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Imgserve is a daemon program to provide common image processing service

Project description

Introduction

Imgserve is a python image processing server designed to provide image processing service, currently supporting only image rescaling, and svg rasterization. It can utilize modern multicore CPU to achieve higher throughput and possibly better performance.

User applications send requests in JSON format over HTTP to a running imgserve, which downloads source image from URL specified in the request object, performs the requested operation on the source image, uploads the result image to the specified destination.

Features

  • Using a multi-process architecture
  • Communication with user applications using JSON object over HTTP
  • Image processing operations currently supported: rescaling, svg rasterization
  • Image downloading with FTP, FTPS, HTTP, HTTPS and local FILE
  • Image uploading with HTTP POST, HTTP PUT (not implemented yet), FTP and local FILE

Installing

Pre-requisit:

  • Python >= 2.5, (in Debian, sudo aptitude install python)
  • Multiprocessing, (Only if python version <= 2.5. In Debian, sudo aptitude install python-multiprocessing)
  • PIL, (in Debian, sudo aptitude install python-imaging)
  • python-rsvg, (in Debian, sudo aptitude install python-rsvg)
  • python-pycurl, (in Debian, sudo aptitude install python-pycurl)

To run tests, additional packages are required:

  • nose, (in Debian, sudo easy_install python-nose)
  • pyftpdlib, (in Debian, sudo easy_install pyftpdlib)

Install

sudo easy_install imgserve

Usage & Server API

Start imgserve daemon with imgserve start, you can run imgserve under root but root privilege is not required, the only difference of running imgserve with root user or a non-root user is where log and pid files are placed:

  • When imgserve is run with root user, log files are put into /var/log/imgserve directory, pid file is put into /var/run/ directory.
  • When imgserve is run with a non-root user, log and pid files are put into ~/.imgserve directory.

You can tell imgserve to which IP interface to bind and on which port to listen using imgserve start -host IP_ADDRESS -port PORT, note low number ports require root privilege to use. If host and port are not specified, their default values are used, 0.0.0.0 (all IP interfaces on the host) for host and 8602 for port.

When imgserve is running, we can send it requests, let’s see an example of a JSON request:

{
  "operationType": "resize",
  "srcURL": "http://upload.wikimedia.org/wikipedia/en/7/70/Ex.png",
  "dstURL": "ftp://upload.wikimedia.org/wikipedia/en/7/70/{$width}-{$basename}.{$ext}",
  "args": {
     "width": 200,
     "height": 120
  }
}

This request instructs imgserve to download the image file from srcURL, resize it to a 200 x 120 thumbnail cropping the sides (top and bottom, or left and right) if necessary, and upload the thumbnail image to dstURL under a new file name which can be set dynamically with special tags in dstURL value. Here are some rules that should be followed for the request to be valid:

  • Must be valid JSON object.

  • Four keys (operationType, args, srcURL, dstURL) are required.

  • operationType currently can only be resize or rasterize.

  • args value must be a collection of key/value pairs (aka JSON object), passing extra arguments to the operation.

  • srcURL is a valid URL of an image, using whatever protocol imgserve supports;

  • dstURL is a URL using whatever protocol imgserve supports along with file name of result image.

    • The value of dstURL can contain following special tags that will be substituted with real values by imgserve, the result string will be the final file name for the result image file that is uploaded to the destination.

      • {$width} is replaced with the width of the result image.
      • {$height} is replaced with the height of the result image.
      • {$basename} is replaced with the basename of the original file name from srcURL.
      • {$extension} is replaced with the extension name of the original file name from srcURL.
    • dstURL looks like a normal URL for FTP and local FILE, but not for HTTP POST, because besides a normal HTML page on which a upload form resides imgserve has to know the field name of the HTML upload form so that imgserve can upload the result image file with that specific field.

      A new syntax of dstURL is invented for HTTP POST: dstURL is the result of concatenation of the URL of HTML page on which an upload form resides, a colon : and the result image file name used when uploading (can also contain special tags that will be substituded with real values), the field name of the upload form to which the result file is uploaded is specified in args with a new key/value pair, ‘field_name’ is used as the key name. Let’s see an example:

      {
        "operationType": "resize",
        "srcURL": "http://upload.wikimedia.org/wikipedia/en/7/70/Ex.png",
        "dstURL": "http://example.com/upload.html:{$width}-{$basename}.{$ext}",
        "args": {
          "width": 200,
          "height": 120,
          "field_name": 'image_file'
        }
      }
      

      This request instructs imgserve to download an image from upload.wikimedia.org, resize it to 200 x 120, rename the resized image file to 200-Ex.png, and upload 200-Ex.png to a remote web site using an upload form on page http://example.com/upload.html, the field name used for file uploading is image_file.

A reply JSON object is replied as soon as a quick validation on the request JSON object has been performed. In the process of validation, a placeholder image that has the same dimenstion with the result image is produced and uploaded to the destination URL.

If the request passes the validation process, a JSON object:

{'dstURL': <destination URL with special tags substituted>}

is returned, otherwise either

{'msg': 'request parse error'}

is returned if the request sent is not a valid JSON object or

{'msg', 'request invalid', 'code': <error code>}

is returned if the request is JSON syntax correct, but some other things go wrong.

After the reply JSON object is returned, imgserve would start the real image processing work and uploads the result image to dstURL, silently overwriting the placeholder file previously uploaded.

Contact

email: wu at madk.org

Project details


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