getContentLength() return -1 only in WiFi?

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:

开发者_开发百科URL url = new URL(file);

URLConnection conexion = url.openConnection();

conexion.connect();

int poids = conexion.getContentLength();

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.

The server is probably sending back a HTTP response that is chunked.

The behavior of the getContentLength() method is to return the 'internal' value of the length of the content, that is available to it. When the client receives a HTTP chunked response, the length of the response is not known, and hence the content length value is marked as -1.

The chunked nature of the response can determined by the Transfer-Encoding header value; chunked responses have a value of chunked. HTTP servers need not provide a Content-Length header value if the response is sent via chunked encoding; in fact, servers are encouraged to not send the Content-Length header for a chunked response, for the client is supposed to ignore the Content-Length header.

As for the actual reason on why the server is responding differently in two networks, well it depends on various factors. Usually servers will opt for a more optimal delivery mode, depending on the nature of the client. For some reason, it has detected that it is better off sending chunked responses for one type of a connection. The answer might lie in the HTTP request headers, but not necessarily so.