GNU Go resignation support

GNU Go 3.6 may resign games under certain conditions. This may cause problems with clients which are not aware of the feature. This page explains under which conditions GNU Go may resign, why it may cause problems with clients, and in what ways those problems can be solved or worked around.

When does GNU Go resign?

GNU Go 3.6 will resign under the following conditions which must all be satisfied:

• The boardsize is 19x19 (or larger).
• The estimated score says GNU Go is behind by at least 45 points.
• GNU Go has no unsettled dragon.
• The opponent has no dragon which is considered weak (without being dead).
• The game has progressed sufficiently far.
• GNU Go doesn't plan to pass.
• Resignation is not disabled.
• GNU Go is run in a mode which supports resignation. See below.

Which modes support resignation?

GNU Go can primarily be run in three different modes. There are additional modes which are mostly of interest to developers but none of those support resignation anyway and will not be discussed further. The three main modes are:

• Ascii mode. This gives a non-graphical interface only using ascii characters to display the board. This mode supports resignation and there are no known problems with it. (There may be problems if some client tries to communicate through this interface but that is strongly discouraged and we don't know of any such clients.)
• GMP mode. The older Go Modem Protocol is used by some clients. This protocol has no way to handle resignation and therefore resignation is not supported in GMP mode.
• GTP mode. The Go Text Protocol allows resignation and resignation is supported in GTP mode. This is the case which can cause problems, as discussed below.

Why can resignation in GTP mode cause problems?

The first version of GTP, implemented in GNU Go 3.0, did not have a resign option. This was added in GTP version 2, used by GNU Go 3.4 and later. However, GNU Go 3.4 never resigned so some clients using GTP have not added resign support yet. These clients may become confused when GNU Go resigns and possibly crash or hang indefinitely.

How can these problems be avoided?

You have at least the following four options:

• Try to upgrade your client to the latest version. Resignation support may have recently been added.
• Switch to another client which does support resignation.
• Disable resignation at runtime by giving the command line option --never-resign to GNU Go.
• Disable resignation at build time using the configure option --disable-resignation-allowed. Alternatively, try to find an already built binary with this option.

List of GTP clients with resignation support

These clients are known to have full support for resignation.

• Quarry.
• The Emacs client gnugo.el distributed with GNU Go 3.6.

List of GTP clients with resignation problems

These clients are known to get into trouble if GNU Go resigns.

• Nothing here yet.

List of GMP clients

These clients cannot support resignation at all and consequently don't have any problems with resignation.

• CGoban 1. (Note: this is not the same as the KGS client CGoban 2.)

Feedback

If you know of any client for which resignation is working or is not working, but is not included in the lists above, please inform us at gnugo@gnu.org. Include version number of the client if possible.

I'm an author of a GTP client and want to support resignation. What do I need to do?

The GTP command genmove can return either a vertex on the board, the string "pass" or the string "resign". Make sure to handle all these cases appropriately. This is documented in the the GTP version 2 specification draft.

If your client is using GTP version 1 you need to first switch to GTP version 2. The details of this are explained in a message to the GTP mailing list.

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