If we get valid values once we start downloading, use those to provide

moderately more sane progress indication.

It's still non-ideal, because, for example, we'll start out assuming everything
is length 1. So we'd have a queue like (1, 1, 1, 1). Then we start downloading
the first resource and see that we actually have (1500000, 1, 1, 1), so we
climb up to 99% downloading that first resource, and then we find out that we
have (1500000, 450000, 1, 1) and we pop back down to 70% or so, and so on as we
discover in turn that the web server lied to us about each file.

The alternative is to just sit at 25% for ages, then sit at 50% for ages, then
75%, etc. Maybe that's better... I guess I just like to see some sort of smooth
upward progress.

This is only a problem for me since I'm hosting a Getdown client on Github
which lies about Content-size in a HEAD request. So OOO projects will continue
to give accurate progress reports.

src/main/java/com/threerings/getdown/net/Downloader.java

@@ -190,14 +190,21 @@ public abstract class Downloader extends Thread
      *
      * @param rsrc the resource currently being downloaded.
      * @param currentSize the number of bytes currently downloaded for said resource.
+     * @param actualSize the size reported for this resource now that we're actually downloading
+     * it. Some web servers lie about Content-length when doing a HEAD request, so by reporting
+     * updated sizes here we can recover from receiving bogus information in the earlier {@link
+     * #checkSize} phase.
      */
-    protected void updateObserver (Resource rsrc, long currentSize)
+    protected void updateObserver (Resource rsrc, long currentSize, long actualSize)
         throws IOException
     {
+        // update the actual size for this resource (but don't let it shrink)
+        _sizes.put(rsrc, actualSize = Math.max(actualSize, _sizes.get(rsrc)));
+
         // update the current downloaded size for said resource; don't allow the downloaded bytes
         // to exceed the original claimed size of the resource, otherwise our progress will get
         // booched and we'll end up back on the Daily WTF: http://tinyurl.com/29wt4oq
-        _downloaded.put(rsrc, Math.min(_sizes.get(rsrc), currentSize));
+        _downloaded.put(rsrc, Math.min(actualSize, currentSize));
 
         // notify the observer if it's been sufficiently long since our last notification
         long now = System.currentTimeMillis();

src/main/java/com/threerings/getdown/net/HTTPDownloader.java

@@ -89,7 +89,8 @@ public class HTTPDownloader extends Downloader
             }
         }
 
-        log.info("Downloading resource [url=" + rsrc.getRemote() + "].");
+        long actualSize = conn.getContentLength();
+        log.info("Downloading resource", "url", rsrc.getRemote(), "size", actualSize);
         InputStream in = null;
         FileOutputStream out = null;
         long currentSize = 0L;
@@ -114,7 +115,7 @@ public class HTTPDownloader extends Downloader
 
                 // note that we've downloaded some data
                 currentSize += read;
-                updateObserver(rsrc, currentSize);
+                updateObserver(rsrc, currentSize, actualSize);
             }
         } finally {
             StreamUtil.close(in);