Default to a 30s read timeout during downloads.

This is configurable via a system property -Dread_timeout=N.

src/main/java/com/threerings/getdown/data/SysProps.java

@@ -95,6 +95,14 @@ public class SysProps
         return Integer.getInteger("connect_timeout", 0);
     }
 
+    /** Specifies the read timeout (in seconds) to use when downloading all files from the server.
+      * The default is 30 seconds, meaning that if a download stalls for more than 30 seconds, the
+      * update process wil fail. Setting the timeout to zero (or a negative value) will disable it.
+      * Usage: {@code -Dread_timeout=N}. */
+    public static int readTimeout () {
+        return Integer.getInteger("read_timeout", 30);
+    }
+
     /** Parses a Java version system property using the supplied regular expression. The numbers
       * extracted from the regexp will be placed in each consecutive hundreds position in the
       * returned value.

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

@@ -15,6 +15,7 @@ import java.util.List;
 import com.samskivert.io.StreamUtil;
 
 import com.threerings.getdown.data.Resource;
+import com.threerings.getdown.data.SysProps;
 import com.threerings.getdown.util.ConnectionUtil;
 
 import static com.threerings.getdown.Log.log;
@@ -60,6 +61,10 @@ public class HTTPDownloader extends Downloader
     {
         // download the resource from the specified URL
         URLConnection conn = ConnectionUtil.open(rsrc.getRemote());
+        int rtimeout = SysProps.readTimeout();
+        if (rtimeout > 0) {
+            conn.setReadTimeout(rtimeout * 1000);
+        }
         conn.connect();
 
         // make sure we got a satisfactory response code