Skip to main content

Generating PDF/A From HTML in Meteor


My live-chat app was a folk of project Rocket.Chat which was built with Meteor. The app had a feature that administrative users were able to export the conversations into PDF files. And, they wanted to archive these files for a long time.

I happened to know that PDF/A documents were good for this purpose. It was really frustrated to find a solution with free libraries. Actually, it took me more than two weeks to find a possible approach.

TL, DR;
Using Puppeteer to generate a normal PDF and using PDFBox to load and converting the generated PDF into PDF/A compliance.

What is PDF/A?

Here is a definition from Wikipedia:
PDF/A is an ISO-standardized version of the Portable Document Format (PDF) specialized for use in the archiving and long-term preservation of electronic documents. PDF/A differs from PDF by prohibiting features unsuitable for long-term archiving, such as font linking (as opposed to font embedding) and encryption. The ISO requirements for PDF/A file viewers include color management guidelines, support for embedded fonts, and a user interface for reading embedded annotations.

Why PDF/A documents matter

In my point of view, it’s a standard file for archiving thanks to key features:
  • The fonts of document’s content will always be displayed the same on all places, not depending on any devices.
  • Documents are safe. For example, no executable file launches are allowed or no external content references are allowed.
(Find more features at https://en.wikipedia.org/wiki/PDF/A#Description)

Several approaches for creating a PDF/A document

At the first glance, I found some approaches as follows:

(1). Paid APIs
  • Aspose PDF: Java-based APIs. It seemed the price was too expensive.
  • PdfTron: Javascript-based APIs. I tried to contact them to know the price but they requested me some information even I could not estimate to answer it.
(2). Free APIs
  • Apache FOP: Java-based APIs. I needed to defined the templates by its own ways (FOP files) instead of HTML and CSS. (I created a hello world app here)
  • PDFBox: Java-based APIs. It looked promising that I could convert a normal PDF document to PDF/A one.
(3). Forking a open source project/building my own PDF/A generating engine
  • pdfkit: Javascript-based project. I needed to know the specification of PDF/A compliance, and to build my own lib for generating PDF/A documents.
Basing on these insights, I decided to go with approach (2).

Apache FOP tryout

I decided to stop this approach. Apache FOP strictly required to provide templates with XSL-FO format which is not supported wisely. Ref: https://stackoverflow.com/questions/10641667/use-of-xsl-fo-css3-instead-of-css2-to-create-paginated-documents-like-pdf/21345708#21345708
  • Due to limitation of formatting support, it’s hard to format content of a PDF if its template is complex such as including images, tables, etc..
  • There seemed to be no tools for converting from HTML, CSS into XSL-FO. But my templates were built on HTML, CSS and Meteor and data was bound dynamically.

PDFBox tryout

Basing on the example of creating PDF/A here, I tried to convert an existing normal PDF file into another PDF/A. There were 3 parts to do:
  1. embed/load fonts
  2. include XMP metadata
  3. include color profile
I used these following tools to verify the result:
With filling some mandatory information, I passed the parts 2 and 3 successfully. But, I have really got stuck at part 1 for a long time.

Eventually, I found the root cause by delving deeper into source code of some libraries PDFBox, PDFBox Preflight, node-html-pdf, PhantomJS, etc.. as follows:

I could not successfully generate PDF/A document by converting the existing normal PDFs generated from Meteor because the PDF generated did not embedded the font fully.

My project used node-html-pdf which in turn used PhantomJS to render HTML into PDF. PhantomJS used Qt for writing PDF. The library always embedded the fonts using Subsetting (meaning only the characters were used in the document were embedded). This did not comply with the PDF/A specification.

I couldn’t do anything here because PhantomJS used a very old version of Qt (only Qt v5.x onwards supported PDA/A). The PhantomJS was also discontinued since Mar 2018.

Besides, I could not use PDFBox to embed fonts fully either. There was a method PDType0Font.load for loading fonts but it also embedded the fonts using Subsetting.

Yay! It worked

I discovered that by replacing the process rendering HTML to PDF with the fonts fully embedded.
Using a different library to replace PhantomJS, I found Google Chrome’s Puppeteer.

Then, I could use PDFBox to convert the normal PDF to PDF/A with including XMP metadata and color profile.


