feat(server+web): 客户端下载闭环——pangolin-server /downloads + 官网下载链接

- server: /downloads/* 公开静态服务(NewDownloadsHandler,DOWNLOADS_DIR 默认
  /var/lib/pangolin/downloads),防目录穿越/不列目录/缺目录不崩,Cache-Control:
  no-cache 保证 CI 覆盖后永远最新。挂在 /healthz 同级(免鉴权)。含 4 项测试。
- deploy.sh: install -d 下载目录 + server.env 注入 DOWNLOADS_DIR。
- web: site.ts 增 downloads.{android,windows}(→ https://api.yanmeiai.com/downloads/*);
  Download.astro 接上 Android/Windows 按钮,iOS/macOS/Linux 改「即将推出」禁用态。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013nMthbVEmQquxBRKb9Fj8u

server/internal/httpapi/downloads.go

@@ -0,0 +1,87 @@
+package httpapi
+
+import (
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/go-chi/chi/v5"
+)
+
+// DownloadsHandler 静态服务客户端安装包(pangolin-android.apk /
+// pangolin-windows-x64-setup.exe 等),供官网下载按钮直链。CI
+// (scripts/ci/deploy-client.sh)把最新安装包 scp 到该目录、按平台固定文件名覆盖。
+//
+// 无需鉴权(匿名下载),但:
+//   - 不暴露目录列表(裸目录 / 不存在的文件一律 404,不用 http.FileServer 的默认
+//     目录浏览行为)
+//   - 防目录穿越(拒绝任何解析后逃出 dir 的路径,而不仅仅是字符串里含 ".." 就拒,
+//     这样能正确处理 "foo/../bar" 这类仍落在 dir 内的写法,同时挡住真正逃逸的路径)
+//   - DOWNLOADS_DIR 在启动时可以不存在(比如还没跑过一次 CI 部署),路由仍要能
+//     注册,只是请求会 404,不能让进程直接崩溃
+type DownloadsHandler struct {
+	dir string
+}
+
+// NewDownloadsHandler 指定安装包所在目录(DOWNLOADS_DIR,默认 /var/lib/pangolin/downloads)。
+func NewDownloadsHandler(dir string) *DownloadsHandler {
+	if dir == "" {
+		dir = "/var/lib/pangolin/downloads"
+	}
+	return &DownloadsHandler{dir: dir}
+}
+
+// Serve 处理 GET /downloads/{file}(chi 通配 "*",支持任意文件名,不限定白名单,
+// 因为 CI 产出的安装包文件名随平台/版本命名策略变化,这里只做路径安全校验)。
+func (h *DownloadsHandler) Serve(w http.ResponseWriter, r *http.Request) {
+	name := chi.URLParam(r, "*")
+	if name == "" {
+		http.NotFound(w, r)
+		return
+	}
+
+	// 拒绝任何路径分隔符之外的穿越:先按 "/" 做 Clean,再校验结果既不是绝对路径、
+	// 也没有以 ".." 开头(即没有逃出 dir),最后拒绝空/根路径。这比单纯 strings.Contains(name, "..")
+	// 更准确 —— 例如 "sub/../file.apk" 清洗后是 "file.apk",本来就没有逃逸,不该被误杀;
+	// 而 "../etc/passwd" 清洗后以 ".." 开头,必须拒绝。
+	cleaned := filepath.Clean("/" + name) // 前置 "/" 后 Clean,任何 ".." 都无法越过根
+	cleaned = strings.TrimPrefix(cleaned, "/")
+	if cleaned == "" || cleaned == "." || strings.HasPrefix(cleaned, "..") {
+		http.NotFound(w, r)
+		return
+	}
+
+	full := filepath.Join(h.dir, cleaned)
+	// 双重保险:确认最终路径确实在 dir 之下(处理 dir 本身含 ".." 或符号链接等边角情况)。
+	relDir, err := filepath.Abs(h.dir)
+	if err != nil {
+		http.NotFound(w, r)
+		return
+	}
+	absFull, err := filepath.Abs(full)
+	if err != nil || (absFull != relDir && !strings.HasPrefix(absFull, relDir+string(filepath.Separator))) {
+		http.NotFound(w, r)
+		return
+	}
+
+	f, err := os.Open(full)
+	if err != nil {
+		http.NotFound(w, r)
+		return
+	}
+	defer f.Close()
+
+	st, err := f.Stat()
+	if err != nil || st.IsDir() {
+		http.NotFound(w, r)
+		return
+	}
+
+	w.Header().Set("Content-Disposition", "attachment; filename=\""+filepath.Base(cleaned)+"\"")
+	// no-cache:CI「仅留最新」在同一稳定 URL 覆盖文件,不能让 CF/浏览器返回旧包。
+	// no-cache = 可缓存但每次须回源校验;ServeContent 带 Last-Modified,未变则 304
+	// (便宜),变了才传新字节 —— 既保证永远最新,又避免每次全量 82MB 回源。
+	w.Header().Set("Cache-Control", "no-cache")
+	http.ServeContent(w, r, filepath.Base(cleaned), st.ModTime(), f)
+}

