Tried to build project as a Java client and got HTTP 400 error

[miko-code]

I tried to build your app as a Java client and got this error

mik@mik-Aspire-S3:~/go-programs$ URL='https://go-endpoints.appspot.com/tictactoe'
mik@mik-Aspire-S3:~/go-programs$ curl -s $URL > tic_testmik@mik-Aspire-S3:~/go-programs$ $HOME/go_appengine/endpointscfg.py gen_client_lib java tic_test
Traceback (most recent call last):
  File "/home/mik/go_appengine/endpointscfg.py", line 133, in <module>
    run_file(__file__, globals())
  File "/home/mik/go_appengine/endpointscfg.py", line 129, in run_file
    execfile(_PATHS.script_file(script_name), globals_)
  File "/home/mik/go_appengine/google/appengine/tools/endpointscfg.py", line 561, in <module>
    main(sys.argv)
  File "/home/mik/go_appengine/google/appengine/tools/endpointscfg.py", line 557, in main
    args.callback(args)
  File "/home/mik/go_appengine/google/appengine/tools/endpointscfg.py", line 458, in _GenClientLibCallback
    args.build_system)
  File "/home/mik/go_appengine/google/appengine/tools/endpointscfg.py", line 335, in _GenClientLib
    build_system, client_name)
  File "/home/mik/go_appengine/google/appengine/tools/endpointscfg.py", line 366, in _GenClientLibFromContents
    raise ServerRequestException(error)
__main__.ServerRequestException: HTTP 400 (Bad Request) error when communicating with URL: https://google-api-client-libraries.appspot.com/generate.  Details: ill-formed JSON: No JSON object could be decoded

[x1ddos]

That URL is just an HTML page with TicTacToe game.
You probably want https://go-endpoints.appspot.com/_ah/api/discovery/v1/apis/tictactoe/v1/rpc or https://go-endpoints.appspot.com/_ah/api/discovery/v1/apis/tictactoe/v1/rest to generate a client lib.