java - getContentLength() return -1 only in WiFi?

Question

I want to know the length of the file, so I tried getContentLength(). It works fine with network connection (edge/3g) but returns -1 with WiFi?
Why? The WiFi is good and the file was found, it can be downloaded but the return of getContentLength() is always "-1". I dont understand. file is a google documents file.
Is there an other way to get the length?

My code is:

URL url = new URL(file);

URLConnection conexion = url.openConnection();

conexion.connect();

int poids = conexion.getContentLength();

Answer 1

It may well be the mobile network changing things for you. For example, the mobile network I use shrinks image downloads automatically (and annoyingly). If the network is "transparently" performing the full download before giving you any data, it can fill in the content length for you.

However, you basically shouldn't rely on having the content length... there's nothing to guarantee that it'll be available to you.