ghostscript4js

Ghostscript4JS

This module binds the Ghostscript C API to bring its power to the Node.JS world

• Introduction
• Motivations
• Prerequisites
• Installation
• Installation options
• Usage
• Team
• Acknowledgements
• License

Introduction

Ghostscript is a suite of software based on an interpreter for Adobe Systems' PostScript and Portable Document Format (PDF) page description languages. Its main purposes are the rasterization or rendering of such page description language files, for the display or printing of document pages, and the conversion between PostScript and PDF files.

Ghostscript can be used as a raster image processor (RIP) for raster computer printers—for instance, as an input filter of line printer daemon—or as the RIP engine behind PostScript and PDF viewers.

Ghostscript can also be used as a file format converter, such as PostScript to PDF converter. The ps2pdf conversion program, which comes with the ghostscript distribution, is described by its documentation as a "work-alike for nearly all the functionality (but not the user interface) of Adobe's Acrobat Distiller product".[3] This converter is basically a thin wrapper around ghostscript's pdfwrite output device, which supports PDF/A-1 and PDF/A-2 as well as PDF/X-3 output.[3]

Ghostscript can also serve as the back-end for PDF to raster image (png, tiff, jpeg, etc.) converter; this is often combined with a PostScript printer driver in "virtual printer" PDF creators.[citation needed]

As it takes the form of a language interpreter, Ghostscript can also be used as a general purpose programming environment.

Ghostscript has been ported to many operating systems, including Unix-like systems, classic Mac OS, OpenVMS, Microsoft Windows, Plan 9, MS-DOS, FreeDOS, OS/2, Atari TOS and AmigaOS.

More resource and info about Ghostscript

• Introduction to Ghostscript

• Ghostscript on Wikipedia

• Ghostscript documentation

Motivations

At time i created this module i do not able to find any module on npm that execute Ghostscript command through its C API, otherwise there are some module that call Ghostscript through the execution of the corresponding shell command. This is good way to start use some library from node, but there are the following drawbacks:

• Performance - The call to the shell command take more time and more resources than call a library C or C++ API directly

from Node.js environment.

• Errror handler - Sometimes you cannot intercept and handle errors in a good and proper way.

To fit all needs Ghostscript4JS has sync and async method so it could be used in a web application where it's very important to not block the event loop, so all request will be served whiout any delay originated by our application.

Understanding Node.js event loop

Prerequisites

Before install Ghostscript4JS youe need to assure you have been installed the following preequisites:

• Install Node.JS see: Installing Node.js via package manager

• Install Node.js native addon build tool see: node-gyp

• Install Ghostscript for your Operating System.

Linux

Debian systems

Install Ghostscript

sudo apt-get install ghostscript

then

sudo apt-get install libgs-dev

At this point you need to set enviroment variable GS4JS_HOME to /usr/lib/x86_64-linux-gnu

Red Hat | Fedora

yum install ghostscript

then

yum install ghostscript-devel

At this point you need to set enviroment variable GS4JS_HOME to /usr/lib64 or /usr/lib based on you architecture

In general based on your Linux OS and architecture you have to set environment variable GS4JS_HOME to point on folder contains libgs.so library.

Windows

• Download last Ghostscript version for your platform x86 or x64

• Install Ghostscript on your system for example in C:\gs

• Add enviroment variable GS4JS_HOME to point on a folder contains Ghostscript DLL and Library files (Es. gsdll64.dll and gsdll64.lib) typically they are located in bin folder of you ghostscript installation for example C:\gs\bin

macOS

• Install Homebrew following the official guide here

• Open terminal and install Ghostscript

brew install ghostscript

• Set environment variable GS4JS_HOME to /usr/local/lib

Official installation guide to install Ghostscript

• Installation from official documentation

• Download Ghostscript

Installation

If you want use ghostscript4js you have to install it. There are two methods for that:

In dependencies of your package.json add the following item:

"ghostscript4js": "version"

then digit

npm install

Example:

"ghostscript4js": "*" for the latest version
"ghostscript4js": "1.0.0" for the version 1.0.0

OR

launch this command:

npm install ghostscript4js --save

Installation options

The module ghostscript4js allow you to use some installation options that you can use when in your operating system something is different against standard installation.

