adjust preview cache

app/controllers/preview_document_page_controller.rb

@@ -5,6 +5,10 @@ class PreviewDocumentPageController < ActionController::API
 
   FORMAT = Templates::ProcessDocument::FORMAT
 
+  TMPFILE_PREFIX = 'attachment-'
+  TMPFILE_TTL = 5.minutes
+  TMPFILE_MAX_TOTAL_SIZE = Docuseal.multitenant? ? 400.megabytes : 1.gigabyte
+
   def show
     result_data =
       ApplicationRecord.signed_id_verifier.verified(params[:signed_key], purpose: :attachment)
@@ -30,34 +34,63 @@ class PreviewDocumentPageController < ActionController::API
                          allow_other_host: true
     end
 
-    file_path =
-      if attachment.service.name == :disk
-        ActiveStorage::Blob.service.path_for(attachment.key)
-      else
-        find_or_create_document_tempfile_path(attachment)
-      end
-
     preview_image =
-      Templates::ProcessDocument.generate_pdf_preview_from_file(attachment, file_path, params[:id].to_i)
+      open_attachment_io(attachment) do |io|
+        Templates::ProcessDocument.generate_pdf_preview_from_io(attachment, io, params[:id].to_i)
+      end
 
     redirect_to preview_image.url(time: ActiveStorage::Attachment.service_url_time), allow_other_host: true
   end
 
-  def find_or_create_document_tempfile_path(attachment)
-    file_path = "#{Dir.tmpdir}/attachment-#{Digest::SHA1.hexdigest("#{attachment.id}-#{attachment.uuid}")}"
+  def open_attachment_io(attachment, &)
+    return File.open(ActiveStorage::Blob.service.path_for(attachment.key), 'rb', &) if attachment.service.name == :disk
 
-    File.open(file_path, File::RDWR | File::CREAT, 0o644) do |f|
-      f.flock(File::LOCK_EX)
+    file_name = "#{TMPFILE_PREFIX}#{Digest::SHA1.hexdigest("#{attachment.id}-#{attachment.uuid}")}"
+
+    file_path = File.join(Dir.tmpdir, file_name)
+
+    File.open(file_path, File::RDWR | File::CREAT, 0o644) do |file|
+      file.flock(File::LOCK_EX)
 
       # rubocop:disable Style/ZeroLengthPredicate
-      if f.size.zero?
-        f.binmode
+      if file.size.zero?
+        cleanup_stale_tempfiles
 
-        f.write(attachment.download)
+        file.binmode
+
+        file.write(attachment.download)
+      else
+        FileUtils.touch(file_path)
       end
       # rubocop:enable Style/ZeroLengthPredicate
-    end
 
-    file_path
+      file.flock(File::LOCK_UN)
+
+      yield file
+    end
+  end
+
+  def cleanup_stale_tempfiles
+    entries =
+      Dir.glob(File.join(Dir.tmpdir, "#{TMPFILE_PREFIX}*")).filter_map do |path|
+        stat = File.stat(path)
+
+        [path, stat.mtime, stat.size]
+      rescue Errno::ENOENT
+        nil
+      end
+
+    total_size = entries.sum(&:last)
+    stale_time = TMPFILE_TTL.ago
+
+    entries.sort_by(&:second).each do |path, mtime, size|
+      break if mtime > stale_time && total_size <= TMPFILE_MAX_TOTAL_SIZE
+
+      File.unlink(path)
+
+      total_size -= size
+    rescue Errno::ENOENT
+      nil
+    end
   end
 end

lib/pdfium.rb

@@ -98,6 +98,7 @@ class Pdfium
 
   attach_function :FPDF_LoadDocument, %i[string FPDF_STRING], :FPDF_DOCUMENT
   attach_function :FPDF_LoadMemDocument, %i[pointer int FPDF_STRING], :FPDF_DOCUMENT
+  attach_function :FPDF_LoadCustomDocument, %i[pointer FPDF_STRING], :FPDF_DOCUMENT
   attach_function :FPDF_CloseDocument, [:FPDF_DOCUMENT], :void
   attach_function :FPDF_GetPageCount, [:FPDF_DOCUMENT], :int
   attach_function :FPDF_GetLastError, [], :ulong
@@ -463,6 +464,43 @@ class Pdfium
       end
     end
 
+    def self.open_io(io, password = nil)
+      io.binmode
+
+      get_block = FFI::Function.new(:int, %i[pointer ulong pointer ulong]) do |_param, position, out, size|
+        io.seek(position)
+
+        bytes = io.read(size).to_s
+
+        out.put_bytes(0, bytes)
+
+        bytes.bytesize == size ? 1 : 0
+      end
+
+      file_access = Pdfium::FPDF_FILEACCESS.new
+      file_access[:m_FileLen] = io.size
+      file_access[:m_GetBlock] = get_block
+      file_access[:m_Param] = FFI::Pointer::NULL
+
+      doc_ptr = Pdfium.FPDF_LoadCustomDocument(file_access, password)
+
+      if doc_ptr.null?
+        Pdfium.check_last_error('Failed to load document from IO')
+
+        raise PdfiumError, 'Failed to load document from IO, pointer is NULL.'
+      end
+
+      doc = new(doc_ptr, [file_access, get_block, io])
+
+      return doc unless block_given?
+
+      begin
+        yield doc
+      ensure
+        doc.close
+      end
+    end
+
     def closed?
       @closed
     end

lib/templates/process_document.rb

@@ -192,8 +192,8 @@ module Templates
       end
     end
 
-    def generate_pdf_preview_from_file(attachment, file_path, page_number)
-      doc = Pdfium::Document.open_file(file_path)
+    def generate_pdf_preview_from_io(attachment, io, page_number)
+      doc = Pdfium::Document.open_io(io)
 
       doc_page = doc.get_page(page_number)