Worker Generate Previews

This worker generates previews from pdf files.

Depricated

This is depricated in favor if couchmagick!

Prerequisites

This worker depends on imagemagick and ghostscript. Make shure the convert program is in the path.

Installation

git clone git://github.com/null2/worker-generate-previews.git
cd worker-generate-previews
npm install

Configuration

Configuration is done in a worker configuration document inside the target database. The worker only process if there exists such a configuration file.

A Worker Configuration File might look like this:

{
  "_id": "worker-config/generate-thumbnails",
  "_rev": "9-a653b27246b01cf9204fa9f5dee7cc64",
  "versions": {
    "medium": {
      "size": "800x600"
    }
  }
}

You can update the config live so that all future processings will take the new configuration.

Note that attachment names which starts with a version name, followed by a '/' are ignored.

size is a expression for imagemagick, so you can do eg. 120x120!, 120x and so on.

Worker Status Document

The worker stores a status document inside the target database. The worker stores its last update seq here and can resume at the point it stopped.

{
  "_id": "worker-status/attachments",
  "_rev": "1-1922b5623d07453a753ab6ab2c634d04",
  "last_update_seq": 34176
}

Document Status Object

The worker updates a status object inside the document. This makes it supereasy to monitor worker status as well as it keeps an atomic lock when many workers listen to the same database. Images are prozessed only once by comparing the attachments revpos property with the revpos property of the status object.

The status object of the worker looks like this:

"worker_status": {
  "generate-stills": {
    "status": "completed",
    "revpos": 160
  }
}

The status field can be triggered, completed or error.

The worker status is scoped by the worker name in order to have many workers processing the same document.

Running the Worker

To start, this needs the following environment variables set:

COUCH_SERVER=http://example.org COUCH_DB=mydb npm start

License & Copyright

(c) 2012 Johannes J. Schmidt, null2 GmbH, Berlin

Licensed under the Apache License 2.0.