server/internal/httpapi/downloads_test.go

@@ -0,0 +1,117 @@
+package httpapi
+
+import (
+	"context"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/go-chi/chi/v5"
+)
+
+// buildDownloadsRouter mounts DownloadsHandler on a real chi router (mirrors
+// how main.go mounts it under "/downloads/*") so the wildcard param behaves
+// exactly as it does in production.
+func buildDownloadsRouter(dir string) chi.Router {
+	h := NewDownloadsHandler(dir)
+	r := chi.NewRouter()
+	r.Get("/downloads/*", h.Serve)
+	return r
+}
+
+func TestDownloadsHandler_ServesExistingFile(t *testing.T) {
+	dir := t.TempDir()
+	content := []byte("hello pangolin apk bytes")
+	if err := os.WriteFile(filepath.Join(dir, "pangolin-android.apk"), content, 0o644); err != nil {
+		t.Fatalf("write fixture: %v", err)
+	}
+
+	r := buildDownloadsRouter(dir)
+	req := httptest.NewRequest("GET", "/downloads/pangolin-android.apk", nil)
+	rec := httptest.NewRecorder()
+	r.ServeHTTP(rec, req)
+
+	if rec.Code != 200 {
+		t.Fatalf("status = %d, want 200; body=%s", rec.Code, rec.Body.String())
+	}
+	if got := rec.Body.String(); got != string(content) {
+		t.Errorf("body = %q, want %q", got, content)
+	}
+}
+
+func TestDownloadsHandler_MissingFile404(t *testing.T) {
+	dir := t.TempDir()
+	r := buildDownloadsRouter(dir)
+
+	req := httptest.NewRequest("GET", "/downloads/nope.exe", nil)
+	rec := httptest.NewRecorder()
+	r.ServeHTTP(rec, req)
+
+	if rec.Code != 404 {
+		t.Fatalf("status = %d, want 404", rec.Code)
+	}
+}
+
+func TestDownloadsHandler_BareDirNotListed(t *testing.T) {
+	dir := t.TempDir()
+	if err := os.WriteFile(filepath.Join(dir, "pangolin-android.apk"), []byte("x"), 0o644); err != nil {
+		t.Fatalf("write fixture: %v", err)
+	}
+	r := buildDownloadsRouter(dir)
+
+	req := httptest.NewRequest("GET", "/downloads/", nil)
+	rec := httptest.NewRecorder()
+	r.ServeHTTP(rec, req)
+
+	if rec.Code != 404 {
+		t.Fatalf("bare dir status = %d, want 404 (no directory listing)", rec.Code)
+	}
+}
+
+func TestDownloadsHandler_PathTraversalBlocked(t *testing.T) {
+	outerDir := t.TempDir()
+	secretPath := filepath.Join(outerDir, "secret.txt")
+	if err := os.WriteFile(secretPath, []byte("top secret"), 0o600); err != nil {
+		t.Fatalf("write secret: %v", err)
+	}
+
+	dir := filepath.Join(outerDir, "downloads")
+	if err := os.Mkdir(dir, 0o755); err != nil {
+		t.Fatalf("mkdir downloads: %v", err)
+	}
+	if err := os.WriteFile(filepath.Join(dir, "pangolin-android.apk"), []byte("apk"), 0o644); err != nil {
+		t.Fatalf("write fixture: %v", err)
+	}
+
+	r := buildDownloadsRouter(dir)
+
+	// net/http's ServeMux/chi normalize ".." segments in the URL path before
+	// routing, so we exercise the handler directly with a raw URLParam to
+	// simulate any escape attempt that might otherwise reach it, in addition
+	// to the router-level request below.
+	h := NewDownloadsHandler(dir)
+	req := httptest.NewRequest("GET", "/downloads/../secret.txt", nil)
+	rctx := chi.NewRouteContext()
+	rctx.URLParams.Add("*", "../secret.txt")
+	ctx := context.WithValue(req.Context(), chi.RouteCtxKey, rctx)
+	req = req.WithContext(ctx)
+	rec := httptest.NewRecorder()
+	h.Serve(rec, req)
+	if rec.Code != 404 {
+		t.Fatalf("direct traversal status = %d, want 404 (must not escape dir)", rec.Code)
+	}
+	if rec.Body.String() == "top secret" {
+		t.Fatalf("traversal leaked secret file contents")
+	}
+
+	// Router-level request: most HTTP clients/servers collapse ".." during URL
+	// normalization, but confirm the end-to-end path also can't reach the file
+	// outside dir and doesn't 200 with the secret's contents.
+	req2 := httptest.NewRequest("GET", "/downloads/../secret.txt", nil)
+	rec2 := httptest.NewRecorder()
+	r.ServeHTTP(rec2, req2)
+	if rec2.Body.String() == "top secret" {
+		t.Fatalf("router-level traversal leaked secret file contents (status=%d)", rec2.Code)
+	}
+}