IIS module and C#: how to modify the page content before sending it to client

Question

I am new to the IIS module and C# area.

I need to modify the content of static HTML files in a specific directory of a website before the website sends the page content to client. The modification includes adding the banner, footer, etc.

Based on my research, I should be able to achieve my goal through IIS Module (correct?). Here is my code:

namespace MyProject
{
    public class MyModule : IHttpModule
    {
        #region IHttpModule Members

        public void Dispose()
        {

        }

        public void Init(HttpApplication context)
        {
            context.PreSendRequestContent +=
                new EventHandler(onPreSendRequestContent);
        }

        #endregion

        public void onPreSendRequestContent(Object source, EventArgs e)
        {
            HttpApplication app = (HttpApplication)source;
            HttpRequest request = app.Context.Request;
            HttpResponse response = app.Context.Response;

            if (request.Path.Contains("my_specific_directory"))
            {
                //add banner and footer to the page content
                //which class, methods, or properties to use?
            }
        }
    }
}

I am not sure whether PreSendRequestContent is the right event to start modifying page content. Could someone point me to the right way to get page content retrieved by IIS?

Thanks and regards.

Answer 1

I think it's better to use the MVC Framework because It's easy to maintain and you can do anything. But here's the process if you still want to modify static HTMLs by a IIS HTTP Module. Hope this helps.

At the first, Add a handler & a build provider to process static HTML files by IIS.

Web.config:

<system.webServer>
    <handlers>
        <add name="html" verb="GET,HEAD,POST,DEBUG" path="*.html" type="System.Web.UI.PageHandlerFactory" />
    </handlers>
</system.webServer>

<system.web>
    <compilation>
        <buildProviders>
            <add extension=".html" type="System.Web.Compilation.PageBuildProvider" />
        </buildProviders>
    </compilation>
</system.web>

Next, Write a HTTP Module & a filter to modify your HTML contents.

HTTP Module:

class ModifyContentModule : IHttpModule
{
    public void Dispose() { }

    public void Init(HttpApplication context)
    {
        context.BeginRequest += (o, e) =>
        {
            context.Response.Filter = new ModifyContentStream(context.Response.Filter);
        };
    }
}

Filter:

public class ModifyContentStream : Stream
{
    private Stream _base;
    private MemoryStream _memoryBase = new MemoryStream();

    public ModifyContentStream(Stream stream)
    {
        _base = stream;
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        _memoryBase.Write(buffer, offset, count);
    }

    public override void Flush()
    {
        // Get static HTML code
        string html = Encoding.UTF8.GetString(_memoryBase.GetBuffer());

        // Modify your HTML
        // Sample: Replace absolute links to relative
        Regex regex = new Regex("(href=\")http:\\/\\/www\\.example\\.com(\\/[^\"']+\\.[^\"']+\")");
        Match match = regex.Match(html);
        while (match.Success)
        {
            string oldValue = match.Value;
            string newValue = match.Groups[1].Value + match.Groups[2].Value;
            html = html.Replace(oldValue, newValue);

            match = match.NextMatch();
        }

        // Flush modified HTML
        byte[] buffer = Encoding.UTF8.GetBytes(html);
        _base.Write(buffer, 0, buffer.Length);
        _base.Flush();
    }

    #region Rest of the overrides
}

}

Finally, Add the HTTP Module to your Web.config

Web.config

<system.webServer>
    <modules runAllManagedModulesForAllRequests="true">
        <remove name="ModifyContent" />
        <add name="ModifyContent" type="ModifyContentModule.ModifyContentModule, ModifyContentModule" />
    </modules>
    <handlers>
        <add name="html" verb="GET,HEAD,POST,DEBUG" path="*.html" type="System.Web.UI.PageHandlerFactory" />
    </handlers>
</system.webServer>