#398

backend/app/controllers/preview_controller.rb

@@ -6,7 +6,7 @@ class PreviewController < ApplicationController
 
     render json: { title: Preview::ThumbnailFetcher.title(params[:url]) }
   rescue Preview::UrlSafety::UnsafeUrl => e
-    render_preview_error(e.message, :unprocessable_entity)
+    render_bad_request(e.message)
   rescue Preview::HttpFetcher::FetchTimeout => e
     render_preview_error(e.message, :gateway_timeout)
   rescue Preview::HttpFetcher::FetchFailed => e
@@ -20,17 +20,18 @@ class PreviewController < ApplicationController
     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'
   rescue Preview::UrlSafety::UnsafeUrl => e
-    render_preview_error(e.message, :unprocessable_entity)
-  rescue Preview::Screenshot::Busy => e
-    render_preview_error(e.message, :too_many_requests)
-  rescue Preview::Screenshot::TimedOut, Preview::HttpFetcher::FetchTimeout => e
+    render_bad_request(e.message)
+  rescue Preview::HttpFetcher::FetchTimeout => e
     render_preview_error(e.message, :gateway_timeout)
   rescue Preview::HttpFetcher::FetchFailed => e
     render_preview_error(e.message, :bad_gateway)
-  rescue Preview::Screenshot::Unavailable, MiniMagick::Error => e
-    render_preview_error(e.message, :unprocessable_entity)
+  rescue Preview::ThumbnailFetcher::GenerationFailed, MiniMagick::Error => e
+    render_unprocessable_entity(e.message)
   end
 
   private

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)
 

backend/lib/package.json

@@ -1,15 +0,0 @@
-{
-  "name": "lib",
-  "version": "1.0.0",
-  "main": "screenshot.js",
-  "scripts": {
-    "test": "echo \"Error: no test specified\" && exit 1"
-  },
-  "keywords": [],
-  "author": "",
-  "license": "ISC",
-  "description": "",
-  "dependencies": {
-    "puppeteer": "^24.10.0"
-  }
-}

backend/lib/screenshot.js

@@ -1,60 +0,0 @@
-const puppeteer = require ('puppeteer')
-const dns = require ('dns').promises
-const net = require ('net')
-
-const forbiddenNetworks = [
-  ['0.0.0.0', 8], ['10.0.0.0', 8], ['100.64.0.0', 10],
-  ['127.0.0.0', 8], ['169.254.0.0', 16], ['172.16.0.0', 12],
-  ['192.0.0.0', 24], ['192.0.2.0', 24], ['192.168.0.0', 16],
-  ['198.18.0.0', 15], ['198.51.100.0', 24], ['203.0.113.0', 24],
-  ['224.0.0.0', 4], ['240.0.0.0', 4], ['::', 128], ['::1', 128],
-  ['fc00::', 7], ['fe80::', 10], ['ff00::', 8], ['2001:db8::', 32],
-  ['::ffff:0:0', 96]]
-
-const blockList = new net.BlockList ()
-forbiddenNetworks.forEach (([address, prefix]) => {
-  blockList.addSubnet (address, prefix, net.isIPv6 (address) ? 'ipv6' : 'ipv4')
-})
-
-
-const safeUrl = async rawUrl => {
-  const url = new URL (rawUrl)
-  if (!['http:', 'https:'].includes (url.protocol) || url.username || url.password)
-    return false
-
-  const addresses = await dns.lookup (url.hostname, { all: true, verbatim: true })
-  return addresses.length > 0 && addresses.every (
-      ({ address, family }) => !blockList.check (address, family === 6 ? 'ipv6' : 'ipv4'))
-}
-
-void (async () => {
-  const url = process.argv[2]
-  const output = process.argv[3]
-  if (!(await safeUrl (url)))
-    throw new Error ('Unsafe page URL')
-
-  const browser = await puppeteer.launch ({
-      args: ['--no-sandbox', '--disable-setuid-sandbox'] })
-
-  try
-  {
-    const page = await browser.newPage ()
-    await page.setRequestInterception (true)
-    page.on ('request', request => {
-      void safeUrl (request.url ())
-	.then (safe => safe ? request.continue () : request.abort ())
-	.catch (() => request.abort ())
-    })
-    await page.setViewport ({ width: 960, height: 960 })
-    await page.goto (url, { waitUntil: 'domcontentloaded', timeout: 12000 })
-    await new Promise (resolve => setTimeout (resolve, 1000))
-    await page.screenshot ({ path: output })
-  }
-  finally
-  {
-    await browser.close ()
-  }
-}) ().catch (error => {
-  console.error (error)
-  process.exitCode = 1
-})