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In the early days, we chose to delegate the responsibility of generating
invoice PDFs to the client side. We simply designed the invoice in HTML
and utilized the customer's browser for PDF generation.
We adopted this approach because it was quick and straightforward to
implement. However, it had its drawbacks. Primarily, it did not generate
identical PDFs across all browsers as it heavily depended on the browser
and its version. Secondly, we aimed to send invoices as PDFs via email,
necessitating server-side PDF generation.
Given that we already had an HTML template for the invoice, our initial
thought was to convert HTML to PDF. There are multiple tools available
for this, such as wkhtmltopdf. However, we hesitated to add another
dependency as it could complicate our deployment process.
We decided to use prawnpdf [^1] for server-side PDF generation. Prawn is
a pure Ruby PDF generation library that offers a wide range of features
for PDF generation. It is user-friendly and highly flexible.
Prawn provides excellent manuals for reference [^2] [^3]. You can check
the details and its functionalities.
The design process was straightforward. The most significant challenge
was dealing with encoding. Unfortunately, the default PDF fonts do not
support all UTF-8 characters. If your text includes some special
characters, it triggers the following error:
Your document includes text that's not compatible with the
Windows-1252 character set.
(Prawn::Errors::IncompatibleStringEncoding) If you need full UTF-8
support, use external fonts instead of PDF's built-in fonts.
As the exception suggests, we should use external fonts for full UTF-8
support. I considered several fonts, such as "OpenSans" and
"DejaVuSans", before deciding on the "BeVietnamPro" [^4] font. It's
already in use on our website and might be useful in our console at some
point. Thus, it seemed sensible to use it for PDF generation as well.
It's open-source and licensed under the SIL Open Font License [^5].
I added the "pdf-reader" gem to read the generated PDF file in the
tests, which allows us to verify its content.
[^1]: https://github.com/prawnpdf/prawn
[^2]: https://prawnpdf.org/docs/prawn/2.5.0/manual.pdf
[^3]: https://prawnpdf.org/prawn-table-manual.pdf
[^4]: https://fonts.google.com/specimen/Be+Vietnam+Pro/about
[^5]: https://openfontlicense.org
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