Question

This is me publicly documenting my mistake so that if I or anyone does it again, they don’t have to spend 3 hours tearing their hair out trying to fix such a simple thing.

Context

I was sending an HttpRequest from one C# MVC ASP.NET application to another.
The applications require an HTTPS connection, and we are using URLRewrite to redirect an HTTP request to an HTTPS url.

One application was sending a POST request with some JSON data in the body, pretty standard stuff. The other application was set up to receive this data with an MVC controller class (CollectionAction and Insert methods for GET and POST respectively).

Symptoms of the problem

The receiving application was running the GET method (CollectionAction) instead of the POST action (ItemAction). The reason for this was that the request coming in to the application was in fact a GET request, and to top it off the JSON data was missing too.

I sent the header "x-http-method" to override the request method from GET to POST (I was already setting the request httpmethod to POST but this was being ignored). This worked but still I had no data being sent.

So now I am stuck pulling my hair out, because I can see a POST request with content-length and data being sent out and I have a GET request with no data or content-length coming in (but the headers were preserved)

Answer 1

Turns out I was using UriBuilder to take a base URL and apply a resource path to it. For example I would have “google.com” in my web.config and then the UriBuilder would take a resource like Pages and construct the url “google.com/Pages”. Unfortunately, I was not initializing the UriBuilder with the base URL, and instead was using a second UriBuilder to extract the host and add that to the path like so:

public Uri GetResourceUri(string resourceName)
    {
        var domain = new UriBuilder(GetBaseUrl());
        var uribuilder = new UriBuilder()
        {
            Path = domain.Path.TrimEnd('/') + "/" + resourceName.TrimStart('/'),
            Host = domain.Host
        };
        var resourceUri = uribuilder.Uri;
        return resourceUri;
    }

The problem with this code is that the scheme is ignored (HTTP:// vs https://) and it defaults to HTTP. So my client was sending out the request to an HTTP url instead of the required HTTPS url. This is the interesting part, URLRewrite was kicking in and saying that we needed to go to an HTTPS url instead so it redirected us there. But in doing so, it ignored the Http-Method and the POST data, which just got set to defaults GET and null. This is what the 2nd application could see at the receiving end.

So the function had to be rewritten to this which fixed the problem:

public Uri GetResourceUri(string resourceName)
    {
        var baseUrl = GetBaseUrl();
        var domain = new UriBuilder(baseUrl);
        var uribuilder = new UriBuilder(baseUrl)
        {
            Path = domain.Path.TrimEnd('/') + "/" + resourceName.TrimStart('/'),
        };
        var resourceUri = uribuilder.Uri;
        return resourceUri;
    }