for some
 	// non critical functionality, such as metadata tags.
 	RootURL string `json:"rootUrl"`
+	// CanonicalURL specifies the original domain, in case we are accessing the
+	// site via some other domain, such as scribblers.fly.dev
+	CanonicalURL string `json:"canonicalUrl"`
 }
 
 var fallbackChecksum = uuid.Must(uuid.NewV4()).String()

internal/frontend/index.go

@@ -45,15 +45,19 @@ type SSRHandler struct {
 
 func NewHandler(cfg *config.Config) (*SSRHandler, error) {
 	basePageConfig := &BasePageConfig{
-		checksums: make(map[string]string),
-		hash:      md5.New(),
-		Version:   version.Version,
-		Commit:    version.Commit,
-		RootURL:   cfg.RootURL,
+		checksums:    make(map[string]string),
+		hash:         md5.New(),
+		Version:      version.Version,
+		Commit:       version.Commit,
+		RootURL:      cfg.RootURL,
+		CanonicalURL: cfg.CanonicalURL,
 	}
 	if cfg.RootPath != "" {
 		basePageConfig.RootPath = "/" + cfg.RootPath
 	}
+	if basePageConfig.CanonicalURL == "" {
+		basePageConfig.CanonicalURL = basePageConfig.RootURL
+	}
 
 	indexJsRawTemplate, err := txtTemplate.
 		New("index-js").

internal/frontend/templates/index.html

@@ -11,8 +11,7 @@
     <meta name="keywords" content="skribbl, skribbl io, skribblio,
             skribbl.io, scribble, scribblers, scribble.rs, pictionary,
             montagsmaler, sketchful, draw and guess, drawmything, free, oss">
-    <!-- Otherwise google will prevent the official hosting from being indexed. -->
-    <link rel="canonical" href="https://scribblers.bios-marcel.link" />
+    <link rel="canonical" href="{{.CanonicalURL}}" />
     {{if ne "" .RootURL}}
     <meta property="og:image" content="{{.RootURL}}{{.RootPath}}/resources/logo.png">
     <meta property="og:image:type" content="image/png">