Class: ActiveStorage::HotCell::Server::Previewers::Pdf

Inherits:
ToolOperation show all
Defined in:
lib/active_storage/hot_cell/server/previewers/pdf.rb,
lib/active_storage/hot_cell/server/previewers/pdf/mutool.rb,
lib/active_storage/hot_cell/server/previewers/pdf/poppler.rb

Overview

What the two PDF previewers share: one bounded page, rendered to PNG on the worker's own scratch, so a pathological page cannot be answered by buffering an unbounded PNG in memory — the file is bounded by the cell's file_size limit and the kernel enforces it. A subclass supplies the tool run.

The result carries no dimensions, and that is what Rails does rather than a concession to make here. A previewer yields io:, filename: and content_type: and nothing else; Preview#process attaches that as a new blob, and the dimensions come later from analyzing that blob like any other. So a drop-in replacement returns no dimensions either.

It is also what keeps the :subprocess claim true. Reading the produced PNG here would mean parsing bytes the tool just made out of a hostile PDF, in this worker, which is exactly what turns a subprocess operation into an in-process one.

Defined Under Namespace

Classes: Mutool, Poppler

Constant Summary collapse

MAX_PAGE = 
10_000
MAX_RESOLUTION = 
600

Constants inherited from Operation

Operation::CONTENT_TYPES

Instance Method Summary collapse

Instance Method Details

#perform(inputs, outputs, page: 1, resolution: 72) ⇒ Object 



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# File 'lib/active_storage/hot_cell/server/previewers/pdf.rb', line 29

def perform(inputs, outputs, page: 1, resolution: 72)
  source, = inputs
  destination, = outputs

  page = positive_integer!(:page, page, MAX_PAGE)
  resolution = positive_integer!(:resolution, resolution, MAX_RESOLUTION)

  render source, destination, page: page, resolution: resolution

  staged = File.exist?(destination.path) ? File.size(destination.path) : 0

  { format: "png", content_type: "image/png", page: page, resolution: resolution,
    bytes: produced!(staged, tool) }
end