References:
[1]. https://www.youtube.com/watch?v=EqII7ilmY8o&feature=youtu.be
[2]. https://stackoverflow.com/questions/38737219/how-to-convert-pdf-to-pdf-a-in-java
[3].http://svn.apache.org/repos/asf/pdfbox/trunk/preflight/src/main/java/org/apache/pdfbox/preflight/PreflightConstants.java
[4]. http://www.pdf-tools.com/public/downloads/whitepapers/whitepaper-pdfa.pdf
[5]. https://medium.com/@raphaelstbler/advanced-pdf-generation-for-node-js-using-puppeteer-e168253e159c
Labels:

Comments

Post a Comment

Popular posts from this blog

Creating a Chatbot with RiveScript in Java

Motivation "Artificial Intelligence (AI) is considered a major innovation that could disrupt many things. Some people even compare it to the Internet. A large investor firm predicted that some AI startups could become the next Apple, Google or Amazon within five years"   - Prof. John Vu, Carnegie Mellon University. Using chatbots to support our daily tasks is super useful and interesting. In fact, "Jenkins CI, Jira Cloud, and Bitbucket" have been becoming must-have apps in Slack of my team these days. There are some existing approaches for chatbots including pattern matching, algorithms, and neutral networks. RiveScript is a scripting language using "pattern matching" as a simple and powerful approach for building up a Chabot. Architecture Actually, it was flexible to choose a programming language for the used Rivescript interpreter like Java, Go, Javascript, Python, and Perl. I went with Java. Used Technologies and Tools Oracle JDK 1.8...
Post a Comment
Read more

Strategy Design Pattern

For example, I have a program with an Animal abstract class and two sub-classes Dog and Bird. I want to add new behavior for the class Animal, this is "fly".  Now, I face two approaches to solve this issue: 1. Adding an abstract method "fly" into the class Animal. Then, I force the sub-classes should be implemented this method, something like: public abstract class Animal{ //bla bla public abstract void fly(); } public class Bird extends Animal{ //bla bla public void fly(){ System.out.println("Fly high"); } } public class Dog extends Animal{ //bla bla public void fly(){ System.out.println("Cant fly"); } } 2. Creating an interface with method "fly" inside. The same issue to an abstract class, I force the classes these implement this interface should have a method "fly" inside: public interface Flyable{ public void fly(); } public class Bird implements Flyable{ //bla bla public void fly(){ System.out.pr...
Post a Comment
Read more

My must-have apps for daily work

There is no doubt that cool apps can help us be more productive and enjoyable at work. For the time being, I really love the following apps which are used by me almost every day. 1. A personal Kanban In fact, a personal kanban is the most useful app for me. Why does it matter? It is not just a to-do list, but it keeps me motivated every day because it helps me be able to know what my "big picture" is. I usually set up my plans together with a path to reach them.  KanbanFlow  is my preferred tool. KanbanFlow 2. A terminal Needless to say, a terminal is a must-have app for every developer, especially the ones use macOS/Linux. Due to its importance, I love to decorate and enhance it to be super exciting with various tools such as  iTerm ,  oh-my- zsh , and  thefuck . ;) iTerm + oh-my-zsh 3. A documentation "ecosystem" As a developer, I can not remember all things that I have experimented a day. Moreover, a document is really useful for sharing an...
Post a Comment
Read more

Git Feature Branch Workflow

Motivator It's important for a team to have an agreement on how the changes of source code should be applied. According to projects and teams size, we will define a workflow or select one from recommended workflows ; the "Feature Branch Workflow" is a candidate. What is it? - One branch "master" for main codebase - Several separated branches for features development Why should we care? - Be super simple and allow each developer works on a particular feature. - A stable codebase (master) benefits for continuous integration (CI) environment - Leverage "Pull request" for Code review How it works? A lifecyle of a feature branch (usually created by a story) 1. Creator creates a new branch from a story.  For example: "ABC-1-setup-projects" 2. Creator checkouts the created branch and works on the branch (commits, pushes) 3. Creator has done the feature, he uses "pull request" to merge his branch into branch "master...
Post a Comment
Read more

Updates to the Scrum Guide - The 5 Scrum Values

This article is available at blog.scrum.org , here I just quote my favorite points and give my comment at the end of this post. Ken Schwaber and Jeff Sutherland, the creators of Scrum delivered a webinar on their latest update to the Scrum Guide .  The update was a simple one, adding the 5 values of Scrum to the Guide: These values sound easy? Well, there are many misunderstandings and common problems when applying these values. Here are some example: Value Misunderstanding Getting the value right Commitment Committing to something that you don’t understand because you are told to by your boss. Committing yourself to the team and Sprint Goal. Focus Focusing on keeping the customer happy Being focused on the sprint and its goal. Openness Telling everyone everything about all your work Highlighting when you have challenges and problems that are stopping you from success Respect Thinking you are helping the team by being a hero Helping peop...
Post a Comment
Read more