Using the Razor parser outside of ASP.Net

When Scott Guthrie originally blogged about Razor, he mentioned that it was fully hostable outside of ASP.Net.  The engine itself is not quite as detached from System.Web as we'd like, but it's close and we're going to get it way closer in the next release.

Having said that, you can still host Razor outside of the ASP.Net pipeline with the current beta! It's a little trickier, and you do technically need to reference System.Web.  I've written a sample console app that I'm attaching to this post called "rzrc" which takes in  a .cshtml or .vbhtml Razor file and runs it through the parser and code generator to produce a .cs or .vb file.  I'll walk through the main logic here and go over what each section does.

However, I was not the first to do this! Full credit for that goes to Gustavo Machado, who wrote an excellent post in which he used Reflector to work out how to run the Razor parser and code generator.  Well done Gustavo!  There are a few things that this version does that Gustavo's doesn't, such as cleaning up the Web-related stuff in the generated code and selecting the language based on the Code Language, but he basically hit it spot on!

The first thing my console app does is get the input file name, extract the extension and look up what Razor Code Language it uses.  This is done using the CodeLanguageService class, which is part of the Razor APIs:

CodeLanguageService languageService = CodeLanguageService.GetServiceByExtension(extension);
if (languageService == null) {
Console.WriteLine("{0} is not a Razor code language", extension);

Then, we fire up the parser and the code generator.  A CodeLanguageService is basically a factory for constructing a Code Parser, to parse the code blocks after an "@" and a matching Code Generator to write the final C# or VB class.

InlinePageParser parser = new InlinePageParser(languageService.CreateCodeParser(), new HtmlMarkupParser());
CodeGenerator codeGenerator =
rootNamespaceName: "Template",
applicationTypeName: "object",
baseClass: "System.Object");

When you run the Razor Parser, you must provide it with an object implementing IParserConsumer.  This interface has callbacks which the parser will call when it encounters various Razor constructs (more details on the Razor parse tree later).  CodeGenerator implements this interface and responds to the these callbacks by generating code.  However, it does nothing with the errors, so in the console app, I've written a very simple IParserConsumer called CustomParserConsumer which wraps the code generator and outputs errors to the console.  I won't put the code here, but it's in the sample, so take a look there if you're interested.

Now that we've got all the objects we need, we can actually run the parser over the input

CustomParserConsumer consumer = new CustomParserConsumer() { CodeGenerator = codeGenerator };
using (StreamReader reader = new StreamReader(inputFileName)) {
parser.Parse(reader, consumer);

Once Parse returns, the Code Generator will have built a CodeDOM tree representing the generated code during the callbacks, so we know that our code is ready to go.  Right now, the Code Generator adds in some web specific things.  For example, when we constructed the Code Gneerator above, we gave it an "applicationTypeName" which (in a web context) is the type name of the class defined in Global.asax, if there is one.  Since we are trying to generate a template that isn't related to the web, we can get the CodeDOM tree from the Code Generator and remove these things.


Finally, we use the CodeDOM to write the code to a C# or VB class file (provider is a CodeDomProvider from System.CodeDom.Compiler):

using (StreamWriter writer = new StreamWriter(outputFile)) {
provider.GenerateCodeFromCompileUnit(codeGenerator.GeneratedCode, writer, new CodeDom.CodeGeneratorOptions());

And we're done!  This is definitely more complicated than we'd like, but there are plans to simplify this API significantly in future releases.  For the most part, all we've done is left the methods our ASP.Net Build Provider uses open and accessible.  I wouldn't bet on these APIs staying around too long, but any API changes from here on should be simplifications.  For now though, check out the sample I've attached and play around!  Note that you must have WebMatrix installed to use the sample. 

I've put some comments in which start with "EXT" which contain tips on how to extend this code to your own use.  Please feel free to take this code and use it absolutely anywhere you want!  Let me know how your using Razor by either tweeting me at @anurse or email me at andrew AT andrewnurse DOT net.

Download the console app here: (3.46 KB)