Home » Archive by category "Kras IT"

Convert HTML to PDF with HTML2PDF Web Service

HTML2PDF Web ServiceRecently I launched my new product HTML2PDF Web Service — a web service for converting HTML to PDF.

In this post I’d like to talk about HTML2PDF Web Service. Why to choose it, how to use it and what technologies were used to create it.

Why Choose HTML2PDF Web Service?

Programmatically generating PDF documents is a painful and time consuming problem that neither makes your developers nor designers happy. With HTML2PDF Web Service you can design your invoices or reports in HTML, style them with CSS and convert the resulting page into a PDF document. Using HTML2PDF Web Service saves your developers and designers time which is better spent making your product better.

Say your web application or mobile app (or any application for that matter) needs to generate invoices or reports in PDF format. Unless you can install special HTML to PDF conversion software you’re probably stuck with some of the libraries available for your language that can programmatically generate PDF documents. To do this you would probably design your document in something like MS Word, LibreOffice Writer or perhaps HTML. After this design has been approved you can start programming your PDF module; setting up coordinates, font sizes etc. And then all of the sudden you notice your library has limited support for doing actual document layouts and presenting tabular data that can span multiple lines. Now you need to write your own routines for splitting text over multiple lines, keep track of coordinates and make sure nothing overlaps. If like me you’ve already been there, it’s quite the nightmare.

So being able to design in HTML, style with CSS (heck, even use a bit of JavaScript) and convert the resulting page to PDF would speed up this process a lot. Am I starting to tickle your interest?

How to use HTML2PDF Web Service

Simply create your soon to be PDF documents in HTML, style them with CSS and if wanted you can use JavaScript as well. The final document is best previewed in a WebKit based browser such as Google Chrome, since that’s the technology HTML2PDF Web Service uses in the background to render the HTML and convert it to PDF.

Here are some examples on how to call the web service. Converting HTML to PDF is easy with the HTML2PDF Web Service. You can pass an URL to the page you want to convert or either send the HTML code with the request.


$ curl -H "X-API-Key: F8802062-4D31-11E3-8F59-BFD4058B6BFF"
       -H "X-API-Username: MyUsername"
       -d '{"content":"<html><head><title>My page</title></head><body><h1>Hello World!</h1><p>I am an HTML page converted to PDF!</p></body></html>"}'
       https://html2pdfwebservice.com/api/convert > page.pdf


#!/usr/bin/env perl
use strict;
use warnings;
use Mojo::UserAgent;

my $ua = Mojo::UserAgent->new;
my $tx = $ua->post(
    'https://html2pdfwebservice.com/api/convert' => {
        'X-API-Username' => 'MyUsername',
        'X-API-Key'      => 'F8802062-4D31-11E3-8F59-BFD4058B6BFF'
    } => json => {url => 'http://domain.com/invoice.html'}
if (my $res = $tx->success) {
    my $pdf_data = $res->body;


require 'net/https'
require 'uri'

uri           = URI.parse('https://html2pdfwebservice.com/api/convert')
https         = Net::HTTP.new(uri.host, uri.port)
https.use_ssl = true
# In case the SSL certificate isn't accepted
https.verify_mode = OpenSSL::SSL::VERIFY_NONE

req = Net::HTTP::Post.new(uri.path)
req['X-API-Username'] = 'MyUsername'
req['X-API-Key']      = 'F8802062-4D31-11E3-8F59-BFD4058B6BFF'
req.body              = '{"url": "http://domain.com/invoice.html"}'

res = https.request(req)
if res.code == '200'
    pdf_data = res.body
    # - or write to file -
    # File.open('invoice.pdf', 'w') { |file| file.write(res.body) }


$settings = array(
    'url' => 'http://domain.com/invoice.html',

$curl = curl_init();
curl_setopt($curl, CURLOPT_POST, 1);
curl_setopt($curl, CURLOPT_POSTFIELDS, json_encode($settings));
curl_setopt($curl, CURLOPT_HTTPHEADER, array(
    'X-API-Username: MyUsername',
    'X-API-Key: F8802062-4D31-11E3-8F59-BFD4058B6BFF'

curl_setopt($curl, CURLOPT_URL, 'https://html2pdfwebservice.com/api/convert');
curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
// Helps to debug in case of issues
// curl_setopt($curl, CURLOPT_VERBOSE, 1);

// In case the SSL certificate isn't accepted because of outdated certificates
// on your server
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);

$res = curl_exec($curl);
// Save PDF to disk
file_put_contents('document.pdf', $res);

Technologies used to develop HTML2PDF Web Service

The most interesting part in developing HTML2PDF Web Service was choosing which technology to use for converting HTML to PDF. After doing research on the subject and testing several solutions I eventually went with a WebKit based solution. By using WebKit it’s easier for the end user to preview their document using a WebKit based browser.

The HTML to PDF conversion server was developed using Go. Go is a fun language to program with, does concurrency in a really nice way and can produce a native executable for Linux, OS X, Windows and some other platforms. Thanks to Go the conversion server is fast, snappy and low on memory and CPU usage. Being able to create a binary executable allows me to sell the conversion server as a standalone product as well.

