fix(proxy): preserve proxied download filenames (#2824)

- Override transparent proxy Content-Disposition with the OpenList object name
- Add regression coverage for incorrect upstream download headers

Signed-off-by: jyxjjj <16695261+jyxjjj@users.noreply.github.com>
Co-authored-by: Codex <267193182+codex@users.noreply.github.com>

Author: jyxjjj

server/common/proxy.go

@@ -59,6 +59,7 @@ func Proxy(w http.ResponseWriter, r *http.Request, link *model.Link, file model.
 	defer res.Body.Close()
 
 	maps.Copy(w.Header(), res.Header)
+	w.Header().Set("Content-Disposition", utils.GenerateContentDisposition(file.GetName()))
 	w.WriteHeader(res.StatusCode)
 	if r.Method == http.MethodHead {
 		return nil

server/common/proxy_test.go

@@ -0,0 +1,54 @@
+package common
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/OpenListTeam/OpenList/v4/internal/conf"
+	"github.com/OpenListTeam/OpenList/v4/internal/model"
+	"github.com/OpenListTeam/OpenList/v4/pkg/utils"
+)
+
+func TestProxyOverridesUpstreamContentDisposition(t *testing.T) {
+	previousConfig := conf.Conf
+	conf.Conf = conf.DefaultConfig("data")
+	t.Cleanup(func() {
+		conf.Conf = previousConfig
+	})
+
+	const content = "archive content"
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Disposition", `attachment; filename="download"`)
+		w.Header().Set("Content-Type", "application/x-rar-compressed")
+		w.WriteHeader(http.StatusOK)
+		_, _ = io.WriteString(w, content)
+	}))
+	t.Cleanup(upstream.Close)
+
+	file := &model.Object{
+		Name: "测试文件.rar",
+		Size: int64(len(content)),
+	}
+	link := &model.Link{URL: upstream.URL}
+	recorder := httptest.NewRecorder()
+	request := httptest.NewRequest(http.MethodGet, "/sd/example", nil)
+
+	err := Proxy(recorder, request, link, file)
+	if err != nil {
+		t.Fatalf("Proxy() error = %v", err)
+	}
+	if got, want := recorder.Code, http.StatusOK; got != want {
+		t.Fatalf("status code = %d, want %d", got, want)
+	}
+	if got, want := recorder.Header().Get("Content-Disposition"), utils.GenerateContentDisposition(file.GetName()); got != want {
+		t.Errorf("Content-Disposition = %q, want %q", got, want)
+	}
+	if got, want := recorder.Header().Get("Content-Type"), "application/x-rar-compressed"; got != want {
+		t.Errorf("Content-Type = %q, want %q", got, want)
+	}
+	if got, want := recorder.Body.String(), content; got != want {
+		t.Errorf("body = %q, want %q", got, want)
+	}
+}