fix(media): 资源交付 - 按内容识别上传类型并统一重试与附件交付 (#678)

Co-authored-by: ddcat666 <26564566+ddcat666@users.noreply.github.com>

backend/internal/assets/access.go

@@ -140,6 +140,10 @@ func ResolveAccess(resource *model.Resource, setting storage.Settings, options A
 	}
 	if resource.Provider == "local" {
 		access.Delivery = DeliveryLocal
+	} else if !InlineMediaType(resource.MimeType) {
+		// A redirect cannot enforce our attachment and sandbox response headers.
+		access.Delivery = DeliveryProxy
+		access.FallbackReason = "attachment_required"
 	} else if options.Purpose == PurposeDownload {
 		// Cross-origin `a[download]` is only advisory. A real browser download must
 		// therefore be enforced by the object store response itself. Downloads use

backend/internal/assets/content_delivery_test.go

@@ -0,0 +1,24 @@
+package assets
+
+import (
+	"testing"
+	"time"
+
+	"infinite-canvas/backend/internal/storage"
+)
+
+func TestNonMediaDeliveryUsesPlatform(t *testing.T) {
+	for _, mimeType := range []string{"text/html", "image/svg+xml", "application/pdf", "application/octet-stream"} {
+		for _, purpose := range []AccessPurpose{PurposeDisplay, PurposeCopy, PurposeProcess, PurposeDownload, PurposeProvider} {
+			t.Run(mimeType+"/"+string(purpose), func(t *testing.T) {
+				r := testReadyResource("aliyun")
+				r.MimeType = mimeType
+				var variants []ResourceVariant
+				got, err := ResolveAccess(r, storage.Settings{Provider: "aliyun", CDNBaseURL: "https://cdn.example", Delivery: storage.DeliverySettings{CDNAuthMode: "public"}}, AccessOptions{Purpose: purpose}, time.Now(), testPlatformURL(&variants))
+				if err != nil || got.Delivery != DeliveryProxy || len(variants) != 1 {
+					t.Fatalf("non-media escaped controlled delivery: access=%+v err=%v", got, err)
+				}
+			})
+		}
+	}
+}

backend/internal/assets/content_type.go

@@ -0,0 +1,16 @@
+package assets
+
+import (
+	"mime"
+	"strings"
+)
+
+// InlineMediaType excludes active XML images such as SVG. Other documents and
+// unknown formats remain uploadable, but must use controlled attachment delivery.
+func InlineMediaType(value string) bool {
+	mediaType, _, err := mime.ParseMediaType(value)
+	if err != nil || strings.HasSuffix(mediaType, "+xml") || mediaType == "image/svg" {
+		return false
+	}
+	return strings.HasPrefix(mediaType, "image/") || strings.HasPrefix(mediaType, "audio/") || strings.HasPrefix(mediaType, "video/")
+}