backend/app/controllers/preview_controller.rb

@@ -18,14 +18,12 @@ class PreviewController < ApplicationController
   def thumbnail
     return render_bad_request('URL は必須です．') if params[:url].blank?
 
-    image = MiniMagick::Image.read(Preview::ThumbnailFetcher.fetch(params[:url]))
-    image.auto_orient
-    image.resize '180x180>'
-    image.format 'png'
-    width, height = image.dimensions
-    raise Preview::ThumbnailFetcher::GenerationFailed, 'サムネール画像の変換に失敗しました．' if width > 180 || height > 180
-
-    send_data image.to_blob, type: 'image/png', disposition: 'inline'
+    attachment =
+        Post.resized_thumbnail_attachment(
+            StringIO.new(Preview::ThumbnailFetcher.fetch(params[:url])))
+    send_data attachment[:io].read,
+              type: attachment[:content_type],
+              disposition: 'inline'
   rescue Preview::UrlSafety::UnsafeUrl => e
     render_bad_request(e.message)
   rescue Preview::HttpFetcher::FetchTimeout => e

backend/app/models/post.rb

@@ -17,8 +17,6 @@ class Post < ApplicationRecord
   MAX_SVG_DIMENSION = 4_096
   MAX_SVG_PIXELS = 16_777_216
   THUMBNAIL_PROCESS_TIMEOUT = 5.seconds
-  RASTER_THUMBNAIL_FORMATS = ['jpeg', 'png', 'gif', 'webp'].freeze
-
   def self.resized_thumbnail_attachment(upload, content_type: nil)
     upload.rewind
     bytes = upload.read

backend/app/services/preview/thumbnail_fetcher.rb

@@ -4,10 +4,6 @@ module Preview
     RASTER_IMAGE_CONTENT_TYPES = [
       'image/jpeg', 'image/png', 'image/gif', 'image/webp'
     ].freeze
-    REMOTE_IMAGE_CONTENT_TYPES = [
-      *RASTER_IMAGE_CONTENT_TYPES,
-      'image/svg+xml'
-    ].freeze
     HTML_MAX_BYTES = 1.megabyte
     NICONICO_XML_MAX_BYTES = 256.kilobytes
 
@@ -100,13 +96,7 @@ module Preview
       nil
     end
 
-    def self.allowed_remote_image_content_type?(content_type)
-      mime_type = content_type.to_s.split(';', 2).first.downcase.strip
-      REMOTE_IMAGE_CONTENT_TYPES.include?(mime_type)
-    end
-
     private_class_method :fetch_image_or_nil, :fetch_image!,
-                         :niconico_thumbnail_url,
-                         :allowed_remote_image_content_type?
+                         :niconico_thumbnail_url
   end
 end

frontend/src/pages/posts/PostImportReviewPage.tsx

@@ -110,6 +110,7 @@ const isRepairRow = (row: PostImportRow): boolean =>
             && hasErrorMessages (row.validationErrors)))
 
 const DUPLICATE_URL_MESSAGE = 'URL が重複しています．'
+const BULK_PROCESSING_FAILED_MESSAGE = '登録中にエラーが発生しました．'
 
 const rowMetadataPending = (row: PostImportRow): boolean =>
     row.status === 'pending'
@@ -314,14 +315,28 @@ const indexedBulkResults = (
         }
       if (result?.status === 'skipped')
         {
+          const existingPostId =
+              result.existingPostId
+              ?? result.existingPost?.id
+              ?? row.existingPostId
+          if (existingPostId == null)
+            {
+              return {
+                  sourceRow: row.sourceRow,
+                  status: 'failed',
+                  fieldWarnings: result.fieldWarnings,
+                  baseWarnings: result.baseWarnings,
+                  errors: {
+                      ...(errors ?? { }),
+                      base: [...new Set ([...(errors?.base ?? []),
+                                          BULK_PROCESSING_FAILED_MESSAGE])],
+                  },
+                  recoverable: false }
+            }
           return {
               sourceRow: row.sourceRow,
               status: 'skipped',
-              existingPostId:
-		  result.existingPostId
-		  ?? result.existingPost?.id
-		  ?? row.existingPostId
-		  ?? row.sourceRow,
+              existingPostId,
               existingPost: result.existingPost,
               fieldWarnings: result.fieldWarnings,
               baseWarnings: result.baseWarnings,