Uploading data with HttpClient using a "push" model
If you have used the HttpWebRequest class to upload data, you know that it uses a “push” model. What I mean is that you call the GetRequestStream method, which opens the connection if necessary, sends the headers, and returns a stream on which you can write directly.
.NET 4.5 introduced the HttpClient class as a new way to communicate over HTTP. It actually relies on HttpWebRequest under the hood, but offers a more convenient and fully asynchronous API.