Provide an alternative PDF previewer based on Poppler

mutool is licensed under the Affero GPL, which has strict distribution requirements.

Poppler is licensed under the more liberal GPL, making it a good alternative for those who can't use mutool.

4 files changed, 74 insertions, 28 deletions

diff --git a/activestorage/lib/active_storage/engine.rb b/activestorage/lib/active_storage/engine.rb
index 1e223f9f17..1385e2aa84 100644
--- a/activestorage/lib/active_storage/engine.rb
+++ b/activestorage/lib/active_storage/engine.rb
@@ -3,7 +3,8 @@
 require "rails"
 require "active_storage"
 
-require "active_storage/previewer/pdf_previewer"
+require "active_storage/previewer/poppler_pdf_previewer"
+require "active_storage/previewer/mupdf_previewer"
 require "active_storage/previewer/video_previewer"
 
 require "active_storage/analyzer/image_analyzer"
@@ -14,7 +15,7 @@ module ActiveStorage
     isolate_namespace ActiveStorage
 
     config.active_storage = ActiveSupport::OrderedOptions.new
-    config.active_storage.previewers = [ ActiveStorage::Previewer::PDFPreviewer, ActiveStorage::Previewer::VideoPreviewer ]
+    config.active_storage.previewers = [ ActiveStorage::Previewer::PopplerPDFPreviewer, ActiveStorage::Previewer::MuPDFPreviewer, ActiveStorage::Previewer::VideoPreviewer ]
     config.active_storage.analyzers = [ ActiveStorage::Analyzer::ImageAnalyzer, ActiveStorage::Analyzer::VideoAnalyzer ]
     config.active_storage.paths = ActiveSupport::OrderedOptions.new
 
diff --git a/activestorage/lib/active_storage/previewer/mupdf_previewer.rb b/activestorage/lib/active_storage/previewer/mupdf_previewer.rb
new file mode 100644
index 0000000000..ae02a4889d
--- /dev/null
+++ b/activestorage/lib/active_storage/previewer/mupdf_previewer.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+module ActiveStorage
+  class Previewer::MuPDFPreviewer < Previewer
+    class << self
+      def accept?(blob)
+        blob.content_type == "application/pdf" && mutool_exists?
+      end
+
+      def mutool_path
+        ActiveStorage.paths[:mutool] || "mutool"
+      end
+
+      def mutool_exists?
+        return @mutool_exists unless @mutool_exists.nil?
+
+        system mutool_path, out: File::NULL, err: File::NULL
+
+        @mutool_exists = $?.exitstatus == 1
+      end
+    end
+
+    def preview
+      download_blob_to_tempfile do |input|
+        draw_first_page_from input do |output|
+          yield io: output, filename: "#{blob.filename.base}.png", content_type: "image/png"
+        end
+      end
+    end
+
+    private
+      def draw_first_page_from(file, &block)
+        draw self.class.mutool_path, "draw", "-F", "png", "-o", "-", file.path, "1", &block
+      end
+  end
+end
diff --git a/activestorage/lib/active_storage/previewer/pdf_previewer.rb b/activestorage/lib/active_storage/previewer/pdf_previewer.rb
deleted file mode 100644
index 426ff51eb1..0000000000
--- a/activestorage/lib/active_storage/previewer/pdf_previewer.rb
+++ /dev/null
@@ -1,26 +0,0 @@
-# frozen_string_literal: true
-
-module ActiveStorage
-  class Previewer::PDFPreviewer < Previewer
-    def self.accept?(blob)
-      blob.content_type == "application/pdf"
-    end
-
-    def preview
-      download_blob_to_tempfile do |input|
-        draw_first_page_from input do |output|
-          yield io: output, filename: "#{blob.filename.base}.png", content_type: "image/png"
-        end
-      end
-    end
-
-    private
-      def draw_first_page_from(file, &block)
-        draw mutool_path, "draw", "-F", "png", "-o", "-", file.path, "1", &block
-      end
-
-      def mutool_path
-        ActiveStorage.paths[:mutool] || "mutool"
-      end
-  end
-end
diff --git a/activestorage/lib/active_storage/previewer/poppler_pdf_previewer.rb b/activestorage/lib/active_storage/previewer/poppler_pdf_previewer.rb
new file mode 100644
index 0000000000..2a787362cf
--- /dev/null
+++ b/activestorage/lib/active_storage/previewer/poppler_pdf_previewer.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+module ActiveStorage
+  class Previewer::PopplerPDFPreviewer < Previewer
+    class << self
+      def accept?(blob)
+        blob.content_type == "application/pdf" && pdftoppm_exists?
+      end
+
+      def pdftoppm_path
+        ActiveStorage.paths[:pdftoppm] || "pdftoppm"
+      end
+
+      def pdftoppm_exists?
+        return @pdftoppm_exists unless @pdftoppm_exists.nil?
+
+        @pdftoppm_exists = system(pdftoppm_path, "-v", out: File::NULL, err: File::NULL)
+      end
+    end
+
+    def preview
+      download_blob_to_tempfile do |input|
+        draw_first_page_from input do |output|
+          yield io: output, filename: "#{blob.filename.base}.png", content_type: "image/png"
+        end
+      end
+    end
+
+    private
+      def draw_first_page_from(file, &block)
+        # use 72 dpi to match thumbnail  dimesions of the PDF
+        draw self.class.pdftoppm_path, "-singlefile", "-r", "72", "-png", file.path, &block
+      end
+  end
+end