Detect if the remote server is really Hudson.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@17605 71c3de6d-444a-0410-be80-ed276b4c234a

cli/src/main/java/hudson/cli/FullDuplexHttpStream.java

 package hudson.cli;
 
-import hudson.cli.SequenceOutputStream.Block;
-
-import java.io.FilterOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
@@ -45,6 +42,9 @@ public class FullDuplexHttpStream {
         con.addRequestProperty("Side","download");
         con.getOutputStream().close();
         input = con.getInputStream();
+        // make sure we hit the right URL
+        if(con.getHeaderField("Hudson-Duplex")==null)
+            throw new IOException(target+" doesn't look like Hudson");
 
         // client->server uses chunked encoded POST for unlimited capacity. 
         con = (HttpURLConnection) target.openConnection();

core/src/main/java/hudson/model/Hudson.java

@@ -2712,6 +2712,7 @@ public final class Hudson extends Node implements ItemGroup<TopLevelItem>, Stapl
         requirePOST();
 
         UUID uuid = UUID.fromString(req.getHeader("Session"));
+        rsp.setHeader("Hudson-Duplex",""); // set the header so that the client would know
         final Authentication auth = getAuthentication();
 
         FullDuplexHttpChannel server;