広場投稿追加画面の刷新 (#399) (#413)

Reviewed-on: #413
Co-authored-by: miteruzo <miteruzo@naver.com>
Co-committed-by: miteruzo <miteruzo@naver.com>

backend/app/services/post_thumbnail_upload_validator.rb

@@ -0,0 +1,34 @@
+class PostThumbnailUploadValidator
+  MAX_THUMBNAIL_BYTES = 20 * 1024 * 1024
+  ALLOWED_CONTENT_TYPES = Preview::ThumbnailFetcher::RASTER_IMAGE_CONTENT_TYPES.freeze
+
+  class InvalidUpload < StandardError; end
+
+  def self.validate! thumbnail
+    return if thumbnail.blank?
+    unless thumbnail.is_a?(ActionDispatch::Http::UploadedFile)
+      raise InvalidUpload, 'thumbnail upload が不正です．'
+    end
+    raise InvalidUpload, 'thumbnail file size が大きすぎます．' if thumbnail.size > MAX_THUMBNAIL_BYTES
+    raise InvalidUpload, 'サムネイル画像の形式が不正です．' unless allowed_content_type?(thumbnail.content_type)
+    bytes = thumbnail.read
+    raise InvalidUpload, 'サムネイル画像の形式が不正です．' if Post.svg_document_bytes?(bytes)
+    unless Post.raster_thumbnail_bytes?(bytes)
+      raise InvalidUpload, 'サムネイル画像の形式が不正です．'
+    end
+
+    attachment = Post.resized_thumbnail_attachment(
+        StringIO.new(bytes),
+        content_type: thumbnail.content_type)
+    attachment[:io].close if attachment[:io].respond_to?(:close)
+  rescue MiniMagick::Error, Timeout::Error
+    raise InvalidUpload, 'サムネイル画像の変換に失敗しました．'
+  ensure
+    thumbnail&.rewind if thumbnail.respond_to?(:rewind)
+  end
+
+  def self.allowed_content_type? content_type
+    mime_type = content_type.to_s.split(';', 2).first.to_s.downcase.strip
+    ALLOWED_CONTENT_TYPES.include?(mime_type)
+  end
+end