--GS4JS_HOME Set the GS4JS_HOME variable that represent the path in your system where is located the ghostscript library

Es. npm install ghostscript4js --GS4JS_HOME="C:/gs/bin"

--GS4JS_LIB Set the GS4JS_LIB variable that represent the file name for the ghostscript library installed in your system

Es. npm install ghostscript4js --GS4JS_LIB="libgs.so"

Only for Windows

--GS4JS_DLL Set the GS4JS_DLL variable that represent the file name for the ghostscript DLL installed in your windows system

Es. npm install ghostscript4js --GS4JS_DLL="gsdll64.dll"

Usage

'use strict'

const gs = require('ghostscript4js')

try {
  // Take decision based on Ghostscript version
  const version = gs.version()
  console.log(version)
  gs.executeSync('-sDEVICE=pngalpha -o my.png -sDEVICE=pngalpha -r144 my.pdf')
} catch (err) {
  // Handle error
  throw err
}

API

version

version() method return an object that contains information about version of Ghostscript library installed on the system. It is important in those circumstances where you have to take decision based on different version. The returned data aee similar to the example repoted below:

{
  product: "GPL Ghostscript",
  copyright: "Copyright (C) 2016 Artifex Software, Inc.  All rights reserved.",
  revision: 919,
  revisiondate: 20160323
}

This is a synchronous method and return the version info or throw an Error to indicate that something was wrong in executing it.

Example - version

'use strict'

const gs = require('ghostscript4js')

try {
  const version = gs.version()
  console.log(version)
  // Take decision based on Ghostscript version
  if (version.revision > 916) {
    // ... some stuff
  } else {
    // ... other stuff
  }
} catch (err) {
  // Handle error
  throw err
}

executeSync

executeSync(cmd) method take the Ghostscript command parameters in input as a string and execute it in a synchronous way. If something wrong happens in calling this method an Error with description and code error will be thrown.

Example - executeSync

'use strict'

const gs = require('ghostscript4js')

try {
  gs.executeSync('-sDEVICE=pngalpha -o my.png -sDEVICE=pngalpha -r144 my.pdf')
} catch (err) {
  // Handle error
  throw err
}

execute

execute(cmd, callback) method take in input the Ghostscript command parameters as a string and an optional callbackand. The execution will be asynchronous so this ensure better performance especially in a web application enviroment, because the Node.Js event loop will not block. This method has optional callback function as input in that case a possible error will be handled by this function. If noone function will be provided the method return a Promise that will be resolved or rejected all as reported in the following example.

Example - execute

'use strict'

const gs = require('ghostscript4js')

let cmd = '-sDEVICE=pngalpha -o my.png -sDEVICE=pngalpha -r144 my.pdf'
gs.execute(cmd, function (err) {
  if (err) {
    console.log("Ooops... something wrong happened")
  }
})

'use strict'

const gs = require('ghostscript4js')

let cmd = '-sDEVICE=pngalpha -o my.png -sDEVICE=pngalpha -r144 my.pdf'
gs.execute(cmd)
.then(() => {
  console.log("All is ok")
})
.catch((err) => {
 console.log("Ooops... something wrong happened")
})

Error

The error raised from ghostscript4js in all of its method is an instance of Error object that cointains a message that describe what happened and at the same time cointains the Ghostscript error code so you can inspect what ahhpened in a better way. At this link Ghostscript error codes you can find all Ghostscript errors code.

Min and Max supported revision

This module was builded based on Ghostscript C API that is compatible with some specifica versions. The module has two properties MIN_SUPPORTED_REVISION and MAX_SUPPORTED_REVISION which respectively indicate the maximum and minimum of supported Ghostscript's version.

Example - Min and Max supported revision

'use strict'

const gs = require('ghostscript4js')

console.log(gs.MIN_SUPPORTED_REVISION)
console.log(gs.MAX_SUPPORTED_REVISION)

The Team

Nicola Del Gobbo

https://github.com/NickNaso/

https://www.npmjs.com/~nicknaso

https://twitter.com/NickNaso

Mauro Doganieri

https://github.com/mauro-d

https://www.npmjs.com/~mauro-d

https://twitter.com/maurodoganieri

Acknowledgements

Thank you to all people that encourage me every day.

License

Licensed under Apache license V2