To get access to the web service there’s also a web application which is written in Perl. My favorite web framework of choice has become Mojolicious for quite some time now and thus HTML2PDF Web Service has been written with it. DBIx::Class has been used for database interaction and Validation::Class is used to validate all user inputted data.

Used databases are PostgreSQL and Redis. The former is used to store user accounts, subscriptions and more. The latter is used to keep track of token usage per user.

Sign up now for a free trial

If after reading all this and you’re still reading, please do sign up for a free trial. The trial gives full access to all the features of the web service so if you like it, please consider buying a subscription.

In case of any questions, please do contact me either through the comments on this page or send an e-mail to support at support@html2pdfwebservice.com.

Getting close to launching HTML2PDF Web Service!

For the last couple of months I’ve been busy developing HTML2PDF Web Service. Due to some setbacks I had to postpone its launch. The way it’s looking now I’ll be ready to launch by the end of the month.

So what had to change?

  • I had to switch from Payment Service Provider, which is done now. Instead of only credit cards I’m now supporting PayPal, iDEAL, Paysafe Card and Mister Cash. Credit Card support should come back later. Instead of recurring subscriptions you can now buy up to 1 year of access in advance. This is due to not being able to support recurring subscriptions anymore because of the PSP switch.
  • The website is now multilingual: currently supporting English and Dutch. Both have their own domain names. I’ve done this to get a better position in the Dutch market.

All that’s left now is changing the way token usage is being calculated and it should be all set to go. The HTML2PDF Web Service is still in beta, so feel free to try it out. Once the web service is out of beta I’ll do another post here with a follow up on used technology (Perl, Go and more!).


Ordered a Nexus 7 tablet

Nexus-7-2013I just ordered a Nexus 7 (2013) tablet for a really nice price. I plan on using it for Android development and website testing. Together with my iPad 3 and Android phone this should cover a wide range of test cases. Now to decide if I should go with Xamarin C# or stick with Java…

Since I’m note a big fan of Java I’m leaning towards Xamarin but the yearly subscription costs are a bit steep if you’re not actually generating money out of mobile stuff. Still, with Xamarin it’s easier and maybe cheaper in the sense of time to develop for both Android and iOS since you can write the core of your application in C# and use that on both target platforms.

Private Wiki – DokuWiki on Lighttpd

I had planned on setting up a private Wiki to use as a personal clipboard collection of useful snippets for some time now but never got around to it. This week I decided it was time to get it done and so I started searching for Wiki software. I ended up trying MediaWiki but ran into installation issues due to PHP’s session.save_handler not being set. After changing it I ran into more issues and with MediaWiki unable to store session data I couldn’t proceed. I’m not sure why MediaWiki requires this setting though as I run several WordPress websites and some other PHP code as well and they’re not having this issue.

Moving on I found out about DokuWiki which is really easy to install! Simply download the package, extract it and you’re done! It doesn’t require special database software such as MySQL – it stores pages on disk. Zero hassle and easy to use as well!

Since I’m not using Apache I can’t use .htaccess files. DokuWiki has a couple of folders which should not be exposed to the outside world. For Lighttpd my configuration looks like this:

$HTTP["host"] =~ "^wiki.example.com$" {
    server.document-root = "/home/example/wiki.example.com/httpdocs"
    # deny access completely to these
    $HTTP["url"] =~ "/(\.|_)ht" { url.access-deny = ( "" ) }
    $HTTP["url"] =~ "^" + "/(bin|data|inc|conf)/"  { url.access-deny = ( "" ) }

And you’re all set!

Trying out LinkedIn Ads

Since I just started my own company I need to get a steady flow of jobs from clients I’ve yet to acquire. My network is expanding fast and I’ve already had talks with potential clients with more to come in the future. I’m also subscribing to freelance job postings but so far those haven’t brought me anything yet.

I was contacted by a marketing company to do some search engine optimization on my website Kras IT but kindly declined their services. My website only exists to provide additional info for my potential clients which I don’t expect to get through Google search or Google AdWords. I actually did have a coupon for Google AdWords but it somehow isn’t valid for already existing Google accounts.

I’m using LinkedIn for my professional network, am a member of several groups and have been contacted by other members in the past for several jobs. So I expect more potential clients through LinkedIn than a Google Search.

Luckily I had received an e-mail from LinkedIn that offered me some advertising funds which I decided to make use of. Running an advertisement on LinkedIn for people who are actually looking for a freelance PHP or Perl programmer seems to make more sense to me than advertising with Google AdWords. It’s also a small investment on my part with a setup fee of only € 4,-.

Will I be getting new clients through LinkedIn advertisements? I don’t know and to be honest I’m not counting on it either. I consider it more of an experiment and am just curious to see how it’ll turn out. One thing I do know for sure is that I’ll be closely monitoring how much money it’s going to cost me as I’m not planning on investing a lot on advertising. I’ll report back on this topic if it has delivered me something.

Are you using LinkedIn advertisements as well? I’m interested to hear about your story or experience in the comments below.