CLX display naming (was Re: Picking Nits on new build)

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[ Apologies to cmucl-imp readers for the extensive quoting.  You may
want to reply to portable-clx-devel only ]

On cmucl-imp, Eric Marsden <[email protected]> writes:

>>>>>> "hr" == Hannu Rummukainen <[email protected]> writes:
>
>   hr> Note that the C language X library special cases unix in display
>   hr> names, so that unix:0.0 makes a local connection. A google
>
> indeed, Paul Foley made the same comment. I haven't been able to find
> anywhere in the X documentation that describes this, but in the Xlib
> source code there is a comment above the function
> xc/lib/X11/ConnDis.c:_X11TransConnectDisplay that says
>
> /* 
>  * Attempts to connect to server, given display name. Returns file descriptor
>  * (network socket) or -1 if connection fails.  Display names may be of the
>  * following format:
>  *
>  *     [protocol/] [hostname] : [:] displaynumber [.screennumber]
>  *
>  * The second colon indicates a DECnet style name.  No hostname is interpretted
>  * as the most efficient local connection to a server on the same machine.  
>  * This is usually:
>  *
>  *     o  shared memory
>  *     o  local stream
>  *     o  UNIX domain socket
>  *     o  TCP to local host
>  *
>  * This function will eventually call the X Transport Interface functions
>  * which expects the hostname in the format:
>  *
>  *	[protocol/] [hostname] : [:] displaynumber
>  *
>  */
>
>
> Together with the special casing of the "unix" hostname (which
> requests a Uhix transport) this leads to the following interpretations
> of the DISPLAY environment variable:
>
>                   :0            most efficient local transport (unix)
>          localhost:0            TCP
>               unix:0            Unix to local host ("magic" hostname)
>     dnet/localhost:0            DECnet to localhost
>           tcp/unix:0            unix (because of special-casing of

It strikes me that a function that does proper display name parsing
would be a useful addition to "standard" CLX.  I'm going to suggest

- ------
open-display-name &optional (display-name (getenv "DISPLAY"))

Parse the supplied display-name, which is expected to be in the format

  [protocol/] [hostname] : [:] displaynumber [.screennumber]

to extract the protocol, host and display number.  The parsing matches
that done in the Xlib C language bindings - there are two special
cases:

 - If the hostname is ``unix'' or the empty string, any supplied
   protocol is ignored and a connection is made using the :local
   transport.

 - If a double colon separates hostname from displaynumber, the
   protocol is assumed to be decnet.

OPEN-DISPLAY-NAME always attempts to do display authorization.  The
hostname is resolved to an address, then authorization data for the
(protocol, host-address, displaynumber) triple is looked up in the
file given by AUTHORITY_PATHNAME (typically $HOME/.Xauthority).  If
the protocol is :local, or if the hostname resolves to the local host,
authority data for the local machine's actual hostname (as returned by
gethostname(3)) is used instead.

- ----

Comments?  The description of xauth defaulting is frightening, but in
that respect it does actually reflect the scariness of the xauth
defaulting.


- -dan

- -- 

   http://www.cliki.net/ - Link farm for free CL-on-Unix resources 
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