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.

1 files changed, 35 insertions, 0 deletions

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