Wget or similar for Android
Using wget or ndk for that is a bad idea : go directly java
and use HttpClient
to craft a post request : example can be found here.
The response will contain your data, ready to be saved to a file.
Additionally, you can put it in an asynch task, progress monitoring : forking an external process like Curl ou wget should be kept as last chance (that communicating with a server is clearly not)