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Updating Request Messages in ASP.NET Handlers and Modules

In an earlier column I showed how to add custom processing to every request or response that your ASP.NET MVC or ASP.NET Web API site receives or produces. In that column, I offhandedly remarked about the kinds of things you can do to those incoming and outgoing requests. I didn't, however, actually provide the code (just as well, probably, because the column was getting into tl;dr territory). My conscience has caught up with me: Here's the kind of code you can put in a handler or module.

In an ASP.NET MVC module, you're effectively limited to adding headers to the incoming request or outgoing response. You can also work with headers in ASP.NET Web API handlers. This code, applied to the incoming request in either enviroment, removes the Accept handler and adds a replacement (assuming that the variable r points to a request or response, of course):

r.Headers.Remove("Accept");
r.Headers.Add("Accept", "text/html");

In an ASP.NET Web API handler, you can also replace the content of the incoming request message, like this:

request.Content = new System.Net.Http.StringContent("{'custid':'A123'}", Encoding.UTF8, "application/json");

If you use this technique, the default model binding process won't load the parameters in your Action method with the content you've just inserted into the message. You'll need to write code like this in your Action method to retrieve that content:

public async Task Get(string Id)
{
  string result = await Request.Content.ReadAsStringAsync();

The code to replace the outgoing request message in a Web API message handler is similar to the code to replace the incoming request:

resp.Content = new System.Net.Http.StringContent("{'custid':'A124'}", Encoding.UTF8, "application/json");

Posted by Peter Vogel on 11/05/2018 at 10:21 AM


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