Android URLConnection class cannot get content lenght using 3G internet connection

Question

I've got the following piece of code:

URL url = new URL("http://myserver.com/getFile.php");
URLConnection conexion = url.openConnection();
conexion.connect();
int lenghtOfFile = conexion.getContentLength();

Everything works fine until I work with WiFi connection. If I try to run this code when there is only GPRS/3G connection available, conexion.getContentLength() returns -1.

Any idea why?

EDIT: I've check the headers using getHeaderFields(). They are different if I use 3G network. Basically there is no Content-Length in this case. Any idea why server returns different headers? I'm not using any special script to provide the file, I only get the file that is placed at given location.

Entire header for the WiFi case:

{Accept-Ranges=[bytes], Connection=[Keep-Alive], Content-Length=[628254], Content-Type=[text/plain; charset=UTF-8], Date=[Tue, 29 Nov 2011 11:22:50 GMT], ETag=["7a0c7-9961e-4af3f38778500"], Keep-Alive=[timeout=15], Last-Modified=[Fri, 14 Oct 2011 09:52:52 GMT], Server=[Apache/2.2.9 (Debian) PHP/5.2.6-1+lenny9 with Suhosin-Patch mod_python/3.3.1 Python/2.6.6 mod_ssl/2.2.9 OpenSSL/0.9.8o mod_wsgi/3.3 mod_perl/2.0.4 Perl/v5.10.0]}

Entire header for the case when using 3G:

{Accept-Ranges=[bytes], Connection=[Keep-Alive], Content-Type=[text/plain; charset=UTF-8], Date=[Tue, 29 Nov 2011 11:20:33 GMT], ETag=["7a0c7-9961e-4af3f38778500"], Keep-Alive=[timeout=15], Last-Modified=[Fri, 14 Oct 2011 09:52:52 GMT], Server=[Apache/2.2.9 (Debian) PHP/5.2.6-1+lenny9 with Suhosin-Patch mod_python/3.3.1 Python/2.6.6 mod_ssl/2.2.9 OpenSSL/0.9.8o mod_wsgi/3.3 mod_perl/2.0.4 Perl/v5.10.0], Transfer-Encoding=[chunked], Warning=[214 warkaz-fe07 "Transformation applied"]}

Answer 1

Are you sure that the server provides the content length by sending the Content-Length header in the response?

From the headers it's clear that your provider has some kind of proxy in place that does a transformation, stripping the content-length in the process. The warning header clearly indicates this. You could try returning a different type of content type (you are now getting text/plain), maybe this particular proxy won't touch it. It's not a great solution of course, there are a lot things carriers may have to "optimize" their network in some way.

You could also try a HEAD request using a range header to get a ballpark of the content size. In that case you'd guess a few ranges, like 100k, 1000k etc to see if the server thinks that's an acceptable range. You could use that fake range for your progress. Again, this isn't a very good solution but if you really need the progress, it's something to try.

In the end it's best to just show the progress as unknown if there's no length known.

Answer 2

Since you are using

new URL("http://myserver.com/getFile.php");

I suppose you are using a personal server that you have set up, and when using WiFi your phone is in your local network and thereby can see your server, but when you are trying to connect via GPRs/3G you are trying to access your local server from the internet.

Answer 3

It is probably due to a limitation from your carrier. Try to avoid needing this value. (for example, by reading the inputStream until you cannot read it).