#398

backend/app/services/preview/screenshot.rb

@@ -1,64 +0,0 @@
-module Preview
-  class Screenshot
-    class Unavailable < StandardError; end
-    class Busy < Unavailable; end
-    class TimedOut < Unavailable; end
-
-    LIMIT = ENV.fetch('PREVIEW_SCREENSHOT_CONCURRENCY', 2).to_i.clamp(1, 10)
-    TIMEOUT = ENV.fetch('PREVIEW_SCREENSHOT_TIMEOUT', 20).to_i.clamp(5, 60)
-    @mutex = Mutex.new
-    @active = 0
-
-    def self.capture(url)
-      acquire!
-      tempfile = nil
-      pid = nil
-
-      begin
-        tempfile = Tempfile.new(['preview-thumbnail', '.png'])
-        tempfile.close
-        status = nil
-        pid = Process.spawn(
-            'node', Rails.root.join('lib/screenshot.js').to_s,
-            url, tempfile.path,
-            out: File::NULL, err: File::NULL, pgroup: true)
-        Timeout.timeout(TIMEOUT) do
-          _finished_pid, status = Process.wait2(pid)
-        end
-        raise Unavailable, 'スクリーンショットを生成できませんでした．' unless status.success?
-        raise Unavailable, 'スクリーンショットを生成できませんでした．' unless File.size?(tempfile.path)
-
-        File.binread(tempfile.path)
-      rescue Timeout::Error
-        terminate(pid)
-        raise TimedOut, 'スクリーンショット生成が timeout しました．'
-      ensure
-        tempfile&.unlink
-        release!
-      end
-    end
-
-    def self.acquire!
-      @mutex.synchronize do
-        raise Busy, 'スクリーンショット生成が混雑してゐます．' if @active >= LIMIT
-
-        @active += 1
-      end
-    end
-
-    def self.release!
-      @mutex.synchronize { @active -= 1 }
-    end
-
-    def self.terminate(pid)
-      return unless pid
-
-      Process.kill('TERM', -pid)
-      Process.wait(pid)
-    rescue Errno::ESRCH, Errno::ECHILD
-      nil
-    end
-
-    private_class_method :acquire!, :release!, :terminate
-  end
-end

backend/app/services/preview/thumbnail_fetcher.rb

@@ -4,18 +4,15 @@ module Preview
 
     def self.fetch(raw_url)
       uri, = UrlSafety.validate(raw_url)
-      page = nil
 
       known_url = KnownSiteExtractor.thumbnail_url(uri)
-      image = fetch_image(known_url) if known_url
+      return fetch_image(known_url) if known_url
 
-      unless image
-        page = HttpFetcher.fetch(uri.to_s)
-        metadata = HtmlMetadataExtractor.extract(page)
-        image = fetch_image(metadata[:image_url]) if metadata[:image_url]
-      end
+      page = HttpFetcher.fetch(uri.to_s)
+      metadata = HtmlMetadataExtractor.extract(page)
+      raise GenerationFailed, 'サムネール画像が見つかりませんでした．' if metadata[:image_url].blank?
 
-      image || Screenshot.capture(uri.to_s)
+      fetch_image(metadata[:image_url])
     end
 
     def self.title(raw_url)
@@ -25,11 +22,15 @@ module Preview
 
     def self.fetch_image(url)
       response = HttpFetcher.fetch(url)
-      return unless response.content_type.downcase.start_with?('image/')
+      unless response.content_type.downcase.start_with?('image/')
+        raise GenerationFailed, 'サムネール画像が見つかりませんでした．'
+      end
 
       response.body
+    rescue HttpFetcher::FetchTimeout
+      raise
     rescue HttpFetcher::FetchFailed
-      nil
+      raise GenerationFailed, 'サムネール画像を取得できませんでした．'
     end
 
     private_class_method :fetch_image

backend/app/services/preview/url_safety.rb

@@ -22,7 +22,7 @@ module Preview
           raise UnsafeUrl, 'http または https の URL を指定してください．'
         end
       else
-        value = "https://#{ value }"
+        value = "http://#{ value }"
       end
       uri = URI.parse(value)