feat(server/m7-363): branding-aware index handler with html/template

web/template.go

@@ -0,0 +1,32 @@
+package web
+
+import (
+	"bytes"
+	"fmt"
+	"html/template"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/config"
+)
+
+// applyBrandingTemplate parses the given HTML source as an html/template,
+// substitutes the branding fields, and returns the rendered bytes. Used
+// by Handler at construction time so each request serves cached output
+// rather than re-rendering. The Vite build (T4) injects the {{ .AppName }}
+// and similar tokens into the head of build/index.html; in dev (vite dev)
+// no tokens are present and the template effectively returns the source
+// unchanged.
+//
+// html/template's context-aware escaping handles XSS for both the
+// HTML-attribute contexts (e.g. <meta content="...">) and the JS-string
+// context inside <script>window.__MINSTREL__ = { appName: "..." }</script>.
+func applyBrandingTemplate(htmlSrc string, branding config.BrandingConfig) ([]byte, error) {
+	tpl, err := template.New("index").Parse(htmlSrc)
+	if err != nil {
+		return nil, fmt.Errorf("parse index template: %w", err)
+	}
+	var buf bytes.Buffer
+	if err := tpl.Execute(&buf, branding); err != nil {
+		return nil, fmt.Errorf("execute index template: %w", err)
+	}
+	return buf.Bytes(), nil
+}