Performing HTTP(S) asynchronous POST requests

In this recipe, we will be adding the sendPostRequest:toUrl: method to the WebServiceConnectAsynchronous class that we created in the Performing HTTP(S) asynchronous GET requests recipe. If we follow the HTTP specifications to the letter, we would use the HTTP POST request when we want to send data to a server for processing. For example, if you fill out an HTTP form (for instance, from a login page), you would submit an HTTP POST request that contains the form information.

To perform a POST request, you should have some data to post to the server. This data takes the form of a key-value pair, just like the GET query request. We also submit the data in the same format as the GET query request, where each key-value pair is separated by & and each key is separated from its value by =. Here is an example.

If we had the following key-value pairs:

firstname: Jon
lastname: Hoffman
age: 44 years

Our POST request will be encoded as follows:

firstname...