worker-convert

CouchDB Worker which converts images using imagemagick.

npm install worker-convert
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Worker Convert

This worker converts images with imagemagick.

Prerequisites

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

installation

git clone git://github.com/null2/worker-convert.git
cd worker-convert
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/convert",
  "_rev": "9-a653b27246b01cf9204fa9f5dee7cc64",
  "formats": [ "jpg", "jpeg", "png", "gif", "tif", "tiff", "bmp", "svg" ],
  "versions": {
    "thumbnail": {
      "format": "png",
      "arguments": [
        "-resize", "135x135",
        "-quality", "75",
        "-unsharp", "0",
        "-colorspace", "sRGB",
        "-interlace", "Plane",
        "-strip"
      ]
    }
  }
}

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.

formats must be an array containing the image formats the worker should handle, strictly speaking an array of file extensions.

You can specify one or many versions to be generated. The version name will be part of the image, eg. for an image named 'image.jpg' there will be generated a thumbnail named thumbnail/image001.png.

Each version can specify a target format, png in that case, and can specify individual arguments, which must be an array containing the arguments passed to imagemagick. The convert invocation in this case would look like

convert image.jpg -resize 135x135 -quality 75 -unsharp 0 -colorspace sRGB -interlace Plane -strip image%04d.png

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/convert",
  "_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": {
  "convert": {
    "image.jpg": {
      "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. The worker status is also per attachment to process only attachments which had changed.

Running the Worker

To start, this needs the following environment variables set:

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

(c) 2013 Johannes J. Schmidt, null2 GmbH, Berlin

Licensed under the Apache License 2.0.

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