Initial commit

Assisted-by: GLM 5.3

internal/web/assets.go

@@ -0,0 +1,90 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: PolyForm-Noncommercial-1.0.0
+
+package web
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"embed"
+	"encoding/hex"
+	"io/fs"
+	"net/http"
+	"path"
+	"strings"
+	"time"
+)
+
+// adminAssets carries the interface sheets, the self-hosted fonts and the
+// glyph sprite of the admin UI, packaged next to the templates so one
+// binary serves the whole product.
+//
+//go:embed static/*.css static/graphis.svg static/fonts/*.woff2
+var adminAssets embed.FS
+
+// asset is one packaged file with its content type and an ETag derived
+// from its bytes.
+type asset struct {
+	body        []byte
+	contentType string
+	etag        string
+}
+
+// assets indexes the packaged files by their URL tail under
+// /admin/assets/. The index doubles as the allow-list: a path the binary
+// does not hold is a 404, so no traversal can reach the disk.
+var assets = func() map[string]*asset {
+	entries, err := fs.ReadDir(adminAssets, "static")
+	if err != nil {
+		panic("web: embedded assets unreadable: " + err.Error())
+	}
+	out := map[string]*asset{}
+	add := func(name, tail, contentType string) {
+		body, err := adminAssets.ReadFile(name)
+		if err != nil {
+			panic("web: embedded asset unreadable: " + name)
+		}
+		sum := sha256.Sum256(body)
+		out[tail] = &asset{
+			body:        body,
+			contentType: contentType,
+			etag:        `"` + hex.EncodeToString(sum[:])[:16] + `"`,
+		}
+	}
+	for _, entry := range entries {
+		if entry.IsDir() {
+			continue
+		}
+		name := entry.Name()
+		switch {
+		case strings.HasSuffix(name, ".css"):
+			add("static/"+name, name, "text/css; charset=utf-8")
+		case strings.HasSuffix(name, ".svg"):
+			add("static/"+name, name, "image/svg+xml; charset=utf-8")
+		}
+	}
+	fonts, err := fs.ReadDir(adminAssets, "static/fonts")
+	if err != nil {
+		panic("web: embedded fonts unreadable: " + err.Error())
+	}
+	for _, font := range fonts {
+		add("static/fonts/"+font.Name(), "fonts/"+font.Name(), "font/woff2")
+	}
+	return out
+}()
+
+// AssetHandler serves one embedded asset by its tail under
+// /admin/assets/. Responses are revalidatable: the ETag is the content,
+// so a deploy refreshes every page while a visit fetches nothing new.
+func AssetHandler(w http.ResponseWriter, r *http.Request) {
+	tail := path.Clean(strings.TrimPrefix(r.URL.Path, "/admin/assets/"))
+	found, ok := assets[strings.TrimPrefix(tail, "./")]
+	if !ok || tail == "." {
+		http.NotFound(w, r)
+		return
+	}
+	w.Header().Set("Content-Type", found.contentType)
+	w.Header().Set("ETag", found.etag)
+	w.Header().Set("Cache-Control", "public, max-age=0, must-revalidate")
+	http.ServeContent(w, r, tail, time.Time{}, bytes.NewReader(found.body))
+}