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

JSF 2 - Dynamically manipulating the component tree with system events

Let's suppose we want to modify the metadata (attributes)  of elements such as render , requried , maxlength but we do not define in JSF tags. The manipulating components can be conducted in Drools  files, for example. How could we do? I think that is what we need to change something of component tree during JSF life-cycle. JSF supports event handling throughout the JSF life-cycle. In this post, I use two events: postAddToView for scanning components tree and preRenderView for manipulating the meta of components before rendering to GUI. I modified my own project from previous post for this example. This is my first further JSF trying out with the project as I said before. :) We define the tags f:event below the form - a container component of the components which we want to work on. The valid values for the attribute type for f:event can be found from tag library document  of JSF 2. <!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml" x...
Post a Comment
Read more

Make simple music program with beep(freq, duration) with Pascal

Pascal is my first programing language when I have studied in high school. It was really exciting for me. :) The Pascal programming language was created by Niklaus Wirth in 1970. It was named after Blaise Pascal, a famous French Mathematician. It was made as a language to teach programming and to be reliable and efficient. Pascal has since become more than just an academic language and is now used commercially . I tried to make a simple music program by using Lazarus IDE on MS Window 7, 64-bit. It frustrated me a few times how difficulty to use Sound command to make a sound. Sound did not work on my compiler and my platform anymore. So far, I just could use beep(freq, duration) from window unit to implement my work. Here is my code. ;) program mysong; uses Windows, crt; const C: Integer = 512; { x = A * EXP(LN(2)/12)} C_: Integer = 542; D: Integer = 574; D_: Integer = 608; E: Integer = 644; F: Integer = 682; F_: Integer = 723; G: Integer = ...
Post a Comment
Read more

AngularJS - Build a custom validation directive for using multiple emails in textarea

AngularJS already supports the built-in validation with text input with type email. Something simple likes the following: <input name="input" ng-model="email.text" required="" type="email" /> <span class="error" ng-show="myForm.input.$error.email"> Not valid email!</span> However, I used a text area and I wanted to enter some email addresses that's saparated by a comma (,). I had a short research and it looked like AngualarJS has not supported this functionality so far. Therefore, I needed to build a custom directive that I could add my own validation functions. My validation was done only on client side, so I used the $validators object. Note that, there is the $asyncValidators object which handles asynchronous validation, such as making an $http request to the backend. This is just my implementation on my project. In order to understand that, I supposed you already had experiences with ...
Post a Comment
Read more

Books Read in 2022

My bookshelf Technical - Operating System: Three Easy Pieces. Andrea Arpaci-Dusseau, Remzi Arpaci-Dusseau. - The Effective Engineer. Edmond Lau. - English Grammar in Use. Raymond Murphy - Mythical Man-Month, The: Essays on Software Engineering. Brooks Jr., Frederick P.  - Peopleware: Productive Projects and Teams (3rd edition). Tom DeMarco, Timothy Lister. - A Philosophy of Software Design. John Ousterhout. - Modern Computer Architecture and Organization: Learn x86, ARM, and RISC-V architectures and the design of smartphones, PCs, and cloud servers. Jim Ledin. Thought Provoking - Đúng Việc. Giản Tư Trung. - A Brief History of Time. Stephen Hawking. - Một đời như kẻ tìm đường. Phan Văn Trường. - Một đời thương thuyết. Phan Văn Trường. - Tinh hoa xử thế - Dám bị ghét. Kishimi Ichiro, Koga Fumitake. - Phép màu để vượt lên chính mình. Nhan Húc Quân. - Scouting for Boys: A Handbook for Instruction in Good Citizenship Through Woodcraft. Robert Baden-Powell. - Thay Đổi Cuộc Sống Với Nhân ...
Post a Comment
Read more

A Template for Software Engineering Standards

Software engineering standard template A well-structured standard acts as a blueprint that guides engineers in their daily tasks and long-term goals. Below, I will outline a template for creating a comprehensive software engineering standard. Header The header serves as the document's identifier. It contains the following: Authors : The people who have contributed to the creation of the standard. Created Date : The date when the document was initially created. Version : The version of the standard. It is typically updated with significant changes. Status : The current status of the document, whether it's in draft, in-review, or official. Next Review Date : The date when the standard will be reviewed for relevancy and accuracy. Table of Contents A table of contents provides an overview of what the document contains, making it easier for readers to navigate through the document. Body The body of the standard comprises: Values : The core beliefs that guide the decision-maki...
Post a Comment
Read more