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HTML to PDF using a WCF Service

· 4 min read
John Reilly
John Reilly
OSS Engineer - TypeScript, Azure, React, Node.js, .NET

TL; DR - "Talk is cheap. Show me the code."​

Some time ago I wrote a post which demonstrated how you could make PDFs from HTML using C# and wkhtmltopdf. To my lasting surprise this has been the most popular post I've written. I recently put together an ASP.NET WCF service which exposed this functionality which I thought might be worth sharing. The code can be found on GitHub here.

A little more detail​

I should say up front that I'm still a little ambivalent about how sensible an idea this is. Behind the scenes this WCF service is remotely firing up wkhtmltopdf using System.Diagnostics.Process. I feel a little wary about recommending this as a solution for a variety of not particularly defined reasons. However, I have to say I've found this pretty stable and reliable. Bottom line it seems to work and work consistently. But I though I should include a caveat emptor; there is probably a better approach than this available. Anyway...

There isn't actually a great deal to say about this WCF service. It should (hopefully) just do what it says on the tin. Putting it together didn't involve a great deal of work; essentially it takes the code from the initial blog post and just wraps it in a WCF service called PdfMaker. The service exposes 2 methods:

  1. GetPdf - given a supplied URL this method creates a PDF and then returns it as a Stream to the client
  2. GetPdfUrl - given a supplied URL this method creates a PDF and then returns the location of it to the client

Both of these methods also set a Location header in the response indicating the location of the created PDF.

That which binds us​

The service uses webHttpBinding. This is commonly employed when people want to expose a RESTful WCF service. The reason I've used this binding is I wanted a simple "in" when calling the service. I wanted to be able to call the service via AJAX as well as directly by browsing to the service and supplying a URL-encoded URL like this:

http://localhost:59002/PdfMaker.svc/GetPdf?url=http%3A%2F%2Fnews.ycombinator.com/You may wonder why I'm using http://news.ycombinator.com for the example above. I chose this as Hacker News is a very simple site; very few resources and a small page size. This means the service has less work to do when creating the PDF; it's a quick demo.

I should say that this service is arguably **not** completely RESTful as each GET operation behind the scenes attempts to create a new PDF (arguably a side-effect). These should probably be POST operations as they create a new resource each time they're hit. However, if they were I wouldn't be able to just enter a URL into a browser for testing and that's really useful. So tough, I shake my fist at the devotees of pure REST on this occasion. (If I should be attacked in the street shortly after this blog is posted then the police should be advised this is good line of inquiry...)

Good behaviour​

It's worth noting that automaticFormatSelectionEnabled set to true on the behaviour so that content negotiation is enabled. Obviously for the GetPdf action this is rather meaningless as it's a stream that's passed back. However, for the GetPdfUrl action the returned string can either be JSON or XML. The Fiddler screenshots below demonstrate this in action.

Test Harness​

As a final touch I added in a test harness in the form of Demo.aspx. Here's an example of the output generated when pointing at Hacker News:

And that's it. If there was a need this service could be easily extended to leverage the various options that wkhtmltopdf makes available. Hope people find it useful.