BlueArchiveToolkit/internal/api/cdn.go

package api

import (
	"fmt"
	"mime"
	"net/http"
	"os"
	"path/filepath"
	"strings"
)

func (s *Server) serveCDN(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet && r.Method != http.MethodHead {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	idx := s.index()
	if idx == nil || idx.ResourceRoot == "" {
		http.Error(w, "resource root not ready", http.StatusServiceUnavailable)
		return
	}
	_, rel, err := SplitCDNPath(r.URL.Path)
	if err != nil {
		http.NotFound(w, r)
		return
	}

	var entry ResourceEntry
	var hasEntry bool
	if s.cfg.RequireIndexed {
		entry, hasEntry = idx.Lookup(rel)
		if !hasEntry || !entry.Present || !entry.SizeMatch {
			http.NotFound(w, r)
			return
		}
	}

	abs, err := ResolveUnderRoot(idx.ResourceRoot, rel, true)
	if err != nil {
		http.NotFound(w, r)
		return
	}
	info, err := os.Stat(abs)
	if err != nil || !info.Mode().IsRegular() {
		http.NotFound(w, r)
		return
	}
	if s.cfg.RequireIndexed && s.cfg.VerifySize {
		if hasEntry && entry.Bytes > 0 && uint64(info.Size()) != entry.Bytes {
			http.Error(w, "size mismatch with release index", http.StatusConflict)
			return
		}
	}

	file, err := os.Open(abs)
	if err != nil {
		http.NotFound(w, r)
		return
	}
	defer file.Close()

	w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
	w.Header().Set("ETag", cdnETag(entry, hasEntry, info))
	w.Header().Set("Content-Type", cdnContentType(abs))
	http.ServeContent(w, r, info.Name(), info.ModTime(), file)
}

func cdnETag(entry ResourceEntry, hasEntry bool, info os.FileInfo) string {
	if hasEntry && entry.BLAKE3 != "" {
		return fmt.Sprintf(`"blake3-%s"`, entry.BLAKE3)
	}
	return fmt.Sprintf(`W/"%d-%d"`, info.Size(), info.ModTime().UnixNano())
}

func cdnContentType(abs string) string {
	ext := strings.ToLower(filepath.Ext(abs))
	if ext == ".json" {
		return "application/json; charset=utf-8"
	}
	if ext == ".hash" {
		return "text/plain; charset=utf-8"
	}
	if detected := mime.TypeByExtension(ext); detected != "" {
		return detected
	}
	return "application/octet-stream"
}