Support external screenshoter

It's a workaround for SEGV with WebKitGTK+...

bin/chupa-text-decomposer-webkit-screenshoter

@@ -0,0 +1,40 @@
+#!/usr/bin/env ruby
+#
+# Copyright (C) 2017  Kouhei Sutou <kou@clear-code.com>
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+
+require "chupa-text-decomposer-webkit/screenshoter"
+
+logger = Object.new
+def logger.debug
+  $stdout.puts("debug: #{yield}")
+  $stdout.flush
+end
+
+def logger.error
+  $stdout.puts("error: #{yield}")
+  $stdout.flush
+end
+
+path, uri, output_path, width, height = ARGV
+screenshoter = ChupaTextDecomposerWebKit::Screenshoter.new(logger)
+File.open(path) do |input|
+  screenshoter.run(input.read,
+                   uri,
+                   output_path,
+                   Integer(width),
+                   Integer(height))
+end

lib/chupa-text-decomposer-webkit/screenshoter.rb

@@ -0,0 +1,216 @@
+# Copyright (C) 2017  Kouhei Sutou <kou@clear-code.com>
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+
+require "webkit2-gtk"
+
+module ChupaTextDecomposerWebKit
+  class Screenshoter
+    def initialize(logger)
+      @logger = logger
+      @view_context = create_view_context
+      @view = create_view
+      @window = create_window
+      @main_loop = GLib::MainLoop.new(nil, false)
+      @timeout_second = compute_timeout_second
+      @screenshot_cancellable = nil
+      @on_snapshot = nil
+    end
+
+    def run(body, uri, output_path, width, height)
+      @on_snapshot = lambda do |snapshot_surface|
+        scaled_surface = scale_snapshot(snapshot_surface, width, height)
+        scaled_surface.write_to_png(output_path)
+      end
+
+      begin
+        timeout do
+          debug do
+            "#{log_tag}[load][HTML] #{uri}"
+          end
+          @view.load_html(body, uri)
+          @main_loop.run
+        end
+      ensure
+        @on_snapshot = nil
+      end
+    end
+
+    private
+    def create_view_context
+      context = WebKit2Gtk::WebContext.new(ephemeral: true)
+      http_proxy = ENV["http_proxy"]
+      https_proxy = ENV["https_proxy"]
+      ftp_proxy = ENV["ftp_proxy"]
+      if http_proxy or https_proxy or ftp_proxy
+        proxy_settings = WebKit2Gtk::NetworkProxySettings.new
+        if http_proxy
+          proxy_settings.add_proxy_for_scheme("http", http_proxy)
+        end
+        if https_proxy
+          proxy_settings.add_proxy_for_scheme("https", https_proxy)
+        end
+        if ftp_proxy
+          proxy_settings.add_proxy_for_scheme("ftp", ftp_proxy)
+        end
+        context.set_network_proxy_settings(:custom, proxy_settings)
+      end
+      context
+    end
+
+    def create_view
+      view = WebKit2Gtk::WebView.new(context: @view_context)
+
+      view.signal_connect("load-changed") do |_, load_event|
+        debug do
+          "#{log_tag}[load][#{load_event.nick}] #{view.uri}"
+        end
+
+        case load_event
+        when WebKit2Gtk::LoadEvent::FINISHED
+          debug do
+            "#{log_tag}[screenshot][start] #{view.uri}"
+          end
+          cancel_screenshot
+          @screenshot_cancellable = Gio::Cancellable.new
+          view.get_snapshot(:full_document,
+                            :none,
+                            @screenshot_cancellable) do |_, result|
+            @screenshot_cancellable = nil
+            @main_loop.quit
+            begin
+              snapshot_surface = view.get_snapshot_finish(result)
+            rescue
+              error do
+                message = "failed to create snapshot: #{view.uri}: "
+                message << "#{$!.class}: #{$!.message}"
+                "#{log_tag}[screenshot][failed] #{message}"
+              end
+            else
+              debug do
+                size = "#{snapshot_surface.width}x#{snapshot_surface.height}"
+                "#{log_tag}[screenshot][finish] #{view.uri}: #{size}"
+              end
+              unless snapshot_surface.width.zero?
+                @on_snapshot.call(snapshot_surface) if @on_snapshot
+              end
+            end
+          end
+        end
+      end
+
+      view.signal_connect("load-failed") do |_, _, failed_uri, error|
+        cancel_screenshot
+        @main_loop.quit
+        error do
+          message = "failed to load URI: #{failed_uri}: "
+          message << "#{error.class}(#{error.code}): #{error.message}"
+          "#{log_tag}[load][failed] #{message}"
+        end
+        true
+      end
+
+      view
+    end
+
+    def scale_snapshot(snapshot_surface, width, height)
+      scaled_surface = Cairo::ImageSurface.new(:argb32, width, height)
+
+      context = Cairo::Context.new(scaled_surface)
+      context.set_source_color(:white)
+      context.paint
+
+      ratio = width.to_f / snapshot_surface.width
+      context.scale(ratio, ratio)
+      context.set_source(snapshot_surface)
+      context.paint
+
+      scaled_surface
+    end
+
+    def create_window
+      window = Gtk::OffscreenWindow.new
+      window.set_default_size(800, 600)
+      window.add(@view)
+      window.show_all
+      window
+    end
+
+    def cancel_screenshot
+      return if @screenshot_cancellable.nil?
+
+      debug do
+        "#{log_tag}[snapshot][cancel] cancel screenshot: #{@view.uri}"
+      end
+      @screenshot_cancellable.cancel
+      @screenshot_cancellable = nil
+    end
+
+    def timeout
+      timeout_id = GLib::Timeout.add_seconds(@timeout_second) do
+        timeout_id = nil
+        error do
+          message = "timeout to load URI: #{@timeout_second}s: #{@view.uri}"
+          message << ": loading" if @view.loading?
+          "#{log_tag}[load][timeout] #{message}"
+        end
+        cancel_screenshot
+        if @view.loading?
+          close_id = @view.signal_connect("close") do
+            @view.signal_handler_disconnect(close_id)
+            @main_loop.quit
+            error do
+              "#{log_tag}[load][closed] #{@view.uri}"
+            end
+          end
+          @view.try_close
+        else
+          @main_loop.quit
+        end
+        GLib::Source::REMOVE
+      end
+
+      begin
+        yield
+      ensure
+        GLib::Source.remove(timeout_id) if timeout_id
+      end
+    end
+
+    def compute_timeout_second
+      default_timeout = 5
+      timeout_string =
+        ENV["CHUPA_TEXT_DECOMPOSER_WEBKIT_TIMEOUT"] || default_timeout.to_s
+      begin
+        Integer(timeout_string)
+      rescue ArgumentError
+        default_timeout
+      end
+    end
+
+    private
+    def log_tag
+      "[decomposer][webkit]"
+    end
+
+    def debug(*args, &block)
+      @logger.debug(*args, &block)
+    end
+
+    def error(*args, &block)
+      @logger.error(*args, &block)
+    end
+  end
+end